Juddering Y axis

Any ideas ? I have an A4 gantry machine and when doing a fast travel in the + direction only, the Y axis makes a nasty high pitch juddery noise in two places on its' travel. I have almost had the whole machine apart and can't find any reason for it. The gantry seems aligned as far as I can tell using squares. The only thing I can think of is one of the linear bearings is causing the problem. If I put pressure on the gantry on the side that the noise is coming from it stops the noise.

Help please.:nightmare:

Rob

edited yip see below, its likely what jazz has said having read his post,an oversight on my part ive had the same juddering on all axis but random instead of specific areas of the machine,as i did i can see why someone would think it was mechanical.

My next job then, is to get the machine unbolted from the bench and slacken, jiggle, check and retighten the rail mountings. I'll probably take out the Y motor and check the feel of the Y slide on the rails.

It is only a hobby machine with ACME screws and delrin, but the hobby seems to be getting it aligned and working smoothly.

When I have got the machine off he bench I will take some pics.

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Originally Posted by cropwell

My next job then, is to get the machine unbolted from the bench and slacken, jiggle, check and retighten the rail mountings. I'll probably take out the Y motor and check the feel of the Y slide on the rails.

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first just disconnect the ballnut mount from the back of the plate,that will free up your z without removeing motors or screw,then slide left to right,if somethings not aligned or theres bother with the bearings you'll feel it tighten as you go,.

If there's nothing obviously mechanical causing this judder then it could possibly be resonance causing the motors to judder. This is a typical mind band resonance problem. Called mind band because it affects motors at mid to high rev ranges or frequency.

To quickly see if this could be the cause then try changing the micro stepping on the drives and see if it changes or moves the point when it happens.
If it's midband res then changing the MS can often eliminate the judder altogether, doesn't fix the problem just changes the frequency to a point it doesn't affect motors.

Well chaps,

Progress has been made ! I took off the machine bed and unscrewed the block with the lead nut in it. The Y axis moved easily and smoothly. BUT when I unscrewed the lead nut block it was 1.2 mm above the mounting on the gantry, so it was bowing the lead screw. I have shimmed the block and now it runs smoothly. I just need to finish reassembling and test it again.

Hopefully, End of Story.