Carbon Fiber rods to stiffen flatbed camera base

I've been thinking of ways to stiffen the base of my 1890s lightweight 11x14" field camera, and I was considering routing 4 channels crosswise and epoxying carbon fiber rods that are used to stiffen guitar necks in them.

I was planning to use these 0.200" x 1/4" x 18" rods--

http://www.stewmac.com/shop/Truss_rods/Carbon_fiber/1/Carbon_Fiber/Details.html#details

Has anyone tried this, and does it seem like a good plan?

David,

I haven't used carbon fiber but your plan sounds to me that it should work. I am assuming here that the base is built from several pieces of lumber like a Korona or a Deardorff...are the individual members not glued together well any longer?

Yes, it's an old American Optical camera glued in such a way that the grain runs in different directions, so it's developed some cracks over the years. I've glued all the loose joints back together and filled the cracks and added an aluminum plate around the tripod hole, and it's an improvement, but I suspect this was never a very solid camera, and it depended on having one of those old style tripod heads with a very large platform (say 10" or 12" square).

The trick is to keep things balanced. In grad school I used "pre-preg" sheets of carbon fiber reinforced matrix on balsawood cores and the result was an extremely stiff board intended as a new roofing material. However, if you applied the sheet to only one side the system tore itself apart as the moisture content of the wood changed. The carbon fiber matrix does not change with moisture content (okay, it changes a miniscule amount compared to the wood), and greatly restrained the wood.

i'd recommend against it as it would be irreversible, but if you do, make sure you add an equal number of pieces to both sides of a board and close to the same position, to prevent the wood from flexing as humidity changes. even a finished piece of wood is not sealed against changing humidity. It just slows down the change.

I have a minor stability issue with my 8x10 Korona that sounds similar in nature to what you are talking about. It's in near factory shape, so I didn't want to do anything permanent so I am building a wooden platform that is the length of the front and rear beds for the entire camera to sit on (on the tripod). My initial experiments show that this will add to the stability considerably without altering the camera at all. It does add a little weight, but with the triple convertible lens, Bogen 3047 head, and a survey tripod, a few extra ounces isn't going to even make a blip on the weight radar. You might consider something like that...

- Randy

David A. Goldfarb said:

I've been thinking of ways to stiffen the base of my 1890s lightweight 11x14" field camera, and I was considering routing 4 channels crosswise and epoxying carbon fiber rods that are used to stiffen guitar necks in them.

I was planning to use these 0.200" x 1/4" x 18" rods--

http://www.stewmac.com/shop/Truss_rods/Carbon_fiber/1/Carbon_Fiber/Details.html#details

Has anyone tried this, and does it seem like a good plan?

Click to expand...

I have experience with both design and construction using composite materials. Given that you are willing to glue carbon rods across the base I am assuming that you don't really care if the original look is maintained and your main concern is function. That having been said the best and easiest way to stabilize the base is to cover the top and bottom of the base with carbon fiber cloth using epoxy. Try your local boat shop as a source of supply. Sand the wood with 80 grit sandpaper before applying the cloth.

The main benefit of applying the cloth this way is that in engineering terms you are placing the strongest material as far away from the neutral axis as possible. Materials that are farther away contribut more to the strength. This can be seen in I-beams where the top and bottom flanges are pushed away from the neutral axis. The neutral axis is a point of zero stress which for a symmetrical I-beam or your camera bed lies at the midway point. In the case of your camera bed the carbon fibre is being allowed to contribute more and the wood less. This same carbon/wood sandwich system is commonly used in advanced high speed offshore sailing yachts. The other advantage is that you are reducing the ingress of moisture which causes the wood to warp. Hope this helps.

Why not just make the base out of 0.50" honeycomb or balsa-core (used in aircarft cabinets)? tim

Thanks for the suggestions. I'm still thinking about this.

The camera base is only flat on one side, so it would involve some more major disassembly to put any kind of sheeting on both sides. A cross section of the base looks something like this, where the raised parts support the rails:

___ ___
| | | |
-----------------
----------------- [darn computers.... see attachment]

To put anything on the top side, I would have to remove the raised pieces that support the rails and get them back on the camera so that the focus track is aligned, etc.--more than I want to do.

While function is my main concern, I also don't want to change the look too drastically. If two or four carbon fiber rods embedded in the wood looked too obtrusive, for instance, I might cover the base with a veneer to match the camera.

Maybe a thin sheathing of one layer of glass laid in epoxy on the underside would be ennough to stiffen it? If you fill the weave with more epoxy when the glass layer just gets tacky, it wouldn't show. It is important to sand the wood before aplying epoxy. Then you, of cource, need to varnish the top part of the base with epoxy as well, so you wouldn't get any warping due to different humidity. Then use ordinary varnish to protect the epoxy from UV light.
If this wouldn't stiffen it ennough you could just put on more layers, or go carbon.

/matti

If you cometics are a concern

Where cosmetics are a concern you can apply a thin layer of cloth over the wood keeping in mind the following points:

1) Sand the wood first. Although epoxy works by Polymerization the bond to the wood will be mechanical and thus relies on "tooth" for adhesion. be sure to remove the previous finish. 80 grit will work well.

2) See if you can find some small scraps of good quality glass cloth. Use "S" cloth instead of "E" cloth as it is stonger. "S" for structural applications, the individual strands are smaller, therefore there are more of them and they made from higher quality glass using a better manufacturing process to lessen breakage.

3) Cover the bottom entirely with cloth; you may want to continue up the sides with this piece as well. On the topside you can cover between the raised bits only to make life easier. You should cover the raised areas and the sides (if not previously covered) with epoxy to create a complete moisture seal. This will look better as well.

4) There are epoxies with a UV shield in them so you don't have to varnish over the top.

5) I have used this method and when the glass cloth is wetted through it becomes nearly transparent and you can see the wood grain through it.

If you are going to stick with the truss rod method I would recommend that you call some wood workers to see if they have a horizontal boring machine. If they do you can get them to drill holes through the entire camera base. You can epoxy the rods in place, put a wooden plug over the ends and no one will ever know what is hidden inside.

Hope this helps, good luck.

Thanks again, these are all interesting possibilities.

Just a small comment if you would opt for glass. I think it would be difficult to wrap the cloth if the radius is too small. It might be better to let the cloth go a couple of mm from the edge.

/matti

Terrance Hounsell said:

3) Cover the bottom entirely with cloth; you may want to continue up the sides with this piece as well. On the topside you can cover between the raised bits only to make life easier. You should cover the raised areas and the sides (if not previously covered) with epoxy to create a complete moisture seal. This will look better as well.

Click to expand...

Actually it wouldn't be possible to cover the raised areas or the top in general, because it would interfere with the operation of the camera. The back slides on the raised rails on top of the bed, and the front standard slides between them.

matti said:

Just a small comment if you would opt for glass. I think it would be difficult to wrap the cloth if the radius is too small. It might be better to let the cloth go a couple of mm from the edge.

/matti

Click to expand...

To wrap fiberglass around an inside corner you should insert a radiused or triangular fillet so that the corner is not too sharp. The insert can be wooden but a compatible foam or putty will also do the job.

To wrap fiberglass around an outside corner you should radius or chamfer the corner so that it is not too sharp.

In both cases you want to avoid breaking the glass fibers as much as possible.