I finally jogged the machine this week and the Y-axis rail is already showing signs of fatigue where the bearings make contact. One or two tracks in particular can be felt with a fingernail, but perhaps not deep enough to catch it. I attempted to spin each individual bearing while still on the rail, and some bearings seemed to have little or no contact with the rail. This seemed somewhat expected due to the cantilevered gantry, where one bearing in each bearing block will experience more load than the other bearing.
I hadn’t made any adjustments to the bearing blocks (per assembly instructions), but last night I deemed it necessary to mitigate observed wear on the rail. Prior to adjustment, I disconnected the threaded hub from the gantry so that I could move it along the rail freely to sense resistance. Nothing seemed problematic when first installed, though resistance seemed a bit too firm for my liking. As I removed the adjustable bearing blocks (I left the bottom and rear static blocks in place), though, I could tell that some bearings were already showing signs of fatigue and didn’t spin as freely (minimally improved when oiled). I was able to adjust all the blocks so that contact to all bearings was more uniform, and so that the rail moved more freely, without introducing play. I also swapped around the adjustment blocks to move any “sticky” bearings into less-load-bearing positions.
That all said, my question is whether these bearings will be considered consumable items? And to that extent, if they are gouging the rail, what about replacing that? (My rail is fine, but I may have some long-term concerns.) The bearing block appears to be assembled with a pressed-in pin, making it not (easily) serviceable, so I presume the bearings wouldn’t be sold independently of the block.
It is normal for tracks to be formed in the Y axis rail. The bearing essentially burnishes the rail to form line contact. Every machine out there (including our prototypes) will end up with these burnished tracks.
In addition to the many prototype machines that have been in operation for years now, we conducted life cycle testing to try to come up with a lifespan for the rail. Our test essentially had the gantry oscilliating back and forth at maximum rapid speed over a 1/4" distance on one spot on the rail for 48 hours straight. We were trying to see if the oscillations would wear the rail in that area to the extent that the gap between the torch (positioned at the positive X axis travel limit) and the slat bed would decrease. In short, we were trying to wear a low spot in the rail. We concluded our test showing that the gap only decreased by a few thou, and even then its hard to say if that deviation wasn’t cause by other factors (ambient temperature change being one of them.
It’s not ideal, but not uncommon for some of the bearings to feel a little bit crunchy. This is actually being caused by the shims on each side of the bearing lightly dragging on the bearing shields. What is most important is that the gantry moves freely (to the extent that any anomalies don’t show up in your cuts). We admittedly put a fair amount of preload on the bearings in order to avoid lash, but we have also seen bearing blocks get shifted as a result of the beating that UPS puts our boxes through. That may have been the case with yours.
Below is a picture of the rail of one of our machines. This tracking is perfectly normal.
The pins actually press out pretty easily to replace bearings. However, we plan to give customers the option to either buy individual bearings, or new bearing block assemblies.
Both rails will also be available for purchase for affordable prices.
Excellent response, Daniel, and thanks for the quick reply! That greatly alleviates my worries. Those tracks are exactly what I’m seeing. I think I just expected it to take some time to develop.
I agree the small wear lines are expected and acceptable. The bearings, I don’t think will wear any worse that the dozens of other machines that use “skate” bearings on their guide systems. I also think that some of that tiny “nit” lines, at least on my machine, is the wearing the couple thou of zinc off from the tube.
I would assume, dependent upon the base material of that tubing; after initial wearing there will/could be some work hardening going on that will decrease wear rate. I am guessing it will be a while before we have to mess with them much other than good maintenance and cleaning.
Thanks for the input, Jeremy. Though, most machines don’t have cantilevered gantries like the CF, which mean the bearing load may be less, or at least better distributed (supposing the CF had two Y-rails, I would expect far less wear over time). My concern was the amount of initial wear in a such a short amount of movement (I’d say I’ve jogged it maybe <20’ per axis so far…being able to feel the groove makes it on par with a gouge). I feel more comfortable now that it’s been adjusted, I agree we’ll be fine in the long run. I may even explore some other options to help support the gantry so that I can take some more load off the bearings.
Absolutely you are right, the cantilever design has more stress for sure, but I feel those 16 bearings take it up with ease. What I did not explain well (at all) is when I was looking into building a 4’x4’ plasma table from scratch I have seen a lot of people have issues with skate bearings and normal dual stepper gantry systems. The main issue is racking that can be caused by accumulation of tolerances from the tubes and probably some people/companies using crappy bearings and/or poorly made carriages. During radius cuts they have a slight “saw tooth” pattern due to this. My crossfire has had excellent radius cuts and I am very pleased with the engineering that has gone into it.
FWIW, I also had a lot of wear initially. My bearing block was WAY out of alignment as UPS basically dropped it from their 747 when they flew over I think lol. So much out of alignment that the weld seam from the bearing block tube ground a line into the main Y axis tube and I was stalling my stepper until I realized what was going on.
I talked with @langmuir-daniel personally on the phone (phenomenal customer service BTW) have since adjusted it and now it is squared up and seems well. I have ran the break in cycle no less than 6 times, in addition to my normal use (will be more now that I made a water table) with no change in bearing preload (I have been watching it like a hawk, removing the lead screw and moving the carriages by hand etc.) Once the initial wear has broke in, I agree that the wear seems negligible.
Quality on the table seems great, overall. In fact, I loved the cantilevered design. Glad my experience with the bearings and rail isn’t unique.
And agreed about excellent LS customer service. @langmuir-daniel (unless there’s another Daniel) texted the night of delivery as I was assembling my table, and giving some guidance about one hiccup I encountered (one of the hubs wasn’t fully threaded and wouldn’t go onto the threaded screw—after countersinking the unthreaded portion, got it to work fine, btw, Daniel).
It’ll still be a several more days until I can fire up the plasma cutter, but things are looking good so far. At least, not bad considering I’m basically re-building my garage around this table.
