Thoughts on filling/reforming stage rack with epoxy?

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hans
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Thoughts on filling/reforming stage rack with epoxy?

#1 Post by hans » Wed Sep 23, 2020 6:31 pm

I have a heavily-used stage with low spot worn into the brass rack gear and noticed that cleaning out old, hardened grease actually made it worse. I think the hardened grease was helping fill in the low spot. Made me wonder if something like that could be done intentionally using epoxy, for example:
  1. Thoroughly clean rack teeth to bare metal.
  2. Apply a thin layer of slow-curing epoxy to the entire length of the rack roughly thick enough the fill in the low area.
  3. Wait until the epoxy is fairly stiff and will not run/sag but can still be deformed with some force.
  4. Apply dry graphite or Teflon lubricant to the epoxy and pinion gear to prevent sticking.
  5. Reinstall the rack and roll the stage back and forth to impress the pinion pattern into the epoxy.
  6. Repeat tightening rack/pinion clearance and rolling several times if necessary until most of the epoxy has been forced out of the high spots and just enough remains to fill the low spots.
Anyone tried something like this or have other suggestions? I think the penalty for failure is pretty low since the rack is solid brass and can be heated to decompose the epoxy for easy removal if anything goes wrong. Obviously the epoxy will not be as durable as brass, but maybe still good enough for years of occasional hobby use?

Hobbyst46
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Re: Thoughts on filling/reforming stage rack with epoxy?

#2 Post by Hobbyst46 » Wed Sep 23, 2020 6:44 pm

From the description I understand (incorrectly ?) that the tips of the teeth of the pinion do not touch the rack. If so, why should it affect functioning ?

Both uniform coating of the rack with epoxy and spreading it with a powder to prevent unwanted adherence seem to me very challenging.

If you go this way, and unfortunately need to remove the epoxy, this should be quite easy with a thin-blade screwdriver or a knife or similar.

However - have you considered shimming instead of filling in ?
Zeiss Standard GFL+Canon EOS-M10, Olympus VMZ stereo

hans
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Re: Thoughts on filling/reforming stage rack with epoxy?

#3 Post by hans » Wed Sep 23, 2020 7:09 pm

Hobbyst46 wrote:
Wed Sep 23, 2020 6:44 pm
From the description I understand (incorrectly ?) that the tips of the teeth of the pinion do not touch the rack. If so, why should it affect functioning ?
This is true, I think, I assume it was hardened grease on the faces of the teeth helping. Some of the grease I removed was very hard, almost plastic-like consistency. There is a small section of the rack corresponding to the most-used stage position that is more worn than the rest.
Hobbyst46 wrote:
Wed Sep 23, 2020 6:44 pm
Both uniform coating of the rack with epoxy and spreading it with a powder to prevent unwanted adherence seem to me very challenging.
Yeah, perhaps, decent chance of just making a big mess.
Hobbyst46 wrote:
Wed Sep 23, 2020 6:44 pm
However - have you considered shimming instead of filling in ?
When the rack is worn heavily in one spot and no longer straight shimming seems difficult. I have had some luck bending the rack to straighten out the low area, but it is difficult to get it straight enough to have simultaneously no backlash and no stiffness/cogging throughout the entire range of travel.

PeteM
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Re: Thoughts on filling/reforming stage rack with epoxy?

#4 Post by PeteM » Wed Sep 23, 2020 11:18 pm

Is the rack of the type with a cut-out behind the teeth to allow it to spring a bit? If so you can adjust it a bit.

Another approach, with many stages, is to move the slide clips to a different location - this moving away from the area of greatest x-axis wear and getting a better feel.

Might also find the same stage cheaply on Ebay - with a busted control or gouged stage but a good rack.

Finally, a plain rack isn't a particularly difficult machining job even for an amateur with a small milling machine if this is a rare and valuable instrument you'd like to see performing as new. You could always acquire a new hobby or a new friend with that hobby??

I don't think the epoxy will hold up /stay adhered that well. It's a pretty concentrated load. What might be possible (since many racks are now plastic) would be to have one 3D printed out of a tough thermoplastic?

Element 56
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Re: Thoughts on filling/reforming stage rack with epoxy?

#5 Post by Element 56 » Thu Sep 24, 2020 12:19 am

Hans, what kind of microscope do you have? Might be a long shot but it's possible I'll have a good rack on hand.

I don't know how successful you'll be repairing it as described. I've done some building up with JB weld with mixed results. The slower curing always seems stronger. Something you can try is a product called Q-Bond. It's basically super glue and plastic powder. You just dump the power on and put a drop of glue on it. It smokes a little and dries fast. Keep building it up until you have enough to work with. You can file it, drill it, sand it or whatever. Might work for a quick repair but I don't know about long term.

Brazing would be the best option if you can't find or make a new one. Or if you have enough good teeth on one end you could flip the rack.

Let me know what you have and I will check my parts stash.

Kirby

EYE C U
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Re: Thoughts on filling/reforming stage rack with epoxy?

#6 Post by EYE C U » Thu Sep 24, 2020 12:34 am

SAND THE TOP FLAT?

hans
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Re: Thoughts on filling/reforming stage rack with epoxy?

