DIY Blast Gun Testing Using a Manometer

[@reelmoody2376]

Mark, I made several mistakes thinking I could save money by buying a cheap blast cabinet. I restored a 1980 MGB and cursed the HF cabinet ($175) every minute wasted trying to get the POC to work right. I also added a $150 dust collector. The second mistake was putting undue wear and tear on my compressor. I was going to sell the cabinet when I heard about the Tacoma upgrade. The third mistake was investing $448 plus the modification time. I have mixed feelings since the HF cabinet now works great at 35 psi, using 70-140 sieve media. Check for flow restrictions. Use the largest dia hose from the compressor to the cabinet. I have a dedicated 12mm hose from blaster to compressor (no quick connects). 19mm would be even better. I also checked/replaced any undersized quick connect fittings in my shop. Good luck on the larger compressor.

[@Preso58]

Thanks for the information. I think my biggest restriction is the cheap foot pedal I bought on Ebay. I am wondering if I can fit a ball valve and operate it with a knee operated lever. I think it's great that you are getting good results at 35 psi. That would cut down the duty cycle on the compressor.

[@gordon6029]

Just love this series. Truth is I could just pop down to the shop here in Canada and buy a gun but yours looks way cooler with the lightening bolt. No, what I love about this series is the science you’re putting into it. Also the casting techniques. Yup, love it!

[@Preso58]

I can report that I am very happy with the blast cabinet now. It still surges a little but the supply of grit coming out of the nozzle seems to be constant. One of the best mod's I did was to fit a knee operated switch to turn the air on and off to the gun. Way better than a foot pedal and there's nothing kicking around on the floor under your feet. kzbin.info/www/bejne/fpnKhWlto5qfetE The mod is shown at about 15:00 Regards, Mark

[@kmcwhq]

Very interesting to watch the evolution. The ultimate key to blasting productivity is Pressure and CFM. Also, a Pressure Pot system is infinitely more efficient than any Suction Gun setup. I have been thru the evolution a couple of times since the early 1980's. My current blasting compressor is a 185 CFM Diesel powered unit. Plenty of air!

[@Preso58]

I would LOVE to have something that can deliver 185cfm although we might upset the neighbours with the noise. I watched a video recently by SV Seeker where he was getting ready to sandblast a steel yacht/replica Chinese Junk using a very large engine driven compressor. He included a very interesting video where he talks to a corrosion consultant about the correct way to prep steel for finishing. Very interesting. I did actually do an experiment where I tried to pressurise the media where it passes through the metering valve. I fitted a second air line with a regulator and gradually added pressure until the media was being pushed up the feed tube to the gun and then added air directly to the gun. It didn't help much. Initially, there was a good flow but then the media was depleted in the line and it just sucked air. I think if I had the room I would use a pressure pot with a large cabinet to collect the media but it's all about real estate in the workshop. I really wanted a smallish unit so I can prep weldments and fabricated parts for paint and powdercoat. Painting brass and non ferrous alloys is always a bit hit and miss but when they are given a good key and you can remove the oxides you can give the coating a fighting chance. Regards, Mark Presling

[@kmcwhq]

@@Preso58 The first go-round about 1981 when I was 21, I found an old portable IR compressor from the 1940's that was 100 cfm, piston type with a massive old Waukesha engine driving it. Made a pressure pot from a 100lb propane tank. And I had neighbors, close. Why they never called the cops is a mystery. I'd never stand for that. (ha). I've watched all of SV Seekers work on his compressor and blasting evolution with interest. Great stuff. My current compressor is similar to his. I think the key between siphon and pressure blasting is the 'acceleration distance'. In a siphon gun, the media has less than 2 inches to get up to the speed of the air flow. Much slippage occurs. In a pressure pot, it has the entire blast hose length (10, 15, 20 feet?) to accelerate up to air flow speed. I've thought about some sort of hose attached to the nozzle of the siphon gun, to give the media more distance to accelerate. Then maybe a secondary nozzle at the working end of that hose? Enjoy your vids very much!

[@ralphzito7609]

Hi Mark, I’ve been enjoying your projects and videos, I’ve been looking to improve my sand blast gun recently, having a similar Hare & Forbes cabinet similar to yours. Seeing your problem with the take up of media from the hopper even with your improved gun, I had the same issue with my set up, I solved this by mounting a small wiper motor with the gearbox removed and an eccentric weight added to the shaft, causing it to vibrate when running. Mounted this to the outside of the hopper near the pickup tube for the media, this improved the flow of the media to a constant stream, no more sputtering. I’m going to fabricate a gun along your design ( can’t cast yet in my workshop) to try to improve efficiency at the nozzle and also optimise the use of available air. Keep up your good work, love your banter 👍regards Ralph

[@Preso58]

Ralph, I have seen some other users mounting vibrating motors to their media hoppers and I believe you can buy an off the shelf and self contained unit which does the job. I have noticed that even though the media isn't being delivered continuously to the gun, it still generates an almost continuous stream of grit at the nozzle. I think that the "gulps" of media are stored in the chamber inside the gun and the flow is regulated by the cross sectional size of the nozzle. For what it's worth, if I wasn't able to cast that gun in aluminium, I would now have it 3D printed in stainless steel. I just had some parts made for another project in 316L stainless and it wasn't as expensive as I thought it would be. The good thing about 3D printed metal parts is that they can have complex, hollow forms and they only require minimal machining afterwards. Sometimes you can get away with just a bit of drilling and threading with a regular tap and die. Regards, Mark

[@ronaldnickell6110]

I guess by now you have a new compressor, and I hope you included an automatic drain for moisture. When I saw your compressor it looked like mine, and I quit using mine because I was afraid the tank would someday explode due to internal rust. I got the H.F. upright oiled compressor with the 21 gallon tank. It works great, and as someone suggested you want to put a cooler before the air enters the tank, with an auto drain. Love your videos. I live in Houston, Texas so I don't know if we have more or less humidity than where you are, but it is quite high here on the Gulf coast.

