[bucsmike]

I'm currently doing the CNC conversion on my G0704 mill with stock lead screws and there is a grinding sound when the y axis is moving inward but not when it is moving outward. I haven't been able to figure out exactly what is causing this so any help would really be appreciated. I have a video HERE for reference.

Thanks,
Mike

[Winnfield]

Is your Y axis gib too tight or too loose? Did you try playing with the motor tuning settings in Mach3?

[wizard]

I'm currently doing the CNC conversion on my G0704 mill with stock lead screws and there is a grinding sound when the y axis is moving inward but not when it is moving outward. I haven't been able to figure out exactly what is causing this so any help would really be appreciated. I have a video HERE for reference.

Thanks,
Mike

How is our repeatability and backlash?

My first thought is that the leadscrew bearings are loose on the leadscrew shaft allowing the leadscrew and coupling to chuck back and forth. When you are moving inward you are pushing outward on the bearings. If this is the case you should be able to see it as backlash or poor repeatability. Try milling a circular pocket to see what happens.

One possibility, though it doesn't sound like it in the video, is that you are loosing steps in the forward direction. This maybe caused by a gib shifting and tightening up. Visually the movement of the slide did seem funny so maybe you did loose steps. Videos aren't perfect. If this was the case though you would be way off position after a few cycles. When working on these sorts of issues it always pays to look at repeatability. One way to do this is to put a dwell in he returned position of a second or two to check position. You don't even need a gage for this for a course indication of error. Just throw some tape on the two halfs of the slides and scribe a line. In any event if it gets progressively worst in one direction than you might be loosing steps.

The point is the more you can quantify the more you can isolate the problem.

[bucsmike]

Ok so I tried adjusting the gib which didn't change anything so I tried adjusting the velocity/accel of the motor way down but there was still a grinding noise just at a lower audible frequency. I also tested repeatability and after about 25 cycles moving back and forth it was still spot on so I also am leaning towards it being the bearings. I will play with the bearings and report my findings.

[bobbyjoe]

Hi Mike

Sounds like the same problem I had with my G0704,I have ballscrews which haven't been installed yet (waiting on some stock) I went ahead with Hoss's phase one conversion which uses the leadscrews so I could get up and running for now, anyway I also had the crunchy grinding noise from the stock bearings after reassembly..You have to make sure you get them set just right with the table all the way back tight to the column when adjusting the preload,make sure it's not sitting with the rubber way cover compressed between the column and saddle, that's enough to keep the bearings from seating properly,another thing to be sure of is when you put those "cheap" 3 pc thrust bearings back in be sure to keep the races oriented in the same direction they came out,,if you look closely at them the bore hole diameters are are different, iirc I measured .396 outer race and .415 for the inner race, almost 20 thou.diff in the race's bore, at least on my machine it was, also make sure you let the leadscrew find the sweet spot before tightening down the lead-nut to the saddle..I had a burr on mine that made it difficult to get it to settle in which caused additional binding..When I took apart the Y mount after getting the grinding noise (using the original 0704 mount ) i had some chatter marks inside the race,if you find that you'll have to try and smooth them out a bit otherwise you wont get a smooth ride on that bearing.. I'd go ahead with ballscrews if you can,that should eliminate the problems associated with the cheesy bearings,, thats just my two cents based on what I found happening with my machine..hope it helps.
Bobby

[bucsmike]

Ok, so I 3d printed a y spacer that could fit around the stock bearing housing since I thought it could be a problem with the y spacer I made and everything works great now. Still not positive what the exact problem was but it definitely was something with the bearings being seated improperly. Thanks for all the help everyone!