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| Drawing a 15 ft and 25 ft arc http://luthiersforum.com/forum/viewtopic.php?f=10101&t=37484 |
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| Author: | ernie [ Sun Aug 19, 2012 8:46 pm ] |
| Post subject: | Drawing a 15 ft and 25 ft arc |
I just looked at my 1 st unfinished steel string that has the sides glued to the blocks. My original intention was to just do a flat top and flat back as this was my first steel string .I radiused the top braces to a 25 ft top and 15 ft for the back.In retrospect I should have marked out the radii for the sides before glueing it to the blocks. How should I trace the outline to the sides? Lay up a piece of 1/8in masonite on radius sanding dish using a compass draw the radius along its length sand to the lines and then transfer this radius to a piece of brown paper 25 ft on one edge and 15 ft on the other, lay the paper on the glued up sides draw out the radii for top and back and plane down to the pencil lines .Or do you have a better suggestion for laying out the top and back radius for the sides prior to gluing it to the blocks?. Your input would be very helpful as this is my first steel string and frankly I/m confused . |
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| Author: | DennisK [ Sun Aug 19, 2012 9:45 pm ] |
| Post subject: | Re: Drawing a 15 ft and 25 ft arc |
So you have the plates braced with a radius, but rims flat, and you're trying to figure out how to get a matching radius into the rims? You can't really radius before gluing the sides to the blocks and gluing in the linings, since those need to be radiused as well, so you're still in good shape. John Hall has a good video of what to do: http://www.youtube.com/watch?v=pz6xzVRA51E Skip to about 5:30 for the actual sanding. I do a more time consuming and approximate method using a finger plane and flat sanding block, but no need to bother with that if you're building with an outside mould and radius dish. |
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| Author: | Shaw [ Mon Aug 20, 2012 1:00 am ] |
| Post subject: | Re: Drawing a 15 ft and 25 ft arc |
Ernie most people use radius dishes like john does in the video but many lay the dish down and hold the guitar mold and all and work that in a circular motion. Some actually use a motorized radius dish. I use a radiusing bar which mounts on a pipe similar to Johns method to sand the radius in the sides and block....Mike |
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| Author: | Trevor Gore [ Mon Aug 20, 2012 6:01 am ] |
| Post subject: | Re: Drawing a 15 ft and 25 ft arc |
I've not checked John Hall's video, but what I do is grab a small piece of wood ~20mm square and about 2mm thick. Drill a hole in it the same size as the "tube" on the business end of a mechanical pencil. Stick the pencil through the hole. Put the rims on a radius dish (say, back down on the 15' dish) then with the pencil and bit of wood, rest the wood on the dish and scribe round the rims with the pencil. The wood will ride the radius dish and the pencil will scribe the correct profile on the guitar. Some people use a standard pencil and a washer to achieve the same end. Pics on p 10-12 (Build). |
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| Author: | ernie [ Mon Aug 20, 2012 8:51 am ] |
| Post subject: | Re: Drawing a 15 ft and 25 ft arc |
Typically making a lot of mistakes on my first SS build, will check john /s video to see what I can learn. I have the radius dishes. I have a good compass from woodcraft that has a flat face and can trace the arching from the radius sanding dish to the sides. I think the reason the sides look wonky was that I should have layed out the radius on the sides first, then planed , install linings , radius sanding. Will go back now and fix my errors  .thanks to all those with suggestions.
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| Author: | Freeman [ Mon Aug 20, 2012 2:33 pm ] |
| Post subject: | Re: Drawing a 15 ft and 25 ft arc |
I simply drew the arcs full sized with Autocad (but you should be able to use any drawing program that can make a circle). I have an engineering sized plotter, but Kinkos can plot it for you. The cool trick is that I also have acess to a cnc laser cutter (I work in a machine shop) - I have cut 16 ga steel in both the arcs that I use. Clamp those on some hunks of wood and route out perfect sanding blocks, radius cauls. It is very likely that a metal fab shop could do the same for you - laser, water jet, several ways to cut it. |
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