[@Preso58]

I have upgraded my compressor system. I have a Chicago "silent" compressor (they aren't silent) and I fitted a large vertical air receiver outside the workshop which is in tandem with the compressor receiver. All the shop air comes from the large vertical receiver so it is mostly cooled to ambient temperature. Any condensation that forms goes right to the bottom of the tank and can be drained off easily (although not automatically). It seems to work well. Regards, Mark

[@graytell1]

Mark I went a along a different path with my machine by using a pressure vessel made from an LPG cylinder and some copper pipe and a few gate valves. With this system there is no suction required to feed the hand piece just a valve to meter the sand under the cylinder. This system has similar pressure above the sand to the pressure in the delivery hose and there is no hand piece required. Just a delivery tube. This system is mounted below the cabinet with a isolating tap between the cabinet and the LPG cylinder containing the sand. The sand supply is continuous and can be increased or decreased as needed I feel the resultant finish on the work piece could be a little better than you are experiencing at the moment. I enjoy your videos. Keep it up. Gray

[@Preso58]

Gray, I sort of dismissed the pressure vessel idea due to the small size of my compressor but I can see why it is a better solution. I also wanted to have a blast cabinet that could be wheeled around easily. I have to store it in a corner and then manoeuvre it around before I can use it. It's like a tetris game! It's all a learning curve but I feel like I have a viable solution at present. It's way better than trying to do it out in the open in a wheelbarrow to try to catch the grit. Regards, Mark

[@soupwell]

Solid use of clipboard. I think you need to tune your jet position with every combination of jet and nozzle sizes. Also, it's not immediately clear to me that the optimum jet position and jet/nozzle size combination will be the same at 100 psi and 10 psi. I understand the limitations of your water manometer, but I think you will need to find a way to test suction at full pressure. This is all about maximizing fluid velocities at critical points in the chamber, and fluid dynamics is notoriously difficult to predict under changing conditions. Your chamber geometry upgrades look like an excellent idea. You might also try moving the media tube inlet off the center line of the gun to one side or the other where it enters the chamber. This would encourage a vortex within the chamber which might be quite useful for maximizing media flow.

[@Preso58]

All good ideas. I knew the tests would be just a guide and the MKII version of the gun will need to be tuned all over again. I tried to research commercial/professional gun setups and I found that they all had the inlets lined up on the centre plane of the gun. I get what you mean about the off centre alignment though. It would be an interesting experiment. Maybe a transparent body would allow for better understanding of what is going on. I recall years ago I was doing some tests with some of my students at a university that had a water flume for testing fluid dynamics. We made a 3D printed model of a race car we were developing and put it in the flume so that we could run dye over the surface to find out what was happening in the boundary layers around features like the wheels and the wings. What a revelation! We found areas where there was almost no flow and others where the flow was actually at right angles to the direction of the water. At the time the accepted knowledge was that you had to "streamline" all the areas of the car around the wheels so there was no turbulence. We were able to show that it wasn't really necessary on an open wheel car of the size we were working on. (it was only 210mm long). The boundary layer was so thick that the open spaces around the wheels were just dead air and got carried along with the car. Sadly, the kids knew more than the judges and the panel of "experts" couldn't understand what they were being shown. Regards, Mark Presling

[@dhc4ever]

Mark, I have found over the years its always better to ask for forgivness rather than permission, especially when buying tools. Wives rarely venture into the shed, dont know whats in there and after a week everything has the same aged patina and dust coating, so doesnt stand out. If she does notice it pull the old " oh that old thing Ive had it foe ages..." Yes you will need 15 amp, I have the same blast cabinet with upgrades and a trade tools 310 ltr min, three cylinder pump ( biggest single phase I could find) and yes it runs about 85% of the time when blasting. One more mod for your cabinet, paint the inside white.

[@Preso58]

Thanks for the info. I will check out what Trade Tools have to offer. They are handy to where I live and they have good stock levels. I have sort of resigned myself to having a second 15 amp line run for the compressor. Regards, Mark

[@dhc4ever]

@@Preso58 15 amp will come on handy for that welding series you know you want to do 😁;)

[@MatthewTinker-au-pont-blanc]

Thank you for another good video. It's nice to have other people do the testing for you! Interesting stuff! I had a 100 litre Compressor that wouldn't feed my plasma cutter, so I went looking for a bigger one, I' thought about 250litres, well, I found a second hand 500 litre three phase (I have three phase) which was cheaper than the the smaller ones! It's worth thinking about bigger if you can house it. Mine's going outside when I finish quietening it, but, it'll pick up it's air from inside the workshop where it's dryer!! Cheers, Matthew

[@Preso58]

I would like to put my compressor outside in a weather proof enclosure. Three phase would be nice. I watched a video by AVE a while ago where he did some experiments with a VFD fitted to a three phase compressor running off a single phase supply. Typically, it was hard to take his antics seriously but there seemed to be some merit in what he was doing. Good idea about locating the air inlet inside the shop.

[@russtuff]

Great series.

[@metalworksmachineshop]

I think the upgrade is needed for sure. Just because home shops dont have a good compressor to feed it air. I have a bone stock HF cabinet, a 80 gallon IR 2 stage compressor. And my cabinet works very good. Also the compressor doesn't run all the time. It will shut off with a continuous airflow. It fills faster than it puts out. I want to switch to a setup like yours just to lower the air pressure needed and use less.

[@Preso58]

I still find I that I am running my blast gun at over 80PSI and one of the selling points for the Tacoma upgrade was that you could run the gun at a lower pressure. I still have a lot of experimentation to do but that was my primary reason for wanting a new setup. My compressor just runs out of supply plus the noise is abominable. I have had some good tips on what sort of compressor I should look for as an upgrade though. Most of the compressors I have been looking at (that I can afford) are only 100 litre or about 30 gallons but I am thinking I could fit a second tank to increase the reserve. Regards, Mark

[@rolliekelly6783]

I had the same thought as Barnezy. If you thread the gun and jet you can adjust the jet position to optimize the media flow for every nozzle size. Yes, I realize I'm not the one doing all of the work, fortunately! I enjoy your videos.

[@opendstudio7141]

Grit and dust might cause problems.

[@CothranMike]

@@opendstudio7141A large straight dog point on one of the set screws could serve as a follow pin for a much needed coarse gage gouge in the jet body. This would allow the jet position to be adjustable to a fair-the-well. Make it one turn over the long distance like rifling only much much deeper.

