Preventing warping on deep carvings

[rcnewcomb]

I've been thinking about trying carbon fiber rods as part of the glue-up. You can find 0.125" rods on e-bay for about $5 for 40" pieces. Imagine the rods inset into a backer board that is then glued on to the main glue-up. I'm thinking of trying this on a mantle piece carved from the Design & Carve series. The piece would be undergoing significant temperature and humidity extremes.

Has anyone else used carbon fiber to control warping?

Thoughts?

[khaos]

I was just thinking about attaching some plywood or straight board with perpendicular grain.. Let me know how the rods work for you.

[mikeacg]

Interesting idea! It will be good to know how that works for you!

Mike

[myxpykalix]

our version of "re-bars" huh? I tried the crossgrain gluing on some very old, very dry walnut and that helped some but because it was such a deep carving it still cupped but not that bad.

[gc3]

I would think that these type of rods would have some specs online for their application. At .125" I doubt the diameter to lenght strenght ratio would be very strong...maybe/maybe not. Solid wood moves no matter the thickness or finish used...period. Also the adhesive you would use to attach these rods would probally move at a different rate than the rods or the wood. With some serious google searches you could find the expansion coeficients of these materials. Have you tried face laminating your material to needed dimensions, this will help make a more stable substrate for carving.



Gene Crain
www.plantasymaderas.com (http://www.plantasymaderas.com)

[navigator7]

@ Randall,
Here are my thoughts:
On the show: How Do They Do It...or whatever it's called.....they were making guitars with routers.
A metal rod is inserted in the back of the neck to the body...and it can be adjusted!
I guess a guitar would never work with this rod.

Wife is getting granite counter tops for Christmas and the counter guys insert steel flatbar in front and behind the sink cutout and epoxy this in.

In concrete, there is something called pre-tension and post-tension. In the first, rods are pre tensioned, concrete is poured and tension released after the concrete is cured. The latter is self explanatory.

It would seem to me, steel rods in a balanced post tensioned assembly through wood would be way cheaper and more versatile than carbon fiber. The creepy thing to me about using carbon fiber is glue. It slips. Unless it is glassed or epoxy....I think the stuff is real slickery.

You can thread a steel rod easy and tighten it!

[rcnewcomb]

quote:I guess a guitar would never work with this rod
Actually musical instrument necks is an application for carbon fiber rods.
->Carbon Fiber Instrument Reinforcements (http://www.lmii.com/CartTwo/thirdproducts.asp?NameProdHeader=Graphite+Neck+Rei nforcements)

[rcnewcomb]

Here is the lattice layout I was thinking of. The horizontal bars would be inlayed deeper than the vertical pars -- or vice versa. The piece to be carved would be glued on top of this so the carbon fiber rods would be completely hidden.

4934

[billp]

Randall,
I have used carbon fiber when doing boat work. I've used it for structural reinforcement ( such as building a carbon fiber deck beam to go underneath a 40 ft tall wooden mast, as well as using it to reinforce/strengthen plywood panels in smaller boats).
The carbon fiber itself is just a matrix for the epoxy resin which is the real strength of this technique, and when combined you get a VERY strong, stiff product.
I don't know if just the .125" rods alone will help you. Take any carbon fishing rod and bend it, and you'll see what I mean.
And then you have the work of cutting the channels, and inserting them as well.
Have you considered using carbon fiber tape instead? I buy it in widths anywhere from 2"to 6"and it's reasonably priced in those sizes. Carbon fiber cloth itself would be great, but it's prohibitively expensive. Here's a link to one site I buy the tape from:
http://www.shopmaninc.com/carbonpage.html
If I were to really go for strength, with low weight I'd consider I would make "miniature carbon beams" by waxing some wood strips and using them as a mold( OR using HDPE/Teflon, etc. to keep the resin from sticking...)Now you'd have a "C channel" shape which you could drop into your dadoes and glue them into place. I'm sure they would be much stiffer than the round rods...
This is an interesting concept that probably has multiple applications. Please keep us posted on your results!

[navigator7]

Randall,
Here is my quick and dirty version of what I called balanced rods...hoping to build on the good ideas Bill gave you.
The three rods run through the mantle. Everything would be in compression and really strong.

4935

[myxpykalix]

Randall you haven't told us how big your carving is going to be? What is the application, ex: fireplace mantel?

You may get away without having to do any of these exotic fixes if you have the option of increasing the thickness of your wood for the carving and decrease the depth as long as that doesn't interfere with the details.

[rcnewcomb]

Yes, fireplace mantles so 48" to 60" wide by about 6" to 12" tall.

[myxpykalix]

Since it is going to be a fireplace mantel, and especially because it is going to be a fireplace mantel subject to a lot of heat I would go out and get you a thick slab of wood and carve on it unless your design doesn't call for what i am thinking you want.

[ron brown]

Structural elements increase in strength with the square of the distance separating the structural cords. Wood warps due to moisture differential in the radial and tangential grains.

