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PostPosted: Wed Dec 26, 2018 9:32 pm 
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I'm looking for a few parts to complete my Reichert era Microstar IV. I need the blue filter, and if possible, the swing out carrier for this filter, that's in the base of the unit. Please PM me if you have these parts.

Carl

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PostPosted: Wed Dec 26, 2018 11:25 pm 
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I think you might mean the neutral density filter and it's housing?


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PostPosted: Wed Dec 26, 2018 11:29 pm 
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Apochronaut,

Right between the 7388 Esb lamp and the diffuser in the lamp inlet optics, there is a filter holder that swings in and out, as controlled by the "blue" knob on the front. The blue filter is missing , and the plastic holder is broken. There is also a neutral density filter, after the inlet optics, that swings in or out of the light path. That part fiunctions fine. If need be, I can provide photos.

Carl

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--- If you're in the Kansas City area and you need help with an Olympus BH-2 scope, PM me. I love to work on these things ---


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PostPosted: Wed Dec 26, 2018 11:36 pm 
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Most of the Microstar 4s I've worked on are missing the blue filter and the filter's holder. Those are a couple of rare items. The filter holder is a good design but made of a horrible material, and over time breaks into pieces of fried plastic, so you really don't want to replace it with a new identical holder. See the images of an unbroken holder. I am currently fabricating simple replacement holders for a few Microstar 4s out of 6061 aluminum; if it works, I'll get in touch with you, or the forum here, and perhaps I can make you one for a nominal charge.

The other thing is the blue filter. It is about 26.6 mm O.D. This is not a common size. The replacement holder I am making will use the more common 32mm size, if I can make it fit in there. Also, the Reichert blue filter is somewhat paler blue than is usually found in the common 32mm size (see image), so one would have to find an equally pale 32mm filter so as not to overdo the filtration.


Attachments:
PC260019-1024x1024.JPG
PC260019-1024x1024.JPG [ 55.66 KiB | Viewed 1965 times ]
PC260020-1024x1024.JPG
PC260020-1024x1024.JPG [ 57.19 KiB | Viewed 1965 times ]
PC260021-1024x1024.JPG
PC260021-1024x1024.JPG [ 54.31 KiB | Viewed 1965 times ]
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PostPosted: Wed Dec 26, 2018 11:41 pm 
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Location: Olathe, KS
wporter,

Yes, that is exactly the part! The plastic gets well blasted with heat from the 20W lamp. The carrier was broken in half, so I concur it's a fragile part. I have it epoxied back together with JB Weld, so it might work. But I don't have the filter either.

Please let me know if you are able to make a replacement. I'm definitely interested. That might also be a candidate for 3D printing.

Carl

_________________
--- If you're in the Kansas City area and you need help with an Olympus BH-2 scope, PM me. I love to work on these things ---


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PostPosted: Thu Dec 27, 2018 12:24 am 
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Apologies for assuming. Any I had with broken filter housings had intact sky filters and busted neutral density filter housings. Perhaps they were used with the sky filter out, more than in. I can see that the heat of the lamp, might over time damage the plastic housing.

I have one small light blue filter that could work but no original parts handy.
It is 27.8mm, big enough that it rests midway across the outside wall of the housing, so it could be attached to the far side( from the bulb) of the housing with some cement that can take a bit of heat or a glue gun. The filter would be about 3 mm farther from the bulb, then. Might be able to cobble a broken filter frame together as long as the eyelet is still intact and working and have that work.

Bill, if you are designing a D.I.Y. part. Why not make it a little bigger, so it can take some more easily found size, small filter disc.

It is possible the filter has a degree of tempering. Although the bulb is only 24 watts, the filter is close.


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PostPosted: Thu Dec 27, 2018 12:56 am 
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Quote:
Why not make it a little bigger, so it can take some more easily found size, small filter disc


Apo, that's the plan. It's almost a case of making the hole to hold a 32mm filter (if that will work in the microscope) and letting the user mount his own filter in the hole with some hi-temp engine gasket RTV (the red kind) and an adapting washer or something. The RTV would allow for differential expansion between the filter and the holder, and allow for easy 'cementing'.