#7 Post by hans » Thu Sep 24, 2020 2:58 am

Element 56 wrote:
Thu Sep 24, 2020 12:19 am
Let me know what you have and I will check my parts stash.
Thanks for the offer, it is a Reichert 410, but I actually have some other stages in better condition already, this well-worn one is just the first I completely disassembled and have been using and messing with, not wanting to learn on the nicer ones. So, there is no real urgent or logical need to fix it, I just though it might be an interesting thing to experiment with and try to give the stage some new life. And I kind of like the character the large dished-out (well into the aluminum) area on top adds -- hard to imagine how many slides must have been loaded/unloaded over the years to carve out such a depression. (The depression is toward the corner where slides are set down and picked up, and doesn't interfere much with flatness in the area where a slide rests when being viewed.)
PeteM wrote:
Wed Sep 23, 2020 11:18 pm
Is the rack of the type with a cut-out behind the teeth to allow it to spring a bit? If so you can adjust it a bit.
Yes it is, the suspended beam part with teeth is what I mentioned bending a bit with needle-nose pliers and some cardboard to protect the teeth. Bending helped a lot, but because the worn area is relatively small, it was hard to get isolated, sharp bends in just the right place. The stage came with some bits of hard rubber packed in the slot, for the same reason I assume, the problem with that is basically the same -- creates a gentle bend over the whole length, not specific enough to correct the small worn area. I have fiddled with clearance between the rack and pinion quite a bit now, and the point I'm at after the bending is, I can either get no backlash in the worn area but slight drag with cogging feel toward the ends, or endpoints well-adjusted but a small amount of backlash in the worn area. Works ok practically, but could be better, I think.
EYE C U wrote:
Thu Sep 24, 2020 12:34 am
SAND THE TOP FLAT?
I'm not sure this would help, for the reason Hobbyst46 mentioned earlier -- it seems like the angled faces of the teeth are probably most important for good meshing.
PeteM wrote:
Wed Sep 23, 2020 11:18 pm
Finally, a plain rack isn't a particularly difficult machining job even for an amateur with a small milling machine if this is a rare and valuable instrument you'd like to see performing as new. You could always acquire a new hobby or a new friend with that hobby??
Element 56 wrote:
Thu Sep 24, 2020 12:19 am
Brazing would be the best option if you can't find or make a new one.
The reason I was thinking epoxy was the possibility of "rolling-in" well-meshing teeth before completely cured, sort of like what I was suspecting had happened with the hardened grease before I removed it. Anything involving cutting teeth in new material or already-hardened added material is probably beyond my ability, if the goal is to actually improve the quality of meshing...

Thanks for all the opinions. If I do end up giving the epoxy thing try I will take some photos of whatever mess I make, for the amusement of the more mechanically-inclined.

Element 56
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Re: Thoughts on filling/reforming stage rack with epoxy?

#8 Post by Element 56 » Thu Sep 24, 2020 3:01 pm

hans wrote:
Thu Sep 24, 2020 2:58 am
The reason I was thinking epoxy was the possibility of "rolling-in" well-meshing teeth before completely cured, sort of like what I was suspecting had happened with the hardened grease before I removed it. Anything involving cutting teeth in new material or already-hardened added material is probably beyond my ability, if the goal is to actually improve the quality of meshing...
Hans,
The "Kwick" JB Weld would be your best option for trying this. It has a 4-6 hour cure time and there's a window within that which will allow for some manipulation without making a mess. I used to use it for sealing the guard on fixed blade knives. Up to a point you can even clean it off during the cure with WD40.

Try it and see what happens! I sure would like to know if it works!

Kirby

Scarodactyl
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Re: Thoughts on filling/reforming stage rack with epoxy?

#9 Post by Scarodactyl » Thu Sep 24, 2020 7:05 pm

Yeah, I say you should absolutely try this, not because of a high chance of success (probably not) but because I really want to see what happens.

hans
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Re: Thoughts on filling/reforming stage rack with epoxy?

#10 Post by hans » Wed Oct 07, 2020 8:44 pm

I had some epoxy mixed up to fill a recess in a Reichert 410 focus cam where the plastic is often split around the shaft, probably caused by over-tightening the set screws, and tried rolling a gear through the left over. There was too much graphite and some clumps messed up the impression on the left side, but the right third actually meshes pretty well with the gear considering there were no existing rack teeth to help guide it. I rolled it when the consistency of the epoxy was similar to a stiff, chewy candy like Starburst. Probably could have waited a little longer even. Graphite needs to be done more carefully, maybe put some on another surface and use a small paintbrush to break up clumps and apply it to the epoxy.
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Greg Howald
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Re: Thoughts on filling/reforming stage rack with epoxy?

#11 Post by Greg Howald » Fri Oct 23, 2020 3:24 am

If you choose to use epoxy to try to do this make certain you remove all optics from the scope before you go near it with epoxy. The are some proxies that 'gas off' as they are setting. Getting that on optics will ruin your entire day. Other than that, well, I've done crazy stuff too. Many times it even worked for me. So it's worth a try.

Greg

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