Chuck and Bill P are on a track that might help cure the problem. Whatever base or structure will need to be more rigid (read stronger) than the entire carving ... as well the glue. All of this will need to grab a surface area with enough bonding strength to hold whatever material one is hoping to stabilize. If there is enough heat involved, remember many epoxies will soften in as little as 130F/55C.

A glass fiber or carbon fiber beam embedded in the mantle would probably be enough structure to stabilize such a carving. The bond's 'peal strength' needs to be considered.

Fortunately, if a carving fails, lives are not normally at risk. It might be advisable to find some partially cured transitional wood that is prone to warp, install your proposed structure and accelerate the drying to test your chosen method.

BTW, steel rods in a guitar neck are one cord in a structure. By shortening or lengthening that cord, the bend of the neck can be controlled. Carbon fiber in guitar necks are, to my knowledge, strictly a beam stronger than the wood attached to it.

Ron

[waynelocke]

Trying to prevent the wood from moving across the grain and hence warping by gluing plywood or other supports to the back of a panel is almost never a good idea in my experience. You only end up further complicating the problem. The wood moves with a pretty tremendous force from changes in moisture content and if you can successfully constrain the movement, the force still goes somewhere and will quite probably result in cracks or splits.

If I was really concerned about getting a flat carving, I would use a pin moisture meter on the wood and use a board which was as evenly dried throughout the board as I could find. If needed you could make a very rough pass and let it sit for a few days the re flatten the back and make another rough pass and final pass.

After getting as flat a carving as I could I would use it as the panel in a frame and panel construction. This would hold it flat and allow movement.

[rcnewcomb]

quote:I would use it as the panel in a frame and panel construction. This would hold it flat and allow movement
So it sounds like a design that accomodates some movement instead of fighting is probably in everyone's best interest. This is good to know as we approach fireplace installers and cabinet makers with carving samples.

Have others on the forum done relief carvings for fireplace mantles? Did you have any pieces fail out in the field?

[gc3]

Here is a link that might give you some useful info...click the "wood shrinkage calculator", on that page are more links at the bottom.

http://www.woodweb.com/Resources/RSCalculators.html



Gene Crain
www.plantasymaderas.com (http://www.plantasymaderas.com)

[gc3]

Forgot to post this one also...

http://www.woodweb.com/knowledge_base/Humidity_Temperature_Wood_Moisture.html



Gene Crain
www.plantasymaderas.com (http://www.plantasymaderas.com)

[garyb]

Randall, its all about lumber selection, thickness & moisture content and the depth of your carving.
Cut my first 3d mantel about 4 year ago for Wayne's camp in Austin. That particular one is on the front page of our website and still hangs on the shop wall & is subjected to a 20-30° daily temp change (summer & winter).

Have cut a lot of mantels since then in red & white oak, hickory, maple, alder, western red cedar and even one in basswood but have never lost one to warpage or pieces falling off.
The cost of adding carbon fibre etc etc is going to drive you out of the market place with 99% of the builders!and 99.9% of the door manufactures.You might want a backup market place. Just my experience of the been there done that syndrome.

[magic]

How about

First flipping the piece over and making a lattice of relief cuts. Then flipping it back and do the actual carving.

Take the finished piece and glue it to a plywood backer. Each square of relief-cut, would be glued flat to the backer- therefore the surface should (I say should) always remain the way you cut it.

This is a similar construction technique to some Portable Dance Floors that helps keep them flat, even in outdoor heat.

I didn't read if it was going to be painted but the "guys across the way" carve everything and screw the panels to the frame and I've never heard them have a problem.

[myxpykalix]

Also keep in mind to try to stay away from pieces that come from the pith (center) of the tree. I have had a few pieces because i wasn't paying attention start to crack after they started curling up because i didn't check before i cut.

[dmidkiff]

Randall,
The last supper that you saw in Dallas had a cup in it. I applied the finish very soon after carving to help minimize cupping. It did have a small amount of cup and I considered trying to straighten it. I thought of plywood backing and cross grain backing of same wood. I decided to leave the cup and used keyholes for hanging. Spaced them so the piece would set on the mantel. It should be able to move as needed without splitting. Sent another out the other day with keyholes and instuctions to rest on mantel. No long term testing but no calls yet!

[ljdm]

My 2 cents......... Quartersawn is less likely to cup, as opposed to plain sawn, due to the rings being at 90degrees to the face of the board in quartersawn boards. If you use plain sawn, carving a large relief area in the opposite side does help somewhat.

[mikeacg]

I'm with Lou on the quartersawn. One of the reasons I bought my sawmill was to get quartersawn lumber for my mission furniture. This is just another benefit!

Mike

[gc3]

Randall try posting your question here

http://www.woodweb.com/cgi-bin/forums/cnc.pl


Gene Crain
www.plantasymaderas.com (http://www.plantasymaderas.com)