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Broken plastic fine focus gear
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lothman



Joined: 14 Feb 2009
Posts: 321
Location: Stuttgart/Germany

PostPosted: Wed Jul 05, 2017 8:59 am    Post subject: Reply with quote

Hi all,

I have a new source for the Labophot 1 fine focus metal gear and I'm searching a test user in order to prove functionality (although I have no doubt that it will work).

So anybody interested? It would send a free sample (Kit with gear and glue...) and hope for a small report. Please send me PN or mail me at lothman24 ätt gmx dot de

regards
Lothar

Edit: I found a beta tester
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ray_parkhurst



Joined: 20 Nov 2010
Posts: 1261
Location: Santa Clara, CA, USA

PostPosted: Sat Sep 16, 2017 7:20 pm    Post subject: Reply with quote

I am Lothar's beta tester for his new gear. It took some time to get to me, as first part was lost in the mail. Second part arrived a couple weeks ago, but work got busy and I only found time this weekend to do the conversion. Anyway, the conversion was a success...see the notes below:

First, here is my Optiphot focus block that I got at the DeAnza electronics swap a while back for $1:





It is a little rough, and of course the fine focus gear does (did...) not work, so prime candidate for a new gear. I was contemplating installing a new shaft and gear, but have been hesitating since I don't have an immediate need for the block. Lothar's beta testing offer came at just the right time.

First step was to remove the fine focus shaft. Normally it is not easily removed if the factory molded plastic gear is in place. In this case, the shaft came out easily:



Next step is to remove the coarse focus knob, which contains the fine focus mechanism. It simply unscrews from the main shaft, keeping the other side coarse knob fixed:



Flipping it over, there are 3 machine screws that hold the fine focus gear mechanism in place on the coarse focus knob:



Removing the screws reveals the fine focus reduction gears:



Turns out there were no remnants of the broken plastic gear. The machine screws were a bit loose, so the former owner probably tried taking it apart and found out the gear was hopeless, hence the $1 asking price.

Time to break out the kit from Lothar:



Removing the knob from the fine focus shaft reveals a small notch where the original plastic gear was molded to the shaft. I know this because I replaced an earlier gear from Lothar onto another focus block which still had the remnants of the original plastic gear in place. This is what the shaft looks like:



Breaking open the kit reveals a couple of alcohol wipes that are useful for cleaning the shaft before applying the Loctite material and the new gear. However, I was a bit worried the gear may have some residual oil, so I used a Tamiya extra small cotton swab:

https://www.tamiyausa.com/items/paints-finishes-60/tamiya-maintenance-material-62000/craft-cotton-swab-87105

to clean the inside of the gear, using some residual alcohol from the alcohol wipes:



Lothar, I would recommend you include a couple of these swabs in your kit. They are just the right size to clean the inside of the gear, and to clean and lubricate the inside of the bearings on the coarse focus knobs.

Attempting to install the gear, I found it was too tight a fit. The gear is the right size, but there was some distortion to the shaft due to the knob set screw. I used a small strip of 220 grit sand paper to sand and polish the end of the shaft:

https://www.amazon.com/PERFORMAX-READY-ABRASIVE-SANDPAPER-ROLLS/dp/B000H5NGFE/ref=sr_1_fkmr1_1?ie=UTF8&qid=1505613680&sr=8-1-fkmr1&keywords=sandpaper+strips+performax+220

The shaft end came out clean and polished:



Lothar, a small piece of sanding strip might be another nice addition to the kit.

After cleaning the shaft once more, I applied the Loctite material to the shaft around the notch where the gear goes:



And then moved the gear into place:



The Loctite material froze in place within a few seconds (!!) so when you use this material be sure you put the gear in the right position first time.

Installing the shaft, it became obvious that the gear can move over a wide range within the mechanism. This might actually be part of the reason the original plastic gears break so easily. If the knob is not installed correctly, only the very edge of the gear might contact the mechanism gear.

I took two pictures to show the extreme positions of the gear depending on how the fine focus knob is installed:

Pulled out as far as it can go:


Pushed in as far as it can go:


Neither position is acceptable, so it's clear when installing the knob you need to tighten it down so that the middle of the gear contacts the fine focus mechanism gear.

