Adventures in Lensboard Making - Three-piece Board...

[Scott --]

Hi, all -

After the last couple of lens boards went together fairly well, I thought I'd try my hand at some joinery. Knew a guy here who needed a three-piece lensboard for an 8x10 he'd rehabbed. Went back and forth with dimensions and particulars, and reached an accord.

The old three piece jobs were actually tongue-and-grooved together, forming "breadboard ends" to keep the panel flat. A lot of current manufacturers, it turns out, either use no joinery and glue that whole 6" cross grain joint, or use a T&G and still glue the entire thing, which defeats the purpose. Ideally, you glue the center few inches, and allow the rest of the joint to "float" which allows the panel to expand and contract with humidity changes without splitting the wood.

The one I made is from some nice mahogany I had from an old project:
http://i80.photobucket.com/albums/j185/bliorg/IMG_1719.jpg

The T&G was a little easier to see before I cut the recess for the back.
Before:
http://i80.photobucket.com/albums/j185/bliorg/IMG_1710.jpg

After:
http://i80.photobucket.com/albums/j185/bliorg/IMG_1716.jpg

That lil' tongue is about 3/32". Wasn't quite sure how I was going to go about making it, but it came together fairly well. Cut the 1-5/8" hole for the lens, sanded in several coats of Waterlox, and it's been out in the sun darkening for a few days.

I had some Krylon "Ultra-Flat" black paint for the reverse:
http://i80.photobucket.com/albums/j185/bliorg/IMG_1715.jpg

I think I might give the front one more coat of Waterlox just for good measure, then it's off to its new home!

I'm having too much fun making these things... ;^)

Thanks for looking.
Scott

[Rob_5419]

Ir looks so professional.

You should be pleased with your wood work skills. I certainly am.

[Frank R]

Classy!

[Jan Pedersen]

How much?

[Doug Kerr]

Hi, Scott,


Ideally, you glue the center few inches, and allow the rest of the joint to "float" which allows the panel to expand and contract with humidity changes without splitting the wood.

I had no idea about thast. Very intersting, and crafty.

You have done a wonderful job on that board.

[Vaughn]

Excellent!

I'm afraid the last two lensboards I have made for my Zone VI are made from a piece of white 8-ply matboard drymounted to a piece of black 4-ply matboard (for the inner side). Cutting the holes out for the lenses with an exacto knife wasn't a fun task. But they work.

Would it have hurt Picker to standardize on a Deardorf 6" board instead of an odd 5.5"?

Vaughn

[Scott --]

Thanks, everyone. Last coat of finish is dry, and the mahogany's suntanning a little more. Hope to have it in the mail in a couple days.


How much?
Dunno, Jan, depends on what materials and what needs doin'. PM me if you've got something in mind.

[Ash]

Hey, Scott....I told ya so!

It'll be a business now! :D

[jmcd]

If you have relatively stable wood, such as mahogany or cherry, and your central panel is quartersawn to limit movement further, you can definitely, and should in my opinion, glue all the way across the 6" joint. This size joint is really more in the baguette board category than breadboard.

On a breadboard joint, the outside portions that are left unglued are pinned, with elongated holes in the trapped panel, to allow for a calculated amount of movement. The pinning keeps the joint tight.

Nice job!

[Scott --]

Thanks, jmcd.

Some reasons why I build joints the way I do, for the sake of full disclosure:

According to the Shrinkulator, on a 6" board, going from relative humidities of 30% to 90% (which was completely reasonable and common where we used to live on the Gulf coast), the mahogany is going to move tangentially about 0.1" (about 2.5mm). Is that enough to split the board? Dunno, but I think it'd be worth the effort to build in compensation. And clearly, a 1/4" by 3/32" tenon won't need pinning.

Also, on a large enough joint, I never glue the breadboards more than a few inches across the center. I'll always pin the center (or drawbore it, which is entirely overkill), and run pins through elongated holes at the edges to keep the joint tight.

Is all this necessary on a 6" board? Doubt it. Grimes glues the entire joint. But I have too many small panels, even of quartered cherry, that exhibit plenty of movement here in the northeast US, to tempt fate. If it's worth building, it's worth over building.

Of course your experience, and mileage, may vary. This is what experience, school, and long hours with an accomplished joiner, have taught me. ;)

[jmcd]

Scott,

Thanks for the reply. I have been running some figures, also.

