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| Need help with potato chip BRW back http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10101&t=52988 |
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| Author: | DanKirkland [ Mon Mar 02, 2020 6:30 pm ] |
| Post subject: | Need help with potato chip BRW back |
I have this BRW back and side set that I'd like to use for a guitar in the near future. The sides are fine but the back pieces were warped like this when I acquired them. Any methods/thoughts to make them behave enough to build with? Or should I just use them for something other than a back?   
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| Author: | Clay S. [ Mon Mar 02, 2020 7:08 pm ] |
| Post subject: | Re: Need help with potato chip BRW back |
If you have a heat blanket and a couple pieces of MDF or MCP (or other flat material) you could heat them up and press them flat similar to what you do for bending sides. You may have to lay the blanket on the diagonal on the one with the "propellor" warping. You might also want to add an extra back brace (or maybe not)to the finished guitar. The original Martin size 1 I have has 5 back braces in what we call a "parlor" guitar today. P. S. Put the blanket on the side you think will be the "inside" of the back and don't roast it too long or too hot. |
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| Author: | Joe Beaver [ Tue Mar 03, 2020 12:18 am ] |
| Post subject: | Re: Need help with potato chip BRW back |
I would do as Clay says. Also, I have had luck by doing the following after what Clay says: Heat and cool the backs a second time just as you would with sides to set them, again as Clay says, not so hot you scorch them. Then spray them lightly on both sides with water and place them between two flat boards and weight. Don't use boards with a melamine coating on them. You want the sides to reach the shop RH while still being pressed under weight for 4-7 days. (The heating will dry the wood out, hence the light spray. If you don't spray them they may stay drier than your shop and will curl on you when the weight is removed. Before you remove them from the weighted sandwich, have the back braces ready to go. Remove the weight, join the backs and install the braces and hope for the best. Good Luck. |
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| Author: | rbuddy [ Tue Mar 03, 2020 12:30 am ] |
| Post subject: | Re: Need help with potato chip BRW back |
I'm working on a macassar guitar right now and the back was at least that bad. Being very stiff also, I shared similar concerns. Joining the back seam was made to work with some weight to hold it flat. Roughing in the outline relieved a lot of the tater chip just by knocking off the corners. As it was sanded to final thickness it was a whole lot tamer. It went into the radius dish easily and made a perfect dome. It's sure worth a try. I was pleasantly surprised with mine. Especially since I have a couple more sets from the same billet doing the same thing. |
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| Author: | Herr Dalbergia [ Tue Mar 03, 2020 2:24 am ] |
| Post subject: | Re: Need help with potato chip BRW back |
Cut out the rough permiter of your guitar body shape get two sheets of metal iron about at least 5mm thick clamp the back between the metal sheets put two or 3 flattening irons like your wife uses for the clothes on the metal flip the package and heat from both sides for about an hour or so... let it cool down while being still clamped foir a day or two if necessary, repeat |
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| Author: | Colin North [ Tue Mar 03, 2020 2:31 am ] |
| Post subject: | Re: Need help with potato chip BRW back |
I've flattened badly warped Zircote back pieces using SSII, then wrapped in alu foil, and used a domestic iron to flatten. Then sticker under weights. |
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| Author: | wbergman [ Tue Mar 03, 2020 9:49 am ] |
| Post subject: | Re: Need help with potato chip BRW back |
Do not heat wood with wax on it. The wax will run like water into the wood and not come out. It will compromise future joints, even if you do not see the wax. The method mentioned above where you first trim off the wax areas avoids this. I have posted about this before and mentioned that I soaked a worse brw set under water for 10 days and it relaxed flat,whereupon I stickered and weighted it and let it dry. It was absolutely flat, but of course I keep it weighted. By coincidence, I bought another bad set of brw just to demonstrate and confirm this. Just a day ago I put it in water. If it again works, I will post pictures of the set before and after. |
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| Author: | Clay S. [ Tue Mar 03, 2020 11:29 am ] |
| Post subject: | Re: Need help with potato chip BRW back |
Good thinking on trimming the wax - usually it is just the ends that are waxed, if anything. I am always reluctant to trim to an outline before I have the plates joined, but as others have said, depending on the model, that could eliminate much of the warping. Because of my less than sanguine nature I would try to flatten the panels first, but cutting to a rough outline (making allowances for jointing the plates) might make things go easier. |
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| Author: | Pegasusguitars [ Tue Mar 03, 2020 6:32 pm ] |
| Post subject: | Re: Need help with potato chip BRW back |