After re-installing the fine focus mechanism assembly into the coarse focus knob, and tightening the 3 machine screws, I needed to determine how to attach the knob. I pulled the shaft so the gear was against the fine focus mechanism, and tightened the knob set screw. This is clearly not the optimum position, and by pushing the shaft to its farthest out position, I could determine the range of positions the fine focus knob can be installed:



This picture represents the opposite (unacceptable) extreme position. Unscrewing the set screw, and moving the knob to the middle of this range, places the fine focus mechanism gear right in the middle of the newly installed shaft gear. Installing the opposite side fine focus knob so it pulls the first knob tight against the fine focus mechanism completes the re-assembly.

So, how does it work? Perfectly! The previous gear I installed worked well, but had the slightest amount of "gear" feel as the teeth engaged. I feel none of that with this new gear, and the whole system works smooth as silk.

Thanks Lothar for allowing me to be the beta tester for this new gear. Hopefully the above recommendations are useful to all.
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Chris S.
Site Admin


Joined: 05 Apr 2009
Posts: 2979
Location: Ohio, USA

PostPosted: Sat Sep 16, 2017 8:50 pm    Post subject: Reply with quote

Ray, that is a really excellent guide! Very Happy I can see many of us looking this up for a long time to come.

Lothar, I'm very happy that you're putting this gear-replacement kit together. Any sense of when it will be available outside of beta? And what it will sell for?

--Chris S.
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lothman



Joined: 14 Feb 2009
Posts: 321
Location: Stuttgart/Germany

PostPosted: Sun Sep 17, 2017 4:41 am    Post subject: Reply with quote

Chris S. wrote:

Lothar, I'm very happy that you're putting this gear-replacement kit together. Any sense of when it will be available outside of beta? And what it will sell for?

--Chris S.

I will list it these days on eBay, comes for 45$ shipped worldwide with tracking.

@Ray
Good idea to add a small piece if sanding paper (would 600 grit be OK), and would some plastic washer help to get a better control for the axial position of the shaft. Since the new gear is broader than my previous version, it should allow more tolerance for the axial alignment.

And thanks a lot for the excellent documentation, very appreciated.

best regards
Lothar
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ray_parkhurst



Joined: 20 Nov 2010
Posts: 1261
Location: Santa Clara, CA, USA

PostPosted: Sun Sep 17, 2017 9:24 pm    Post subject: Reply with quote

lothman wrote:


@Ray
Good idea to add a small piece if sanding paper (would 600 grit be OK), and would some plastic washer help to get a better control for the axial position of the shaft. Since the new gear is broader than my pervious version, it should allow more tolerance for the axial alignment.

And thanks a lot for the excellent documentation, very appreciated.

best regards
Lothar


600 grit is a bit fine but it might do the job.

I like the idea of a small washer to help with positioning the gear properly over the first plastic gear. The washer would need to be fairly thick.

edited to add: it might be good to provide several thin washers so that the spacing can be custom-tailored. There will be lots of variation in placement of the gear since once you start to push it over the notch you can't see the notch any more, and the gear is about twice as long as the notch. In my case I would have needed about 4mm thickness worth of washers...Ray
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martincito



Joined: 09 Feb 2013
Posts: 145
Location: Ipswich, Suffolk, UK

PostPosted: Fri Mar 02, 2018 4:01 pm    Post subject: Reply with quote

I have a Labophot focus block built into a rather amateurish imitation of a stepping motor driven Bratcam. I put it together several years ago and am reluctant to dismantle it as it is more or less doing what I want and experience has taught me to resist the temptation to try and fix everything that isn't definitely broken. However every so often - say once or twice in a stack of 300 images - it will jump several steps giving a blurred band in the final stacked image. I'm tempted to start again with a Stackshot but would hate to spend all that money if my current rig could be easily fixed. As a start, it would be useful to know if the infamous damaged fine focus gear could give rise to these jumps.

