Hi All
I have a DIY CNC router I built myself, out of aluminum extrudes. I mainly use it for cutting aluminum, in form of 10mm thick plates. Out of those I produce plates and planks of various shapes, containing grooves, slots and holes - the standard 2.5D machining. Using 4mm end mills.
In order for the workpieces not to become loose while the machine is working, I set the machine to cut all the way down minus 0.1 - 0.2mm so there's something to hold the pieces... Also I use SolidCAMs iMachining feature to cut the plates.
Another relevant detail is that I set the Z-level manually, and that eventually became the cause of the accident. A few weeks ago, apparently because I had made a small mistake in the Z-level, the machine had cut one of the pieces all the way and it had became loose. Subsequently the loose piece had impacted the spindle several times, since I wasn't there to stop the machine. As a result the spindle became noisier (or changed the sound it makes while spinning) also one of the ball-nut-screw assemblies became noisier too. Luckily there was noting bent. So I set another workpiece and put the machine to work - no problem, the machine worked fine. Also after few workpieces done the noises in the spindle and screw seem to disappear.
All that continued until the last week, when the machine started breaking end mills like "crazy". Usually one end mill goes through three plates producing tens of parts before it wears out (and it doesn't break, it starts to squeal loudly). That's about 15 hours of non-stop work. And now I need four end mills to finish a single plate. All end up broken.
My first thought was that something in the machine had became loose and started re-tightening every bolt. I did find loose bolts in a quite crucial spot - holding two of the linear bearings of the X-axis. I tightened them and put some "liquid steel" epoxy glue, to make sure those bolts never become loose again. The glue also binds the bearings to the frame besides the bolts. So I thought the problem was solved, but after three more broken end mills in the span of 2 hours I realized that the problem isn't solved at all. I continued looking for loose bolts and found none in the whole machine. I used an indicator see if there was an actual play in any of the axes, and found "none". I mean whatever play there was, it was well within acceptable tolerances and the way it was before the accident. So no axial play in any of the screws, no play in any of the linear bearing, the frame is nice and tight. the connections between motors and screw are tight and "healthy"
So now I'm out of options.
The two things that remain are:
The screw that had became noisier could have dints made by the bearing balls at the positions where it was at the moments of impact. So the nut-screw assembly is mainly tights except wen it "hits" those specific spots. but that would mean the end mills should break when they reach those few specific spots and they break at random places, and not near the said problematic spots of the screw (since i know at what positions that axis was when the impacts occurred).
The other weak point that remains is the spindle. There could be damaged bearings, or even slightly bent shaft. The spindle doesn't show any obvious play when I try to move the shaft back and forth. Can damaged bearing be a problem even if their play can't be felt by hand?
Obviously the spindle is the biggest weak point that could be the cause, but due to my "brilliant" engineering unmounting the spindle is going to be a tough job, so I needed someone to confirm my suspicion before I undergo the procedure... Also as more experienced machinists you might suggest something I haven't thought of. Of course you can't tell for sure since you haven't even seen the machine, but I'm interested in your opinion, as to what might be the most likely cause?
Thanks a lot in advance!
Best regards
Ivan