Thread: Help with settings!
25KHz is working fine now I have the dip switches sorted. Also the motors are less hot since I enabled half current SW4.
However there is ANOTHER issue! All axis move nicely except the side-to-side one (Mach 3 calls this X). Strangely it goes in one direction (to the right in the video) fine and in the other it makes a horrible rubbing noise. It's the ballscrew, but I don't get exactly what the issue is. Can anyone help?
It is running with a rotating ball-nut arrangement, so the ballscrew is tensioned between the gantry sides. I've played with alignment of the ballscrew and even thought it seems to be straight and central with the ballnut it always makes that sound. The only way I can get it not to make the noise is if I press the left end downwards (as it moves towards it), but as the gantry moves to that side it automatically pulls it back up again to be aligned with the ballnut, so it it only works one time, I can't fix it like that. Interestingly the problem reduces massively if I fix the ballscrew at the right end only, or hold it softly by hand, but I worry this might not be very accurate. Actually the ballscrew is not straight, but when tensioned and aligned it is, not that this makes it work well.
I guess it is some problem with the moment force in that direction but how I'm supposed to cure it, I've no idea; just the that end hang freely so it can bob up and down?
Video 1 - Ballscrew tensioned tightly and straight.
DSCF8166.mp4 video by tenson_uk - Photobucket
Video 2 - Ballscrew held at one end only by hand.
Last edited by Tenson; 29-09-2012 at 07:11 PM.
Tenson I have just gone through this same senario for three weeks. I replaced the ballnut because it did not have enough bearings in it, Read my build log for why. Turns out that after chatting with dean it was all down to resonance and tuning the steps correctly. Try changing your steps to a lower figure, eg from 1/8 to 1/4. It may be a mechanical problem but this is worth checking. I went from 1/8 to 1/4 and it got worse. Then went to 1/5 and the machine is sweet!!
bruceThe more I know, I know, I know the less. (John Owen)
How much tension is it under when tight.?
How are you aligning the screw with nut.?
Have you checked there's no play or slop in the rotating ballnut.?
When leaving the one end lose does it work ok without holding it and if so does the screws lose end move up or down when Z axis travels along it length.?
I see in the video with you holding the end that the screw is a sloppy fit where pass's thru the gantry sides. Is this correct or have you removed a bush or anything.?
Really would think that if you nipped the screw up at each end just enough so the screw can slide slightly then move the Z axis to each end a few times it will align it's self then tighten the ends.
So the problem was a bad ballnut, or a resonance with the steps or both? Would you link the relevant part in your build log, please?
Hi Jazz, what you describe in your last sentence is exactly what I did to align it. The holes are over-sized because I couldn't align the ballnut mount perfectly during construction. After doing the alignment procedure you describe that it makes the horrible sound even though it all looks true. However bare in mind it always does it in one direction only. It certianly seems like the moment force in that direction (nut pulling the z gantry rather than pushing) causes the resonance.
Yes with only one end fixed the other end bobs around as the Z gantry moves.
Ok first bruces(motoxy) problem was micro stepping and resonance not ballnut or alignment.
Your problem seems and sounds more like alignment. I think your just going to have to keep tweaking each side untill you get the alignment correct.
Not keen on the over size holes has the screw isn't locked and can move around.?
Sorry can't help any more than that.!!
The screw is of course fixed when tensioned up. I'll play some more tomorrow, maybe adjust the ballnut mount rather than the ballscrew and try different microstepping. I do wish I didn't bother with a rotating ballnut on the X axis and just had them on the main gantry. On the positive side, the main gantry despite being about 50Kg will do over 10,000 mm/min :)
It seems unlikely to be the problem, but I would check that the ballnut is concentric to the screw. When the ballnut rotates does the ballscrew move up and down a bit? If so you should tweak it until it doesn't.
Good to hear the X-axis is working well, you've got 10m/min on a RM1610 ballscrew - can you remind me what length the screw is please, 1.5m?
Did you also use a rotating ballnut on the sideways axis? The main reason I regret it is the extra height of the gantry making it less strong.
The long axis is 1610 with and 1.5m. I don't know if it is fully reliable at 10m/min but jogging it doesn't stall.
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