How to cut Phenolic plastic sheets?

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barryjyoung

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I want to just say a few things and ask a couple of questions. Hope I don't annoy.


Delrin is a brand name owned by DuPont for their products made of Acetal material. It is quite dense yet easily worked with very sharp milling cutters. It is slick and smooth and would be ideal for darkslides for film holders except for two things. It is hard or impossible to find in sheets .050 thick which is how thick Korona darkslides are, and it is not rigid enough in thin sections over the length required for a 7x17 holder. In my opinion. However, unlike ABS or PVC, Acetal does not seem to attract dust like a magnet which many people overlook when trying to find darkslide and septum material. So, if you are willing to have floppy darkslides and if you think it will fit in your Korona holders (I do not believe a .062 sheet will fit into a Korona light trap and it does not in mine), then have at it with Acetal sheets. By the way, removing that .012 excess thickness,,,,you don't even want to go there.

Jason: I believe the septums in our Korona film holders are made from a material called believe it or not "fish paper" which is used in the electronics industry as an insulator. It ranges in price from $350 to $400 per 48x96 sheet. Ouch! I think a better material is what the original Korona dark slides were made of which seems to be Vulcanized Fiber in four laminations .010 thick joined with an adhesive only along the periphery of the piece. I do not know why, but that is how it is. The darkslides are .050 thick. The septum is also .050 thick. Please toss corrections at me if I made an error here folks.

I will be obtaining some of this material and would be happy to furnish enough to you for your needs at my cost if you are interested. I can also offer you darkslides with wooden handles attached and a septum made to fit if you are interested in bypassing all the work all together. You see, I have already bought and am awaiting delivery of the tooling required to manufacture 7x17 Korona pattern film holders commercially. I expect with CNC capabilities that I will be able to offer double light trap 7x17 holders for something less than $300 each which is a significant savings over available holders.

Now for my question. Though I have a viable design for light trap, does anybody know where I can buy the brass comb used in the light traps of better quality film holders? I would like to make a world class product and frankly without the brass comb, these holders will have to compete on price point alone.

Thanks, hope I didn't ruffle any feathers, especially with the other holder manufacturers.
 

barryjyoung

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I found the "brass comb" material, thank you for listening to my rantings and ravings. It is called "finger stock" (Thanks Jim Chin) and is readily available in very snazzy berryllium copper for long life. Maybe I will offer both felt and fingerstock light traps for those who want the very cheapest and those who want the very best.
 

Jim Chinn

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Barry, on the holders I have made I use the fingerstock and then "wrap" the fingers with felt to complete the light trap. McMaster Carr and MSC both sell felt with an adhesive backing that works perfectly.
 

barryjyoung

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So felt not velvet? My Korona holders have felt on a cheap and shoddy stainless shim stock lock seamed V shaped gizmo, but my fancy schmancy holders have brass fingerstock with a velvet strip covering it. I have found fingerstock thanks to you, and will be receiving my first quotes and samples soon. These electronics houses, and plastics supplies take forever. Did I read somewhere that you are using Garlock XX for darkslides? That is a vegetable fiber right? Is it rigid enough to push through the light trap on a film holder? All the vegetable fiber materials I have looked at have been way too noodley to push into a light trap if they are only .050 thick. Also, the black paper phenolic, is it really really really opaque or just kind of opaque? That is another sample that is taking forever. So far I have looked at fish paper (too flimsy but MIGHT make a good septum if I could find it thick and cheap enough), Vulcanized Fiber (perfect for septums in every way except expense, wow it is spendy, like $450 for a 4X8 foot sheet), Nitrile Impregnated Densified Fish Paper (cool stuff lightweight rigid and completely opaque, but it only comes in thickness .032 and thinner I need .050, and it is $10 per square foot if I laminate it and I need like $55 bucks worth for one 7x17 holder and that is too much for me to sell them for less than $300) Plastic Laminate from Wilsonart and Formica (too rough on the back and too thin). What were the original darkslides made of? One of mine has delaminated and it is 4 sheets cemented around the periphery only, but they look like some sort of paper and the outside looks like celluloid to me. Anything you can tell me would be of immense help to the entire ULF community, or at least to those who want affordable film holders.


Jim Chinn said:
Barry, on the holders I have made I use the fingerstock and then "wrap" the fingers with felt to complete the light trap. McMaster Carr and MSC both sell felt with an adhesive backing that works perfectly.
 

barryjyoung

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Garolite, not Garlock...OK, I found your previous post. Thank you.
 

Jim Chinn

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The garolite xx works fine at 11x14 for stiffness. Should be ok for 12x20 with the 12" cross dimension. I think if you go bigger you might need to go with something else. I did make a pair of darkslides for someone restoring a 20x24 camera who had 2 holders but broken slides made of wood. For those I used .063 aluminum had had it powder coated black. He has had no problems.

I am not sure what the garolite is made of, but it is a laminate. From looking at peices I have cut and chipped before going to the water jet it looks like more of a fiber component.

Barry, PM me your address and I will mail you a small sample scrap of garolite xx I have sitting around so you can get an idea of what it is. If I can find them I have a couple scrap pieces of two different fingerstock profiles laying around also you can have.



For the light trap you could use velvet as well I suppose. I went with the felt only because one of the vendors ( I think it was McMaster Carr) had an adheisive backed version in a couple different thicknesses and it was the first one I experimented with. I also took apart an older Kodak/Grafmatic 8x10 (1950s vintage I think) holders and they difinetely used felt as well.
 

barryjyoung

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Hi Jason:

I just measured septums on holders from two different manufacturers including one from Gundlach for a Korona. They both measured .070 thick but they are very old and the material looks like fish paper, so they probably were .0625 (1/16th) inch when new.
 

barryjyoung

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I just went out to the workshop and cut a corner off the piece of Garolite XX Black that Jim Chinn so graciously mailed to me. Thanks Jim.

The garolite cut on the bandsaw with a fine blade and on the table saw with a regular carbide woodworking blade. I then sanded it on a stationary disk sander and belt sander. It sands beautifully but makes an awful stink.

This garolite material is apparently a type of paper based phenolic. The stuff I finally ordered was also a grade XX paper based phenolic but unlike the Garolite material, this is very slick and smooth like ABS plastic. The Garolite has a textured surface very much like paper. They both saw well and sand well and stink like the dickens during sanding.
 
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