[@gh778jk]

Prezza ! Mate, pall.... Manometers, black water.... 'a bit of a mess'.... I figure your missus is about as happy as mine, when I get up to this sort of stuff.... Toodles! Paddy PS : about 30 years ago, I walked the length and breadth of a nuclear plant, just using a clipboard ! Now, I had clearance, so no harm was done, but I only identified at the main entrance...and was allowed everywhere, just by walking around with a clipboard and a rather worried look on my face. They are (clipboards) powerful weapons indeed !

[@Preso58]

I watched an episode of "Better Call Saul" where Mike Ehrmantraut did almost exactly the same thing with a clipboard. You are correct. Clipboard = authority

[@frankmarson2425]

Overalls a concerned look and a tool caddy/box works wonders too

[@AJR2208]

Hi Mark, I just came across your videos today and have learnt a few things and had a few laughs as well. Cheers to your methodical approaches to problem solving and more so, to sharing your mistakes along with what you figured out. We all learn that way. "The Greatest Mistake a Person Can Make Is To Be Afraid Of Making One!" With your compressor, here are a few tips that might help you; 1. To keep everything as dry as you can, get a "Water Separator / Regulator Combo" or fit an extra Water Separator after this and before your air hose. Other water separators are available to be connected between the final stage of the motor and before the air reservoir. These can be very expensive though and are typically fitted to high pressure air compressors. But, with a bit of googling, commonsense and careful fabrication you could make your own. 2. Frequently purge your air reservoir (as much as every 10 minutes in high humidity), to drain your tank and reduce pumping water into your airlines. 3. If you have enough air pressure, make a manifold block on your cabinet. Have one inlet & 2 (or as many as you like) outlets for the block. One for your gun and the other to feed down into the bottom of your hopper. This one will "Fluff" your medium and help your pickup line deliver with more ease. 4. You could put a third air hose into your hopper, connected to an air ejector before the the pickup end of your feed tube. This will help to overcome the gravity on the blasting media and make your gun "Air Venturi Ejector" work with more ease. 5. On your next prototype, design a spiraled chamber in your gun to increase the airflow over the pickup stem and directing it out the nozzle. It will also help scavenge any media that builds up inside your gun air chamber. You need to increase the "Low Pressure / High Pressure interface for the Air Venturi Ejector to maximize pickup and eject. 6. Good luck with it all :) (maybe I should have watched your next video before posting this comment?)

[@Preso58]

Anthony, thanks for the tips. I still haven't got my new air compressor! We are due to leave on a holiday to the UK and Europe next week and our rubbish Aussie dollar is buying just 56 British pence and about 60 Euro cents so it's going to be an expensive holiday. 😥

[@AJR2208]

@@Preso58 Safe Travels Mark !!

[@TheUlrikkaul]

I really like the Austrlian humor. When i bought the "HF" type blaster cabinet, i discovered that my 2.9 kW compressor was not up for the job, i bought one more compressor. After 2 years i got tired of the 2 compressors hammering away, i built my own 5.9 kW compressor with a 300 liter tank. I have enough compressed air now.

[@Preso58]

Ulrik, do you have a three phase supply to your workshop? I believe that many parts of Europe get a 3 phase connection to their utility company as standard. It certainly doesn't happen here. It's even worse when you live on acreage like we do. The distance from our street frontage to our meter box is around 70 metres and the power cable goes underground so it's almost out of the question to upgrade.

[@bullvine2062]

I've had my blasting gun for years with a few adjustments. Now I've attached it to a petrol pressure washer. No dust and continuous 250 bar pressure, far better. Also consider using a VFD to control the compressor. It's really effective and efficient. Also copper cooling coils from the head to the tank. From 84c down to 5c or less. Inline water filter and perfect..

[@Preso58]

I have since added a very large receiver to a new "Chicago" silent air compressor (which isn't really silent at all) and this give me a much better reserve of air and it also acts as a sort of cooler since most of the heat stays in the main compressor tank. This upgrade alone has improved the performance of the blast gun out of sight. If I had the room I would use a pressure tank for the blast media but space is already hard to come by in my workshop. Regards, Mark

[@gregghooper]

G’day mate Just a few thoughts After spending many hours dicking around with my old Commercial industrial bead blaster cabinet having the same issues with the Medium surging in the suction line. I found by using a gravity feed hopper on top of the cabinet feeding the Handpiece to best. Keeping the bead clean and dry was also very important to keep it running well. Good luck with the compressor btw. Hoops

[@CothranMike]

Just use any old screw augur type system to fill the hopper. It is possible to use inlet air pressure to power a coarse threaded augur via an air wheel mechanism, but I recommend a tight fitting system if you go this route.

[@Preso58]

I would very much like to have a gravity feed hopper above the cabinet but I don't have a lot of space left in my shop. I have to store the blasting cabinet out of the way and trundle it away from the wall so I can attach the dust cyclone. It's working pretty much how I want it now and unless I decide to do anything really big it should serve my needs. The whole compressor thing is really just because my old one is getting past it's use by date. I am looking at getting a Chicago silent type. For around $1200 I can get a 100 litre, 16CFM machine.

[@Kevin-gx8lc]

Hey Mark, when I saw you using your 'Manometer' I just thought it was a tongue in cheek gadget to go in your 'Man cave' or 'Manshed' etc! Great test... I would have loved to have been a fly on the wall of your 'scones' discussion. Of course, you could always buy your Missus a new compressor for her birthday... what more could she want? Can I suggest that you wear a crash helmet if you suggest this, and perhaps, a cricket cod-box... there are certain parts of your anatomy you might wish to protect! Great vid. Greetings from Southport UK.

[@olivier2553]

For testing, what about blowing sand in a bucket for 30 seconds and weigh the result with different settings?

[@Preso58]

Good idea. I might do that when I get the MKII gun finished.

[@MegaBCAD]

If you get a new compressor put radiator in between the pump and the tank with a water catch to cool the air and condense the water out be for the tank best thing I did no water in the tank you need dry air for the sandblasting aswell Or just run two compessers

[@Preso58]

Bradley, What sort of radiator? Is it a specialist item or accessory for compressors or did you make your own?

