previously accurate homebuilt kit machine won't cut perfect circles any more

Check it out, my fineline automation FLA-200 (2x4) machine used to cut perfect circles, but suddenly it does this:

http://i.imgur.com/CDGchla.jpg

Is that the product of backlash? How would I determine the exact source of the problem?

Thanks!

According to Ahren of cncrouterparts.com, if I'm using the original one piece acme nuts, that could be the problem. I replaced the original acme nut on the z axis a while back, so I'm going to do that with the one that moves the z along the gantry. That'll be fun, taking off the z, replacing the part and then putting it back together. Hopefully that will fix it.

And that wasn't it. I installed the dumpster acme nut and it's still doing the exact same thing. I don't believe it's the G-code as it looks fine in Mach3, so it has to be the hardware, right?
I've uploaded the g-code and aspire file here: http://www.mattclara.com/misc/aspire...te-channel.zip in case anyone wants to take a look anyway.

Looks like backlash. Check for loose couplers.

Fun problems i discovered with my FLA100 and how i handle them:

The 2 allen screws that hold the X acme nut to the gantry, first off, isnt perfectly level. I had to shim the hell out of mine to get it close.

Second, those 2 hex nuts come loose. id shim it and tighten down and maybe even add some LocTite.

Also those goofy bearing blocks on the x and y, but especially the x, come loose VERY easily. Or i should say out of alignment.

I added a bit of loctite after disconnecting the whole YZ gantry from the X bearing blocks. Packed 2x4s under the machine to hold it up. Used C clamps to hold the bearing blocks tight against the machine, but, not TOO tight. Just enough so that all 6 bearings were making contact. Adjusted my set screws carefully, but quickly as i had loctite in.

So far its improved a bunch. I havent had to redo the bearing blocks once.

BUT! Junk does get into those x bearings. Even with my dust collector. Im constantly making sure nothing gets in those blocks. I recently tried to cut some alu on it and i notice that stuff is stuck on the surface of the bearings good. Probably going to have to pull all the bearings off and give them a good cleaning.

Lastly. I had a circle/arc issue with my first board, the HobbyCNC board. Man when i went to a Gecko i couldnt believe the improvement. It was like a totally different machine.

Now on top of all this, whats your PSU?

I have one of the 36V switching supplies. I can hear it when its first started and i do a jog, that the current will spike/drop, and this is after its ramped up to velocity. Temperature affects this thing bad. I'm looking to put together a good torroid PSU. Just need to find the caps.


Now, after actually looking at the 2x4 and seeing its a dual x motor design:

I hadve buddy who had issues because his limit switches werent 100% aligned on the x. he has a rack and pinion design. Spent an evening measuring backlash/difference and shimming each side of the X. Any latency issues in your I/O will contribute to this as well.

Looks like I never completed this thread. It was one set screw on one of the rack and pinion parts had come loose and there was some slack in it as a result. When it changed directions it was a split second before the pinion started spinning due to the slack. I took the set screw out, added a drop of locktite CA and screwed it back in and haven't had a problem with it since.