Y Axis jerks

[theremin]

Hi,

Another newbie here--I received my Shark Pro Plus earlier this week and have been working on getting it set up. I was relieved to see that UPS didn't dump the boxes in the yard or throw them about or anything else like some of the stories I've read (whew!) In fact, everything arrived in perfect shape, and even without a helper I didn't have any problems putting it together and get it up and running in an afternoon. Here's my question though--the X and Z axes both work perfectly smoothly, but the Y axis has a noticeable jerk to it as it runs, especially at higher speeds (but is noticeable even when running slow). It's not terrible, but you can definitely feel the jerking at the gantry. The rails and leadscrew are perfectly clean. I'm wondering if it is some kind of alignment issue where maybe something got knocked out of whack in transit. Is there some procedure for alignment of the leadscrew/nut that I need to go through?

Thanks!
Dave

[Tim Owens]

I would not think an alignment. I would spray the shafts with dupont silicon telfon spray (or any silicon spray) and this should fix your issue if it is a contamination on the rails.

Thanks

Tim

[theremin]

Thanks Tim--I hit the shafts with a little silicone spray, and there is no difference. Maybe "jerking" isn't the right word--it sort of pulses along, shakes as it moves. The other two axes don't do this, and Y does it mostly at higher speeds. I don't know if this is normal behavior for the Y axis or not since I'm new to this stuff. Just to test, I swapped the X and Y axis at the controller, and it stayed with the Y axis on the machine, not the Y output of the controller, so it isn't a controller issue. Any other ideas?

Thanks,
Dave

[theremin]

A quick update--I pulled the table off and turned the leadscrew by hand. It was fairly easy to turn, though not as easy as the X axis (not surprising given the extra weight that the Y axis has to pull). But, I loosened the screws holding the leadscrew nut to the gantry, and it became much easier to turn. I turned on the controller and used the jog control with the nut slightly loosened, and the Y axis ran much smoother. So, I pulled the gantry up close to the motor, retightened the leadscrew nut and then loosened and tightened the motor mount screws. Turns out a couple were already loose (maybe part of the problem?). At any rate, with everything tightened back up it is doing much better. There is a fair amount of play in the gantry if you put any pressure on one end or the other, and I guess that could cause some binding here and there. I think that this play is probably due to flex in the frame, and is probably normal (I'd welcome any feedback that others might have on this if I'm wrong here). I doubt it will give any problems in use as long as I don't try to hog off too much material at a time--it wasn't designed as an industrial strength behemoth that can take big bites out of hard metal after all!

But the bottom line is that it's doing a lot better now--I think that shipment probably caused the leadscrew to become slightly misaligned and binding a bit. The Y axis travel isn't competely smooth like the other two axes, but it's much smoother than before. Given the extra weight and size of the gantry, the difference in smoothness between the X and Y axes isn't surprising.

Dave

[theremin]

As another followup--I've gotten to try the Shark out now, and put it to a pretty good test: cutting some fairly complex inlays out of mother of pearl using a tiny dental bur mounted in a high speed dental handpiece (@320,000 rpm). Perfectly smooth cuts! No problems in any axis. Of course the next test will be using a regular router and hogging out wood, and we'll see how that goes. But, if it can cut these inlays with that level of precision, I don't foresee any problems with bigger work. Getting the feed/plunge speeds right and taking the right amount of material off in any one pass seem to be the issues to work out. When they're figured out, all is well...

At any rate, the Y axis issues seem to be gone.

Dave