Grinder disc comparison and cleaning off mill scale

[@richardreynolds3597]

Hey Greg, although I am relatively new to welding I have found the Scotch-Brite Clean and Strip XT Pro Disc work incredible for mill scale removal. The down side is that are pricey. Thank you for the video.

[@makingmistakeswithgreg]

Thanks for the tip, I will have to try one of those. I have used cheaper discs like that for cleaning paint off steel, which they work way better than a normal grinding disc. Paint causes 99% of discs to just load up.

[@slayerspam]

I don't know how these aren't more popular. Maybe it's because they're only really good for one thing? And cause they're expensivelike you mentioned. I love them, though. I use them for painting houses too, where paint is peeling badly, because I can feather the edge of the damaged area fast.

[@makingmistakeswithgreg]

@@slayerspam honestly I think they just aren’t well known. I know the dirt cheap ones don’t work at all, I bought one of those to “try” and was disappointed. The better one I tried worked far better, but I am sure that’s nowhere near as good as the Xt pro. Paint is a bear to deal with since it flat out clogs everything up, especially sand paper. The more you try remove it faster the worse it gets lol.

[@sebastianleicht]

Very informative Video, man thanks for this comparsion! I used flap disks a long time for general purpose but now swiched to the "hard-Rock-type" for milscale and heavy grinding Jobs. I also don't have a prefered Brand except for cutting-disks, here i like Klingspor most. My 125mm grinding disks are Harborfright and the 230mm are from Bosch. I wasn't aware that "Pferd" is common in overseas. And that "cardide-disk" was very impressive. I think I'll try to find one here and give it a try!

[@makingmistakeswithgreg]

No problem 😀. Around here a local big box hardware store sells Pferd and I believe the company has a big distribution center in the state too, which makes access to their products easier. I have found their products to work really good and have been using them for years. So far that oddball flat disc has been holding up decent. No doubt the surface is no longer as rough as it started off as, but it still cuts good. It’s kind of shocking how thin it is and what it can do. I think I will keep a few in one of my toolboxes just because I can fit them in a small area and they cut so well. If I needed to grind a weld down fast it would be the way to go I think. I will be doing more tests going forward on discs because I think it would be fun and it would be fun to put things to the test 😀

[@sebastianleicht]

Many thanks for your your great work!

[@bruced1429]

Well done video on grinding discs. You showed the Walther Flex Cut, I use these discs when I have dirty rusty mill scale steel . They are pricey but for removing anything from steel fast. The finish does show grinding marks though. I use a lot of Pferd wheels especially their one that has the rolled edge as it gets right into fillet welds, try some of those, they also have a similar one for aluminum which works amazingly well.

[@makingmistakeswithgreg]

I will have to try those walters, I have heard they are good but I have not run one yet. I have seen those pferd with the rolled edge, they are expensive and I tend to use carbide burrs to cut into a inside corner if I need to. I know they would produce a far better surface finish (and easier to achieve) but for what I do I never have to grind down welds. I have a couple projects coming up for furniture making so I will likely try that out too 😀. Thanks for the tip on the aluminum one, I definitely need to look into that, since I do a fair amount of aluminum. I tend to take bar soap and a 40 grit flap disc inorder to grind down aluminum. The shop smells nice but the soap particulate everywhere sucks lol.

[@veejaybomjay8145]

Greg, try 3M Cubitron paper disks, I have used them for a couple of years and they obsolete both flap disks and hard rocks. They are faster and leave a better finish than either of the above mentioned duo. They are not cheap but are pretty long lasting.

[@makingmistakeswithgreg]

So a paper back that uses a plastic backing like that red flat disc at the beginning? I will have to give those a shot for sure 👍, thanks for the tip.

