Chatter in one direction

[HeadScratcher]

A pic says a thousand words, so here is a video to demonstrate the problem https://www.youtube.com/watch?v=H7qaG4fT9qs

[elanjacobs]

Just to clarify what you've written in the video description; when you reversed the direction of the cut path the chatter happened on the other side (which would make it the same direction on the X-axis ie. towards the camera)?

[HeadScratcher]

Yep that's right the chatter was still towards the camera coming the other way, which suggests that my initial thought of it being related to position furthest away from the X axis ball screw was not correct.

[elanjacobs]

I don't know much about the hardware side, but it sounds like the servo driving the ball screw doesn't like travelling in that direction for some reason :?

[HeadScratcher]

Same motor and controller on the Y axis and it doesn't do it in either direction, so thinking it isn't hardware related, it could still be related to the unsupported X axis, but don't know why it only does it in one direction. Still brain storming ideas...

[HeadScratcher]

Might be worth swapping the motor out, just to eliminate it as a potential issue.

[elanjacobs]

Might be worth swapping the motor out, just to eliminate it as a potential issue.
Sometimes that's the only way to find electronic related issues; if the problem moves with the part you've got a starting point at least.

[mark david]

Hi, is the spindle rotation with or against the direction of cut?

[elanjacobs]

Hi, is the spindle rotation with or against the direction of cut?
The problem is there both ways. It doesn't sound like a spindle problem, it sounds like an axis motor problem.

[mark david]

I notice that the ball screws are very high up on your gantry maybe if they were lower down closer to the cutting plane might be more rigid.Still a bit strange should only chatter in one direction though.

Is your cnc a home built machine ?


The problem is there both ways. It doesn't sound like a spindle problem, it sounds like an axis motor problem.

[HeadScratcher]

The ball screw although high up isn't very far from the linear rail. Basically the linear rails are sitting on the top bars, then then two bearings, then the plate like the one in the video, and then the ball screw mounting bracket is attached from the top side, so in terms of rigidity it would be hard to get it any closer.

Yes it is home made by me :D

If I was an alignment issue I would expect chatter in both directions. I should mention that top linear rail isn't overly secure at the moment where the Y axis is.

[epineh]

Are you missing a ballscrew on one side ? Looks like you are going to use two on that axis but haven't put the second one in yet. With only one on one side I am surprised it is working as well as it is. The racking effect will be greatly amplified having one side driven and the other floating in the breeze, especially near the undriven side.

Also I have found that a little coolant goes a long way when cutting aluminium, I use WD40 applied liberally and get much better finishes on my home-made machine.

Cheers.

Russell.

[epineh]

Also have you measured the pockets, I would expect the dimensions to be a little off as the "loose" end will tend to be out of position to the driven end, the cutter would tend to "push" away from the material instead of "being pushed" by the machine, if that makes any sense.

[HeadScratcher]

Yes it is missing a ball screw on the left side. I have been stalling fitting it since the whole Y gantry has to come apart. The ball nuts fit in between the Y axis extrusions and the ball screw goes through it. Since I have been working my way up to he aluminium piece I have been putting it off until the alloy pieces are done.