October 3-7—JOSHUA TREE, CALIFORNIA: Annual show; Sportsmans Club of Joshua Tree
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 Post subject: Wild M420 focus mount problem [Fixed!]
PostPosted: Wed Jun 13, 2018 2:31 pm 
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Well, I got a little caught up in bidding on eBay and ended up buying a Wild M420 (at what I think was a good price). I really should get the standalone makrozoom lens working first but I was hoping this would be a shortcut to the same end result (not to mention it's more fun to have eyepieces).
Unfortunately it arrived with a couple problems. Two minor ones on the base (which has a precision x-y stage), a broken-off thumbscrew and a few loose rollers, neither of which are likely to cause problems for me. The real issue is the focus mount. Focusing works smoothly as I turn the knob until I hit a certain point in the rotation where it suddenly loses grip and the head falls to the bottom of the rail. I'm hoping this is possible to fix because the image I see through the eyepieces looks really darn crisp! Has anyone run into this problem before?
I will get some pictures of it in a few hours, but it's the original Wild-only version with a cylindrical stand, not the later Leica one.
edit: here's a picture:
Image


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 Post subject: Re: Wild M420 focus mount problem
PostPosted: Mon Jun 18, 2018 8:08 pm 
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OK, I had a look through the service manual and started to get it apart.
Step 1: remove the makrozoom objective. Very easy to do, it's a dovetail connection held on with a single screw.
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Step 2: unscrew this hex screw (then two others) to get the focus drive housing off of the head
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That's as far as I got, because this screw is STUCK on. Is there a product that would help loosen it that would be safe to use?

On the plus side, removing the objective did give me a chance to get eyes on the problem:
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Unsurprisingly it is a broken gear. The head uses a rack and pinion style gear mechanism and one of the teeth is just straight up gone. The whole thing is also fairly worn, it must have seen a lot of hard use.

So at this point I am not 100% sure how to proceed. While it appears to only be a single part that's broken I doubt I'll be able to find a replacement just for the pinion? This may mean I'll need to replace the entire focus drive by cannibalizing one off a (more) broken scope. It looks like the M5 and M8 stereoscopes might have compatible focus drives in addition to other 400 series makroscopes. And of course I'll have to get this screw unscrewed somehow to access it.


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 Post subject: Re: Wild M420 focus mount problem
PostPosted: Thu Jun 21, 2018 9:52 pm 
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OK, I did try putting a little bit of liquid wrench in the thread and leaving it overnight. Unfortunately as events unfolded I couldn't go easy on this screw:
Image
Turns out you can strip a hex screw even with a perfectly sized wrench (3mm). We finally got the screw extractor seated, and after the application of some tremendous force it suddenly popped.
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Yup, whatever son of a fish last maintained this did use loctite or some other epoxy.
Once I knew that, though, I was able to get the other two out by exerting a lot of force and pressure. Both popped free and came quietly thereafter.
Image
This allowed me to move the rack down and get a look at the collar that holds the focus mechanisms together:
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thankfully these screws were much easier to get out, since if I stripped one of them I'd definitely be up a creek.
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With the collar off, the knobs on the right side unscrewed:
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Allowing me to get two separate parts, the right knob with a small threaded section that goes into the collar, and the left knob which has the pinion gear attached:
Image
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I think the next thing I'll have to do is get one of those two-toothed key things to get this unscrewed. This part is officially past where the service manual goes, so I am getting into uncharted territory here.

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Not only is the pinion badly worn, you can also see it appears to have been hand-cut, and the teeth are diagonal relative to the long axis of the pinion. I am not sure why.
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The rack also shows some wear, but nothing catastrophic. Hopefully replacing the pinion will be an adequate long-term solution (especially since I don't plan to abuse it; I don't know that that's what happened here, this may be normal wear and tear; but based on the state of that gear I think there is an outside chance that the lab it was in was staffed by overexcited howler monkies.)

So, I guess once I figure out how to get it loose I'll see if I can have a replacement made. I have had Al Meekins at gearsmade.com recommended, so I will probably try there first.


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 Post subject: Re: Wild M420 focus mount problem
PostPosted: Fri Jun 22, 2018 10:43 am 
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wow!
The epoxy was likely put on at the factory. Also the two screws you picture have those very interesting lock washers from switzerland. You are VERY lucky that you didn't run into a big headache with those. I ended up having to drill out three of them because I snapped Wiha (Willi Hahn german made) allen keys in them. They would not budge. I drilled carefully and got three barrel shaped rings. The two parts separated. There were three threaded studs with conical drill starts in them. These unscrewed with two fingers. No thread locker at all. Just impossible to break loose lock washers. It was one of my more remarkable repair experiences.

