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Andy73
11-20-2015, 03:28 PM
I don't know if this has come up before, but I have run into this problem a number of times and lost a lot of bits and product over it. I hope I can explain it in an understandable way.

Sometimes the Z drive screw will spin in the housing without the spindle changing its height. The block with the “nut” that is attached to the back of the spindle—don't know what it's called—seems to allow the nut to spin so that the screw turns but does not raise or lower the spindle. This means that sometimes it thinks it has retracted the spindle 1 inch to pass to the next piece, but it only moves a few tenths, effectively changing the Z zero. I hope this makes sense.

Can anyone help? Can the nut be tightened down, or is there something else I can do?

Thank you very much for your time and any assistance you can provide.

james mcgrew
11-20-2015, 03:32 PM
I it were.loose it.would be.a constant problem. Sounds.like.step loss to me

Andy73
11-20-2015, 04:19 PM
I it were.loose it.would be.a constant problem. Sounds.like.step loss to me

I get what you mean, but I can actually see the Z stepper and screw turning and the spindle not raising/lowering.

Gary Campbell
11-20-2015, 10:59 PM
Andy...
Obvious answer: Contact Tech Support

But in the mean time, can you post a picture of what you mean by "housing", "block", "nut" etc.?

CosmosK
11-22-2015, 01:50 PM
The ballscrew has a ballnut. The nut is in some sort of rectangular housing behind the spindle as you describe. I'm not sure how it is attached, but sounds like the nut is spinning in its housing which shouldn't be happening. The good news is that sounds entirely fixable.

Andy73
11-23-2015, 09:26 AM
The ballscrew has a ballnut. The nut is in some sort of rectangular housing behind the spindle as you describe. I'm not sure how it is attached, but sounds like the nut is spinning in its housing which shouldn't be happening. The good news is that sounds entirely fixable.

You nailed it! That sounds like exactly the problem. I researched ballscrew and ballnut and it fits it to a T. Thank you very much!

CosmosK
11-23-2015, 01:29 PM
did you get it tightened back down? Was there a set screw or something? (I haven't dug that far into mine)

Andy73
12-02-2015, 09:17 AM
did you get it tightened back down? Was there a set screw or something? (I haven't dug that far into mine)

There is no set screw. The threads of the ball nut are actually nylon-ish inserts--4 oval-shaped ones in the sides and O-rings at the ends. These were stripped, and the only way to fix is to purchase a replacement ball screw/nut/upper bearing from Camaster for $186, which we did. Received and installed it yesterday, and I'm back in business.

Here is my theory: if you were to run the X to the right limit and hold PgDn (Z down) until the spindle hits the lower allen screw mechanical stop, the machine does not know to stop turning the Z motor, and the threads of the ball screw get stripped out. I don't know enough about the software to set a lower Z limit...does anyone know? I can't have this happen again.

CosmosK
12-02-2015, 11:07 AM
Interesting, glad you got a replacement.

the z lower soft limit is in the wincnc.ini file

looks something like this:
lobound=z-20

I have mine set way below the spoilboard because I drill the spoilboard often.

I'm not sure what the z-20 is in reference to. I think it might be the table position set when you calibrate your FTC switch (or similar). I could be wrong, but I think it is not an absolute z position, but a relative one.