[@RKELLEHER40]

Howdy, Brother! Your subscriber comments are all great and helpful. I just wanted to add that your videos are very educational and also save me a lots of time and money. Thanks again and Drive-On, Cowboy! 🤠

[@makingmistakeswithgreg]

Saving time and money is a win win 😅. Glad you have taken away something from my content 😀

[@mariodesmo]

I bought some Harbor Freight flap disc, and cut off wheels in a pinch. I was there, and I needed the discs that day so I bought some. They seem to work okay for the most part, but I haven't used them extensively either. Maybe include some HF discs for a comparison/benchmark? Good video, Thanks

[@makingmistakeswithgreg]

I actually like their Bauer cut off discs, and their Hercules flap disc has done me real well so far. I think they probably cost more per material removed than others and might not be the fastest, however atleast in a pinch I can get a decent option. I definitely will do some full on testing of a bunch of components flap discs, that would be fun and I think we could all benefit by it.

[@douglasthompson2740]

A. while ago I started noticing flap discs offered in 'flat' and 'beveled' (like yours in the video). I keep a few of the 36 grit around in the flat style for a broader cut as it lays almost flat in use but I notice it loads up pretty quickly and doesn't seem to wear the flaps all the way back as the beveled does. That being said because holding at an angle is habit with me the flat quickly turns into a taper! Mill scale does as you say load them up rather quickly in the 36 you get an aggressive cut to start with then as I wear out and don't put the beef into holding it down it produces a polish that seems even harder to cut through afterwards.

[@makingmistakeswithgreg]

Yeah, I think the fabric the grit is on literally polishes the scale which makes it tough to cut through lol. So far I haven’t found a perfect milscale disc that’s cheap. I am going to be trying some Walter milscale specific discs soon and I am hoping those perform decent.

[@sporadic29414]

You ever try the silicon carbide strip discs? They remove paint and mill scale very fast w/o removing metal. I use the small roloc ones in a die grinder mostly, but they have 4.5" angle grinder discs as well.

[@makingmistakeswithgreg]

I need to try them, I have only used the cheap knockoffs that aren’t as durable. The cheap one worked great on paint so I would think the more expensive one would be far better. A normal hard rock wheel is hopeless on grinding paint, it just loads up and cooks due to the heat lol.

[@175Larry]

I use a masonry wheel to remove mill scale. It cuts off the mill scale but doesn't take off much base metal and also leaves a pretty good surface.

[@makingmistakeswithgreg]

I Definitely need to try that 👍

[@ThePinkPanth3r]

I was trying to clean milscale off a 12"x4" 1/8 inch plate i picked up to start practicing welding on. Got terrible patchy results with a 27grit disk. Gave up and tossed it in vinegar overnight, ill probably pick up 30% vinegar from hardware store for next time. It worked well though, had a few darker looking stubborn patches that i hand sanded off.

[@makingmistakeswithgreg]

I have heard vinegar works good, I have never tried it. Some of the scale can be a bastard to clean off. It’s smarter to use methods that don’t make a ton of dust in the air to get the scale off 😀.

[@ThePinkPanth3r]

@makingmistakeswithgreg I just got a welder for Christmas and was using it for the first time around when you replied. Yeswelder mig-165ds pro, it was very cheap off Amazon on sale and a coupon. I just maimed an old lawnmower blade and had alot of fun. I dont have a table so I'm sitting on a tiny chair, in front of a short stack of buckets with a brake rotor on top (keep buckets from melting) and 12"x12" aluminum plate on top of that

[@morenothing4u]

Use the Harbor Freight Hercules masonary grinding wheel. It wears faster than the Menards Mastor Force and Dewalt Si-carbide masonary wheels. But leaves a better surface finish. The Dewalt one is way tougher and loads like a Al-oxide wheel. Great for actual use on masonary.

[@makingmistakeswithgreg]

Thanks for the tip. I will try one out next time I am there 👍

[@DIY_Tony]

Hello Greg, thanks for all your videos. By the way, your preference for battery powered grinders being slower and safer, they do make corded grinders with variable speed, such as the Makita, though they are usually more expensive.

[@makingmistakeswithgreg]

Interesting, every grinder I have owned has been a single speed. I might have to look into that. I do find the metabo plug in ones I have are pretty good with their safety clutch, but the speed in which they operate make they far more dangerous without a doubt when it comes to Throwing debris and controllability.