[@suzukichopper]

@@Preso58 Lots of ways to go about it. One design I saw used coiled copper tube down the length of a 60 gallon tank with a desiccant filter at the bottom and drain, then a straight shot back up to the tank. LOTS of guys are pretty anal about their air setups so it's pretty easy to find lots of ideas on Google, along with a lot of arguments lol Good luck!

[@MegaBCAD]

Mark Presling I used a condenser out of a old aircon it has the smaller pipes for easier connections but any thing that has surface area to cool the air and and let the water condense out of the air before the tank if you have a email I could send some pics it’s still a bit ruff at the moment As I was moving it but the air is pretty well dry and cold before it gets to the tank where before it was up to 140 c measuring the out let pipe from the compressor I’m in wa and on the humid days I could get over. Litre of water out anything else just ask

[@AlbiesProductsOnline]

I think if you redid the test again but try adjusting the nozzles position with the higher sizes you would get better results

[@Preso58]

When I finish the MKII version I will be re tuning it so I have kept the manometer setup for that purpose.

[@AlbiesProductsOnline]

Shouldn’t the media come in towards the rear of the cavity, bring in where you are is going to cause turbulence where you want flow and suction I think you would also stretch the chamber out 50% to give it more area to create the centrifugal forces you require

[@Preso58]

I have had lots of suggestions about what the interior architecture of the gun should be. I am thinking that having a transparent body would be the only way to test different designs short of a full computational fluid dynamic scenario. Regards, Mark

[@yambo59]

Nice results on the gun engineering. I will agree with bradley carlson below, DRY air and plenty of it are paramount to keep the sand moving and the duty cycle high as possible, nothing eats up air like a sandblaster, just like an open hose. Me and a friend were doing a ground up restoration on his car and we decided to sandblast the frame --- his compressor was way too small and that became obvious very quickly as the duty cycle was very short with the compressor at full pressure and larger hoses and fittings. So he bought a new 3x larger compressor and that took care of the duty cycle problem. But the sand absolutely had to be dry or it slowed the flow and occassionally clogged the hose, even with water filters in place. Once we got it dialed in we loved cleaning parts with it, nothing like it to get back to bare metal without leaving grinding marks on using nasty chemicals, but one must wear serious breathing protection outside a cabinet - the silica sand we were using had warnings all over it about permanent serious lung damage (silicosis) from breathing it.

[@Preso58]

Thanks for that. I am considering upgrading to a Chicago silent air compressor but I might keep my old belt driven machine since many people have suggested running two compressors in tandem. The garnet I am using seems to be quite coarse compared to materials I have seen others using. I can understand why having dry air would be important if the material is quite fine. I am starting on the MKII version of the gun and I have ordered some clear acrylic tube to see if I can make a transparent gun so I can visualise what is going on inside the cavity of the gun. Should be interesting.

[@yambo59]

@@Preso58 - Youre so welcome - I like the clear gun idea as a learning tool, to actually see the behavior of the sand should provide valuable clues to what changes need to be made if any. I love a good DIY project, but yours are on another level than some of us less equipped folk so its fun to watch something be engineered, designed, cast and machined from the ground up. Your garden bridge was a wonderfully enjoyable piece of engineering work that could only be executed by someone with patience, knowledge and the use of good sound engineering principles, very nice work and a great video series as well.

[@sheph7ceo799]

Anyway to tell if the surging is caused by the air compressor? The air has to be constant in pressure and volume and despite looks the performance of the compressor may be suitable. Just speculating but the new internal streamline design of the gun should help but the real performance improvement should come from the addition of the lightning bolt. I recommend that you should bring up the need for a compressor AFTER the neck massage.

[@Preso58]

I am going to upgrade the compressor soon anyway. It is getting on and the pressure vessel must be getting quite corroded by now. It is also incredibly noisy with the motor running at 2800rpm. My friend has a 3 cylinder unit that runs with a 1440rpm motor and it just chugs away but has a good throughput of air. Scones rule! 😁

[@CraftedChannel]

Add a second compressor for extra air when blasting, no need for a bigger unit. Consider increasing pick up tube diameter as it will allow more air flow. As the tube diameter increases or decreases, the speed of the air may increase or decrease in reverse relation to tube id. Remember the sand is always falling in the moving air. Thus, tuning the tube ID for best combination of airspeed and volume may allow your gun to improve dramatically.

[@Preso58]

I can watch the grit falling inside the column of pickup tube. It seems like that is not really an issue any more, The gun seems to be able to store the grit inside the cavity and it is ejected from the nozzle in a steady stream. I think I am happy with the way it is all working now. I am still looking to upgrade my compressor though.

[@CraftedChannel]

@@Preso58 I'm thinking of a cascade of compressors for my shop. ALL of them outside the building. Man is not fit to share space with a pounding air compressor. The silent ones are growing in popularity but are not as productive per KW. But, I image a portable pancake or two plus one big compressor. Any combination of which can be turned on. When I need spritzing or tire filling air the small one will do, when I'm blasting the whole works running. When I'm running an impact maybe 1 or two small ones. I think it's a lack of 3 dimensional thinking to imagine only one unit can be utilized. Why not 2 plumbed into same shop system? With the valves you can limit or expand which tanks are filling and with switches, which and how many units are doing the filling. Those are my general thoughts.

[@opendstudio7141]

The irony of it all, but very interesting to watch the progress. Limited budget... Appears that a field trip to the scrap yard might be in order here. :)

[@markfryer9880]

Hi Mark, don't be so fast to get rid of the old compressor. In fact it hasn't done all that much work and you will be amazed at what a good service can do for it. Start by ensuring that the tank is properly drained of water condensation which will help in lifting blasting media. Check the air filter and clean it, replace if necessary. Change the oil and check the drive belt for condition and tension. If it is still working keep using it as all the compressors available today at hobbiest price points are made in China and you know what that means. Consider making an air drier for your compressor to provide good clean dry air for your workshop.

[@Preso58]

Mark, I will need to disconnect everything and drag it out from under the bench to do a thorough service on it but you have shamed me into doing just that. I was considering scrapping it a few years ago because it was so inefficient and when I checked the filter it was almost completely blocked with mud wasp nests. No wonder it couldn't breathe!

[@Custercounty01]

Matt I strongly suspect that with the larger nozzle sizes, you were trying to consume more air than you compressor could provide and thus the air pressure was in fact dropping below the 10psi threshold. Unless you verified this while flowing through the particular nozzle configuration?

