🔧 Grouting CNC Tubes for Enhanced Stability and Damping! 🔧

[@BryanHoward]

I’ve been adding expanding grout to the tubes while the machine is assembled. I was unsure how it’d work out as it would be easy for the air to get trapped on the ceiling of the tube. Adding some holes in the middle of the horizontal tube for air and excess water to escape worked well. I fill the tube on both ends and the expanding grout will push all the air out the middle of the tube. Getting it into the tube in less than 5min is best. It'll expand more pushing out the air and water. If you wait longer than 10min you'd have to through it out.

[@glennburrow4364]

I would love to see a bench test of sections of square tubing with the different stiffening and mass-loading techniques applied. Test them for stiffness and resonate frequencies and things.

[@FilterYT]

Awesome Brian, I'm enjoying your projects!

[@mistr_clean7557]

I've been planning the same when I rebuild my moving bed as a modified print NC style moving gantry like you've done. I have no need for base or frame disassembly so I'm not worried about filling the tube however I have planned on capping my x and y rails with 3d printed caps with a hole in the middle for wire routing and putting a piece of captured 1" pvc through the center for the through hole. It being surrounded by the Portland cement I'll be using

[@PiefacePete46]

Looking forward to seeing the outcome... my gut feeling says there should be a significant improvement. Many thanks.

[@BryanHoward]

I've got a feeling it'll cut steel much better at low RPM with these changes

[@glennburrow4364]

I see those long tubes and it makes me wonder if a technique like post-tensioned concrete would help. Maybe cast in some thin-wall pvc and then post-tension with all thread? That wouldn't be practical with every tube, of course.

[@BryanHoward]

It'd sure help with any possibility of cracking keeping it under tension.

[@gorak9000]

I was going to say in the last video, there were a TON of resonances and vibrations, especially as the spindle ramped up and down, and while it was cutting too. Will be interesting to see how it affects that now that the tubes are filled. It would be interesting to know how much the whole machine weighs now. I got a "crane scale" and just my z-axis head casting (not counting the motor and the spindle) on my machine is 575lb. I'm guessing the motor is another 250-300lb, and the spindle itself probably 90 to 100lb. That's almost 1000lb just in the part of the z-axis that moves (plus another unit of that in the counterweight). The whole machine according to the datasheets is 11,600lb. That's where the rigidity of a real VMC comes from - just a metric sh1t ton of cast iron!

[@BryanHoward]

Yeah I think on the base of the machine the vibration is higher now because the gantry and risers are all filled in. The vibration that would have been going there is now getting sent down into the base of the machine and resonating. The video does make it look worse than it is because I usually have the phone camera mounted on a carbon fiber stick and 3d printed holder. That whole setup is kinda flimsy but at the same time does a good job showing when and what RPM the machine starts to resonate. I’ve got no idea how much it weighs now. Don’t have an easy way to measure it either. I could probably estimate the weight in solidworks as I have the machine in cad 1:1

[@gorak9000]

@@BryanHoward I would expect a solidworks estimate would be fairly accurate, especially if you made a test volume of the grout to see what weight / density it comes to after it's cured.

[@BryanHoward]

@@gorak9000 I’ve been pouring the excess grout into a small plastic bucket. It’s hardened and I can find out its weight and volume displaced in water. Plug that into a custom material in solidworks and that should give a good estimate of the weight.

[@PiefacePete46]

@@BryanHoward : Check to see if your bucket has volume markings molded into it... some do. It could save you from "splashing your boots"! 😜

[@PiefacePete46]

@gorak9000 : Absolutely right... when it comes to damping, mass is King. The obvious downside is that it is probably heavy! 😉 Organ pipes only work through resonation... I bet they don't sound so good if you fill them full of grout!

[@glennburrow4364]

Could you talk more about the type of grout you are using? I saw Sika 212, but that isn't an expanding grout. Are you using additives?

[@BryanHoward]

As far as I understand, grouts labelled as expanding and non-shrink are basically the same thing. Calcium aluminate is the active ingredient that does the expanding. Non-shrink probably puts in about the amount to counteract water evaporation where full on expanding is trying to expand into every crevice.

