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I'm happy with the lap joint on the X-brace I just cut but I noticed another issue.......the radius on bottom of my X brace.

I'm using a 28' radius on the top. I bought the dish from Axehandle and it came with a a 28' reference (concave on one side and convex on the other). These appear to all be CNC machined so I'm guessing they are accurate. Anyhow, I used the reference to mark the radius lines on my X-Brace arms, planed down close to these lines, and finished sanding in the radius dish with 80g sandpaper. I marked the bottom of the braces with pencil so I could determine when I had cleaned up the entire length.

At first I was removing material from the ends of the X brace and worked till the pencil line was removed in the center of the brace. Often I switch the brace end for end in case I was putting pressure unevenly.

So the problem.........when I was done sanding I checked the brace against the template.......and the very ends of the braces are radiused too much. The middle fits perfectly........just the ends of the braces swoop up a little. Surely this is an issue with my sanding technique. What can I do differently?

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Formerly known as Adaboy.......

Darryl,

I've never had much luck with using a dish to radius braces. My problem was trying to keep the braces perpendicular to the surface (if that makes sense).

There are lots of ways to skin this cat, but I've settled on using the brace cutting jig that Tracey at LutheirSuppliers.com sells

He advertises here, so I guess it's ok to link to them
http://www.luthiersuppliers.com/products/p6.html

Just press the brace material in (make sure it's centered end to end), and tighten the knob. Then you can use any pattern following cutter or even a luthiers friend. I cut mine on my router table with a pattern bit. \

Here is a review Bill Cory wrote back in 2006
http://web.mac.com/magads/Site/Tool_Rev ... Maker.html

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Jim Hansen

Yep, it happens to me sometimes too. You can't just push the brace straight forward and back, you have to sweep it to follow the curve. Or in my case since I use a flat sanding board to radius braces, the problem mainly happens when I over-sweep, so I hit just the corner at first, then sweep along the curve, and then hit just the other corner at the end. Easiest solution I've found is to make your braces a little over length, so you have 1/4" or so at each end to sacrifice. But usually I can get them smooth to the ends anyway, by careful feeling of the curve as I sweep it along the sandpaper.

Sanding two braces at a time clamped together also helps with the perpendicular thing.

Edit: Todd said the same thing.

That's what I did.......except I had one brace taped on top of the other to minimize deflection. Still ended up with the ends oversanded.

Maybe I should use shorter strokes? If the brace rotates side-to-side a little, maybe that causes the ends to be oversanded? If so, the side by side brace would work better. I am holding the brace in the middle and sanding with one hand. Maybe I should leave my brace taller then needed and plane the entire line and not sand at all?

Dennis, am I understanding you that you spin your braces around in the dish like a clock? Does that sand the ends (that are covering more area) more than the central part of the brace? That is what is happening to me though I'm sanding back and forth in a straight line.

I think I will remake my X-Brace as on a small 00 body especially I don't want excess radius......especially right at the rim where I wouldn't mind it being less radius. I just need to figure out how to do it right this time.

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Formerly known as Adaboy.......

There are jigs that allow you to do this on the table saw . I find the top braces work better for that than the backs.

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

+1 I used to sand in the radius dish till I tried this - works great and not as hard as it seems.

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Steve Smith
"Music is what feelings sound like"

No, not that way... more like a pendulum. Moving the brace in the direction of its grain, but angling the front end downward a tiny bit as you start, and sweep to lifting up the front end and pushing down the back end as you swing through the pendulum motion. It should be a lot easier in a radius dish than it is on my flat board, since all you have to do is make sure you have full contact with the abrasive at all times, and even pressure on both hands. Here's a picture of what I mean.

What I have done is to join my X and then with some double stick tape, tape it to a piece of flat 3/4" mdf. I use really thin double stick tape and run the tape on the whole X. I then sand holding the mdf. The whole X is supported and it is easy to get even pressure. Works like a charm. A squirt of acetone will release the X from the double stick.
L.

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Cut to size.....Beat to fit.....Paint to match.

Dennis, you may be on to something there. I used one hand in the middle and it seems I was putting force onto the front of the brace. One time I realized I had my finger on top of the brace out in front of my hand. So I probably was inadvertantly sanding more off the part of the brace in front.......and when I swapped the brace end for end, I probably did the same thing to the other end. Maybe two hands would be better? Or maybe applying a bit more pressure to the back of the brace when moving forward and more pressure to the front of the brace when moving backward would work.

Thanks for taking the time to make that drawing!!!

Link, that is a good idea. Do you sand in a straight line or use a semi-circle movement?

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Formerly known as Adaboy.......

A little of both. You can mark the X with pencil and sand a touch and use a hand plane to quickly remove the high spots which are revealed when the pencil marks are sanded away. Keep repeating with the plane and you will minimize the sanding you do. Also it seems when sanding anything that the ends of things will get more sanded than the middle. With this in mind you would want to have the center area of the X the last thing that gets sanded. You sneak up on it so to speak. When you are there you stop. Once everything is perfectly shaped to the radius if you keep sanding it will take more material on the ends of the X on you will be over radius-ed. ( is radiused a word ?) Use a light touch, the mdf is heavy enough to apply the right pressure. I have some 180 for my disk that works well for the final sanding and gives a good glue surface.
L.

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Cut to size.....Beat to fit.....Paint to match.

Darryl, as Todd said. There's pics on p. 7-8, shows how to mark the braces and plane them to keep the bottom square, with pics on the same page of one way to do the X-joint (here used for cutting the many notches needed for lattice bracing). There's also the hand method shown on p11-17 et seq. For curving the bottoms, there's also the fixture shown on p7-6, with instructions on how to make it on p4-49.

If you're doing clean-up by sanding in a dish, the trick is to keep the pressure constant all over...as Todd said!

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Did you ever try holding the brace at the ends,
so as not do deflect them?
Take swipes in one direction.
Give that a try.