If the screw you drilled out bears weight you should replace it with one made by UnBrako or Holokrome.

You need a pin wrench to take the knob off. Photograph the disassembly because there may be a clutch or focusing friction adjustment in there. Sometimes those are difficult to get re adjusted after. There was probably one guy at the factory that did that and with a particular lubricant too. You can get a snap ring plier , right angled and use it too though you may break it.

the angulation of the pinion teeth is to improve the smoothness of the focusing knob. They are not hand cut. They may be rolled with a knurling type tool but it doesn't look it.


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 Post subject: Re: Wild M420 focus mount problem
PostPosted: Mon Aug 27, 2018 8:37 pm 
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A couple weeks back, GearsMade mailed me the knob back, asking me to remove the pinion gear. I had thought it was simply taken apart by unscrewing it with the pin wrench holes, but how wrong I was. I got it mostly taken apart, but the last step has completely defeated me:
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I don't know if this is threaded, epoxied or perhaps pressed together, but it's a mess.

So I've had to cancel having it remade, and instead I found a focus drive designed for a different microscope entirely (I am not sure which!) which was semi-compatible. By this I mean it is a rack and pinion with a fine and coarse focus knob which has a flat front with screws to attach a head mount, rather than just having the head mount directly attached to the rack. This meant I could make an adapter with holes to match the M420 head and the focus drive and attach the whole thing together.
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Here's a picture of the focus drive with the adapter attached and drilled. Rather than making it from aluminum, as might have been sensible, I went to our local woodworking shop and got some Bolivian ironwood. This is cool stuff, with a specific gravity slightly over 1 so it actually sinks in water when dry. It should work similarly to aluminum while a) being a bit easier for me to work with, and b) looking very fancy in a 70s paneling sort of way. I had to do a few iterations of adjustments on this to get everything lined up nicely, but it worked surprisingly well, and the first one I drilled ended up working with modifications. If I did it again there are things I'd probably do differently, but I'm pretty happy with it.
The other down side was that the new focus drive takes a 1 1/4 inch diameter shaft, much thicker than the one the m420 was originally attached to. So I made a temporary replacement with an oak dowel, drilled down the center with the threaded section from a carriage bolt inserted:
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This is not a permanent solution unfortunately, as the wood does allow too many vibrations at max mag. It is also susceptible to termites. So I will eventually replace it with a metal one. But nevertheless the m420 is now functional!
Image
This is a quick stack I shot at low mag. I am currently moving so the table the m420 is on does not have a power outlet nearby and I thus fiber optic lighting isn't available yet, so I used cheap 'UV' LED flashlight to illuminate this petroleum-included quartz. It would need more pictures to really turn out, but I am nevertheless pretty happy with it. It's a really nice piece of equipment, and it's really, really nice for it to not be sitting in my parent's living room in pieces anymore.


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 Post subject: Re: Wild M420 focus mount problem [Fixed!]
PostPosted: Mon Sep 10, 2018 9:05 pm 
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I have been having lots and lots of fun with my M420 since I got the basic setup completed, mostly taking photographs of faceted stones which I'd previously had trouble getting consistent results on. However, the wooden pole (in spite of its charming appearance) allowed too many vibrations for serious work at higher magnifications, so I was on the lookout for a 1 1/4 inch shaft to replace it, either one made for a microscope or possibly one I could have machined given how simple a part it was. Instead, I came across something better: a used Olympus SZX-ILLD100, one of their brightfield/darkfield stereo stages. I'd also found out the focus mount I'm using is off an Olympus, so I knew they'd work together. I just got it in, and I think the whole setup looks pretty snazzy:
Image
This has resulted in a huge increase in stability, as you would expect. Unfortunately it only takes a 30w bulb, and I think it's got some sort of problem because the brightfield setting is more of a dull glow, with the darkfield hardly having any visible illumination at all. 30w seems kind of weak to start with, though, so I may take this chance to upgrade to LED or fiber optic illumination. I know there's been a lot of skepticism of using LED lighting for colored stones here in the past, but those threads are a bit older so maybe the situation has changed. This ebay user offers a simple retrofit that's ready to go for this particular base as-is: https://www.ebay.com/itm/LED-lamp-house ... 2357353805
Maybe a bit pricier than I want to do, but I'll need to figure something out.
I may or may not miss the X-Y table that the other base came with, though. I have used it once for photographing a mineral thumbnail. I guess a removeable x-y table is another thing to look for in case I need it.
The other potential downside is that the lens is over the light well but not perfectly centered. I might have to replace the focus mount/head coupler with one that's slightly thicker if that ends up being a problem.


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