[@muzzarobbo]

Interesting stuff, thanks for sharing! For the table i would maybe add a steel sheet (12 or so mm) and then have grout underneath it to dampen the surface. it could then be flattened and have threads put in it for workholding. I have done a bit of research on controlling machine tool vibrations and i think adding mass is a decent strategy with your high speed spindle, it will lower the frames resonant frequency, hopefully further away from those of the cutter. For heavier cuts, stiffness and low weight is preferred to bump up the res freq as high frequency has less energy and therefore amplitude. damping should then come from a lightweight foam rather than grout. I have built a VMC with 200x200x16mm steel SHS and still havent decided exactly what im going to do to stiffen/dampen it. Cheers

[@BryanHoward]

I’ve been thinking about how to do the table and thinking of 2 sheets of 1/4” (6.35mm) spaced apart with short sections of steel pipe tubes. If I could find them at a decent price with internal threads that would be even better. Have about a 20mm gap between the 2 steel sheets. If the ID of the holes in the sheets is the same as the OD of the tubes I could drop them in and put small tack welds on the inside to keep them from coming out with little possible heat distortion. Add some thinner steel strips to the sides and pour grout in from one side and vibrate out all the bubbles. I’d have to rent a mag drill but besides that it should go together easy and have a good deal of damping. I’m not finalized on any design but leaning for a composite of steel and grout as it seems to be working well for me.

[@muzzarobbo]

@@BryanHoward yeah it would depend on the locational accuracy required for the threads, i was thinking if you get the cnc to do it afterwards that would be the most accurate. but maybe your method with solid round bar between the two layers and drill/thread in post. i suppose the thread will never be a super accurate locating feature unless it also had a taper/counterbore on top.

[@BryanHoward]

@@muzzarobbo Yeah trying to get a fixture plate as accurate enough where I can just drop in pins and be within the tolerances I would like is well beyond my means. I’d be able to mark with a spod drill some of the holes on the CNC but others would be past the work area the machine could reach and I’d have to do them by hand. I’ve gotten used to tramming in a part to the machine or just working with the vice as it’s already trammed in. With the threaded holes and clamp, tram some metal fixture or the workpiece itself I can build up a modular setup that is accurate. Just is a slower process than dropping pins in.

[@das250250]

I filled a beam with sand and it seemed to do a great deal of damping. Maybe you can try that with the stand seeing it doesn't need to be overly stiff .

[@rekcams]

Loving how much work you put into your machine and making it better as well as sharing it with the community. Is your machine the standard size or did you make it bigger

[@BryanHoward]

It's a standard size but I'm running a 4" x 3" gantry tube. Well there is actually a 3" x 2" steel profile on the inside too. I built my machine from originally my own CAD files that I recreated in SolidWorks from the beginning so there's probably small changes here and there from the standard PrintNC.

[@rekcams]

@@BryanHoward if I ask, your cad design, would you share it to see what you have done to make it. Like what you have done but I use fusion 360

[@BryanHoward]

@@rekcams It hasn't been updated in 6 months so not everything is the same github.com/bhowiebkr/PrintNC_Pro_Solidworks

[@marianodiaz461]

how are you going to remove any screws after the grout hardens? for example if you have a prang and the rails are y out of alignment? also what short of grout you are using?

[@BryanHoward]

I’ve found that grout hardening around threads is not to be much of an issue. It doesn’t lock them in place. For sure you don’t want to grout over any bolt heads. The 3 tubes on the bottom have bolts going both up and down. So I’ll have to recess the cap inside the tube to not grout over them.

[@intelligenceservices]

perhaps could have filled it with rusty iron and aluminum filings, the dissimilar metal would have a decent amount of mass and dynamic response to vibration, as well as possess a dangerous inherent self destruct feature for added safety awareness.

[@BryanHoward]

That would be impractical

[@vstolpner]

How much do you figure the machine weighs at this point?

[@BryanHoward]

Honestly no idea at this point. If I had to move it to another garage I will be hiring a rigging company to move it in one go.

[@T0tenkampf]

Have you had enough experience with your decision to use grout instead of more "traditional" epoxy granite to make a call on whether it is worth the cost savings versus performance?