Carl, the only problem with 3D printing is having to use a heat-resistant plastic or resin. Are such things available for 3D printers? I have to admit to knowing nothing about 3D printing resources. How would you get the drawing file, scan the existing part somehow? Or just use a much simpler design?


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PostPosted: Thu Dec 27, 2018 1:50 am 
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Location: Olathe, KS
Yes, heat resistance would be the problem with 3D printing. Maybe some of the uv curable resins would be up to the task, but I don't know.

Now that I know that I'm not likely to find exact replacement, I may pull the bottom back off and have anoth look. I may just be able to cement a larger disk on the carrier, rather than in it.

Carl

_________________
--- If you're in the Kansas City area and you need help with an Olympus BH-2 scope, PM me. I love to work on these things ---


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PostPosted: Thu Dec 27, 2018 2:26 am 
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Location: Olathe, KS
The thing barely gets out of the light path as it is. If the OD were much bigger, it probably wouldn't.

Carl

_________________
--- If you're in the Kansas City area and you need help with an Olympus BH-2 scope, PM me. I love to work on these things ---


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PostPosted: Thu Dec 27, 2018 1:30 pm 
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Posts: 2526
The one small pale blue filter I have is not larger than the original housing, so it wouldn't be a problem in terms of it being oversize but you are correct; at some point a larger size would be too much. However, if say 32mm filters turned out to be the best choice but slightly too big, the new mount could be designed to cradle the filter a bit off center, so that when swung out it clears the path. It would still be possible to use an easily available larger filter size, just a certain amount of the surface measured from one edge would be utilized.


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PostPosted: Fri Dec 28, 2018 7:01 pm 
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Location: Olathe, KS
Apochronaut, PM sent.

Carl

_________________
--- If you're in the Kansas City area and you need help with an Olympus BH-2 scope, PM me. I love to work on these things ---


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PostPosted: Sat Dec 29, 2018 4:02 pm 
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Location: USA
Here is a substitute holder I made for one of my broken ones. Works great. Longer post coming after I get a chance to draw it up.


Attachments:
PC280027-1024x1024.JPG
PC280027-1024x1024.JPG [ 71 KiB | Viewed 1796 times ]
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PostPosted: Sat Dec 29, 2018 8:09 pm 
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The simple new holder is made from a piece of scrap 6061 aluminum. The only slightly 'critical' dimensions are 1 through 5:

1. The large hole; it is 0.253" (6.48mm), for a slip-fit over the existing pivot bushing (which has an O.D. of 0.250").

2. The small hole; it is 1/8" (3.16mm), for a press-fit of the 1/8" stainless rod (5/8" long, super-glued and hammered lightly into the hole to protrude about 1/2" (12.7mm). This rod is where the cable wire loops over the holder to work the filter in and out of the light path.

3. The distance between the holes: center-to-center is 1.16" (29.5mm). This dimension was gotten from the original plastic holder.

4. The bar thickness; this has to be less than the length of the existing pivot bushing, so that when tightening the bushing screw, the bushing is secured, but the bar is still free to pivot.

5. The semi-circular slot (groove) for the filter glass is about 3/32" (2mm) deep, cut with a round saw or abrasive blade using a hand-held rotary tool (Dremel or equivalent, in the US), and having a width of a little more than the thickness of the filter.

The overall length of the bar is arbitrary, mine was about 1.8" (46mm). The bar width was about 0.485" (12.3mm).

I added the washer over the inner end of the bushing to keep the bar from wobbling as much.

The best way to find the position of where the groove needs to be cut is to mount the bar in place in the microscope, swing it down into position, and mark the bar with a dotted line (see image) where the OD of the field condenser diffuser glass is, behind the bar. This will give you the best place for the filter, whether 26mm or 32mm. Then remove the bar and cut your groove, glue in the filter, etc.

