RobF -> RE: Specs in a guitar plan (Feb. 14 2018 14:43:14)
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Hi Jason, here is a quick take on a straightforward way to do the assembly, I don’t actually do it this way but I’m confident it’s going to work. First, in this method, the edge of the sides meeting the top are kept flat and the taper will be defined on the edge of the side that meets the back. For the workboard, take a piece of stable plywood about 3/4” thick and cut it out with the body area wide enough to accommodate whatever back joining method you choose and with a 3” wide neck extension protruding 320mm out from the 12th fret portion of the plantilla. Then cut a piece of high ply 1/4” plywood in the shape of your plantilla, giving it a few mm extra width but keeping the 12th fret line accurate, and laminate it to the body portion of the workboard. Draw the the shape of the plantilla on this. The result of this will give you a workboard which has the body portion sitting 1/4” proud of the neck extension. Now, to obtain a neck rise of 1.5mm, for example (but a reasonable rise to choose), make a shim out of MDF about 1.5mm less thick than the thickness of the body lamination and tape it to the nut end of the neck extension. If you use 1/4” ply for the body lamination the shim should be a little less than 5mm thick. The beauty of using a shim is you can easily adjust the neck rise in subsequent builds by changing the shim. Even if you want to build flat, I would recommend doming the lower bout portion of the body to about 1.5mm under the bridge. That’s still pretty flat looking. The laminations of the high-ply lamination can be used as witness lines to show the symmetry of the dishing. Only dish the lower bout area to about 2 to 3mm inside the outline of the body. This will allow you to keep the sides flat but will bring the dome to inside the width of the liners. For your body taper, dimension the sides to be about 2mm less than the body depth at the end block. Joint the top edges but the back edges are ok as they are off the saw. When the sides are bent and dimensioned to fit the body join them to the top - flat - and attach the end block. Now for the taper. At this phase in your career I think you won’t regret ordering or making a 15’ radius sanding dish. You can always sell it later. I know a lot of builders scoff at using dishes, but this will get you to your goal with the least headache, IMO, and more importantly will enable a good, solid attachment of the back to the sides. Mark the sides at the heel to be about 1 to 2mm shallower than the desired overall depth at the heel. If measuring from the inside make that 3 to 4mm. The reason it’s less than the overall depth is because the top and back will each be adding about 2mm to the depth. Don’t stress if the body depths are a little off from the plan’s. Now, if you’re going to use a dish to obtain the final shaping, take a block plane and taper from the upper bout side of the waist to the marking at the heel. Be mindful to plane with the grain when doing this. Then take the sanding dish and rest it on the sides. You’ll see the taper you planed into them has already done a lot of the work for you. It’s helpful to mark the edge of the sides with chalk to show when all of the edges have been hit by the sanding board. Also periodically measure around the sides while sanding to ensure you are keeping consistent dimensions on the treble and bass bouts. Once the taper/dome has been established, attach your liners to be about 1mm proud of the side edge and once dry, resand. You now have tapered sides ready to accept the back. Also, using the dish presumes the back braces will be radiused to 15’. That’s a new discussion, but it’s dead simple and fast to do that with a block plane. Hope this helps. It’s just one way to go about this, but it should get you your guitar without too much fanfare. I have to get back to the shop so I’ll proof-read this later to make sure I haven’t messed up any of the measurements. But the method is sound.
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