Official Luthiers Forum!

ok so first off hi everyone! I have been lurking around this site for a while learning about guitar making and plan to start one this coming mid summer or fall. but in the meantime I want to get quite a few jigs and odds and ends made. ok so anyways for making a radius dish does anyone know of a good free design program I can use to get a segment of an arc for a 25 foot radius? I am not currently familiar with any autoCAD or whatever design programs but could certainly learn if that would be the only option. I tried downloading a few free basic programs but none seem to offer what i am looking for. I want to use the arc to make rails for my router and prefer if the arc is exact.

I am fairly comfortable with math and could just work out a bunch of points and connect the dots or just use some kind of 25 foot long string but hey what are computers for ( besides learning about guitar making obviously ).

Matt

Hi Matt and welcome to the OLF!

I set my radius with a screwdriver, a tape measure, and a pencil. Cut it out with a jigsaw. It wasn't quite smooth, so I slapped a piece of sand paper between the concave and convex pieces, wiggled them around a bit, then flipped the paper and repeated a couple of times. A smooth circular radius is sort of self correcting. Probably 15 minutes total, I had a template that matched perfectly.

Going from that to a functional dish was not as smooth. My jigs have had a little flex in them so I haven't ended up with a dish I like yet. I had a time squeeze and ended up buying a dish for my top. I haven't given up on making others yet, but it was way easier to give my credit card to one of the OLF suppliers. Not as fun or interesting, but it generated a lot less MDF sawdust on the back porch.

Miek

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Mike Lindstrom

here are some links that helped me out greatly. you said that you are comfortable with math, but if you have any questions feel free to ask. i tried the super long string and also the bend a wire between two points methods and was completely dissatisfied with the results, so this is what worked best for me.

http://gicl.cs.drexel.edu/people/sevy/l ... mpass.html

http://www.ukuleles.com/Technology/calcarc.html

even if you print out a perfect radius, you are still left to sand down perfectly to a line. some would argue that being perfect here is not essential, but hey, its in my personality so its what i aim for. so basically what i did (if you read the long compass link) is instead of using a pencil in the long compass to draw an arc, i made a sled to hold my router and routed out a perfect arc using the same method. its kinda annoying because you are basically making a jig to make a jig to make a jig, etc. it works great though. my radius dishes turned out wonderful and are really accurate. and on top of it, i felt good about the work i did, which is almost more important. i hope that all makes sense. if not, ask here or send me a private message.

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sweat the small stuff.

oh, at the bottom of the second link, there is a spread sheet (arc calc) to help you determine some of the distances you will need.

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sweat the small stuff.

When you are ready to rout out your first MDF radius dish do it outside with the wind at your back. It makes an enormous mess!
Terry

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It's not what you don't know that hurts you, it's what you do know that's wrong.

Call Tracy at Luthier suppliers and save yourself the dust and trouble.

Try this link.
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=17072

Check out this thread.
http://www.luthiersforum.com/forum/viewtopic.php?f=10102&t=7750&hilit=radius

viewtopic.php?f=10102&t=7750&hilit=radius

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"An adventure is only an inconvenience rightly considered. An inconvenience is an adventure wrongly considered." G. K. Chesterton.

thanks for all the replies! who knew you guys would be good at building guitars and so helpful

I think in the end I will go and order the radius gauges from luthier supplies. I like the idea of being able to use them for so many different things and having a relatively permanent template to make several dishes from.

Matt

I plugged in these numbers today and got these other numbers I used the excel program above and the one in my original post that was pointed out, and here is what I got for a 16" chord and a 24" chord. I tried them in both programs and they came out to be the same. Well, apparently I can't post a Word document, but the formula is a handy thing to have.

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Brad Tucker

By the way, Matt, welcome to the OLF. Lots of really great information here, and lots more in the archives!

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Brad Tucker