Engraving small font - the bit digs deeper and deeper as the job goes on. 6040z

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Originally Posted by lucan07

I cannot see this being the problem more likely the simple options, ER11 thread damaged and not locking collet properly, .

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Could you speculate on how this would cause the bottom section of the Z axis motor coupling to move into contact with the screw underneath, leaving a gap in the coupling assembly which should not be there it as can be seen in the video?
:D

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Originally Posted by magicniner

Could you speculate on how this would cause the bottom section of the Z axis motor coupling to move into contact with the screw underneath, leaving a gap in the coupling assembly which should not be there it as can be seen in the video?
:D

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The coupling can slip down onto the ballscrew and off of the motor shaft without the screw or the axis actually moving poor grip and gravity with a little help from vibration, also the video of the screw is someone elses problem not stated by this poster as far as I can tell.

If a betting man I would look at first item discounted as the problem, thin double sided pads probably applied towards edges with a little give amplified at centre as a helix screw into piece pulling it up or pulling the bit down with forces generated to clear the chips, the solutions are being given without identifying the problems which is illogical.

Post #1 (Quite obviously by the OP)

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Originally Posted by xoneeleven

Hello All,
We have begun testing engraving some plexiglass with small text. (1/4inch plexiglass, with 10point font)
.................................................. .................................................. ..................

Mark

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Post #5 (Clearly by the OP - the clue is in that name's the same)

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Originally Posted by xoneeleven

Here is a YouTube video of the issue, and I have attached a photo.
Attachment 18222

http://www.youtube.com/watch?v=vKDzOAWZZvk&feature=youtu.be

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Quote:

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Originally Posted by lucan07

also the video of the screw is someone elses problem not stated by this poster as far as I can tell..

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Really?
I'll Speculate That You're Speculating Again! ;-)

OK so I mixed up the poster of one part of thread it does not change the point that whatever is moving 3.75mm should be easily identifiable, if the ball screw is dropping the retaining nut on base would be 3.75mm below expected position and obvious. this is obviously a poor design the retaining of ballscrew appears to be on wrong end but unless ballscrew dropping 3.75mm an easily visible amount another fault is likely to be the problem.

And the clearly visibly out of place coupling lower half in his video would suggest?

OK I'll give you this one, either the ball screw has moved down or the driven side of the coupling has moved down -
Discuss
:D

Having seen similar problems with thin acrylic on several occasions that were put down to software issues which is why as a non machinist I got involved, I identified the cause in every case as the helix screwing action pulling material up or mill down I have noticed same thing happen with acryilic since I started to use a CNC flexibilty and its tendancy to grab the mill or get a little soft and sticky whichever cause it seems most likely to me. It just strikes me that this is another situation where the obvious has been discounted at the outset by poster a way to eliminate would be try a straight router bit no helix and see if problem still occurs.
"Material Table = very thin stickypad mounted to the aluminum CNC table (this is not likely causing the issue)"

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Originally Posted by xoneeleven

Bit = fine needle bit (not sure of the lingo to describe)
Intended engraving depth = 1.25mm

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Obviously the tool pulling down in the chuck or the material pulling up then?

If it has a helix its a good bet, not exactly clear exactly what bit is being used from that description but if a cheap PCB micro mill with a tight helix turning fast enough to soften and grab then yes my bet.

Another possibility on the 6040z (especially with the standard electronics) is missed steps that occur on upward Z travel. Not sure if that can be ruled out in this case as I haven't watched the video, but could apply in other cases.