[@garymucher9590]

Of course the suction capability helps, but you also have to get the blasting media to flow easier in the tube up to the gun. I see some suction tubes with secondary tubes along side it to allow air in. While I am not a pneumatic engineer, I think some work on that end could help as well. JMHO

[@Preso58]

Gary, The metering valve on the outlet of the hopper allows the air to mix with the media supply. I did a separate video on that a while ago. Regards, Mark

[@askquestionstrythings]

yep, the general rule with fluids (including air) is no sharp corners. That gen 2 design should be better.

[@Rick_Bagnall]

A "Wife Approval" graph! I've never seen one before! I imagine the flow of the graph would be different in every household which is why one doesn't see them more regularly (lol) As for the "Ray Gun" blast gun, When you first presented the picture I immediately though of the same thing, making Gen 2 with rings and lightning bolts. That's how I would add a bit more flair and fun to the project. I love the videos, especially the humorous parts. Thanks for another good one!

[@Preso58]

Rick, I sort of feel that I have to put at least a few rings on the new gun!

[@danharold3087]

Air flow from the compressor is important too. Add an air pressure gauge between the hose and gun. Then test with the same pressure at the gun with air flowing. Cheers.

[@billbaggins]

good results mate. wondering if a gravity feed hopper would work better and just use the old gun to cycle media from cabinet to hopper 🤔

[@Preso58]

I like the idea of a gravity feed hopper but I have very limited space to store the blast cabinet. I had to make room in my wood shop by removing part of my sink cabinet! I do have to wheel the entire unit into the middle of the space to use it and this was one of the reasons I had put off buying a blast cabinet for so long. I originally thought I would have to store it outside under an awning. As it is now it is doing what I want but I think I can tweak the performance of the gun with the markII version.

[@billbaggins]

Sheds are never big enuf

[@johnwallace9002]

I think you should adjust orface distance when you change either orface and see what the suction does, you might be choking the ceramic orface with too large a volume of air expanding before it gets into the ceramic.

[@Watchyn_Yarwood]

Another great video! Love the "live" charting of your wifey conversation! I for one am looking forward to Gen II. I see you have put a lot of thought into the design and I am anxious to see how it improves media delivery. May I make a suggestion regarding the air compressor? Research the benefit of adding a second tank to your present setup. You might pickup a trashed compressor with a good tank for cheap. I just this year finally bit the bullet and purchased a single phase 5hp, 80 gal compressor. I have 3 phase service but I could not justify the additional cost of the compressor. I'm still on the fence about a sand blaster, hence my extreme interest in this project of yours. I have always had excellent service from HF tools. I started by buying a 1" impact for my then trucking business back in the late 1980s when they were mail order only. Now retired, my brothers and I have one 15ft, two 6ft rotary mowers and several riding mowers. I have been sharpening blades on them for over 15 years with a 4 1/2" HF grinder and it's still going strong! I have very few tools here on the farm that are not HF. Thanks to you, HF is in the running for my blasting cabinet.

[@Preso58]

William, I think the blasting cabinet that I bought is a good unit for the price that I paid and I knew going in that it would need a lot of upgrades. The reality is that in the "Hobby" and "home shop" class, there is not a lot to choose from here in Australia. Our market is too small to support locally made product and we are too far away from the rest of the world to make good quality imports affordable. China is relatively close and so the bulk of what I can afford comes from Chinese manufacturers. I know that Harbor Freight cops a bad rap from US makers but there is definitely a place in the market for what they supply. I put off buying a sandblast cabinet for years in the hope that I could convince the guys at the school where I used to work to buy one. That way I could use theirs if I wanted to. (I kept my keys to the workshop!) I can't see myself using mine everyday but the ability to be able to clean an awkward shaped component is worth it. Regards, Mark

[@millie19301]

I just bought some sanding primer at the automotive store, 16 oz can cost $8 US ($11.4 Aus). How does that compare to what you pay? I always run a straight 1/2 ID hose from my compressor to the sand blaster without valves to reduce restriction. I also went with a 60 gal holding tank and that gives me better continuous blasting. I would have like to see you blast the piece 1/2 with the new nozzle and 1/2 with the HF nozzle.

[@Preso58]

Steve, I just checked and a 400 gram can of spray putty (aerosol) is AU$11.99. A 2 litre can is AU$51.99. The straight paint in the 2 litre can needs to be thinned and sprayed from a gun with a large nozzle size but you can really lay it on thick with that method. I use an aerosol can for quick jobs like building up a finish on small 3d printed patterns but I will use a gun for bigger jobs. When I get the MKII blast gun finished I will try to do a direct comparison with the original setup. I am starting to think that I might be able to add a holding tank outside my shop to increase my reserve of air but I will definitely be upgrading the compressor soon. Regards, Mark

[@paulcurtis9852]

The "manometer"....the true measure of a man!

[@JustAnotherMaker]

Cracking series. Thank you. Those rings need to be added.

[@badjuju6563]

What about varing the suction tube diameter?

[@rallybbek]

I like the idea of trying a smaller suction tube also, seems like it would travel up it smoother... 🤔

[@Preso58]

I am going to do some more tests when I get the MKII version of the gun finished. Stand by!

[@sparkyinanissan]

Clipboard AND scones, living the dream. I was wondering if having either having an internal taper on the nozzle tube or a bored out tube with a screw in tip would improve efficiency of the air supply. It just seems like a unwanted restriction to me. Or am I missing the point? Great video anyway, I now know what not to do, mention new tools to the wife.

[@Preso58]

Steve, I was also wondering how important it was to keep the passages inside the jet as large as possible since the volume of air is just as important as the pressure. I have had several people point out that having lots of restrictions in the supply line is a bad thing. I like the idea of having a separate screw in tip rather than having to make up a new jet with different size openings. I might just steal that idea. Regards, Mark

[@johnjohn-ed9qt]

I don't know that the "surging" in the pickup tube is significant to the feed. I suspect that you have a steady feed at the gun, and what you are seeing if essentially sloshing of the region where a phase transition occurs between a heavier fluidized state and the media being carried by the flowing gas. The sloshing is a similar effect (not the same mechanism) as the bounce in your water column test.

