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Radius Dish Help

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Radius Dish Help

Postby Christopher Perkins » Thu Feb 28, 2013 8:24 pm

Hello all

I've completed my first build and am finally in the process of gathering all the standard tools i need to begin to build guitars. After seeing my first build, my wife has been amazingly supportive of my move to gather everything I need. However, (unfortunately), I have been put on a budget to accomplish this, and the 2 radius dishes I need (15' and 25')... (and the rosette cutter lol), put me over budget. Is there any "tricks" of the trade I could use to maintain the necessary 15' and 25' radius size while clamping up the braces? That is to say....is there any way I can continue to build guitars...bypassing the radius dishes....? Any help or suggestions would be greatly appreciated.
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Re: Radius Dish Help

Postby Bob Gramann » Thu Feb 28, 2013 10:49 pm

You can make your own radius dishes very cheaply. I pulled a 1/4" piece of masonite into a near sphere by calculating the deflection at a foot from the center, making a rim of that height, and pulling down the center with a flat head bolt. The same dish is very useful for sanding the rims. You know you're obsessed with building. You might as well surrender now and forget about the budget. You're going to spend everything you have anyway.
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Re: Radius Dish Help

Postby Bryan Bear » Fri Mar 01, 2013 1:55 pm

Looks like I am again piggy backing on Bob's coattails. I use a radius dish of similar design. Mine is a frame made of 2x4s so 3 1/2ish inches tall with a 1/2 inch plywood top. That plywood has a circle cut out of the center with a 20 inch (I think, could be larger) diameter. The dish itself is two layers of 1/8 inch masonite laminated together with a bolt buried between them (in the center). The bolt fits into the frame and allows me to tighten it down giving an ever increasing "radius". Technically it is not a true radius but close enough for the amount of dome you put in a top or back. I put blocks of differing thickness between the masonite and center of the frame to give a positive stop which allows me to tighten the dish down to various "radii."

The whole arrangement was hastily made with scrap materials to get me started. I have never found the need to replace it with "proper" dishes.
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Re: Radius Dish Help

Postby Christopher Perkins » Fri Mar 01, 2013 2:04 pm

Would u mind posting some pics? This sound like exactly the sort of thing I was looking for! ! I would love to see if its something I could build relatively easy...
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Re: Radius Dish Help

Postby Bryan Bear » Fri Mar 01, 2013 2:37 pm

I'll try to remember to take some pictures this weekend. It is much harder to describe than to make, so let me know if you need a better description or more clarification. Originally the dish was built into a large plywood bench top in the corner of my workspace. When I was making a new shop on the other end of the basement I was anxious to brace a top before I had gotten around to making a more permanent version of the old one. I ended up putting the frame together in about 15 min. to get me running and never changed it, So yes, you can make it easily. One thing to consider is how high your go bar set up will be and how long your bars will be because the thickness of your frame will factor in. My old one had all the adjustment under the table top so it only sat about 3/4 of an inch above the bench top. The new one is more than 4 inches tall. Fortunately for me my go-bar deck is just the bench top and a reinforced ceiling. . .
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Re: Radius Dish Help

Postby Barry Daniels » Fri Mar 01, 2013 2:50 pm

Have you looked in the library?
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Re: Radius Dish Help

Postby Bob Gramann » Sun Mar 03, 2013 3:16 pm

And, my 25' dish.
Attachments
25foot dish.jpg
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Re: Radius Dish Help

Postby Alan Carruth » Sun Mar 03, 2013 4:01 pm

I've got the jig for making radius dishes, if you need it.

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Re: Radius Dish Help

Postby Bryan Bear » Sun Mar 03, 2013 4:24 pm

Here is my adjustable radius dish. The pics are not great; I can't get to my computer to resize images right now so I had to do cell phone pics and crop them down.

Despite being haistily made, it is quite functional. The circle cut out is 20". Not shown in the picture is the stop block that gets sandwiched between the bottom of the Masonite and the cross peice. As mentioned I can use different thicknesses to provide a positive stop for the various radii. It is worth mentioning that the laminated Masonite will eventually take a set to whatever dome it is left at. I laminated the two peices with contact cement and ther is some degree of cold creap. Occasionally, I turn the dish upside down and weight it down for a day or two to flatten it enough that I can pull it back to whatever radius I need.

image.jpg


On top you can see one of the radius templates (the one I use for tops). I check that I t matches the dome I have dialed in and then use that to mark my braces. Then I plane them to match and do final sanding/fitting in the dish.

