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What do you do to flatten warped backs
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Author:  truckjohn [ Sun Jun 12, 2016 4:56 pm ]
Post subject:  What do you do to flatten warped backs
Hey guys.

I am going through the wood stash and I find that a lot of the backs i got (for cheap) start at quarter and run to flat sawn... And predictably they are warped in the flat sawn areas.

What methods do you guys use to flatten these sections? It's pretty annoying as many of them want to crack when I simply weight and sticker them.
Author:  Clay S. [ Sun Jun 12, 2016 6:09 pm ]
Post subject:  Re: What do you do to flatten warped backs
You can try steaming them to soften the fibers and then place them between two pieces of plywood or other flat surfaces (clamped or weighted).
You may be able to iron them flat with a household steam iron.
Author:  wbergman [ Sun Jun 12, 2016 6:46 pm ]
Post subject:  Re: What do you do to flatten warped backs
Do not heat any wood with wax anywhere on it. When wax is liquid, it flows like water into the fibers and will never come out.

I had an interesting experience with some perfectly quartered 1/4" BRW that was severely warped when I bought it. The short story is that I soaked it in water for over a week, and eventually in the water it returned to the flat condition that it was in after it was sawed. I then stickered and weighted it and it dried OK

If you do not have wax on it, you can make or buy a heat press. Basically, you use a heating blanket (two required for backs) and lay it on a flat surface and heat it and put some weights on it. It's analogous to bending a side, but the "bend" is flat.
Author:  Colin North [ Mon Jun 13, 2016 3:13 am ]
Post subject:  Re: What do you do to flatten warped backs
I successfully flattened a warped zircote back using SSII, little spritz H2O, wrapped it in alufoil and ironed it flat.
Stickered and weighted it flat immediately, no problem.
As others said, no wax please.
Author:  Michael Keller [ Tue Jun 14, 2016 6:26 am ]
Post subject:  Re: What do you do to flatten warped backs
Image

A very warped set of brazilian rosewood that I flattened out using my kitchen oven, two sheets of aluminum and a few clamps.Put the aluminum in the oven at 280 for 20 minutes to get hot. take out and place both back pieces between the aluminum and gently press down slowly. I had no problem getting them to go down together completely flat. a few clamps around the edges and back in the oven for 15 more minutes. Let cool for several hours and they came out perfectly flat and have stayed that way in the finished guitar.Be sure there is NO WAX on the ends of the back sheets. On this set I used a razor blade to scrape ALL the wax residue off before heating the wood.
Author:  Michael Keller [ Tue Jun 14, 2016 6:27 am ]
Post subject:  Re: What do you do to flatten warped backs
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Author:  DennisK [ Tue Jun 14, 2016 7:02 am ]
Post subject:  Re: What do you do to flatten warped backs
Michael Keller wrote:
A very warped set of brazilian rosewood that I flattened out using my kitchen oven, two sheets of aluminum and a few clamps.Put the aluminum in the oven at 280 for 20 minutes to get hot. take out and place both back pieces between the aluminum and gently press down slowly. I had no problem getting them to go down together completely flat. a few clamps around the edges and back in the oven for 15 more minutes. Let cool for several hours and they came out perfectly flat and have stayed that way in the finished guitar.Be sure there is NO WAX on the ends of the back sheets. On this set I used a razor blade to scrape ALL the wax residue off before heating the wood.

Where do you get aluminum plates like that, and how much do they cost?

Water can sometimes be used to flatten things, but it usually doesn't last. I have an oak back that wants to cup despite being almost perfectly quartersawn. I tried wetting the concave side and stickering it with weights overnight, but it just went right back to its old shape. So today I wetted it again, joined it while it was flat, so now after drying again it's S shaped. Next operation will be to wet it flat yet again, plane it to thickness, and then it will be flexible enough to brace which will hold it to the proper shape for the rest of its days.
Author:  truckjohn [ Tue Jun 14, 2016 8:30 am ]
Post subject:  Re: What do you do to flatten warped backs
Wetting for a short period of time doesn't seem to work. The time that "wetting" did work for me... I had a badly warped board. Threw it out on the deck in about October and when I found it again in April - it was straight and stayed that way... But it sat out in the snow and rain the whole winter... Went through a bunch of freeze/thaw and wet/dry cycles.

I tried wetting and ironing last night. No love so far.... It flattened out fine but then bowed back when it dried out. May not be hot enough. I will try again tonight with less water.

Thanks
Author:  Barry Daniels [ Tue Jun 14, 2016 10:44 am ]
Post subject:  Re: What do you do to flatten warped backs
It needs to be clamped flat after applying the heat. Otherwise it wants to return to its natural shape.
Author:  Michael Keller [ Wed Jun 15, 2016 7:27 am ]
Post subject:  Re: What do you do to flatten warped backs
Dennis,

I went to a small machine shop near where I live. Payed $40 dollars. Considering the cost of the rosewood, it was a very small charge to get it into useable shape.They came out perfectly flat, but I was a little concerned about the warp coming back. I glued the two halves together and cut out the guitar shape, thicknessed the back to .095 and let it sit for about two months. Still perfectly flat.


michael keller
www.kellerguitars.com
Author:  truckjohn [ Wed Jun 15, 2016 7:38 pm ]
Post subject:  Re: What do you do to flatten warped backs
Ok... The clothes iron trick needs to go into an FAQ somewhere.

Wood more or less dry
Turn clothes iron up to "nuclear".
Iron wood flat - it gets hot and pliable like bending sides.
Stack and sticker with weights

Ta-Da!

It's not machinist straight edge straight... But it's straight enough to joint, glue braces and not cause issues.
Author:  Bryan Bear [ Wed Jun 15, 2016 11:22 pm ]
Post subject:  Re: What do you do to flatten warped backs
Great news!
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