z axis torque

Even after removing the anti-backlash springs, loosening the nuts which hold the bed to the z-posts, very very liberally soaking the entire system with engine oil and loosening the belt, my z axis still has a tendency to bind and stop moving.

Is there a strategy for maximizing torque out of the nema23? Is there an optimal type of threaded rod to use? Any other suggestions?

Cheers,
L.

Make sure your threaded rods are straight. Take them out and roll them on a table
and make sure that they are not bowed anywhere.
I fought with mine for several days before ripping it apart to see what was wrong, and only then did I find out that one of my rods had a slight bow in it. I replaced it with a new straight one and everything ran fine.

liav () said
> Even after removing the anti-backlash springs, loosening the nuts which hold the bed to the z-posts, very very liberally soaking the entire system with engine oil and loosening the belt, my z axis still has a tendency to bind and stop moving.

my reply
I feel your pain. Mainly because I had the same problem.
I was building a darwin/bit from bytes v2 and I found that the grub screws had allowed the cornor brackets to move and as a result had to rebuild it from scratch.

liav Wrote:
-------------------------------------------------------

Is there an optimal type of threaded
> rod to use? Any other suggestions?
>

For the z axis I would suggest you try 306 stainless steel, as the zinc plating of zinc plated rods can flake off and cause jamming.

Check the squareness of your Z rods as well; they need to be parallel to the vertical smooth rods to prevent binding as the bed travels up and down. A couple mm off on the bed hole dimensions can mean that your Z axis is trapezoidal instead of square, which will cause binding at certain heights.

Also check the tightness of the Z rods on the lower corner blocks and the z tie brackets - keep em pretty loose. I use a bit of bearing grease on everything, it stays pretty much where you want it. Without the belt attached, you should be able to spin each Z rod with your fingers on the threaded rod; with the belt attached, you should be able to spin one Z gear with a bit of effort and move the entire Z axis.

Also, you can try dialing up your Z axis current, and switching the stepper driver to full stepping for more torque. I've been using full stepping on my 2nd printed Darwin, so far it's worked pretty well.

Hope that helps.

Wade

I haven't looked at the darwin design for a while, but how easy would it be to remove some of the constraints on the z-axis?

Hi Triffid_Hunter ()

you said
I haven't looked at the darwin design for a while,
but how easy would it be to remove some of the constraints on the z-axis?

My reply
I had untold trouble with the Z-axis. In the end I opted for a rebuild
using only three Lead screws instead of four. which reduced the friction by 25%.


Also I found that having two nuts on each thread (bit from bytes design)
increased friction and did not seem to add any benifit that I could see
as the bed itself pushed down on the nut making sure there was no movement
or lag when you switched from up to down on the Z axis.

I think I know the problem you are seeing here...

The threaded rod can be zinc treated in two different ways.

Different suppliers of threaded rod use different zinc coatings methods. The cheapest threded rod is usualy the better type to buy for Reprap builds.

The cheaper threaded rod I will call it the "good stuff" where a nut will spin very easily the zinc coating is plated I believe.

The other type of threaded rod the "bad stuff" is coated in zinc by a chemical process.
I think its called something like dipped zinc. The dipping method gives a thinker rougher coating of zinc that nuts do not spin easily on. Making it much better at stopping rust but not very good as drive shaft.

So Bad stuff for structural members and good stuff for drive shafts solves the problem. On bad stuff you might need to put a lock nut on the end or hold it in a vice to wind a nut to position with a spanner, it can be that tight to get a nut into position.

So before you buy it in a store just try spinning a nut down the threaded rod first. If is an online purchase check the description as some suppliers state the type of zinc coating.

I think that plated Zinc looks brighter than the dipped Zinc which looks dull.

An after thought on this post is of course some Bad Stuff might just have been in the electroplating tank longer or have been nearer to the Zinc electrode.

Edited 2 time(s). Last edit at 01/16/2010 06:34AM by BodgeIt.

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