Stainless Steel - Quick and dirty flex test

Mostly Printed CNC - MPCNC Hardware Development
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Just watch out for some stepsticks claiming to be able to do 20A. Sure the mosfets may be rated to 20A but in a stepstick format they are hardly possible to cool well enough to sustain such current. Modern SMD mosfets are cooled via PCB so even a big heatsink on top will not help if there is no sufficient PCB area to carry away the heat from the junction. Somewhere in the fine print they normally claim a lot lower number but even then I would add a big asterisk next to it …

The other issue is that sense resistors are normally not set for such current. I could believe claims of 3A in stepstick format or maybe 4A if there is a blizzard blowing through the area all the time.

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Hi all,
I understand the challenge heavy/stiff/speed.
Because of what available to me and because I’d like to have a table not too small , 3’x3’ table.
I plan to mill small aluminium parts, wood and also to cut motorbike vinyl coverage)
I have access to stainless, OD 25mm but only 2 thickness
0.078I" and 0.049"

Would it be a good idea to use the thicker for the frame and X Y axis and the thinner for the Z axys ?

Thanks

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Outside rails have only vertical loads, and you can support them mid span, so you could go thinner. But then the weight doesnt matter so it’s just the cost difference.

The z axis does not really deflect from bending of the tubes. It deflects from the center assembly. You could go thinner but again the weight is not huge so there is not much downside to going thicker.

The gantry rails are most important stiffness-wise so you sould want those to be thicker. Yes it adds weight but I think it would be worth it.

And in general I don’t think that weight matters that much if you are milling. For a 3d printer or pen plotter there is advantage to higher accelerations but milling it’s okay to haul around a little extra weight.

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Thanks Jamie for you help.
The thicker is available 6 meters or nothing, so I’ll use it on rails and Gantry.
nothing left because of the size I want so 'll go thinner (sold cut the size you need) for the Z

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That’s basically what I did for my lowrider (still under construction): 0.083" wall tubing for the X rails and 0.049" wall for Z.

I was also considering 0.095" 1020 low carbon steel. It would of been almost 2x cheaper than stainless but I would have to protect these from corrosion somehow (probably smearing on a coat of inhibitors from time to time) so I decided the savings would not be worth the hassle.

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I just got in some 1"/0.065" DOM from speedy metal. I could not test it with a full width since I only have 4’ lengths but it is certainly better than the SS I have. It is hard to say but a 46" span seems to be somewhere near 0.5mm deflection, vs the Stainless at about 1mm. Those numbers are not to be trusted too much but it is stiffer. The cold working really does seem to add a lot to it. On top of that it is extremely consistent 25.45-25.49mm round and smooth. It will certainly need some coating as we talked about in the other thread, paste wax or some other similar non silicon dry coating.
Less than half the price…should I even make a 23.5mm version of the new version? For that price a little wax is no big deal!
https://www.speedymetals.com/pc-3494-8242-1-od-x-065-wall-dom-steel-tube.aspx
https://www.speedymetals.com/pc-4494-8276-1-od-x-0065-wall-tube-304-stainless-steel-annealed.aspx

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The 1010 steel pipe that I tested above was of the DOM variety. It is slightly stiffer than stainless ones I tested, pretty much as predicted by theory. Theory predicts 1mm deflection for a 48" span when material has 193GPa modulus, however an improvement of only 10% or 0.9mm is predicted at 210GPa.

That said, DOM or “seamless” as it’s called when applied to stainless pipes is a really nice process and that 1010 pipe was by far the most consistent and the straightest of the bunch that I tested. I went for seamless stainless because of a very good price I got from local metal yard, if I had to choose between welded stainless and DOM carbon steel, I’d probably pick DOM steel. Especially if we can find a good way to keep it from rusting. Would ACF-50 be a good fit?

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This looks like a solid explanation, Plastic. Pre-stressed-ish. Stainless DOM would be cool but speedy does not seem to have it and all the other places seem to be significantly more expensive. I now live at least 45-hour away from either metal supplier so speedy is a good option for my smaller builds. Just trying to tie up loose ends while working through a new build.

For less than half SS prices and slightly better performance and dims I think this will be the new recommended.

ACF-50 seems cool, Never heard of it, but looks promising. As soon as I cut this batch of rails up I will de-grease a cutoff and leave it outside and see how bad it gets, maybe test some common coatings.

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Paste wax would probably be the best. I use it on my cast iron table saw top. It’s humid as shit in the summer time here and so far no rust, at least since I got it into the shop, stupid bats.

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Why non silicone? Rails not in contact with the wood or some other ?

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Silicone and woodworking, or anything that will get painted or coated, even glued are a bad bad idea. Any tiny sign of it and coatings and paints will not stick to the wood and or you will get fisheyes. It can mess up things up for a very long time.

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Silicone is evil.

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David Hasselhoff and I must respectfully disagree.

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This guy tested a few. The video is long and rambling and definitely not PG rated (don’t watch with kids around), but images speak for themselves (ACF is one of the two shiny sectors).

My main concern would be if it will be sticky enough to collect sawdust.

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That’s why I said paste wax. It’s try to the touch in a few minutes.