[@douglasthompson2740]

One other topic is the difference in price between 4 1/2", 6" and 9" wheels. I basically quit using my larger faster grinders because the price of wheel skyrockets when you go up even one size. Bigger wheels probably last longer but not as long as it would take to amortize the higher initial cost (plus I am getting too old to swing the monsters except on flat work)? Thanks again for your videos.

[@makingmistakeswithgreg]

Over winter I hope to tackle the grinder disk testing. I have a feeling there will be some standout ones, some terrible ones, and vast majority are probably the same lol.

[@colinhudson3723]

I've been using the sanding discs for years now ( 'paper' ) and they work well . They cheap and I keep a few grit sizes . I do have the hard wheels and flap discs too but only keep a handful . The paper discs do disintegrate when you hit a edge sometimes 😂

[@makingmistakeswithgreg]

I always worried about the paper cut from one of those discs lol 💀. I use the paper to give a distinct finish to stainless plates I weld for art, I find that they give a much more consistent and distinct finish.

[@colinhudson3723]

I've had chunks fly off ...lol . It's my own fault though trying to round off sharp corners . Hell I'm on my 3rd backing pad this year lol. As you know we can't have sharp corners when working in public places , apartment blocks and people's homes. Just too lazy to switch out to a grinding disc 🤦even though I'm running 3 grinders on site sometimes 😂

[@makingmistakeswithgreg]

@@colinhudson3723 I hear you lol. I generally am too lazy to use multiple grinders so I end up using a single disc to do everything. Then I complain later about the surface finish could have been better because it took too much time to prep something so it looks good after paint 😂

[@douglasthompson2740]

Comparing flap discs will be very interesting. The Chinese seem to be making most of them as with everything and they have a zillion brands some pretty good and some just thin garbage. I pretty much stay away from the top dollar ones as I don't think they give you the mpg that the middle of the road ones do. So I am waiting to see your outcome. Hope you throw in a time test as well to see how they each stand up comparatively.

[@makingmistakeswithgreg]

I have seen the same thing. I have bought the expensive brands and they seem to work great for 20% of the wear, but after that they perform worse than cheaper discs. The middle of the road ones seem to perform better after the initial wear. I have been stockpiling discs to do a grinder disc shootout over winter. I wanted to do it sooner but I figure why not test 20-30 discs to see what’s actually worth the money.

[@dennisyoung4631]

Walter Flexcut Mill Scale disks? I bought some these a while back. They last decently, and work well. Also for mill scale, phosphoric acid works well. It isn’t near as nasty as HCl/Muriatic acid on stuff in the area - not growing rust on everything in the area.

[@bioniclife]

"Works fast, doesn't last"...TRUTH! I just dunked 1" AR400 in muriatic acid to remove scale prior to welding. I was hoping it would quickly remove it and I could kill 2 birds with one stone. WOW that stuff is thick! I ended up having to grind some off. I too used a hard rock wheel after wearing out a flap wheel in a few minutes. I then followed the hard wheel with flap and it produced decent enough results. While I have your attention, any tips on welding 1" AR400 in a Tee joint? I chamfered the edges on the smaller pieces. Plan on using 7018, preheat to 500ish and cover with sand to cool. This will be a splitting wedge for a log splitter. Thanks in advance.

[@makingmistakeswithgreg]