With a quartersawn board, our radial movement will be approximately half of what the tangential movement would be if the central panel were flat sawn. As Scott noted, that quartersawn board is more difficult to come by, especially in the wider dimensions, but it is worth it in terms of the longevity of the board, and ensuring that your board fits in varying conditions.

If you took a 6" wide quartersawn mahogany board and subjected it to moisture such that it reached its fiber saturation point, and then took it down to very dry conditions, movement would be .174". That is a lot of possible movement, with one of the most stable woods.

Scott, I'm glad to see you insisting on excellent quality. Again, nice job.

[Randy H]

Hmmm... 5/32 (roughly) in a board that only has 3/16 "land" on either side, top and/or bottom. Gives enough latitude for light leakage. I had never really thought about wood lensboards having that kind of give. I do know that once upon a time, I attempted to use a 4-1/2 inch square laminated to a 4 inch square to use in an old Korona. Warped all to h-e-double hockey sticks. Tried a center peice, and two verticals, laminated to a backpiece. Even worse. I appreciate the hell outta somebody that knows what they are doing. I have stated elsewhere, that I know metals. Heat, beat, paint to match. Grind it off and start over if it don't work right. Wood is a little hard to buld back up after the "oops".

[jmcd]

Hmmm... 5/32

That is how much the board could move, in the worst possible moisture differential. This is the ugly board for sale at the garage sale, which has been doomed to a damp corner of a leaky garage, then left on the Patio in Arizona for the summer. This is an example of extreme possible movement in an otherwise well made board, of excellent materials.

Most people are careful to not expose their gear to these possible extremes, for extended periods of time. And for those brief exposures to an extreme, such as photographing in the mist or a hot day in Death Valley, Scott's varnish will limit moisture exchange within the wood, so movement will be less than the possible extreme. (Shellac is also excellent at limiting moisture exchange.)

[Jim Galli]

I'd be happy to test some of those boards in the most adverse of conditions. Where I live, 8% humidity is about the yearly average. Torture for things made of wood and proof that the folks who built the Kodak 2D's in the 1920's really knew what they were doing!

[RichardRitter]

Yes that figure of 0.100 (5/32) almost 1/8 of an inch is a bit wrong. If this was true the bed of an 8 x 10 Wisner camera that has unfinished section would move almost a ¼ inch. The camera in the summer would swell up so badly it would not work. Same would go for a Deardorf or any wooden camera.

Lens boards have been built for over a 100 years using the 3 piece bead board method. I have seen then built with quarter sawn and flat sawn wood and there is no difference in the way they move or work. If there was a problem with flat sawn wooden lens board we all would of known about it long ago. I have seen lens boards made of flat and quarter sawn wood from all of the leading camera makers.

[wfwhitaker]

If this was true... the camera in the summer would swell up so badly it would not work...

One June I travelled from the SF Bay Area to southeastern Virginia where it was face-dripping humidity. My Pocket Expedition locked up and would not focus. Taking it back inside to the air conditioning freed it up. No disrespect to Richard; just an anecdote. But I've never had any problems with lensboards moving, old or new - even those with "breadboard ends" which I made myself and glued all the way across...

[Colin Graham]

I made some mahogany boards the exact same way and glued the entire joint. No problems with any of the six I made. I worry more about the stresses from a copal three and a big chunk of glass.

[Ash]

I just made a lens panel from a flat piece of fibreboard. I'll get my coat :D


I need to find a source of hardwood sheets, and then buy myself the big drill hole cutters to allow me to make perfectly circular holes without snapping the bloody boards!

I'm gonna see about this counter-recessed lens board. I'll post some pics of my cheap-ass layman construction when I'm done ;)

[RichardRitter]

Yes a Wisner will swell up. This is due to the tight fit Wisner used on the sliding parts and the fact the wood is left unfinished. I have 2 Wisners that both did this to me years ago. The cameras no longer have this problem. I seal all the raw wood.

[Randy H]

Yeh, I worked in a building in CA, just south of Santa Cruz. We installed an ornamental/architectural staircase in a high-end office building. My gawd, did they over-engineer the hell outta that thing!! You woulda thought they were gonna have a major 'quake or something. OH DAMN! They did! And right after the one that destroyed the bay bridge and several businesses and buildings, etc etc, the building we worked in, and the staircase we built was ready for business as ususal the next day. Builld it cheap like some (planned obsolescence) or build it for the long haul. Same money.