Rack engagement adjustment

[spiyda]

I've been a bit concerned before about the lack of adjustment on the z axis rack
Well, it finally let me down a couple of days ago, jumping teeth.

The rack and pinion themselves are in pretty good condition but I think they may be replacements made to fit.
The teeth only just engaged in the rack. and finally jumped a tooth or to and caused a head crash ( twice  )
Once I realised what the problem was, I set about making the engagement adjustable.

I didn't take pictures as I was more concerned with fixing the issue, but it wasn't complicated, a description should be enough.

I could have stripped it right down and put the plate that the stepper mounts onto on the mill, but decided I didn't want to lose the camera calibration.

The main issue was getting plenty of light on it to see what I was doing !

So - I removed the cover, then three screws that hold the linear bearing slide in place , lifted out the whole moving part of the "Z" axis and temporarily fixed it to the top of the arm with an elastic band.

I then taped a protective bit of paper over the mirror.

Then out came the top stepper mounting screw ( the cylindrical spacer between the plate and stepper will drop down)
The hole for the mounting screw  is just over 3mm diameter and is counterbored.

At this point, I  used  a dremel type tool in to elongate the 3mm part of the hole toward the right, as far as the edge of the counterbore.  ( about 2mm )

The whole area was then cleaned up with a vacuum and airline

To reassemble, you need to get the spacer on the screw, so the five screws that hold the main plate to the arm came out next and the plate comes off, giving access to get the spacer on the screw plate.

The original screw is a capscrew M3 x 25

I replaced it with a capscrew M3 x 30 with a couple of 3mm washers.
The washers are standard diameter as anything bigger may foul the rack ( depending on the rack style you have)

Then its just a case of reassembling it all...

for the final adjustment, I loosed off the rack and ran it up and down with a bit of paper between the rack and pinion, and pushed the rack hard onto the pinion before doing up the screws. this seemed to give a nice clearance.

One other thing I did which is probably not necessary, but seemed to be a good idea... ( if you have access to a lathe or can source the spacers)  is shorten the spacers by 2mm to get more engagement on the rack.



Anyway, it all seems to be working now, except that I have to go out into a workshop at zero degrees C. to make a nozzle to continue !

the sooner we have a good source of nozzles guys, the better !


a couple of notes

one longer screw will be needed capscrew  M3 x 30  ( I have few spare if anyone needs one)

The rollpin to fix the pinion to the stepper shaft is 1.5mm  ( again, I have a few spare )

The capscrews seem to need a 2.5mm allen key ( hex wrench)

[Mike]

Note that RV4s and 1s are somewhat different designs - the 1s heads I've seen use plastic racks as the rack isn't carrying the weight of the rotate motor ( which is in the arm and uses a belt to drive the head)
Rack issues are probably less likely on the 1s due to the lower weight

[alanambrose]

Yeah the 1S rack is fairly easy to adjust without taking it off the machine. I did a quick look for replacement parts and without taking it off to measure the teeth, it looked like the rack and pinion were fairly standard parts with a little bit milled out of the top of the rack.

A.