[@Preso58]

I was initially disappointed to see the surging in the supply tube but as you have pointed out the feed from the gun nozzle appears to be constant. I just watched another KZbinr's video showing the operation of his cabinet which is fitted with a Tacoma metering valve and it seems to be very similar to what I am getting so I am counting my solution as a win. Regards, Mark

[@garagemonkeysan]

Interesting series. Great story. Funny graph at end. Cheers! :)

[@simonpalmer8033]

What about feed tube sizes, does this also have a bearing on the outcome? So many variables I think.

[@Preso58]

Yes, There are a multitude of different combinations of pressure, air volume, media size and composition, air and media delivery tube cross sections but the most significant seems to be air volume rather than pressure. I tried to do some blasting in my wood shop the other day and the air line in that area is a small bore PU retractable air line and the results were very disappointing. I am thinking that when I get my new compressor I will run a dedicated large copper tube to the blast cabinet and do away with the foot pedal and substitute a ball valve that I can operate with my knee.

[@simonpalmer8033]

Thanks for the reply. That's a good idea. I think I should try the same with a light media, I was thinking of crushed glass as it apparently gives good results. Keep up the good work. All the best from the UK 👍

[@fernandoitajahy3942]

Very good!!! Congratulations.

[@yvesdesrosiers2396]

G'day Mr P. Way to go all out on your scientific assessment of your gin.(wow I am using big words 😁) Rooting for you on that compressor. If you are looking for quite you can't beat a scroll unit, down side is the price. Eastwood has one at a decent price. Have a good weekend.

[@Preso58]

I always check out the Eastwood catalogue with envy. Unfortunately, like most things, the Australian Eastwood store only stocks a fraction of what the US version does and it's all expensive due to our crappy dollar. 😥

[@yvesdesrosiers2396]

@@Preso58 I quite understand that. I placed a $250 order and once converted it came out to $350. Ouch

[@method408]

Love your videos, great work

[@HTHCLLC]

The Presling Ray gun. Well done sir. You make R&D like it used to be in America. Here is is too easy to just go buy it and trust "They" did the R&D. (And they did....kinda) can't wait for the next vid.

[@iTeerRex]

There's no science with out the lab-notebook (clipboard) lol. Mr Presling, you mentioned a version 2 in the works, so i wanted to make a minor suggestion. From fluid dynamics.. when a fluid changes direction it causes friction, and of course the sharper the turn the higher the friction. The sand at the metering valve makes a 90dig turn, and at the gun about 75dig turn. If these angles were decreased it may increase sand flow. At the metering valve gravity well also help the sand into the pipe. This may produce a more consistent sand flow plus increased velocity. Looking forwards to v2, Cheers!

[@Preso58]

Tameem, the flow at the metering valve is very low velocity and as you have observed it is helped by the weight of grit above the opening. The flow at the gun is also quite slow until it mixes with the high velocity air in the vicinity of the tapered opening of the nozzle. The best way of visualising it would be to make a transparent body for the gun and the metering valve but that is getting a bit beyond what I can scrounge from my scrap box. I'm afraid like most examples of the design process, there are always conflicts and compromises. Regards, Mark

[@iTeerRex]

@@Preso58 No, not compromise.. I meant changing the angles from 90 dig turn to say 45 so it flows better. I wish i could post a drawing here.

[@garyskowbo3564]

Hi Mark, looks like fair results. The nozzle end improvements look good, just wondering though if eliminating the chamber behind the media inlet would help the venture effect. Definitely looks like a new compressor could help.😊 Thanks for another great video, looking forward to the rest of the journey,and it will save the rest of us a lot of time and aggravation.👍😀

[@Preso58]

Gary, someone else commented about the volume behind the media inlet in the gun but I was wondering if that are was acting as a buffer to store any media that was being sucked up into the cavity before it gets ejected from the nozzle. I badly want to make a transparent body for this gun so I can see what is going on inside the chamber!

[@garyskowbo3564]

Well I have not obtained a formal education beyond high school, however the experience I have gained over the years would suggest that keeping the volume as minimal as possible at that point would be better. Again just my opinion, I hear you a glass unit would be so much fun.😁

[@ianbertenshaw4350]

Looks like something from Flash Gordon!

[@andrewthompson5736]

Has anyone tried a fluidised bed

[@joerogi8401]

P, Your media feed tube is able to deliver more material than the gun can use. When it backs up at the gun the suction drops and thus the flow. Don't worry about the media flow in the delivery tube the delivery out of the gun is all that matters. Your drawing of a venturi is wrong, the low pressure point in a venturi is at the narrowist point, see if you can get the media delivery closer to that spot. Also a shallower angle (larger radius ) in the venturi might help, you want a laminar airflow if possible. Third point, how do you expect to be taken seriously with a clip board when the accompanying pocket protector is absent, seriously mate. JG

[@Preso58]

Joe. I had reached the same conclusion about the flow of the media up the delivery tube and the flow coming out of the nozzle. It must be arriving at a rate faster than it can be ejected out of the nozzle. I take your point about the laminar flow etc, the design, as always is a bit of a compromise in terms of what I can cast, what I can machine and how comfortable it is to hold. I actually do have a pocket protector! I used to wear it to work when I was teaching. Sadly I could never be organised enough to stock it with three different coloured biros.

[@scotthaddad563]

Good series of vids, thanks.

[@HoutmeyersP]

I am a bit puzzled here. How come you think that the nozzle and the jet opening are stil optimal if you use 100 psi instead of just the 10psi you used to do the test. Do another test at 20 psi....maybe the numbers tell a very different story then. Why would the numbers go up linear because you use higher pressure ???

