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Glass Platen

Posted: 07 Jun 2009, 13:43
by jradi
I'm interested in collecting thoughts on the glass platen. I saw a couple of versions built on the instructible site. I'm particularly interested in the newest version that uses two side supports with drawer slides.

The part that I have a hard time visualizing is how to actually build the frame to hold the glass. How does the frame hold the glass?

Re: Glass Platen

Posted: 07 Jun 2009, 14:57
by spamsickle
I think the part that holds the glass is the same in both versions, but he's added the side columns and platen-supporting rollers in the update.

To hold the glass, there's a groove at the bottom of the frame on both sides that the glass slides into. At the bottom of the "V" there's a dowel (or something else) that keeps the pieces of glass from banging into each other. You can either use a router to make the groove, or glue/nail thin strips of wood to the frame.

Re: Glass Platen

Posted: 07 Jun 2009, 19:21
by james415
Actually I all of the glass photos are mine. There are two versions, but they are the same except for the locomotion mechanism.

For construction, I would just take a 1x2 piece of hardwood for the side rail with a thin piece of molding tacked to the bottom edge. Place the glass and add another strip of molding to the top of the glass to hold it in. This will form a perfect channel to hold your glass. Leave the back open and the glass will slide in and out for easy replacement.

I did not use a router because I did not think most people had them. I wanted this to be something easy to duplicate and very modular. I have access to a commercial book scanner so this is really about getting the word out there for me. If you go with a table router, make sure your bit matches the thickness of the pane perfectly so there will be no slop. Keep the edge super straight and you will have an ideal product.

Dan asked me to post a full how-to in the forums so I am working on it in my spare time. It will be up pretty soon though.

Cheers,
James

Re: Glass Platen

Posted: 15 Jun 2009, 17:23
by Karyudo
I'm looking into anti-reflective glass. Products like Mirogard and Tru Vue Museum Glass are used for framing art, and promise to reduce reflections through either coatings or very fine etching. Mirogard seems to be available in 2 mm (= 0.7874" or about 3/32") thickness -- probably about standard for this kind of thing.

Don't know of any local pricing, but should be less than $50 for the sorts of sizes we'd need.

Re: Glass Platen

Posted: 21 Jun 2009, 00:23
by spamsickle
The custom framing department in the local Jo-Ann store (a national chain of craft stores) just quoted me a price on the phone of $150 for a 20" x 24" piece of Museum Glass, but said I could use a coupon to get 60% off if I bought two. I think I really only want 16" x 20" pieces, but it looks like it would still be at least $100 for two panes. I understand there is a cheaper "almost as good" product (also by TruVue) called "Masterpiece Glass," which may be sold at Michaels (another chain of craft stores), but I haven't called them. I think Aaron Brothers also sells Museum Glass, and if any of you have a relationship with an independent framer, they might be able to get (and pass along to you) a better price on the stuff.

There may also be cheaper "anti-reflective" glass out there, if someone wants to do some legwork. My understanding is that Museum Glass absorbs ultraviolet light to help preserve what's underneath it, in addition to simply being anti-reflective. Since that feature is not required for our application, it may not be worth paying a premium to get it.

Re: Glass Platen

Posted: 21 Jun 2009, 09:31
by jimb
I need to reconnect with the framer I have been speaking with to find out the brand, but he quoted $25 for a 12x15 sheet of non-reflective glass. I could ask on proce for the larger sizes. Sadly he won't or can't cut a 45 deg bevel on one edge.

Re: Glass Platen

Posted: 21 Jun 2009, 21:31
by spamsickle
Well, I stopped by Michaels to check out their "Masterpiece Glass", and to me it's indistinguishable from "Museum Glass." They were asking $80 for a 16"x20" piece, and didn't mention any discount coupons, so I drove on up to Jo-Anns.

Jo-Anns regular price on 16"x20" Museum Glass is $85, but with the 60% off deal, I got two pieces for $70.

They also had something called simply "anti-reflective" glass, and the regular price on that was $10 for 16"x20". It looked like glass that had had a diffuse surface sandblasted on it -- it wasn't clear if you just held it up and tried to look through it, but rather looked frosted. Since we're not framing, I pressed it down on a piece of paper, and you could clearly read the text through it, but it still seemed to diffuse the image a little. It might work for people, but I think they should probably evaluate it in person rather than ordering it through the mail.

JoAnns also sells "Museum Acrylic", but it's more expensive than the glass, so I didn't inquire about the price.

Re: Glass Platen

Posted: 24 Jun 2009, 16:13
by Karyudo
Another data point:

I got a quote of $28 (CAD) for a 12" x 16" piece of anti-reflective glass (no brand disclosed or guaranteed, although the woman I spoke to on the phone today said Tru-Vue is a type they typically sell).

Re: Glass Platen

Posted: 24 Jun 2009, 19:08
by Karyudo
Going to buy some glass tonight! I'm going to get some non-reflective glass (12" x 16" x 2 mm; $28 CAD) and some non-non-reflective (i.e. regular!) glass (also 12" x 16" x 2 mm; $18 CAD). I plan to take some test shots....

Re: Glass Platen

Posted: 24 Jun 2009, 19:33
by Carlos Pombo
anti-reflective "glass

Anti-reflective glass is not good for photo-scanning some documents. (some)
We will find old books with pages rippling throughout the volume. In some cases portions of the page will not be in contact with the glass and the resulting image will be cod, fog, without clipping.
Now talking about reflexes let me say from my experience that the best angle to open the book is 85 degrees so that the reflections, as the shadows of light.
This angle does not prevent us from maintaining the optical axis of the lens orthogonal to the plane of the page.
Carlos
photographer