image.jpg
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Re: Radius Dish Help

Postby Louie Atienza » Sun Mar 03, 2013 4:42 pm

I made a dish radiusing jig a while back that was adjustable, and it works great for me. I did so because everyone seems to gravitate toward 15' and 25' and I wanted to be different
Attachments
01-The Jig.JPG
02-CloseUp Hinge.JPG
03-Bottom View.JPG
04-Bearing Points.JPG
05-Carved Dish.JPG
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Re: Radius Dish Help

Postby Louie Atienza » Sun Mar 03, 2013 4:44 pm

Additional views... NOT for indoor use!!! Bryan's and Bob's technique is a lot less messy!
Attachments
06-Base With Pin.JPG
07-Dish View.JPG
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Re: Radius Dish Help

Postby Bob Gramann » Sun Mar 03, 2013 6:33 pm

Louie's comment about indoor use is an understatement. The first MDF radius dishes that I made with a router I made outdoors. There was still way too much dust. I don't do any major routing of MDF anymore. It just seems unhealthy.
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Re: Radius Dish Help

Postby Bob Howell » Wed Aug 30, 2017 3:27 pm

Bryan Bear wrote:Here is my adjustable radius dish. The pics are not great; I can't get to my computer to resize images right now so I had to do cell phone pics and crop them down.

Despite being haistily made, it is quite functional. The circle cut out is 20". Not shown in the picture is the stop block that gets sandwiched between the bottom of the Masonite and the cross peice. As mentioned I can use different thicknesses to provide a positive stop for the various radii. It is worth mentioning that the laminated Masonite will eventually take a set to whatever dome it is left at. I laminated the two peices with contact cement and ther is some degree of cold creap. Occasionally, I turn the dish upside down and weight it down for a day or two to flatten it enough that I can pull it back to whatever radius I need.

image.jpg


On top you can see one of the radius templates (the one I use for tops). I check that I t matches the dome I have dialed in and then use that to mark my braces. Then I plane them to match and do final sanding/fitting in the dish.

image.jpg

I'VE GOT THE 1/8"MASONITE and am going to make this radius dish. Two sheets, bolt pulling the bottom one down. 24" frame. Any hints for success? Looks simple.
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Re: Radius Dish Help

Postby Bob Gramann » Wed Aug 30, 2017 3:48 pm

Bob, since the original discussion 4 years ago, I have replaced my 25' radius dish. It seemed to get more flexible over time to the point where it was unreliable for gluing in the gobar deck. I had used .25" masonite for the curved surface. I replaced it with a CNC carved 25' dish for about $70. When I thought about the dust I'd make if I carved it myself, the premade one looked cheap. And, I don't have anymore gaps when I glue.
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Re: Radius Dish Help

Postby Barry Daniels » Wed Aug 30, 2017 4:12 pm

I bought a commercial CNC dish that was made out of 3/4" MDF. It was not stable and ended up warping even though I have a humidity controlled shop. However, the dishes I made by laminating two layers of MDF together have not moved a bit. I did the routing outside to prevent dust problems.
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Re: Radius Dish Help

Postby Bob Gramann » Wed Aug 30, 2017 4:36 pm

I didn't add Barry's part. I have two commercial dishes, now. I glued each to a 3/4" piece of MDF as soon as I got it. I had no expectations of stability for them left at one layer.
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Re: Radius Dish Help

Postby Bill Raymond » Wed Aug 30, 2017 6:17 pm

Nothing wrong with building with a radius dish, but one is not absolutely necessary. One can trim braces to the correct radius of dome, and simply glue the top to uncontoured sides. Many guitars have been successfully made that way. The sides where the back is glued can be either contoured by trimming them carefully to fit or left uncontoured, but still narrower at the headblock than at the tail.
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Re: Radius Dish Help

Postby Barry Daniels » Wed Aug 30, 2017 6:46 pm

If you are going to build more than one guitar, I would definitely make or buy dishes. It makes your joinery so much better and it is easier too.
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Re: Radius Dish Help

Postby Bob Howell » Wed Aug 30, 2017 7:02 pm

I have made two om guitars with the method in Cumpaino's book and looking to improve. Making a L-00 from Grellier's plans now. Think I can get decent results without dish on top but it would improve the bottom. So much to learn and tools,and jigs to make.
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Re: Radius Dish Help

Postby Barry Daniels » Wed Aug 30, 2017 7:37 pm

Radius dishes and go bars make the work so much easier. They pay for themselves pretty quickly.
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