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

[magicniner]

Post #1 (Quite obviously by the OP)

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

Mark

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

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


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

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

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

[lucan07]

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.

[magicniner]

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

[magicniner]

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

[lucan07]

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)"

[magicniner]

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

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

[lucan07]

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.

[xoneeleven]

Today, we are going to pull off the coupling, and wrap a sheet of aluminum onto the spindle, and re-attach the coupling.
This may add enough friction for the coupling to stop slipping.


Right now, we believe it is a coupling issue where it is either damaged or badly designed. We are located in North Idaho and nowhere near a place to take the bad coupling into a store to replace it. So we have to rig it until we can find an online store to order a replacement coupling.

I will post an update with news on this failure or success. :)

[lucan07]

It may be better to run a drill though the coupling and tap it put an m2 or m3 screw in for each side to lock on as an addition to clamp would be better than a shim but as that coupling is two pieces held together by a piece of rubber which is a just a friction fit I still think it may not be your problem and nothing to stop rubber coming away if ends stay in place. Check mill not slipping in collet and put a dial guage on top of acrylic to make sure not lifting seen acrylic do this many times, if using a bit with a helix try a straight router bit, also if it misses steps on upstroke it will get deeper. Anything movinng 3.75mm is going to be obvious so material or bit moving or missing steps sound much more likely to me.

[Fred]

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.