How to radius the top.

mikeyb2 · Sep 14, 2016

Hi everyone, i'm in the process of building ukes 2 and 3. Number 2 body is built ready for finishing. It has a flat top as on my first build. This time I want to introduce a radius to number 3's top. I built a radius dish for the backs but I'm thinking a radius stick would be easier to make for the top as only the lower bout edges need to be radiussed as I understand it. Also for a tenor, what radius?
Any ideas on building such a stick and using it so that the upper bout remains flat whilst introducing a radius to the lower bout, would be most welcome. Thanks Mike.

Wildestcat · Sep 15, 2016

Hi Mike. I don't think you need to worry about the complication of trying to match the gluing face of the sides to the curvature of the top. Just sand them flat all over. The top is flexible, and with the very slight curvature built into a uke top it will just sit down on the flat sides without undue clamping pressure. I use a flat transverse brace above the soundhole and only radius the lower transverse brace and the fan braces. The radius dish I made for my uke tops I think was was targeting 25 ft, but ended up with a calculated 21 ft radius.

mikeyb2 · Sep 15, 2016

Hi Paul and thanks, I was thinking of about 25' radius. And another thing that came to mind is the bridge. Will the bottom of the bridge need to be radiussed also? I'm guessing it will..Cheers.

Timbuck · Sep 15, 2016

All i did was get some 10mm MDF and cut it to the shape of the top and with some 60 grit abrasive I sanded a hollow by hand in the area around the centre of the LB it didnt take very long and I ended up with a depressed hollow area about 1.5mm deep..I now use this to clamp my tops too when I fit the braces when I clamp the bridge plate it causes a raised bump of about 1mm in the top in the bridge area..I made a sanding block with a slight convex curve just to put a bit of a radius on the bridge bottom..But thats on sopranos only...When I do an occasional Tenor I use my MDF 25' radius dish that I made on the pedestal drill with a simple Go-bar deck...(Go-bar deck is the space between a shelf and the bench and some sticks)

mikeyb2 · Sep 15, 2016

Thanks Ken, do you radius the bridge plate also?

Timbuck said:
All i did was get some 10mm MDF and cut it to the shape of the top and with some 60 grit abrasive I sanded a hollow by hand in the area around the centre of the LB it didnt take very long and I ended up with a depressed hollow area about 1.5mm deep..I now use this to clamp my tops too when I fit the braces when I clamp the bridge plate it causes a raised bump of about 1mm in the top in the bridge area..I made a sanding block with a slight convex curve just to put a bit of a radius on the bridge bottom..But thats on sopranos only...When I do an occasional Tenor I use my MDF 25' radius dish that I made on the pedestal drill with a simple Go-bar deck...(Go-bar deck is the space between a shelf and the bench and some sticks)

Timbuck · Sep 15, 2016

mikeyb2 said:
Thanks Ken, do you radius the bridge plate also?

No it's only about 1mm thick I just let it bend and let the glue do the rest.

Wildestcat · Sep 15, 2016

mikeyb2 said:
Hi Paul and thanks, I was thinking of about 25' radius. And another thing that came to mind is the bridge. Will the bottom of the bridge need to be radiussed also? I'm guessing it will..Cheers.

Hi Mike. I fit my bridges by fixing a sheet of thin 180 or 240 grit abrasive paper to the top (masking tape around the edges), mark the centre line and bridge front location and sand with short transverse strokes until the bottom of the bridge is showing contact all over. This is easier if a rudimentary handle is fixed to the bridge with double sided tape, and the bridge base is cross hatched with pencil or crayon.
Here is a picture (of a guitar bridge) to clarify:

As Ken said, no need to radius the bridge plate.

mikeyb2 · Sep 15, 2016

Thanks once again Paul and Ken, i think you've given me a good idea of what I need to do now. Cheers. Mike.

Vespa Bob · Sep 16, 2016

I'd like to add my thanks too, as I had the same questions. I learn something every time I visit here!

Bob

mikeyb2 · Sep 17, 2016

and just to help with this task, I knocked up a quick radius stick. Took about an hour including glue drying time. I referenced from Rudy's(site member) drawings which I had kept from building a 15' dish. The pictures speak for themselves.

How to radius the top.

mikeyb2

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Wildestcat

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mikeyb2

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Timbuck

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mikeyb2

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Timbuck

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Wildestcat

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mikeyb2

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Vespa Bob

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mikeyb2

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