[@Preso58]

I knew that the results that I was getting at such low pressure would be a bit skewed. I intend to do the tests again when I get the MKII version of the gun finished. I tried running the pressure at 20PSI and it just sucked the water straight up to the gun and sprayed it out of the nozzle. I realised after the video was published that I have a vacuum gauge so I will try to use that to run the tests at realistic pressures. I am keen to see if the results "scale". Regards, Mark

[@canadianavenger]

I've been watching along as you go. Have a couple of thoughts. First, you should repeat your test, tuning the position of the jet for each size, as the optimal position likely shifts. It may even shift further with the change in nozzle diameter. Secondly, the geometry of your internal cavity. I think the more tapered shape towards the nozzle would be definitely be better removing that vertical wall you have at the end of your current barrel shape. This should allow better flow of the media towards the nozzle. Also I don't think there is much advantage to having much, or any cavity behind the point where the media is introduced into the cavity (in fact it may be counterproductive), so you may want to look at moving the entry point back, or bringing the rear wall of the cavity forward. You should be able to do a lot of tuning with positions and geometry using 3D printed parts, before you commit to another casting.

[@Preso58]

Mark, unfortunately I have already printed the new core box but I take your point about the shape at the aft end of the cavity although I am now wondering if the larger volume is helping to store a supply of grit as it arrives at the gun. I am noticing that the gun is able to supply a near continuous supply of grit but it is not being sucked up the tube in a continuous supply. I would love to be able to 3D print a whole bunch of transparent gun designs so you would be able to observe what is happening inside them as they work. Most SLS and SLA 3D printers are able to print good strong prints in transparent resin or powder. Sadly, those printers are still out of reach for most hobbyists. Regards, Mark

[@canadianavenger]

indeed the volume to the aft may be the cause of your pulsing feed, though I suspect it is also because of geometry you had at the front.

[@fernandoratag]

Hey Mark, great videos! I have an issue. So i'm testing my homemade Gun using 2mm airjet, and using a 6mm Nozzle. When i open the air, the slurry pump are studdering. I have tried adjusting the jet position but seems not getting rid of the studdering. Is it because i'm not using air regulator? Do you think the air pressure were too high? What psi should i use for this setting? I'm gonna keep the 2mm jet for the whole test. Please help. Thank you Mark. Nando-Indonesia

[@Preso58]

Fernando, I still get some interruptions in the supply of media but it doesn't seem to make a lot of difference to the amount of media being delivered to the part you are blasting. I believe that the nozzle can only supply a certain amount of media and the excess is kept in the cavity inside the gun. I am still planning to make a blasting gun with a clear plastic body so I can see what is happening inside the cavity surrounding the internal jet. I usually use a pressure of around 80PSI but I have heard that you can reduce that to 50PSI. It is probably more important to make sure you have a relatively large reserve of air which means having a very large receiver and decent size pipe work to supply the air. I did a video on a recent upgrade to my compressor and air storage here kzbin.info/www/bejne/fpWymKeqoZWErdk it starts at about 10:00 The new setup works much better and I can keep the pressure drop to a minimum. Regards, Mark

[@MasterofCrude]

Nice. Very NICE !!!

[@bobvines00]

Mark, Did you try different sizes of media feed hose? Maybe the guns can't handle the amount of media being lifted, causing the media to back up.... Or am I forgetting where you already covered this? I was wondering how the "discussion" about upgrading the compressor went, but your "real time wife approval factor" chart answered that quite well. ;) Looking forward to the ray gun testing. If you design a functional ray gun, maybe the blast media surging won't matter. Just zap the items/victims clean! ;D

[@Preso58]

I badly, badly want one of those laser scaling guns. They are badass! I am going to do some more tests when I get the MKII version of the gun finished.

[@downunder5594]

Can you give me the distance from end of jet to end of nozzle please

[@Preso58]

Hi, if you send me an email I can give you the 2D drawings for the gun and all it's parts. I must say I never really measured what the offset is. I just adjusted the position of the jet until I was getting the best vacuum. I am thinking that there are lots of variables like the pressure of the air supply, the volume your compressor can deliver and the type of blast media you intend to use. You can find my email address on my channel page under "About". Regards, Mark

[@mousegouse]

"Real time Wife Approval Factor" chart was the best 😆😆😆, quite relatable......downhill after the Scones and a really sharp decline when you mentioned the Compressor 🤣 ...good luck ....love your videos😎

[@ShainAndrews]

I've tried a few of their products. I personally think they are shit. Tried having a conversation with them a couple of years ago to sort out the performance issues. Made a second purchase, tried that out. Noticed some improvement, but not much better than what you demonstrated. I'm not pressure or volume limited as I can push 28 cfm at 175 psi all day long. I was "updating" my $1300 cabinet) so none of this HF stuff). Fussed around with varied pressures, nozzle sizes, nozzle position, media types. I've run cabinets in the past where you knew when the media hit the gun and stayed there. Suction/media delivery is always weak. When I had my fill of that tomfoolery I purchased a pressure pot. No regrets since that decision.

[@Preso58]

Shain, I am starting to reach the same conclusion. I initially ruled out using a pressure pot because I have limited space in my workshop. I am considering mounting the pressure pot permanently on the wall and then wheeling the cabinet to where it is mounted and I will just use the cabinet as an enclosure to collect the grit. Regards, Preso

[@ShainAndrews]

@@Preso58 During my research I ran across another company called Pirate Blasting. They have a bit more information on line, but I determined to get the majority of the information required speaking with distributors. I was so put off with my prior exchanges I wasn't about to let somebody else sell me more sliced bread. I'm of the opinion a proper mixing valve should be where the performance is at. Seems like it should be located in the bottom of the cabinet, with air injection set horizontal with the media suction line directly across from it. Ball valves for media, and air injection to dial everything in. Foot control to start and stop the operation. I'll eventually get something like that built. Moving media between the cabinet to the pressure pot is not ideal, but I can blast to a much more uniform finish in less time trying to get a suction equivalent. I've had cheap guns where you stick the hose in a bucket of media that worked much better than what is being offered for these cabinets.

[@Preso58]

Shain, I watched a video by Stefan Gotteswinter recently where he showed a little desktop blast cabinet with a sort of cassette at one end of the enclosure. It appeared to be a pressurised container with a small bore PU hose to deliver the glass beads. It was made in Austria and called a Logiblast. He said it cost around 400Euro. The results he was getting were truly impressive. kzbin.info/www/bejne/oKW6mpKPgsiNmqs The footage starts at 00:27 I doubt I could get on here in Australia and I was already committed to what I built by the time I saw it. Regards, Preso

[@AmateurRedneckWorkshop]

Great job on the sand blast gun. Your wife is easier to get along with than mine. 😁😉

[@petergregory5286]

Great work on the gun. Looking forward to seeing your improvements. Judging from the last set of results you seem to need an upgrade to your method of working on or with your wife. Sorry, can’t help you there,failed miserably twice. Swapped mine in for a partner and she and I have been together 20 years. Not suggesting that you try this method of negotiating, a new compressor against half a house with new bridge are not good odds. Regards to you and do pass on my regards to your good lady.

