Hey, I’m coming from the machining world vs the wood working world. The the milling machines I have use ballscrews and have high tolerances.
We have a 5x10 PRO unit, and I’ve got everything up and running on it. It was a custom build with LinuxCNC and ClearPATH servo’s. I’ll share this in the build log a bit later. But, I’m to the finial stages of calibrating everything. I know we have some backlash, I’m having a really hard time measuring because the machine is so springy. Also, it changes depending on weather or not it’s loaded or not (Cutting vs using touch probe). I wanted to know what sort of expectations I should have with this setup. Also note: this machine is a 12" gantry, not the standard 8" which probably adds a bit more spring to the gantry. I’m a bit OCD coming from the machinist side of the house, complete with .00005" Dial test indicators… Go easy on me.
Compared to a mill my guess is that most large format gantry routers could be considered “springy”
I’d actually turn this back around and ask you: What are you trying to accomplish with this machine? Asking and answering that might help get you the advice you need from folks that are working with similar machines/materials.
Engineers and Machinist have a phrase, “Everything is a Spring”. Even a Bridgeport mill, or a K&T Universal Head Mill.
Anyway, this CNC is for for a Maker Space. Answering What I’m trying to accomplish, well, that’s a rather hard question to answer. It’s a multi purpose router. I have NO idea what the users will be doing. Best I can say, is just about anything. So, Slabbing, paneling, general carving, etc etc… Materials will be anything from foam, wood, plastics, and maybe some aluminum depending on how it does.
Being OCD, I’m just trying to limit my expectations and save myself from going down a rabbit hole. After getting my touch probe up and working, and measuring a 1" gauge ring. I can get an avg of 1.0000" on the ring, but, X is coming back as 0.9977" and Y is reporting 1.0024" So, that’s around 2.3 thou out for the X and 2.4 thou out for Y.
Do you all implement backlash compensation In Mach or in the new controller?
Here’s what I would do: Get the machine as square as you can:
From there I would make sure that everything is adjusted in per our specs (spring tension on the rack drives, properly adjusted belts, etc)
I wouldn’t obsess over it past that… Given that it’s at a maker space where people are going to be doing all kinds of oddball stuff it’s all about learning the best machine/workflow for the job.
If you try and chase some tuning for a project/operator that you cannot predict you’ll go mad. Just make sure that machine is in spec and functioning properly, and give people the tools to check that it’s in spec. Perhaps signs saying “check belt tension XX weeks” or “grease monthly” or “check square routinely”
If you do that, the machine will perform repeatably and reliably and you can keep people focused on learning and using it for what it’s good (And not good) for by actually doing stuff.
Squared the frame with 1/16" During assembly. Checked the gantry after everything was finished up using the 4 corners method (Only able to do it 5’ x 8’ as we have ATC in the rear, and a section in the front for other odd-ball stuff). It was dead on as much as you can tell using a tape measure.
I’m handling the maintenance we in the shop twice a week. I didn’t see anything about putting any kind of lubricant on the rack and pinion till recently. I have some CRC PTFE Dry lube coming to use. I won’t be using grease. I actually need to clean the linear rails, they’re getting a bit gunked up.
I had a half to 1 thousandth of backlash on my 4x4 pro when I was calibrating out the backlash. I was doing it mostly to see what I could get it to, not because it really mattered. With a large cnc router like these (especially yours with the 12" high gantry), there is going to be way more deflection than that when you put any kind of cutting load on it, so the backlash doesn’t really matter if its only a couple of thousandths.
If you want to measure backlash on this kind of machine, don’t start by measuring it at the tool. Put a dial indicator on the gantry or sides and measure it at the motor. If you find repeatable backlash there, some of it might be servo following error which you can tune out with more I (from PID) input, although I would expect Avid to have dome this as best at it can be done.
Once you work that out, any additional “backlash” in the system could be loose bolts (or belts), but is otherwise just “it’s not that stiff”. Put a dial indicator on the tool and manually wiggle the spindle; you’ll see
I suspect that the VAST, VAST amount of work on your machine will be using wood based materials. As a forester, we know that wood is hydroscopic and can expand and contract depending on moisture and temperature 3 to 10 percent is typical.
So, don’t worry about your machine being calibrated to less than a micron. At some point in the humidity-temperature cycle, the parts you are processing will be perfect to your spec - then they will change - just make sure you measure them at the correct “hydroscopic point”. :-).
I won’t even get into tangential vs radial shrinkage / expansion - other than T=2R.
Setup your machine then throw out your micrometer and just enjoy the specs of your machine since you already purchased it.
Go easy on me.