[@BryanHoward]

Have you had enough experience with your decision to use grout instead of more "traditional" epoxy granite to make a call on whether it is worth the cost savings versus performance? I’ve looked into it. They have very similar properties but there are situations where you’d want to use one over the other. Epoxy granite mix works well when you mould it and it comes out of the mould naked. The material holds up very well to chipping and leaves a nice surface finish. Characteristically it’s overall better but much more expensive, makes a mess of everything when applying and working with large amounts of epoxy is not good for your health breathing all that in. Grout on the other hand is very cheap from the hardware store, just add water and pour. In this particular case of adding infill to horizontal tubes, expanding grout is the sure winner as you would not be able to get an epoxy mix to flow into and expand in the tube correctly. If I were building a CNC with moulded parts with internal steel skeleton vs the exoskeleton like I’ve done I would probably be doing epoxy. If I was building a welded steel frame and just needed to add much more mass and rigidity to that frame I would do grout filled tubular steel.

[@stanholmes4293]

Have you tried cutting at a slower feed rate? To me your feed was too fast for the cutting depth you were taking.

[@BryanHoward]

I’ve been running the BAP300r with a chip load of 3 thou (0.0762mm) IPT. It’s hard to run a 24k rpm spindle at recommended SFM into steel. I’ll probably look at a different spindle in the future but 24k rpm is nice for aluminum.

[@stanholmes4293]

@@BryanHowardThe feed rate is the speed the cutter/head moves across the work piece. Try slow that down.

[@BryanHoward]

@@stanholmes4293 You can't just slow down the feed without slowing down the spindle rpm. that's how you burn out tools. I'm using a high rpm spindle so there a minimum I can't go less than. I could go slightly slower to reach 1.5 thou IPT but even that is going to cause some rubbing with these ones.

[@jvandervyver]

@@BryanHoward Looking into PrintNC, for someone who is new to CNC Mills, why does that burn out a tool? Does it overspin when the load isn't high enough or something like that?

[@BryanHoward]

​@@jvandervyver The most important factor when determining feeds and speeds is the chip load for a given material and the tool diameter. Generally you want to be taking at least .001-.002” per tooth. I’d say even .001” is too low. If you cut a thinner chip than that the tool will start to rub against the material instead of cutting it. This makes a lot of heat and wears out the carbide tool very quickly. If you cut too thin of a chip in aluminum you are very likely to melt the aluminum. It'll get all gummed up and possibly break off the endmill. There’s also chip thinning which is another factor when calculating it but I won’t get into that. If your machine can’t handle a minimum chip load than you can reduce your depth of cut With the PrintNC, it’s happy to cut aluminum at the max 24k RPM with a single flute endmill. When trying to cut harder materials like steel, iron, or high carbon steel hard milling, you have to reduce the RPM considerably in order to reduce the load on the machine. The PrintNC isn’t designed to handle cutting steel but it can be done with light passes on the stock machine. A knee mill will do a much better job cutting hard materials. My machine started out as a PrintNC but it has so many changes to it that I wouldn’t even consider it one anymore.

[@davidpupu]

add aluminium 15-20 mm sheet as your base, level it and add tons of threaded holes

[@BryanHoward]

I’m probably going to make a steel sandwich with 2 x 1/4” sheets with 20mm of grout between them. Lots of threaded holes.

[@davidpupu]

@@BryanHoward why not aluminium plate its easier to fly cut removing some battle scar once in a while

[@BryanHoward]

@@davidpupu That is true. The footprint of the plate I’ll use will be bigger than the machine’s cutting area (just so I can attach it to the 3 horizontal beams), and I’d like to get grout damping as close to the workpiece as possible. I’ll likely use some aluminum plate as a consumable waste board that I could reface over time attached to the steel plate. The cost of aluminum around here is also very high compared to steel. And the coefficient of thermal expansion of steel and grout is very similar to much less likely to crack up the grout over time. I keep it in the garage so like right now +30C in the summer and -20C in the winter

[@davidpupu]

@@BryanHoward also disimilar metal have dampening effect. when u bolt the aluminium sheet dont remove the under side protective plastic. directly bolt to your steel beam. so after u grout in between the beam u can remove the sheet some day with easy. because the protective plastic still there

[@nionut]

You machine would be more stiffer if you designed shorter gantry in X and make it travel more in Y.

[@BryanHoward]

That is true. It was originally a PrintNC and I think the reasoning behind them doing it that way is to allow you to slide in larger sheets that are bigger than the size of a machine. How do you prefer the layout of it how it is everything is very accessible on it.