[@Preso58]

Peter, I should set the record straight, she doesn't ever question my purchases. She's great! ❤

[@mclem4u]

I could use the manometer with great exaggerated results. Only one problem though, if my wife was around at the time of measurement she would challenge my measurements numbers and give much lower accurate results! Lol

[@ianbertenshaw4350]

We are going to have a discussion about finances and holidays - wrong ! She is going to talk and you gunna listen ! 😂

[@fragglepoop7185]

Wow... casting always fascinates me.. Why I'm here.. Gun Looks great...BTW 👍.. From personal experience you are wasting your time with suction fed guns tho 🤷. Build your self a pressure fed unit.. Just copy a sealey one.. Straight sided bit of tube With a grit flow valve pointing straight down at the bottom Into a t piece.. Just use a 1/2" brass ball valve to meter the grit.. .... And use tungsten carbide nozzles.. I'm using a 4mm nozzle at the end of 13mm blast hose .. I'm Running off twin 3.5hp single phase compressors. At 60 psi... Blows suction feed out the water big time... Less pressure... Loads more work done.. Just Leave the trap door open on the bottom of your cabinet dumping into a bucket thru a course sieve.. If you only have one 3.5hp single phase compressor go down to a 3mm nozzle so the compressor can keep up.. .. You'll never look back trust me....

[@fragglepoop7185]

www.blastitclean.co.uk/page4.html

[@Preso58]

Interestingly, I just watched Stefan Gotteswinter's latest video where he shows the replacement he bought for his suction fed blast cabinet. It was a quite small pressure fed gun which he runs with glass beads. He is lucky he lives in Europe where it still seems possible to buy quality products for the home shop.

[@Preso58]

Interesting. I may eventually go down this route.

[@lv_woodturner3899]

Only 10 psi, all you need is to make a 30in manometer and fill with mercury, which should be readily available in your shop. Just kidding, these days I do not even have a thermometer with mercury in the house. Things change over time. I can see the benefit of a larger compressor, but not sure why you would want a 3 phase motor with VFD unless you want to go AvE style and control amps to get variable speed based on load. A link in case you have not seen this. kzbin.info/www/bejne/sHq0kHSDaMehrdE I love the chart at the end. Tell your wife your viewers recommend you get a bigger compressor. I am eager to see the performance of version 2 design of the gun. Dave.

[@Preso58]

Dave, I read your first sentence and started to wonder what part of the planet you lived on that allowed for the sale of mercury "in the shop". 😂 "Surely you jest" I thought and so it was. I did watch AVE's video on the VFD compressor experiment. Typically, I walked away a little confused. It's sometimes hard to know where the serious stuff and the joking are in his videos but it sounded like a viable idea. I am starting to think about one of the Chicago silent compressors though. There is a 3 motor version that looks like it would do the job. Regards, Mark

[@lv_woodturner3899]

I do recall mercury spilling out of some broken instrument when I was in high school, back in the late 60's. I do not recall how it was cleaned up, but some small amounts got under aluminium extrusion on the edge of the table. It looked like it consumed the aluminium but I think it just prevented the aluminium oxide from adhering to the base metal so it just oxidized - but rather fast. My friends and I did not think about the toxicity. AvE is a mixed bag. Some very good information, and sometimes a lot of unnecessary "fluff". I looked up the Chicago silent compressors. Similar models sold in the US, even HF is now selling some under the new brand McGraw. Dave.

[@lockbuilder]

Mark, I do have a Tacoma Company upgrade on my cabinet. I made a video for you showing the mixing of the air and media in the suction line. Hope this helps! kzbin.info/www/bejne/jH2Tn3WspMZ2j5o

[@Preso58]

Wow, I didn't expect you to put up a video reply! I think I got a better look at your media supply in the shot showing the regulator pressure. It does look a lot like what I am getting now although the aluminum oxide you are using looks a lot finer than the garnet I am using. I like the rubber plug design too. I am running my cabinet with a much higher pressure, probably around 80psi but my biggest issue is CFM which is why I want to upgrade the compressor. Thanks so much for the feedback. It certainly does help. Regards, Mark

[@lockbuilder]

@@Preso58 I didn't notice it when I filmed or edited, but your right, the best shot of the media was during the pressure regulator shot! Lol

[@frankmcalinden8090]

Hi Mark Interesting video...I upgraded my h+f based on the Tacoma upgrade....Its a lot better than the old setup but my compressor has trouble keeping up. Im thinking of upgrading to one of those chicago hush types....Watching Rays garage upgrade , he sets the gun pressure to 40 psi with the petal pressed...I havent tuned my gun as yet, i came across another video see link which explains the setting up of the nozzle see link.....kzbin.info/www/bejne/Z5yVZoCfq91sisk...Just got a vacuum gauge of ebay so will set it up soon and try it out.. Cheers Frank

[@Preso58]

That's interesting. I have a vacuum gauge so I will try to set it up when I test the MKII gun. That way I should be able to run it at realistic blasting pressures. Someone else sent me a link to the Chicago range of silenced compressors. I have started a wish list! Thanks for the video link.

[@chrisosborne6957]

Have you seen Keith Rucker's video on this kzbin.info/www/bejne/eZi9iGV9d9uNh9U

[@Preso58]

Chris, yes I did watch that video quite early on and where he shows the adjustment of the metering valve it looks very similar to the sort of flow I am getting using a much coarser garnet. I was initially disappointed but the last test I did shows that I can get a pretty good continuous flow of garnet from the nozzle of the gun so I guess that is the solution I was looking for. I still want to upgrade my compressor though. It's a bit like me, old, shabby and lacking in performance. 😁

[@davidmuller1958]

youre awesome man. hope youre doing well.

[@Preso58]

Thanks. I have been using that gun attachment for a few years now and it works really well. I don't regret the work involved even though you can buy these guns off the shelf. Regards, Mark