1 inch AR plate is no joke, you definitely have the right idea for how to handle it. I do have some recommendations, hopefully they help you successfully weld that. AR400 classifies as a material that “attention to details” matters hugely. You must do everything I say exactly or you will likely have premature failure. 1: you must use 7018 straight out of a hermitically sealed pack or out of a rod oven. Hydrogen embrittlement will cause underbead cracking with this material. 2: lower the preheat to approximately 250 degrees. At 500 the heat affected zone can go into the tempering/annealing point of the material during welding, and that’s not good. 3: AR400 has a issue with allowing interpass temperatures (how hot it gets between passes) to reach too high. You want these to not exceed 400-415 degrees, which will likely mean giving it time to cool between passes. 4: definitely give the material time to slowly cool. The extra time will allow any dissolved hydrogen to escape. It will also give time for shrinkage to happen at a slow controlled rate. 5: it is common to weld material like that with lower strength rods and just put bigger welds (in size for the thickness of material). In the case of what you’re doing 7018 is a lower strength rod and is suitable, however the weld will not be as strong as the base material. Depending on design it may be acceptable or you may have to put more passes. 6: if I were you I would keep a log of the process you used to weld it. All Temps, times, rods, notes on how it welded. It sounds stupid but if it fails you can go back and have something to work off of to help determine what went wrong. Ar400 should not pose a big issue for you provided you don’t impart hydrogen into the weld and you don’t allow the material to cross much over 400 degrees. With that said, full disclaimer: I have welded a ton of AR plate, but for the purpose of cladding something. I dont recall ever welding a 1in thick piece of AR to another piece of Ar (or normal steel). In cladding purposes or simple plate repairs the material is normally 3/8th to 1/4 inch and not upwards of 1 inch. Doing fillet weld configuration with a beveled top plate edge on 1inch material is a ton of weld and a lot of opportunity for things to go wrong. No doubt I believe you can do it if your confident with your 7018 skills, but you must be prepared for the possibility of failure. What I worry about the most is as one weld solidifies it will pull the material, imparting stress on it. A few more passes will put even more stress on the material and leverage it against the cooling off welds. Doing a open grove multi pass weld on 1 in plate will impart a lot of stress on the material. Think of it trying to bend concrete like a leaf spring, it doesn’t bend much. Under stress or impact shock the welded area could fail. I wish I had experience with that thick of material combined with multi pass welds to know what to expect, but you’re in uncharted territory for me. Follow the info I gave you and complete the job. If for some reason something doesn’t work, I will figure out with you the next plan of action. I am probably overthinking this but I have seen enough failures on higher strength steels to know what can happen lol.

[@michaelwhiting878]

That is a lot of very good information, and is probably worthy of its own video.

[@bioniclife]

Greg, thank you so much for taking the considerable time it took for that reply!👍🏻 I had to buy a 50lb can of sealed Lincoln Excalibur 1/8" 7018 rod since they didn't have 10lb tubes. It won't be opened until I am ready to weld. The unused rod will be stored in an ammo can with oxygen absorbers for other, less critical projects, down the road. Thanks for the tip on dropping the pre-heat temp. I actually bought a 250° temp stick a month or so ago, seeming, at the time, to remember that was the target temp. I had since seen other info on the 500° (ain't the internet great?). The other day, I picked up a cheap Harbor Freight infrared thermometer (not the gun, the one that looks like a key fob). After your comment, I'm re-thinking the sand quenching and may have my sons help with monitoring temp and controlling temp with a propane/oxygen rosebud during the entire process. Of course, this will all be on video, and we will call out Temps, time between welds, etc. There will be edits, but I will try to convey the important details. I will tag you when I upload the video. I'm not a great welder, but the few higher stressed projects I've put together have not fallen apart after 20 years. But those have all been mild steel welds. I definitely put myself in the "self-taught farmer" category. Without sounding cavalier, I'm OK with it failing, not my preference, but I'm accepting that it's a possibility. I will probably forget a few things as I dive into the welding (I think today), but it will be on video and, hopefully, showing a successful outcome. And, by that, I mean that it holds up to the stresses of the splitting process. Maybe my experience will help others going down this road. Thanks again! Kevin

[@beyondmiddleagedman7240]

A decent rod oven isn't too expensive, doesn't cost a lot to operate and will save you in the medium run in rod cost and weld quality. And storage in ammo cans may work, but you need dessicant packs (big ones) over oxy scavengers. It is the hydrogen you are trying to eliminate.

[@andreashoiby4333]

Unrelated question but here goes - I got 7048 sticks that I use for tacking. They are awesome for that. They are made exclusivly for vertical down though but I'm struggling to get any decent welds doing that. You got any experience with them?

