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Vintage refractor restoration-powdercoating heads up

Classic Equipment Refractor
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#1 Jamesarakaki

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Posted 24 October 2021 - 02:25 PM

I recently had the good fortune to purchase a 76mm f/15 SYW vintage Japanese refractor in near excellent condition. 

The seller had begun to restore the instrument and in fact it was usable, but found no interest within the family. It had been purchased new in the mid 1960s by his father. It was obviously a labor of love as he had taken great care- sanding and restaining the tripod legs, cleaning and touching up the mount, and disassembling and taking the OTA and finder apart to have the tubes professionally powder coated.

 

Unfortunately, his dad had moved to smaller quarters and could not put the instrument to use. 

 

As acquired it appeared to need only minor touchup- a tripod leg locking bracket had been removed and taken to a welder to have a threaded boss rebrazed onto the band. It needed to be painted satin black. The dewshield and objective cell had chips in the black paint and needed touchup or repainting.

 

On disassembly I looked into what seemed to be an oddity- the interior of the tubes had no black paint applied. With the objective cell and focuser off, I could see no trace of black paint on the tube wall or on the glare stops, not even in the tiny crevices where the glare stops meet the wall of the tube. It looked like it had been manufactured this way, which made no sense.

 

However, there was white powdercoating overspray near the interior ends.

 

What happened is this:

 

Powdercoating, being an electrostatic process, needs to be applied to clean, conductive and heat resistant surfaces. The powdercoater took the main and finder optical tubes and stripped the paint off using an ultrasonic process. This scrubbed ALL the paint off, including the flat black interior. The process is very efficient and leaves almost nothing behind. 

I masked off the tube and applied a coat of flat black spray paint as best I could. However, there were two glare stops that divided the tube interior into three chambers. Careful probing with a dowel revealed that the aluminum sheet metal was too thin to press out without damage.

 

The larger opening of the stop nearest the objective was about 10.5" in from the end. Getting spray paint into the center chamber proved impossible. Even rolling tapered paper tubes to direct the spray into the chamber was unsuccessful. 

 

I managed to paint the faces of the glare stops with a brush taped to a dowel. However, the wall of the tube between the two glare stops was still reflective. This was a section 14" long.

 

I managed to apply a black flocked paper lining in between the glare stops by rolling two flocked paper tubes(fuzzy side it). One tube was 10 inches long, the other 5 inches. The seams were taped and the paper cylinders curled in on themselves so they could be slipped into a 2" diameter aluminum 'carrier' tube. I prepared a smaller plastic pipe by taping off the end, so I could use it to push the rolled flocked paper tube out of the 2" carrier tube. This allowed me to first insert the long 10 inch flocked paper tube through the forward glare stop, which had an opening larger than 2 inches. Once the paper was inside the chamber and up against the rear stop, I held it in position with the inner 'pusher' tube and retracted the aluminum carrier cylinder, letting the paper tube spring open. Naturally, the seam was still curled in on itself, but I teased it tight against the inside of the tube wall with a dowel. Once fully open it hugged the inside of the tube. 

 

The second 5 inch flocked paper tube was also inserted, the end of the 2 inch carrier tube just clearing the glare stop. The flocked paper was pushed out, this time holding the carrier tube end right behind the forward glare stop. When fully opened and in position, the shorter flocked cylinder overlapped the longer by an inch. The result was a dead black interior chamber.

 

With the center chamber flocked the open ends were easy to do. The completely flocked tube is dead black.

 

 

 

Naturally, now that the scope is ready for testing, we have a week of rain now.

 


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#2 c2m2t

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Posted 24 October 2021 - 02:31 PM

Hi James!

You'll need to add an image or two of this fine scope that you so carefully described...so others may appreciate it a bit more...more than a mental image will allow!! grin.gif

 

Cheers, Chris.


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#3 mdowns

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Posted 24 October 2021 - 02:43 PM

Chris is right James.I sent you a pm with some uploading  attachment help.      Michael


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#4 norvegicus

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Posted 24 October 2021 - 03:09 PM

You could have had the interior powder coated matte black. Probably would have needed to redo the outside at the same time though.

 

But flocking paper works fine and is easier and much less expensive.


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#5 Jamesarakaki

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Posted 24 October 2021 - 11:45 PM

Norvegicus:

   I'll look into that on my current ATM project- I have a bare aluminum tube 4.5" dia for a 4.25" f/15 refractor. I'll need to do about 48" of tubing interior with glare stops, and I'd thought to do this with bristol board or similar thin hard rag paper with an india ink wash. 

 

 But the idea of matte black interior powdercoat is intriquing.  Using thin aluminum stops with circumferential friction tabs would be neat- they could be blanket formed over a cylindrical slug and pushed into place with a disc and dowel. The powdercoat would likely hold them in place if the aluminum is thin, like .010 or so. They'd have to be laser cut but likely doable with a small 60 watt cutter. I'd have to price it out.

 

I moved to the Sacramento CA area from the SF Bay area where I used a lot of different shops for prototyping work. Waterjet and laser shops are efficient and cost effective for flat shapes, but there aren't that many shops in my area now.

Most are bigger industrial shops that don't like these fussy little projects and charge accordingly. 

 

 I was going to have the exterior powdercoated white- wouldn't they have to do interior and exterior at the same time? That would be cool if they could do black AND white.