The groove for the filter is filled with Hi-temp RTV, the edge of the filter is cleaned and smeared with the same, and the filter is bedded into the groove, and the whole thing propped up to keep the filter planar with the bar, until the RTV hardens. Then an additional fillet of RTV is applied to the bar-filter joint for extra strength. One could even skip the making of the groove (the most problematic part of the fabrication) and glue the filter edge directly to the side of the bar, but I didn't try this.

To test the RTV, I ran the lamp for several hours with the scope baseplate screwed on, to see if the temperature would be a problem, or if the RTV would fail, etc. No problems; the RTV got harder, the temp of the bar got up to no more than 130F (oddly 300F on the diffuser glass). The RTV supposedly can take 700F. Tugging on the filter, the RTV seems strong enough, but I didn't pull it out of the groove, so am hoping for the best. In service it is under almost zero stress, so I think it should work OK over the long term.

It may seem that the bar blocks some of the light, since some of the filter is recessed into the groove, but the lamp is so close to the blue filter, that if one traces the light from the filament of the lamp to the edge of the diffuser, one can see that only the center 75% or so of the filter is used. Actually, the larger 32mm filters might be a bit better (if one can find a filter that is not too dark blue.)

To help the positioning of the filter when swiveled into place, some sort of 'stop' can help. The microscope has a pin for this purpose, underneath in the base, right under the blue-filter control knob; the 1" lever worked by the knob runs up against the pin, to control the in-positioning of the filter. I've seen some of these pins bent to adjust the stopping of the lever, but personally prefer leaving the pin straight, and instead sliding a rubber cylinder, or the like, over the pin. This way, the pin doesn't break off from being bent, and changing the position of the stop is just a matter of changing the rubber cylinder size (one could even just wrap tape around the pin until it works).


Attachments:
PC280019_1024x1024_LABELED.JPG
PC280019_1024x1024_LABELED.JPG [ 118.63 KiB | Viewed 1784 times ]
PC280026-1024x1024.JPG
PC280026-1024x1024.JPG [ 53.87 KiB | Viewed 1784 times ]
PC280028-1024x1024.JPG
PC280028-1024x1024.JPG [ 39.43 KiB | Viewed 1784 times ]
PC280023-1024x1024.JPG
PC280023-1024x1024.JPG [ 141.16 KiB | Viewed 1784 times ]
PC290019_1024x1024.JPG
PC290019_1024x1024.JPG [ 327.83 KiB | Viewed 1784 times ]
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PostPosted: Sat Dec 29, 2018 9:12 pm 
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Great creativity and engineering, congratulations.

I have used red high-temp RTV several times to build heaters that operate at up to 210C. In my experience, it never failed, even after hundreds of hours at that temp.

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PostPosted: Sat Dec 29, 2018 9:52 pm 
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Joined: Wed Oct 21, 2015 10:18 pm
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Location: USA
Thank you for the compliments, Hobbyst. If it helps someone restore this function in their Microstar 4, well worth it. Though you can fix things a bit with white-balance adjustments, etc., better to fix things at the source. Plus it's really annoying to have a disfunctional knob on one's microscope.

Good to hear about your experience with the RTV, also.


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PostPosted: Sun Dec 30, 2018 8:11 pm 
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Joined: Fri May 15, 2015 12:15 am
Posts: 2526
wporter wrote:
The simple new holder is made from a piece of scrap 6061 aluminum. The only slightly 'critical' dimensions are 1 through 5:

1. The large hole; it is 0.253" (6.48mm), for a slip-fit over the existing pivot bushing (which has an O.D. of 0.250").

2. The small hole; it is 1/8" (3.16mm), for a press-fit of the 1/8" stainless rod (5/8" long, super-glued and hammered lightly into the hole to protrude about 1/2" (12.7mm). This rod is where the cable wire loops over the holder to work the filter in and out of the light path.

