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Hello everyone,

I have a question about radiused workdishes. I made a couple of dishes a while back, one 15' and the other 25'. Today, I was making one of the brace shaping jigs that Bruce so kindly shared with me and when I compared the curvature to the curvature of my dish, they didn't match. I measured my work dishes and the 15' is actually 13' and the 25' is 22'. Would it be possible to brace the top and back at these dimensions or would this be too much curvature? Should I reroute the dishes to 15' and 25' or maybe even 20' and 28'?

Jeremiah, how did you determine your arc? I used my deck and two 1/8th inch by two inch by two feet maple blanks. Tapped a small nail in the deck, let out fifteen feet of tape, made an arc with a pencil held against the fifteen foot mark and swiped across. Then I bandsawed that mark out and sanded to a nice edge. Did the same with a 25 foot measurement with the blank tacked to the deck perpendicular to the tape.

I don't know what to tell you to be honest, what you have might just work if you redid your braces. I know some folk back up their first dish by gluing it to a second blank, I use mine single.

Mario might remember the link to the long-compass on the internet, a cool way to make an arc using a couple of sticks.Dickey38362.8871064815

Webpage for the Long Compass

So this is another way to do it.

Bruce,

Which brace shaping jig is Jeremiah talking about? I can't seem to find it. Is it in the resources?

Jeff

Bruce,

In response to your question, I determined that the dishes were off by laying a straight edge across the top and measuring the amount of deflection in the middle. I've done it about three times and I always get the same measurement. I've measured the rails that I used and the measurements were correct to achieve the radii I was wanting, but I think that the weight of the router may have made them give some in the middle increasing the amount of deflection.

May I stop here and say that I was rather proud of myself at the time in the method that I devised to get the radius. I had read of many of ways to achieve the desired radii and I came up with this idea. If anyone else is doing it this way, I swear I've not read of it and we must have just come up with the same idea. It wouldn't be hard to fathom since we're not talking about designing a suspension bridge or something of the sort but this is what I did. I took a piece of poplar about 3/4" x 3" x 30" (w x h x l) and drew a centerline down the middle. I then measured the correct amount of deflection for the desired radius and made a mark on the centerline at that point. Then I took a 1/2" square poplar dowel 30" long and drilled small holes every 2" along its length. Then I aligned the ends of the dowel with the piece of poplar and nailed brads into both ends of the dowel. Then I pulled down the center of the dowel to meet the deflection mark on the centerline of the board and nailed a brad in. Then I nailed in brads along the flexed dowel along its length. Once that's done, I took a pattern trimming bit and routed the board flush with the flexed dowel and voila! a completed rail with the correct radius. I then screwed this rail to another board the same size and once again flush cut to give me a set of rails. I know it's not Einstein, but it seemed to work for me or so I thought.

Probably some I posted on my website: www.dickeyguitars.com go to MISC and PICS, then to PhotoPhinish page

or just look here:

Jeremiah,
What you are describing is called a fair curve. Draftsmen have used the approach to draw curved lines for hundreds of years. The part of your approach that I've never seen before is to use the stressed dowel as a guide for a router bit. Most people just draw the line on the wood, cut it out on the band saw and then sand smooth.

If it were me, I'd just make the braces have a 22' and 13' arch in them. The difference in the final guitar would be so small that almost no one would ever tell.

That being said, there is a value in doing what is necessary to make the guitar be as close to exactly what your original intentions were. Lutherie can be thought of in terms of process control. If you make what you build repeatable, then you can alter a small number of design features and know that those are the only differences and therefore likely to be the reason for the differences in the sound/performance of the intsrument.

Yes, I know I could have drawn out the curve and used a bandsaw, but I just didn't trust my eye. I wanted a close to perfect curve which is why I used the dowel and flush trim router bit. I think I may just try to redo the dishes and shoot for 20' radius for the back and 28' radius for the top. Therefore, if I'm off by a little bit, the curve will still be within what seems to be standard. Since this is my first guitar, I want to stick with what has been tried and trued.