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#6 norvegicus

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Posted 25 October 2021 - 06:28 AM

Norvegicus:

   I'll look into that on my current ATM project- I have a bare aluminum tube 4.5" dia for a 4.25" f/15 refractor. I'll need to do about 48" of tubing interior with glare stops, and I'd thought to do this with bristol board or similar thin hard rag paper with an india ink wash. 

 

 But the idea of matte black interior powdercoat is intriquing.  Using thin aluminum stops with circumferential friction tabs would be neat- they could be blanket formed over a cylindrical slug and pushed into place with a disc and dowel. The powdercoat would likely hold them in place if the aluminum is thin, like .010 or so. They'd have to be laser cut but likely doable with a small 60 watt cutter. I'd have to price it out.

 

I moved to the Sacramento CA area from the SF Bay area where I used a lot of different shops for prototyping work. Waterjet and laser shops are efficient and cost effective for flat shapes, but there aren't that many shops in my area now.

Most are bigger industrial shops that don't like these fussy little projects and charge accordingly. 

 

 I was going to have the exterior powdercoated white- wouldn't they have to do interior and exterior at the same time? That would be cool if they could do black AND white.

I think they would have to do both at the same time.  There might be some "overspray".  It is a plastic powder that is applied electrostatically and then baked to melt it into a coating.  You apply the powder with a gun that puts out a cloud of charged bits of plastic.  I think they could apply to the inside, wipe the powder off the outside, then apply the outside powder, then bake.  That's how I'd do it.  I have a home powder coating kit.  It's easy to do but the size of the piece is limited by the oven.  I use a toaster oven so only can do small pieces.



#7 Jamesarakaki

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Posted 25 October 2021 - 05:03 PM

Is that the powdercoating setup sold by Harbor Freight and Eastwood? I thought about getting one as it's a lot less nasty than home anodizing (not to mention more consistent, color and luster wise).

 

I think HF sells white, black and yellow gloss powder. Do you know of other suppliers that sell home shop quantities? Satin black is what I want for some external fittings...unless you can just take fine steel wool to gloss black powdecoat?

 

I've been considering making tube rings by aluminum brazing 3/8" or 1/2" standoffs to short lengths of aluminum tube, since a metal supplier I go to will sell slices off long lengths. Much cheaper to get a 5/8" or 1" long ring of 1/4" or 1/2" wall aluminum tube rather than a solid plate. I think I paid $6 or $7 each for 1 inch long aluminum rings with 4-1/2" ID and 5" OD. I need to cut curved recesses in these rings to braze 1/2" standoffs into. The plan is to cut the rings in half through the brazed on standoffs, thread the standoff segments in one half and drill out the other half for clearance for socket head cap screws. I don't see the need to hinge rings since loading and unloading of a tube assembly is usually done with a dovetail bar these days. These rings would be installed and left in place.

 

Because of the braze anodizing would look terrible. Powdercoating would be much better. DIY powdercoating of small parts would be much cheaper.



#8 norvegicus

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Posted 25 October 2021 - 05:29 PM

Yeah I have the Harbor Freight kit.  Works fine.  You do need an air compressor to go with it.  

 

HF sells matte black powder, $7/lb:  https://harborfreigh...lack-93306.html  

 

You can buy small quantities on Amazon.  

 

I used the matte black when I restored a tripod, for all the little metal bits.  Worked great, looks better than new.  It's my go to method for small metal parts now, less work and a nicer finish than rattle can paint.


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#9 Jamesarakaki

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Posted 25 October 2021 - 07:15 PM

Cool! Going to HF...


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#10 Jim Curry

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Posted 26 October 2021 - 06:39 AM

While doing a few refractor builds 3 years ago I experimented with flocking vs. paint for internal reflection control.  I wasn’t happy with paints, you can look at the darkest of production scopes at a low angle and see they are reflective.

 

Here’s a thread of an experiment I conducted: https://www.cloudyni...aint/?hl=+flock


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#11 Jamesarakaki

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Posted 26 October 2021 - 07:32 PM

IMG_3164.jpg Interesting- when I first tried flocking I messed around with the adhesive backed stuff and it was a PITA. I wound up using flocked paper with a plain back from Hobby Lobby and relied on cutting the paper to the tube inside circumference. No adhesive. As long as I cut accurately the paper would hug the inside of the tube. I found that taping the paper into a tube with the flocking inside I could partially roll it and slip it in place first. 

 

It seemed that flocking the tube wall just behind the objective cell had an immediately noticeable effect. Past the first glare stop it seemed like the tube wall was mostly in shadow and the flocking at least in the one I fooled with had little effect, with the black paint doing the job.

 

In the case of my new to me vintage Yamamoto there was nothing at all on the inside, and failing to even paint it past the first glare stop I resorted to flocking with my ship-in-a-bottle method. I don't have the black paint to compare it to but now it's like DEAD black. 


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#12 Jamesarakaki

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Posted 26 October 2021 - 07:34 PM

oops- guess the pic loaded. That's the interior of the Yamamoto after taking off the objective. Nice powdercoat outside, bare metal inside except for the overspray powder...



#13 Jamesarakaki

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Posted 26 October 2021 - 07:39 PM

DSC03286.jpg DSC03286.jpg Okay, let me see if I can add pics of the scope. It was purchased by the original owner around 1965.

 

The original .965 eyepiece holder was swapped for a Vixen 1.25" holder taken from another Vixen focuser. There was the identical part sitting on top of the focuser of my Celestron 4.5 Newtonian as well, so I think Vixen uses it often in different assemblies. On the scope here it's holding a Celestron prism diagonal and one of my Optica B/C Orthoscopics.

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