Best wishes,
Martin
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ray_parkhurst



Joined: 20 Nov 2010
Posts: 1261
Location: Santa Clara, CA, USA

PostPosted: Fri Mar 02, 2018 7:07 pm    Post subject: Reply with quote

Martin...another one of my Labophot units had a similar characteristic. The gear was not completely broken, so it "sort of worked" most of the time, but had a periodic slippage that might be noticeable as a jump in a stack. Eventually it broke completely and I plan to replace it with one of Lothar's gears when I have time. One fear I have is that the larger gear which the small broken gear meshes with may also have a problem, but so far the two I have fixed only had issues with the small gear and both worked perfectly after replacement.
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Chris S.
Site Admin


Joined: 05 Apr 2009
Posts: 2979
Location: Ohio, USA

PostPosted: Fri Mar 02, 2018 10:44 pm    Post subject: Reply with quote

Ray, thanks for the data point—very useful. I’ve returned/rejected a number of focus blocks because the fine focus knob showed a hesitation, followed by a slight jump, every once in a while. I’ve assumed this was due to the well-known issues with this gear, but never took such a block apart to see.

Martin, given Lou's experience, I’d swap in Lothar’s gear in a heartbeat. Not so much to save money against a StackShot rail, but because a motorized focus block is so nice to work with.

--Chris S.
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martincito



Joined: 09 Feb 2013
Posts: 145
Location: Ipswich, Suffolk, UK

PostPosted: Sat Mar 03, 2018 2:23 am    Post subject: Reply with quote

Thanks for these replies Ray and Chris. I'll start summoning up the courage to open up the focus block. If I find anything interesting I'll post an update.
-Martin
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Smokedaddy



Joined: 07 Oct 2006
Posts: 1098
Location: Phoenix, Arizona

PostPosted: Thu Mar 29, 2018 8:46 pm    Post subject: Reply with quote

I purchased a Optiphot focus block 'knowing' that it didn't work. I fixed my MM-11 before so I figured I could fix this one *IF* the gears weren't damaged (other than the pinion). I could hardly turn the knobs because of all the old grease. I took it completely apart to clean everything with brake cleaner and relubricated everything. I do mean completely, dovetails, gibbs, nylon guides and all of those little cylindrical bearings. The pinion gear was on the shaft but it rotates on the shaft. Looks like I need a new 6mm 18t pinion gear. I put it all back together and it seems to work but not for long.

I just thought I'd post a few cell pics showing the dovetail disassembled in case you decide to do that yourself someday.











-JW:


Last edited by Smokedaddy on Thu Mar 29, 2018 10:16 pm; edited 1 time in total
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ray_parkhurst



Joined: 20 Nov 2010
Posts: 1261
Location: Santa Clara, CA, USA

PostPosted: Thu Mar 29, 2018 9:14 pm    Post subject: Reply with quote

The pinion gear looks like it just broke loose of the shaft dovetail and is not completely broken. I see one slightly broken tooth but only on the edge. So...I think you may be able to de-grease the shaft and the gear and use loctite to re-install it. Might be worth trying before getting a whole new gear.
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lothman



Joined: 14 Feb 2009
Posts: 321
Location: Stuttgart/Germany

PostPosted: Sat Mar 31, 2018 5:31 am    Post subject: Reply with quote

Smokedaddy wrote:

I just thought I'd post a few cell pics showing the dovetail disassembled in case you decide to do that yourself someday.

-JW:


I hope you let on of the linear guides installed, because otherwise you might not get them reinstalled in the same position and perhaps loose perpendicular alignment towards the optical axis.

Usually the plastic gears had a shrink fit on the shaft and over the time cracked due to becoming brittle over the time. As Ray suggested gluing it back should fix your microscope, otherwise let me know ;-)
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Smokedaddy



Joined: 07 Oct 2006
Posts: 1098
Location: Phoenix, Arizona

PostPosted: Sat Mar 31, 2018 11:11 am    Post subject: Reply with quote

lothman wrote:

I hope you let on of the linear guides installed, because otherwise you might not get them reinstalled in the same position and perhaps loose perpendicular alignment towards the optical axis.


I took pictures. I reassembled everything just like it was including the orientation of all 8 bearing guides.

I'd rather put a new pinion on since there are a couple of issues with it. I ordered one from you a few days ago. <g>

-JW:
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