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>> Ukulele Hints >> Radius Dish for Radius tops and back?

Message started by msrvfx on May 6th, 2005 at 12:53pm

Title: Radius Dish for Radius tops and back?
Post by msrvfx on May 6th, 2005 at 12:53pm
Hi everyone,

Looking to make, or buy if I have too, radius disk for doming my tops and backs. I have seen where they can be bout, but $75 seems pretty pricy. The radiusing is suppose to help pump more sound volume as well as strengthen the tops and backs.

Anyone have some instructions for making accurate radius dishes?

Mark in Portland

Title: Re: Radius Dish for Radius tops and back?
Post by Wood_Butcher on May 9th, 2005 at 5:57pm
Hey Mark,

Try googling "radius dish sanding board.  This shouild get you to a site named larenzo.home. mindspring/etc.  Some intersting pictures that might help.

Mark in Lake Stevens

Title: Re: Radius Dish for Radius tops and back?
Post by msrvfx on May 9th, 2005 at 8:59pm
Hey Mark, thanks.  It is a good site.
Appreciate it.

Mark in Portland

Title: Re: Radius Dish for Radius tops and back?
Post by hapakid on May 11th, 2005 at 12:06pm
A friend of mine who makes mandolins created a dome board by making a luthier's work board out of 3/4" plywood. A work board is created by running a keyhole router bit in a checkboard pattern across the work surface so that you can slip carriage bolts into the slots and bolt down work pieces with odd shapes. Once the board is routed, it becomes very flimsy. My friend then put some supports under the edges of the board, then flexed it downward to make it concave. Then he mounted it on the bottom of a go deck and used the set up to create flexed tops for his mandos.
This might not make any sense, so I'll try to find pictures.
Jesse Tinsley

Title: Re: Radius Dish for Radius tops and back?
Post by Road_Toad on May 11th, 2005 at 5:55pm
Another way to do it would be use matboard or cardboard and cut out a few concentric shapes to create a layered dish by stacking the outside cutouts. While it's not as perfect as a machined disk, it's cheap ;D.


Title: Re: Radius Dish for Radius tops and back?
Post by ukeman on Jun 5th, 2005 at 3:39pm
Aloha all!

Here's how I make my radius dishes:

you will need:
1. Router with a 1/2" diameter flush bit.
2. a drill and bit equal to the diameter of a shelf pin or a cut off bolt 3/4" in length.
3. scrap ply for a workbase and 1x materials for the jig.
4. a string or length of rod or wood equal to the radius of whatever size dish you like make. ie. for a 15' radius dish a 15' rod or string.

here goes:

start with the work base of the jig...30 x 30' 3/4' ply base is good!

ok now take your string or long rod...drill a tiny hole through the rod or stick on one end so you can anchor this point....15' away or whatever radius you decide...fix a pencil.....draw an arc on a piece of 1x 4 width wise, or a sheet of butcher paper. If using a sheet of paper, a good idea..transfer arc on paper to length of 30" x via scizzors and adhesive.
Now cut this arc out on the bandsaw and get it perfect via sanding to the curve that you drew. ..double stick this to another 1x4 and pattern route. Hint keep the arc so that is located high on your 1x4 or 1x6...you should now have 2 smilely faces out of 1x....cut to 30"

step 2.  nail each smiley faced 1x to the left and right edge of the 30x30 inch workbase...you now have a workboard with left and right arched smiley rails and open top and bottom.

step 3. find center of the workboard and drill in a hole 1/2" deep the same diameter as your 3/4" length of cutoff bolt and epoxy in to the hole this cutoff shaft...this is your index pin....ok workboard is complete!

now to make the trammel board or shooting board for your router.
step 1. Take a 1x6 about 36' long..find center and drill a 1' diameter hole..actually any size bigger than your 1/2" flush bit. Install bit into router and mount router and base onto the 1x 6 with the bit sticking out of the hole..
step 2. Place shooting board on your workboard ..on one end of the shooting board attach a scrap 1x2 on the underside of one end of the router shooting board..a cleat so to speak....now cozy up this cleat to one end of the workboard rail and the shooting board can only travel north and south along the arched smilely rails of the workboard.....on the opposite end add the second cleat and now the shooting board is really finished..it can travel only north and south along the arc of your workboard.

to use:   take a piece of 3/4 MDF or nice birch ply...for ukes 14" x 16" is cool...find center and drill a 3/8" deep hole same size as the diameter of your pin in your workboard.

insert mdf piece onto pin of workboard...should rotate like a square record! Think Flintstones!
Place Router shooting board on north end of workboard onto the rails...move shooting board south till the bit is flush with the top surface of your mdf below  maybe 1/2" from the top...simply adjust your router bit height on your router base to just touch the beginnning point of whereever you like the radius to begin...like I mentioned a 1/2" from the top is cool.

ok all nice then lets begin:
move shooting board a tad north...so now the bit is a a tad above the new dish surface and turn router on..nothing should happen cept the sound of the router spinning..now slowiy move shooting board southward and you are now creating 1 pass of dust and the dish will want to spin like a bat out of hell...Stop..yes its a weird process...check out the hints below before you go any further!

Hint: use your elbows to control the spin rate of the workpiece that is now being radiused...lower the shooting board no more than a 1/4" at a time...the router cannot eat so much mdf if you move it more than a 1/4' at a time....
last hint: you will find that you can lock the shooting board in place easier and control your southward movement by giving one side of the shooting board more pressure than the other..in other words you dont have to move the shooting board southward equally. If you pressure on side it will automatically lock a bit at a time...keep moving till you meet center...keep clearing dust out of your way...stop whenever you feel like it, just keep the shooting board always in contact with both rail surfaces and take mini passes....till you reach center....and you are now finished.
With a orbital sander you now can make a quick interior sanding of your radiused dish to smooth out the concentric circles...and it will now be an actual professional and accurately radiused dish....Yes much dust....first board is a tentative attempt, kinda weird making concentric router passes. But please make more than one...you are already set-up for at least one fixed radius so make at least 2 or 3.

oh  screw in the side arcs to the workboard so you can remove them easily and attach another pair of 30" rails that will you give you another radius...yeah may as well make a couple of different radii workboards while you are at it. Yes its messy but sure beats paying 75.00 for a premade one! If you like back the finished 3/4" radius board with anther 3/4' piece of mdf...you will reduce the warpage

ok hope this helps   laters ukeman

Title: Re: Radius Dish for Radius tops and back?
Post by Geoff on Jun 8th, 2005 at 2:33pm

I know that you told me this last summer...but..

What radii do you ue for front and back of concert ukes?


Title: Re: Radius Dish for Radius tops and back?
Post by ukeman on Jun 9th, 2005 at 9:56am
howzit Geoff.....miss ya...hope mayhaps to see ya in November at the Sheraton.  Anyhow heres the poop:

all my ukes any size I use a 25' radius dome for the tops..pretty miniscule on an uke.

for my backs I use a 15' radius..also pretty miniscule..ergo you can simply go with the 15 for both. If you use the 25" it will almost appear to be flat.

My thinking...get the dome in tension but not maxxed!

ok  laters   ukeman

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