I sell lots of sets on the web. To do so requires photos that show the color, and to accomplish that I spritz the wood with water. By the time I've photoed a few sets, they have all begun to warp. When I'm done I get both sides of every piece wet and then dead stack the pile on cement with weight on top. By the next day they are always flat, and then I sticker them to dry further. I'm mostly doing koa and mango and this might not work with an oily exotic, but no harm in trying. Good luck!-Bob |
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| Author: | bluescreek [ Wed Mar 04, 2020 9:01 am ] |
| Post subject: | Re: Need help with potato chip BRW back |
I have BRW that have propellered like that. I have tried many techniques all mentioned here. The only thing that worked was thin it. glue up and brace. there is a lot of run out in the set and may never go flat till braced. |
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| Author: | wbergman [ Wed Mar 04, 2020 2:50 pm ] |
| Post subject: | Re: Need help with potato chip BRW back |
Update on my "experiment". After three days under water, no change--which is exactly the progress that I had on the previous set, which then after 10 days under water relaxed to dead flat. |
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| Author: | ThomLuth [ Thu Mar 05, 2020 9:40 pm ] |
| Post subject: | Re: Need help with potato chip BRW back |
I've been trying to think of Ervin Somogyi's, article on this subject. Finally, it dawned on me that he referred to them as potato chips, and I found it: Flattening Rosewood Potato Chips, American Lutherie, 1988. Issue 14. As I recall, he had some very warped BRW backs, which he wetted, and then drilled holes in two aluminum plates, clamped them on both sides of the back and heated them. If you cannot get the issue, I have it "somewhere" around here. |
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| Author: | bluescreek [ Sun Mar 08, 2020 6:55 pm ] |
| Post subject: | Re: Need help with potato chip BRW back |
10 day underwater? that I will try thanks |
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| Author: | wbergman [ Mon Mar 09, 2020 5:07 am ] |
| Post subject: | Re: Need help with potato chip BRW back |
Some thoughts on practical approach. I made a frame of cheap boards on the basement floor and lined with plastic. The first time I did this I put weights in plastic bags to hold the BRW down. The plastic bags so that the weights would not stain the BRW. This time, I put the warped BRW in a big bag. The first bag, though 3 mils, was plastic that tore easily. The second bag was a different kind and better, so I just put some scraps of MDF on top for weight. But I am thinking that a plastic liner is enough and for weights you could just put water in some plastic buckets on top of the BRW. Water only needs to be as deep as the water that the BRW is in--no need to fill the buckets to the top. I guess if the BRW does not flatten after 10 days or so, then follow the other post to lay it out on the floor and put weight on top and leave it to gradually settle and dry. |
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| Author: | bluescreek [ Mon Mar 09, 2020 5:43 am ] |
| Post subject: | Re: Need help with potato chip BRW back |
will see how this works thanks |
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| Author: | wbergman [ Sat Mar 14, 2020 9:17 am ] |
| Post subject: | Re: Need help with potato chip BRW back |
Update on soaking. Not so good this time. After 10 days, not completely flat and after another couple of days no change. HOWEVER, the wood became very pliable, so it is now stickered and weighted. It will sit for a couple of months before I examine it again. |
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| Author: | Clay S. [ Sat Mar 14, 2020 9:57 am ] |
| Post subject: | Re: Need help with potato chip BRW back |
Be careful stickering wet wood. Some woods "sticker stain" easily, other woods not so much. I don't know where rosewood falls in this regard. |
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| Author: | wbergman [ Wed Mar 18, 2020 2:14 pm ] |
| Post subject: | Re: Need help with potato chip BRW back |
Bad news update. I need to withdraw my endorsement of the long soak. Although not yet totally dry, the sides split the long way. So they will become bindings or some other parts. The backs seem OK so far, and I do have extra side sets. Alas, they were beautiful sides with lots of landscaping. |
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| Author: | Clay S. [ Wed Mar 18, 2020 2:26 pm ] |
| Post subject: | Re: Need help with potato chip BRW back |
If you can get the splits to come together well, you could try gluing them with Titebond three. Some people have reported that it holds up to the heat required for bending. Possibly you could use them for laminated sides ? |
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| Author: | Herr Dalbergia [ Sat Mar 21, 2020 2:04 am ] |
| Post subject: | Re: Need help with potato chip BRW back |
Not a surprise that the sides cracked. Flooding with water was a bad idea itself. For moving to woodfibers against each other, so, for bending wood you need heat, not water. See my above post how to do it, Ervin Somogyi showed this method to me, I tried it several times, and it works.... Soaking dry wood with water and drying it again fast will lead only to one thing.....cracks..... |
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