3. The distance between the holes: center-to-center is 1.16" (29.5mm). This dimension was gotten from the original plastic holder.

4. The bar thickness; this has to be less than the length of the existing pivot bushing, so that when tightening the bushing screw, the bushing is secured, but the bar is still free to pivot.

5. The semi-circular slot (groove) for the filter glass is about 3/32" (2mm) deep, cut with a round saw or abrasive blade using a hand-held rotary tool (Dremel or equivalent, in the US), and having a width of a little more than the thickness of the filter.

The overall length of the bar is arbitrary, mine was about 1.8" (46mm). The bar width was about 0.485" (12.3mm).

I added the washer over the inner end of the bushing to keep the bar from wobbling as much.

The best way to find the position of where the groove needs to be cut is to mount the bar in place in the microscope, swing it down into position, and mark the bar with a dotted line (see image) where the OD of the field condenser diffuser glass is, behind the bar. This will give you the best place for the filter, whether 26mm or 32mm. Then remove the bar and cut your groove, glue in the filter, etc.

The groove for the filter is filled with Hi-temp RTV, the edge of the filter is cleaned and smeared with the same, and the filter is bedded into the groove, and the whole thing propped up to keep the filter planar with the bar, until the RTV hardens. Then an additional fillet of RTV is applied to the bar-filter joint for extra strength. One could even skip the making of the groove (the most problematic part of the fabrication) and glue the filter edge directly to the side of the bar, but I didn't try this.

To test the RTV, I ran the lamp for several hours with the scope baseplate screwed on, to see if the temperature would be a problem, or if the RTV would fail, etc. No problems; the RTV got harder, the temp of the bar got up to no more than 130F (oddly 300F on the diffuser glass). The RTV supposedly can take 700F. Tugging on the filter, the RTV seems strong enough, but I didn't pull it out of the groove, so am hoping for the best. In service it is under almost zero stress, so I think it should work OK over the long term.

It may seem that the bar blocks some of the light, since some of the filter is recessed into the groove, but the lamp is so close to the blue filter, that if one traces the light from the filament of the lamp to the edge of the diffuser, one can see that only the center 75% or so of the filter is used. Actually, the larger 32mm filters might be a bit better (if one can find a filter that is not too dark blue.)

To help the positioning of the filter when swiveled into place, some sort of 'stop' can help. The microscope has a pin for this purpose, underneath in the base, right under the blue-filter control knob; the 1" lever worked by the knob runs up against the pin, to control the in-positioning of the filter. I've seen some of these pins bent to adjust the stopping of the lever, but personally prefer leaving the pin straight, and instead sliding a rubber cylinder, or the like, over the pin. This way, the pin doesn't break off from being bent, and changing the position of the stop is just a matter of changing the rubber cylinder size (one could even just wrap tape around the pin until it works).

nicely made part , Bill. Looks permanent.


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PostPosted: Sun Dec 30, 2018 9:07 pm 
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Joined: Wed Mar 04, 2015 2:24 am
Posts: 96
Location: Olathe, KS
Wow Bill,

Thanks for the excellent post!

Carl

_________________
--- If you're in the Kansas City area and you need help with an Olympus BH-2 scope, PM me. I love to work on these things ---


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PostPosted: Sun Dec 30, 2018 9:26 pm 
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Joined: Wed Oct 21, 2015 10:18 pm
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Location: USA
Quote:
nicely made part , Bill. Looks permanent.


Thanks very much, Phil.

As far as being permanent, it probably depends mostly on the durability of the RTV over time, exposed to the UV from the lamp (temperature not being a problem); worst case, the filter falls out after a year or two. If it does, just reglue it in; an easier fix than with the original holder, for sure.

Quote:
Thanks for the excellent post!


My pleasure, Carl; and thanks to you for raising the issue and getting me off my butt, to finally fix my own scopes!


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