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Saline feels more realistic…

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I’ve encountered ACF-50 (and a similar product called CorrosionX) in the aviation industry. Both remain tacky for a long time. I think they’d be a saw dust magnet.

I agree with @barry99705, that paste wax is a good option. There’s also a variety of products sold for use on cast iron table saws and such that would work OK. I think they’d all need occasional re-application.

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Conduit is still cheaper than DOM tubing. 5ft of 3/4 conduit is about $5 so a 2x2’ machine would use about $15 worth of conduit (3x5ft), the same machine made out of 1" tubing would come to ~$50 for tubing. Not sure if that $35 alone is worth keeping the conduit version around, but given conduit is galvanized, it could be slightly less maintenance.

Given for longer spans one really wants a larger tube, I would look into a possibility to unify metric and imperial with a 1.5" version. 1.5" is exactly 38.1mm which should be close enough to use the same parts. I did some quick googling and found a bunch of tables from Sizes of steel tubes and pipes - Železiarne Podbrezová . 38 or 38.1mm is listed in all US, EU, JP and RU standards tables. I also cross-checked what tubing is available in Estonia where I’m originally from. We have a very low population (1.5M) so anything remotely rare would be hard to get. I found both stainless and carbon steel to be available in 38mm. Of-course more research is needed to fully gauge general availability of that size.

Another size that has significant overlap between the standards is 31.8mm or 1.25". I did not see this readily available in Estonia but 32mm is available which can be forced into the parts but I don’t know what the ramifications would be. @vicious1 what is the tolerance of the parts that hug the pipe? I know the documentation says “interference fit” (0.05mm @ 25mm) but what happens if the pipe is larger/smaller than that?

EDIT: 1.25" EMT is 38.4mm OD so in theory if it’s possible to design for 38.2 ±0.3mm it should work for conduit, imperial and metric tubing.

EDIT2:

I ran some numbers to see how much weight advantage would a 3/4 conduit version have over a “generic” 1.5" version which would be one reason to keep this version around. 3/4 EMT has wall thickness of 0.049". Everything in the 1.5" size seems to start from 0.065". So the gantry of a 2x2’ build would “gain” about 990g (850g → 1840g). However, the middle itself w/o rails on my MPCNC (with all the bolts and bearings and Z axis) weighs 2308g so the weight gain would be about 30% w/o a tool. For CNC use, DW660 adds another 1500g so the total gain is only 18%. 1.25" is available in 0.049" wall thickness thus the weight gain there is ~310g or only 9% of the total gantry weight of a 2x2’ machine. I personally wouldn’t worry much about the weight gain but then again I don’t 3D print with my machine (yet).

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Yeah, I figured, :no_mouth:. Really dislike this 3 version hole I dug myself into…This version might currently already fit 25.4-25, maybe 1-2 different parts…23.5 all new. Maybe, I guess I should really look into this and see how far off it will be. Hmmmm.

Pastewax it is. So in the end, rust is not an issue, with some light occasional use the bearings will ride on a clean path, this is just for some aesthetics I think. Anything will probably work just fine, If you have an issue using some wax on the rails once a year, spring for the stainless. I am just trying to offset some of the cost, meet in the middle.

That is what I am working on. Currently larger or smaller really really effects the angle of the gantry tubes, compounding a few times, more than just tolerance stacking. The new one, might have much much less of an effect. It does still rely on the Z axis to help set the angle but in a very different way. Not compounding means the effects for a different size are multiples less error. With this in mind I will put a little more thought into it.

At some point it just can’t be that variable. For example think of the corners, We could pretty much use anything smaller than the intended design and it would work pretty good. At some point the offset block would be pretty far off but still functional, then eventually you would run out of the clamping gap. The feet could be made in two pieces and that could accommodate a larger range. BUT everything is a bit stiffer if they are a more exact fit. So 25-25.4…really no big deal, feet-corners-rollers-gantry…then you hit the Z axis. That needs to be a precision fit. That in turn defines a lot of the center geometry. The more size flexibility you build in, in the end, you end up loosing space to mount a tool.
I started this new one with the intention of working with all three sizes, the 120 bearing offset will just barely fit all three, but then I think I would sacrifice rigidity just for me not wanting to maintaining three sets of parts, so we are back to 3 sets.

Hmmmm, I have some ready for testing, back burner.
So now really before I would even consider going bigger I would have to see really proof the rails impart any significant amount of error vs plastic parts in a reasonable sized build. I really tested the crap out of my 24"x24" footprint build and with a huge load and the frame deflection was not measurable with my dial indicator. Remember it is that first very tiny load we fight, the initial endmill engagement with the material, not the large constant load. One it gets a bite and loads up everything is fine as the system gets to the end of the elastic zone.
LR…yes that could use larger rails for sure (or a different cross rails system), but the MPCNC…I really don’t thinks so other than allowing for larger builds as this would also mean larger plastic printed parts which in turn means more springy elastic zone. So we would have to use other materials in the build, no longer an MPcnc (pro version?).

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P.S. This thread is really helping. Some of the details I did not care to define or “solve” are really getting worked out. Thank you everyone!