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

**xoneeleven** · 20-04-2016

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** · 20-04-2016

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.

**lucan07** · 20-04-2016

Originally Posted by 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.

Good point I seriously doubt this slipping coupling is the problem its two pieces held together by the friction of the rubber alone so if ends stay firm nothing to stop rubber moving.

**lucan07** · 20-04-2016

In fact that's the only thing that makes sense if everything else is secure the rubbing coupling is causing enough friction for the stepper to miss steps so that the Z axis is losing its integrity.

**magicniner** · 20-04-2016

What you talkin' 'bout Willis?

**cropwell** · 21-04-2016

Some thing is pulling that coupling apart. If it were just loose on the stepper shaft there is no force to pull it downwards. I would recommend running the program but just cutting air and looking at the Z axis to see what exactly is moving.

**magicniner** · 21-04-2016

If that red bit in the middle is the least bit squidgy you and drive it in either direction and it will push the two metal sections apart ;-)

**xoneeleven** · 25-04-2016

We checked the nut at the bottom, and it was fine.

So, we took both the couplings off and examined them further.

The first thing we noticed was that the couplings appeared to be mounted slightly too low. So, when we put the motor housing back on, it may have been pushing the couplings down on the cylinder.

Here is what we did to patch/remedy the issue:

1: Used a dremel tool with a cutoff wheel to lightly score the cylinder (to create some friction for the couplings to adhere to)
2: Moved both coupling halves up slightly on the cylinder.
3: Reassembled and ran a job.

So far, the results are positive. There is no slippage of the couplings.

NOTE: We did originally try to wrap a tiny sheet of aluminum around the cylinder to use as friction, but the tolerances of the couplings to the cylinder was too tight. It would not fit. So, we came up with an alternative idea in scoring the cylinder to create friction.

Anyway... Thanks for the tips. The tip on the aluminum sheet is what mainly led us to success. (that idea eventually led us to consider creating friction using a different method)
Let's hope this stop-gap method works over time.

**Clive S** · 25-04-2016

Originally you said the cutter bit was being dragged down into the job I don't think fixing the coupling will have anything to do with the first fault as the two halves of the coupling are not fixed together. So either the bit was loose and came out of the collet or the fixed bearing is faulty. Only time will tell.

**magicniner** · 25-04-2016

If the bottom coupling was slipping on the shaft most slip would have been when working against the greater force required to lift the Z axis rather than when lowering, resulting in Z gradually slipping down,

- Nick