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Z axis - ARRRRRR

Posted by stephen george 
Z axis - ARRRRRR
September 14, 2009 10:14PM

I have rebuilt the bits from bytes reprap v2.0.0. twice now and still I cannot get the Z axis to work. (@#!@#!!!!)

The motor just spins with the grub screw gouging a nice circle into the spindle.
If I tighten the screw I crack the plastic and spend 1/2 hour reglueing it.

I have read through the Z axis recomendations and as far as I can see everything is fine. The Z axis can be moved up and down by hand. And individually the four
axis spin nicely with a belt so loose it almost skips.

So my question is

1) Is super gluing the spinle to the cog a bad thing to do?
(because I am really running out of things to do)

2) How much torque is too much. Can I measure it? Do I have a duff motor?

3) Will the motor be damadged if it does not turn?
(am I overriding some sort of safety feature by welding the cog to the spindle)

Thanks ever so much for any replies.

Re: Z axis - ARRRRRR
September 15, 2009 04:07AM
I don't have experience with that machine, but the normal thing to do would be to file a flat on the motor shaft so that the screw locks it without relying on friction alone.

When filing or gluing near the motor don't forget to protect the bearings with some bluetack, plasticine or masking tape.

The only way to damage a motor is to exceed the temperature rating of the windings by applying too much current. As long as it runs less than 100C you should be safe.

No a stepper motor is not damaged if it stalls, it only takes a little more current than when running. On the other hand a DC motor takes a lot more current when it is stalled (can be ten times) so can be damaged.

Re: Z axis - ARRRRRR
September 15, 2009 04:44AM
I can see your problem. I've had such an acrylic set and both Z & Y couplings cracked shortly. Glue won't help for long.

I highly recommend getting a coupling like this:

Those are expensive but work very well.

FiveD Firmware fork (supports Arduino Mega): [github.com]
Re: Z axis - ARRRRRR
September 15, 2009 06:58AM
Actually the glue actually works well.
I believe the glue is stronger than the acrylic.

I use Loctite 406

It sits in my fridge (next to the mustard).
I would say approximately 15 parts in myrep rap have been glued together.
And stayed that way

Re: Z axis - ARRRRRR
September 15, 2009 07:04AM
My Z axis is up and running - YERSSSSSSS
Thanks nophead. Really appreciate the help.

For the record I did as nophead said and filed the Motor spindle.
This helped but still did not work.

So I added a small washer in between the Grub and the spindle. (Held in place with
blue tack). This increased the surface area of the filed area on the spindle
with the rather pointy grub.


Re: Z axis - ARRRRRR
September 16, 2009 04:13AM
I have the exact same machine, I use glue to get my z axis to work properly.

Oh and just a comment, on your extruder, make sure that you have set up those 4 screws with springs to be as tight as possible, the little square pieces of plastic with small holes make sure you've got at least 2 pieces(or 3 if you can) between the springs and the big bolt, I think you get 4 of them.The effect will be that the small bearing will put much more tension that pushes the filament onto the screw. And tighten those screws as much as you can(and I do mean as much as you can, it really makes an unbelievable amount of difference).

I spent 6 months with an extruder that wouldn't work properly because of this.
Re: Z axis - ARRRRRR
September 17, 2009 02:26AM
Hi letsburn

thanks for the tips. I see what you mean about the fours screws with springs
having to be tight.

However I found that after "sharpening" the screw thred with a die(at least that's
what I think it's called) the extruder gripped the ABS with no problems even though the four screws were loose. Which was a real pain as I had to wind the thing manually rather than just pull it. Just thought I would mention it.

So I assume you have a working reprap. What's it like? Feel like the time you got your first car?

Re: Z axis - ARRRRRR
September 18, 2009 08:31PM
Using 406 loctite is not a good idea, as it won't stick for long, to the motor shaft, even roughing the surface of the spindle.

What could work is filing down the end of the grub screw so that it has a wide flat surface instead of a point.
This will work alongside filing down a flat on the spindle of the stepper motor.

I am unsure what would be the best adhesive for this, but I can advise against using 406 loctite, maybe araldite or some other epoxy would work

Edited 1 time(s). Last edit at 09/19/2009 05:03PM by Grogyan.
Re: Z axis - ARRRRRR
September 19, 2009 06:23AM

I use 406 loctite to repair snapped parts from the kit.
I am not using it to glue to the metal spindle.
I don't have to as the Z axis works fine.

Thanks for your help though

Re: Z axis - ARRRRRR
September 21, 2009 02:51PM
It felt great to get it to extrude and print. I almost threw the whole thing out the window a few times because I couldn't get it to work properly. But it works fine now.

The only real problem I've been having has been the screw making the filament getting all twisted(as it goes in the remaining filament gets twisted around and around), this caused a jam when I left the extruder running without supervision. Unless I untwist the ream of filament, it would jam after about 2 hours or so of running (poetically about 90% of the way through making me a new gen 3 extruder, I've decided to say stuff it and just go to building my parellel extruder design from the get go next time)

One warning about gluing the Z axis is that when you're oiling up the drive rods, don't add too much. The oil (I use 3 in 1, it works great as a lube for your axis) will dissolve the glue if it gets to it.

I wish I had a die, I found sharpening threads to be really difficult, but fotunately I found that tighening those screws works great.
Re: Z axis - ARRRRRR
September 21, 2009 03:02PM
Do you mean the filament's twisting before it gets to the extruder because of the way it unwinds from the supply of filament? What have you got supporting your filament? Is it in a reel or a wound circle?

Nophead's solution to the twisting was to sit the circle of filament in a hanging basket hung on a pivoting support above the extruder head, so that as the filament feeds out the basket rotates avoiding so much twist on the plastic filament.
See his entry for 5th November here where there is a good photograph of the setup.

Re: Z axis - ARRRRRR
September 21, 2009 03:10PM
yeah I saw that design. The problem is that I have my reprap on a desk in my room and there is no spot that I can attach a raised spindle to.
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