Do I need to change the rack of my Leica microscope ?

[Marco68]

HI,

I have the following issue with my Leica DMLS microscope : if I hold the stage control knob and then wiggle it, in a specific position of the stroke, I see that the stage vibrate (and because of the magnification through the lens, I get an annoying vibration of what I see through the eyepiece ).

At the beginning I thought that there was some play between rack and pinion and I have tried to push the rack closer the to pinion, but then I noticed that this "vibration" happen only for roughly 2 mm of the stroke (which is more or less the tooth width) so I am starting to think that some tooth of the rack is worn out. Does it make sense that I change the rack ? where can I find a similar rack (Leica DMLS microscope) and how critical is to change a rack ? (I am not an expert in precision mechanics at all !!)

PS: I think the worn out tooth is on the rack and not on the pinion, because if it were on the pinion, I would get the same vibration again every time I do a full rotation.. while I have this issue only in one single position (+/- 1 mm).
On the other hand, I can not see any gear worn out.. but probably the wear is so small that it is not visible but it is magnified when I look at my sample through the lens.

Thanks for any help !!

rack and pinion.jpg (132.77 KiB) Viewed 2001 times

[MichaelG.]

I would suggest thoroughly cleaning the rack before you consider replacing it.
A spot of hardened grease can cause the symptoms you describe.

MichaelG.

[Marco68]

Thanks Michael,

How do you suggest to do it ? Just a brush ?

Dismounting the rack for a better cleaning and remounting could be critical? I am afraid i will not be able to align it again as before.

Thanks

[MichaelG.]

Assuming that it’s the rack in your photo ... it is flexibly sprung by those slots, so alignment should not be a significant problem.

I would certainly dismount it.

MichaelG.

[Marco68]

Thanks. I will then dismount clean it and I can get it measured/scanned with a CMM (measuring machine) to check the teeths dimemsions.

[MicroBob]

I would suggest to also clean the bottom of the cog teeth with a tooth pick. There might be bits of cover slip embedded in the plasic.
When mounting the rack again just fasten the screws loosely, then move to one end, apply light pressure towards the cog, tighten a bit more, move to the other end, apply light pressure towards the cog, tighten a bit more and so on. You can check the rack with an ordinary ruler and by visual inspection.
Otherwise if I had access to a nice measuring machine I would use this, just because I like measuring instruments a lot!