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Flattening Warped Wood


fryovanni
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Last night I recieved a few tops from Mike that he needed surfaced. The tops were twisted and cupped, and there was no way to sand them as is. The Walnut looks great, and was worth saving so I flattened them. I took pics of how I go about this and thought I would post them up (with Mikes okey dokey of course).

This is what I recieved.

walnutviewofstack.jpg

Cupped and twisted :D

Here is a link to the photo gallery. The pics are number 1-8 through the process, and a few other pics have descriptions in the title.

Gallery

The process is pretty simple.

1- Place a bit of craft paper down as a base.

2- If the piece has much thickness you will need to spray it with water to generate steam, soften the wood a bit,and offer a degree of protection against scortching.

3- Cover the wood with more craft paper

4- Place heat blankets over the craft paper/wood

5- I place a sheet of steel over the blankets (offers a degree of stability and protects my blankets)

6- Place a good size flat board over the sheet steel (quilted Honduran Mahogany is prefered *if that is all you have laying around LOL)

7- Place a few billets on top for a bit of weight after you have started the heating(the wood softens enough to prevent it from cracking). Heat the wood to 300-350 degrees F for a few minutes, turn the blankets off for about ten minutes, Then cook it again for about ten minutes (be sure you have heated the wood completely to 300 degrees and it will hold the new set). Then allow it to cool down while still weighted in place.

8- Place the pieces in sticks and clamp lightly or weight. Allow a few days or weeks for the wood to come back to equalibrium moisture content (depends on how much water was used and how well you cooked it, Note the craft paper also helps absorb moisture during the later stages of cooking)

Thicker bits of wood(within reason* I am speaking of drop tops and what not) can be done the same way. Thicker and larger wood would have to be heated in a steam box or use a much larger heating mechanism that could deliver heat deep into the wood without burning it up.

Peace,Rich

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Agreed, extremely helpful and useful info here. I remember this info from when my Purpleheart body blank warped on me and I asked for advice. Great stuff.

I don't know what the consensus will be, but I vote for this to be a pinned topic. This is info many people will get great use out of for years to come. It may be better suited in another thread if it is to be pinned, but either way this is some info that should be readily available in my opinion. Thanks for the thread and info Rich! J

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Just a quick note on those heating blankets I use. I bought a pair of 6" x 36" blankets. This allows me to work with wood up to 12" wide for this kind of application, and use one top and bottom for bending sides or bindings. Very handy way to get the most bang for your buck :D .

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A new use for heating blankets its nice to know there are things to learn. Thanks Rich.

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  • 4 weeks later...

anyone else chuckle when they saw those boards? Makes my wood that i have not look bad at all... which brings me to a question related to this topic. How much warpage is acceptable in the back and front boards when building an acoustic. I have some nice mahogany for my back that is slightly warped, but its not too bad. Will the bracing tend to pull the wood in if its not that bad? or will the warping wanna pull away the braces? Id post a picture but i cant find my camera cord.

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anyone else chuckle when they saw those boards? Makes my wood that i have not look bad at all... which brings me to a question related to this topic. How much warpage is acceptable in the back and front boards when building an acoustic. I have some nice mahogany for my back that is slightly warped, but its not too bad. Will the bracing tend to pull the wood in if its not that bad? or will the warping wanna pull away the braces? Id post a picture but i cant find my camera cord.

Mike was using these for drop tops, not acoustic backs.

You really want stable wood for backs and tops on acoustics, building in tension(unwanted tension) is a bad idea. If a top or back is mildly bending, you can heat it up and work it back to shape. If it is radically twisting it would take several sessions with a fair bit of heat to get the wood retrained and stable. Each time you heat wood it will lose a bit of strength (not bad if it is one or two sessions), but many with high heat and you may lose a lot of strength. So use good judgement when doing this for acoustics, and absolutely flex the wood at the end of the process and see if it is still going to perform as you want it to.

Peace,Rich

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anyone else chuckle when they saw those boards? Makes my wood that i have not look bad at all... which brings me to a question related to this topic. How much warpage is acceptable in the back and front boards when building an acoustic. I have some nice mahogany for my back that is slightly warped, but its not too bad. Will the bracing tend to pull the wood in if its not that bad? or will the warping wanna pull away the braces? Id post a picture but i cant find my camera cord.

Mike was using these for drop tops, not acoustic backs.

You really want stable wood for backs and tops on acoustics, building in tension(unwanted tension) is a bad idea. If a top or back is mildly bending, you can heat it up and work it back to shape. If it is radically twisting it would take several sessions with a fair bit of heat to get the wood retrained and stable. Each time you heat wood it will lose a bit of strength (not bad if it is one or two sessions), but many with high heat and you may lose a lot of strength. So use good judgement when doing this for acoustics, and absolutely flex the wood at the end of the process and see if it is still going to perform as you want it to.

Peace,Rich

Thanks to Rich's help the walnut came out beautifully! :D

0205082009xn3.jpg

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