I have had my mpcnc working for some time now, but managed to hasten the assembly enough that it ended up with unpainted DOM tubes. As soon as surface rust started to show, I read up on these forums and started using carnuba to fend off rust.
The wax does tend to slough off on the bearings after a few operations, but the debris is easily wiped off the tubes and bearings with a cloth. I imagined if they were painted it would take a lot longer for the paint to wear off leaving the desired bearing surface to roll on… and there may be a significant amount of hard to remove debris after a while.
However I like to imagine things that never happen a lot. So I was wondering what the overall experience is for those who painted their tubes.
Did you sand down the bearing lines before use?
Does the paint create bumps that result in artifacts?
Is there paint debris caused by wear that can be hard to remove (vs like wax).
I seem to recall some pictures on the forums where paint wore away under the bearings almost immediately. I haven’t felt the need to paint my rails, but they’re galvanized conduit and pretty lightly used (unfortunately).
I started off with just light oil. The problem I had was after a few sweaty arms graze the tubes, a week later surface rust would be apparent in the area. The wax seems to be doing much better at resisting this… but still after a month or so if I don’t wax the salty fingerprints they will start to surface rust.
I live in Sacramento, where the air is generally arrid. My garage where the Cnc resides rarely gets over 20% RH most of the year. However during heavy rains it gets soggy wet (thanks to poor drainage under and around the garage slab). Still pretty steel friendly overall though, compared to say a coastal town with salt spray.
I more so ask for the long term knowledge… if/when I do have to reassemble the machine or make another, I want to make it better if possible. I mean, waxing the fingerprints isnt too much, but if I have a way to eliminate any maintenance then I am all ears. Painting tubes prior to assemble is not much extra work if it eliminates ever having to think about wax. From what Tom mentioned, painted DOM sounds like it works out pretty well in the end.
I painted the conduit on my ZenXY v2. Of course those are POM wheels and not steel surfaced bearings so the level of wear is quite different.
I used high heat paint that needs a bit of baking to fully harden, which worked well, but one track on one rail ended up flaking off still. Overall, I did it for the aesthetic, the conduit certainly didn’t need it, and the one track isn’t visible from the normal viewing position, so I left it.
Most paint will not stand up to more rhan a few passes of steel bearings, and I wouldn’t expect it to. Wax should actually be better at holding up, since it remains flexible, though it will also come off. Oil will of course stick to the sawdust and chips, but is a good storage solution.
My Primo got some surface rust on the rails from some dampish things stored on the table, but has been pretty good for over a year.
I thought I said painting doesn’t stand up based on what I’ve seen on the forums but that I have no direct experience as I don’t have DOM and haven’t painted my galvanized rails.
I interpreted the paint wearing away quickly under the wheels as a good thing. I figured paint would only make the surface less accurate, and the bearings constantly rolling in those areas would continuously remove rust as it forms more or less. Otoh if the paint chips off leaving non rolling surfaces exposed, that would not be good.
Yeah painting galvy is generally a bad idea. I wouldn’t recommend doing that since the zinc is already there protecting even better than paint. Sometimes I have to paint over galvy at work; requires etching with acid first and even then adhesion can be dicey.
Stainless tube would certainly be preferable, but in my case the difference in price between stainless and Dom was more than just a little… would have at least doubled the costs for me to build my mpcnc.
Another thing that I have observed after several hours of operations, is my bearings dig into the pipes a little bit. That means they will eventually will have a rut that degrades accuracy, and will need replacement. This brings me to another related question… for the guys using stainless:
Do the bearings eat away much at stainless tubing?
I ask because working a lot with stainless at my old job, I became familiar with how it work hardens. We learned to cut very slow and deep to prevent work hardening on the numerous “fda grade” robots we made. I imagine a bearing rolling repeatedly over the same area would harden the bearing line, which seems like it would slow down the wear process a lot.
I have stainless tubes (think they are galvanized), and they seem to take the wear from the bearings very well. I’m not sure about work hardening though, I think that’s more an issue about temperature than mechanical forces?
It had been a long time since my matsci class… so I am foggy on the exact nature of the changes that occur in stainless as it work hardens, but I do remember the charts only involving strain, and it has to do with the compaction and alignment of the grain structure in the metal. Temperature can also affect grain structure (how we can anneal/harden steel), but work hardening (aka strain hardening) does not require specific temps. In fact it can easily happen on ice cold stainless (also, consider cold rolled steel and why it can be preferred).
One of the diy experiments that to me really illustrates how strain hardening works… take a piece of plastic bag and stretch it out to just before it breaks. Now take and pull apart the stretched section, but in a direction perpendicular to your first stretch. Notice how during the first stretch the plastic gradually got stronger… but after being stretched it is very weak and falls apart easily in the perpendicular direction. It is easy to feel and even see the realignment of the internal structure of the plastic. The molecules get stretched parallel to each other, greatly increasing modulus in that direction (and in turn reducing modulus perpendicular to the strain). Strain hardening in metal is the same exact process… just different grain materials with different size/shaped micro structures.
Price was a deciding factor for me as well. Not only is the DOM cheaper normally, but I work for a company that deals in steel tube, and we don’t carry stainless. The result is that I am able to get DOM at just barely over the mill price (When buying by the ton. Literally.) The difference between what I pay for steel DOM and stainless, I could afford to replace my tubes many times over for the difference.
I have some tool wax that I use for my tablesaw, but I haven’t gotten around to doing the Primo with it. I also didn’t get the LR yet. The Primo is a year old, and got a few spots of surface rust from having some damp rags around. My tablesaw in the garage was decades old, but got a spill on it, which ended up rusting, which is when I bought the wax. It hasn’t had a problem since.