Problem found: the pulley wheel on my X axis had play in it due to a loose grub screw. This was causing a very small delay in the X axis responding to moves, I guess a bit like inconsistent backlash. Thanks for all your help on this, I really appreciate your input.

On a hardware note, I have nema 23 steppers with 3/8 d shaped shafts, and the 22 tooth pulley wheels with 3/8 round bore with a grub screw to keep in place. I have read on Joes CNC forum that some people have glued in the grub screws to stop them loosening, which has worked but I feel isn't an elegant or long term solution. Is anyone else having a problem like this?  Are pulley wheels available with a d shaped 3/8 bore? 

 

Good job !
Glad you found it.
Russ

Use thread lock, you get it in different strengths, right up to permalock which you really dont want if you ever plan to remove the setscrews in the future.
Common brand of such products is loctite.
Hood

You can also use Sleeve Retainer (by Loctite also).
Clean the shaft and bore with carb cleaner or alchahol first.
A little dab l' do ya.
Pretty permanent though .... will be a bi*ch to get off if you ever need to, but it won't slip.

If your threads are deep enough in the pulley you can also use 2 set screws, one on top of the other.  Put first in tight as the devil plus 2 rounds and the next the same.  This acts like a jam nut, only its more like a jam bolt.   Another thing that will help is the type set screws you use.  Some have knurls on the point that act like a lock washer and will run in cut the will have to cut their way out (just slightly).  I would use those against the shaft and flat nose for the back up that would be bottoming out on the first set screw in the thread.  I used this method along with medium or some call it screw grade Loctite.  If you do use any form of liquid lock though be sure everything is good and clean like RC said.

Brett

Thanks for the suggestions. The grub screws are bad, they have soft heads that just allow the Allen key to mash up. I'll be getting new grub screws for sure, and may try Chaoticone's idea for jamming two screw in. It may be a bit tight, I think there's about 4-5mm of thread. As far as loctite compound goes, is 638 OK?

I tend to use 270 if I want it to be fairly permanent, especially as I use a lot of A4 stainless setscrews.
Hood