[@makingmistakeswithgreg]

I have heard of 7048 but never have ran (or seen one). I looked up the full spec sheet and you are indeed correct, it was designed to run vertical down. I can tell you that I don’t know if I could even get those rods to run here, I couldn’t find a distributor that has them In stock. Based on my experience running 7018 downhill (which it’s not designed for and can have slag inclusions doing) it’s all arc gap. With 7018 you basically have to operate blind, you cant see what the weld pool was doing. It was very difficult to keep a proper arc gap because it was tough to figure out what the arc gap actually was. My guess is that 7048 is similar, but slightly easier to control. Getting it to work right will require a straight in to slightly upward pointing angle. It will require practice, I would setup a flat plate of 6-10mm (around 1/4in) at near vertical (a slight angle off vertical will help and as you get better put the plate vertical) and run downhill practice welds. It may help to do a slight side to side motion to get the weld to stick to the plate. It definitely won’t be easy that’s for sure. The only rod I tend to run vertical down is 6011 on thinner metal like 1/8 (3.2mm) or thinner steel. That is very easy to control.

[@andreashoiby4333]

Thanks the reply, mate. I can't be arsed with downhill. Uphill 7018 is enough of a challenge for me still. Those 7048 are amazing for tacking though, as I mentioned. Easiest restarts ever through millscale and rust and everything. Been using them for old Rebar with no issues

[@michaeldvorak5556]

If you do a shootout with flap discs, try different abrasive materials. From what i understand, silicone carbide is better for removing mill scale.

[@makingmistakeswithgreg]

Great idea. I have been collecting discs for about a month now and I plan on testing them all. I will have to do like you mentioned and see how much of a difference the type of grit matters.

[@shaneisaac1184]

Paint stripper or poly discs work reasonably well on mill scale...need some push pressure for thicker scales though.

[@bmalovic]

30:49... You missed the spot, at 5 o'clock 😄 Kidding of course

[@mrturbo8001]

If you have time. Soak it in vinegar overnight. It will remove it and much safer than muriatic acid.

[@makingmistakeswithgreg]

Definitely will try that, thanks for the tip 👍

[@toyotatundra0455]

I noticed you're don't have a video on welding table. Is it really that important to have a dedicated table for welding?

[@makingmistakeswithgreg]

So I did do a welding table comparison video found here: kzbin.info/www/bejne/d6C8aHWIoKt1n9Usi=Pa4jY3GmJsDbDHkI . I am a big fan of big heavy chunks of steel for a table. They last forever and can be bought affordable used 😀

[@ScubaDude68]

Late to the show here, but I’ve been using those metal diamond grit disks to cut through mill scale. No real risk of the thing exploding and last a real long time.

[@makingmistakeswithgreg]

The flat ones like the diamond cups, or the ones that are like cutoff wheels?

[@ScubaDude68]

The cut-off wheels that are advertised to last 1000x or so more than the traditional ones. They of course are way slower at cutting, but chew through mill scale when worked at a steep angle. Even if used only to scratch up the surface, a flap wheel will do the rest no sweat. I think the key is just to break up the “surface tension” of the mill scale, so to speak. I’ve also used the disks normally used for cutting tile in the same way.

[@CameronDC-Grimes]

What about strip disks, they are purple and they remove rust like no other. If you need to remove paint it's the fastest of everything I've seen

[@makingmistakeswithgreg]

You are right, those will chew through paint. I had to buy a disc like that when I had a bunch of painted angle iron I had to clean up. The paint would completely clog even a hard rock disc instantly. I ended up buying one of those hoping it would work and it was exactly what was needed lol. Only downside was they cost a fair amount, but time is money and they saved hours. I am going to be testing a few brands of those soon 😀.

[@dcraft1234]

A lot of my issues is thick galvanizing. Much of my free scrap is heavy galvanized and clogs up even a hard rock quick. I have to keep going to a sharp clean edge to clean that gummy shit out.

[@makingmistakeswithgreg]

I bet, that kind of material is tough to deal with. Have you tried to use bar soap on the grinder disc with any success? Otherwise Walter’s milscale disc might be the way to go, it would be less likely to load up. Even still it’s going to be a challenge. Some form of acid might be the best option to strip it off, which brings its own issues lol.

[@dcraft1234]

I finally tried one of those pferd specialty disks. I am pretty impressed! Cleaned fast and did not clog up with either mill scale, thick galvanizing, or paint. If they last halfway decent, I doubt I'll ever use a hard rock again. Thanks for the videos!