Excessive play in the XZ movement

Hi chazaswell,

after you assembled your Stepcraft there is a long path ahead of you if you want it to work properly.

To summerzie:
you need to find the compromise between play of the messing-wheels against the rails and the friction they cause.
Each of the axises (the y-axis having two) have a messing-wheel with a little screw. If you tighten the screw, the wheel gets pulled against the rails. The tighter it is, the less play you have on that axis.
On the other hand, if you screw it to tightly, the motors won't be able to move the wheels (and thus the axis) leaving you with a play-less, but immobile machine.

So you have to experiment and find a good compromise between those two extremes.
There are other problems that will arise when you are fine-tuning your machine, such as not perfectly aligned rails (especially on the y axis), loose connections between motors and the threaded rods (or the drive belt) etc.

Try it out and come back if you hit a dead end 🙂

Maybe this will help: building tips video Also don`t forget the "First Steps" document on SC homepage.

I've recently completed assembly of my 840 and with a few rebuilds from original assembly to tweak the setup. I've managed to get a fairly tight tolerance in the X Y Z. My best results have come from very firm tightening of 6mm screws onto the track roller holder. The rebuild was initially as a result of the rollers becoming loose with significant play and vibration - something I am striving to reduce. Since then I've had the X and Z loosen off slightly and I've had to re-tweak the tension bolts - I still need to find a better way of preventing the 3mm tension screws from moving (causing some play till re-adjusted) - but I do seem to have solved the track roller setup... see below...

The inner race of the bearings, the brass spacer and the track roller with washer all seem to work best when tightened. They all lock together to form a solid 'axle'. This 'axle' should not place any load on the bearings - if the bearings are getting tight there is a problem in the 'axle' setup. You'll need to work that till the bearings are free.

To tighten recommend the following process (in addition to the items in the assembly video)
> loosen off all roller tension screws (3mm)
> ensure you can get a tight 'axle' on each roller and still have the roller spin freely (and all consistently)
... may need to play with orientation of washers and perhaps even swap them round to get a good fit. Make sure the washer doesn't sit on the end switch bracket but flush on the surface.
> Put rollers in the linear track - ie slide the assembly into the track. Ensure there is just a bit of play in the tracks (ie rollers not tightened by tension screws - yet!)
> Remove the assembly - tighten the 'axle' screws tight (track roller)
... Slide assembly into the linear track again - double check there is still play (sometimes tightening the screws causes the track roller to move - loosen off and repeat if required to get some play.
... I actually put a small amount of loctite on the screws to make sure they don't come loose (small amt - don't get in the bearings!! - I don't want them coming loose again!)
> Now comes the technique - basically as shown in the assembly video
> Tighten each 3mm tensioning screw to remove all play
> Tighten the extra 1/4 turn per the video.

The above technique ensures the tension screws are flush and tight... I tried lots of variations till the above worked best.

Now... need to resolve the tension screws loosening off at times - causing play. At this stage I simply insert the hex key and re-tension by feel. Keeps it all tight.

I've found the Y axis ok for now - If it is too tight you will get motor skip then the whole Y axis is out to lunch.... lots of patience to get that setup right too - that's a combination of track roller tension and drive pulley load on the end of the lead screw.

Any ideas on preventing tension screws loosening would be appreciated before I try some options...

Hope that helps...

About the Loctite: never use the red one (262 or 271), but use the blue (242) instead if you want to be able to disassemble the machine or a part of it for maintenance or repair.

I'm taking my time adjusting track roller tension and tuning prior to assembly. I think that I'm on the right track but am concerned about many comments about stiff axes and particuarly about skipping steps and then the code going wrong and routing too deep, etc.. Although I plan to do a lot of testing, my two test hardwood timber pieces for a guitar neck alone are £30 each and the final cut will be made from vintage Cuban Mahogany so MUST work. My first generation GCode file is huge (MeshCAM estimates a 15 hour cut time) but the feeds, speeds and depths per pass are very conservative and the cut time might be able to be substantially reduced.

So far, the XZ module moves freely/unpulsed with no grease on both Z and X axis extrusions when the track is tilted (i.e. under gravity). Is this a good rule of thumb to gauge setup/tuning? How much resistance can the stepper motors cope with before problems will definitely occur?