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| How to straighten out plywood solera http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10101&t=55481 |
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| Author: | Ken Nagy [ Fri Jan 27, 2023 4:21 pm ] |
| Post subject: | How to straighten out plywood solera |
I bought a 2 X 4 sheet of 3/4 sheathing to cut 2 solera's from. Didn't realize it wasn't flat! I cut them out with my big, trusty ryoba, but now how do I get them flat? Nothing stock is going to be flat, is it? Screw 2 x 4's squared up on to the back? Get them wet, and weigh them down on the floor? Plane them down? Don't have the sander, so that won't work. I never worried about flat on any violin or cello form, they are just to bend ribs around. Maybe should have bought a better grade of plywood. Is there such a thing that is really flat? MDF seems pretty flat, as long as it doesn't get wet. Thanks for any help. Ken |
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| Author: | jfmckenna [ Fri Jan 27, 2023 4:23 pm ] |
| Post subject: | Re: How to straighten out plywood solera |
Is it a good quality plywood like a Birch ply? I've got a full sheet of Birch and it's pretty darn flat at 3/4 in ply. I would assume you are going to laminate the plywood? If so then perhaps gluing and screwing the opposing arched sides together might force it flat? |
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| Author: | doncaparker [ Fri Jan 27, 2023 4:31 pm ] |
| Post subject: | Re: How to straighten out plywood solera |
You can make a torsion box, but that means a pretty thick solera. If you were going to double the thickness, JF's idea is a good one: Glue the concave faces together. I think you are better off finding a better grade of plywood. A single layer of 24mm Baltic Birch is what I favor for this sort of need. But even with that, you need to pick out your pieces. I was at Woodcraft a few weeks ago to pick out some Baltic Birch, and I really needed to sort through what they had. Many pieces had a bow or twist in them. |
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| Author: | Clay S. [ Fri Jan 27, 2023 4:53 pm ] |
| Post subject: | Re: How to straighten out plywood solera |
Hi Ken, You could either buy a better piece of plywood (sande ply?) or build a simplified torsion box (use a center support and leave one side open so you can rest hand tools in it that you are using. Alternately you could just screw a couple of strong backs to the bottom that would allow you to clamp it in a vise. I just use a relatively flat piece of maple plywood that I screw things to. Rather than dish out the soundboard area I cut out some rubber impregnated cork material and lay that on top of the plywood. I can then vary the doming depending on the type of instrument I am building by changing the "rubber solera". |
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| Author: | Ken Nagy [ Fri Jan 27, 2023 6:51 pm ] |
| Post subject: | Re: How to straighten out plywood solera |
Well Clay, the one solera will do double duty as a baroque solera. I have a couple baroque guitar plans that are ALMOST the same size and shape, one is just about 5mm bigger all the way around. The other is a shorter, fatter Vihuela, that will have a shorter scale in G, with 7 courses! I cut out a shape the is big enough to make a plaster cast of a dished solera, so I end up with a domed solera. That way the body will have a dish in it! The fretboard is even with the belly, so a dish gives more clearance. A dome works against you; or so the guy with the plan said. I cut the hole out, and that one lays pretty flat now. The other I can double on the bottom. Maybe I'll put a picture in tomorrow morning when I'm on the computer. |
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| Author: | Jim Watts [ Fri Jan 27, 2023 6:59 pm ] |
| Post subject: | Re: How to straighten out plywood solera |
MDF is flat. I laminate a couple of pieces together and finish it off by letting it soak up some finish, it works pretty well. I prefer baltic birch however, but MDF works. |
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| Author: | Clay S. [ Fri Jan 27, 2023 9:09 pm ] |
| Post subject: | Re: How to straighten out plywood solera |
Hi Ken, Lutes are similarly constructed to the Vihuela - fingerboard flush with the top, and some dishing between the bridge and neck. Apparently the Vihuela stood in for the lute in Spain. The workboard is also handy for doing repair work |
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| Author: | Ken Nagy [ Sat Jan 28, 2023 9:48 am ] |
| Post subject: | Re: How to straighten out plywood solera |
I didn't think about making the solera extra big for clamps. The smaller one for the tiny Torres will work for that though. Screw and glue on smaller boards bent the opposite way on the bottom, and it should be good. Attachment: IMG_1222 2.jpg Here is the baroque solera. It is basically a holder for the plaster cast. Set it on the table, and make sure the neck support is flat with the cast. I will need around 3 times more plaster of Paris than I have; just a rough estimate. The bridge area is cut into the plaster. The bridge is glued on first. There is no way to clamp it after it is built. I will use the plywood dish to glue it with the proper curve. Attachment: IMG_1220.jpg Attachment: IMG_1221.jpg
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| Author: | Clay S. [ Sat Jan 28, 2023 2:45 pm ] |
| Post subject: | Re: How to straighten out plywood solera |
If you have some sawdust and wood shavings you could "bulk up" your plaster of Paris by mixing it all together before you add the water. Plaster of Paris sets up fast and hard. Plaster of Paris was a way to get an extra coat of spackle on drywall in a day when used as a first coat - it dries fast, but pull it tight because it doesn't sand easily. |
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| Author: | Ken Nagy [ Sat Feb 04, 2023 5:20 pm ] |
| Post subject: | Re: How to straighten out plywood solera |
I put the plaster of Paris in, and it came out! Cool. I put clay around the edge, and over the face of the form. I didn't get complete coverage on the face, but it seemed slippery. Attachment: IMG_1223.jpg I unscrewed the outside, and it came loose easily from the face. The pieces of clay that were on the plaster rolled right off. Attachment: IMG_1225.jpg The bottom wasn't flat, so I worked on that with a saw and a scraper first. It is strange stuff. I don't know if it is because it was only 50 degrees in the basement, but it is like spackling paste that isn't quite hard. It IS hard, but it scrapes easy making chips, not dust. The scrapings are cold. Attachment: IMG_1224.jpg The plaster mold fits tight in the solera base. The base stays flat because the mold is flat. The neck support bends up! The go bar will put it in its place. Attachment: IMG_1226.jpg
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