Radius Dish Usage [Diagram] - created 03-21-2011

Carter, Greg - 03/21/2011.07:59:18

I am building my first acoustic guitar and am perplexed (duh!). I have radius dishes for the top and back, different radii (20' and 25'). I am worried about adhesing sandpaper (by tape or spray contact cement or glue or ...(?)) to the radius dish to radius the sides and sand the braces to shape, and then to come back and place my nice back or top on that radius dish for go-bar gluing. I presume I don't need two dishes for each radii, but peel off the sandpaper before it is used in a go-bar deck. What glue/tape/spray do you recommend so that I do not have any residue that gets on the back or top? Or should I just leave the sandpaper on the dish and cover it with some appropriate weight fabric (thick enough that the sandpaper grit does not work its magic)?

Don't worry about it. Just don't sand your plates out to finished state before you glue the braces on. I leave my sandpaper on the dish, it actually helps hold the plates in place as I glue my braces. If you are worried about it then put down a layer or two of newspaper.

Leave the sandpaper on. It lasts for a very long time outside of a production environment. I use heavy paper (poster paper)over the sandpaper when using the go bar deck. A couple of layers of newspaper work as well.

Edit: Mark posted at the same time.

Supergrit.com sells large PSA-backed sandpaper disks ( http://supergrit.com/products/products_discs-cloth.asp ). They make it very easy to put and keep sandpaper in a dish. I put a layer of thin closed-cell foam between the plate and the sandpaper in the dish, not to protect the surface but to make sure there is pressure everywhere across the plate.

Great advice, all. Thank you. While I have your attention, if you leave the sandpaper on, I presume you stay with one grit (perhaps 80-100 grit or so), and that you don't move to higher grits when sanding the braces to final radii? Just stay with the original grit?

Again, thanks for the advice. That makes things a lot simpler. by the way, a shout-out to Mark Swanson: I am using your FatBoy plans. Great design and a great plan. I notice no side braces on the plans. Are side braces optional or do you recommend them (and you just stayed true to the original design that did not have them)?

I stay with the original grit.

Hey Greg! I would really like to see your guitar when it's all done so make sure that you post some photos.

I use cloth strips on the sides, so I don't need to mess with the wooden ones. If you are used to wood side braces then use them, no harm done.

(perhaps 80-100 grit or so)

I use 60 grit.

If you do not have a powered dish, then it really takes a bit of work to get the whole rim on the sphere - 60-grit helps it go a bit faster. I scrape the rim afterward to get rid of the inevitable fuzz.

The other trick to make it go faster is: Grind a bit, then block-plane down the high-spots, then back to the grind.

I'm with Bob, I don't glue anything to the the dishes. I have 3 grits of the 24" disks of sandpaper and it works just fine using 3 or 4 spring clamps to keep the disc from moving when sanding the rims.

Takes 10 seconds to change grits. (Like Chuck said, hit the rims with a scraper just prior to gluing).

I used this method years ago to make up a 25" diameter using 9"x11" sheets of sandpaper to cut and glue segments to the disc. It's a bit of a pain to glue them down but it works in a pinch.