Disc Sander for scarf joints leaves radius

beatnik · Post by **beatnik** » Wed Jul 16, 2014 9:55 am

If the belt sander works for you, go with it.

JPG · Post by **JPG** » Wed Jul 16, 2014 11:17 am

Ed in Tampa wrote:Raise the table above the center line of the sanding disk. In fact you might want to sand on very top with the table set just low enough to let you engage the width of the wood you are sanding.

Also if you are using the velco system there is flex in it that could be causing the problem.

Bingo I think!:)

And I also think the belt sander is the method of choice!

dusty · Post by **dusty** » Wed Jul 16, 2014 11:32 am

algale wrote:I am joining some narrow strips of cedar for my long-delayed canoe project. The strips are 6 to 9 feet in length by 0.25 inches thick by 0.75 inches wide with bead and cove on the long edges. The scarf is supposed to be across the 0.25 inch thickness of the strip and is about 2 inches long (1:8 ratio).

The canoe book shows the scarf joint being made on a disc sander with a temporary fence set up at a shallow angle. The blunt ended strip is simply fed along the fence into the disc standing on its 0.25 inch edge with the 0.75 inch face pressed into the disc.

Looked easy in the book, but when I tried this on my Shopsmith, the result was a scarf with a very pronounced radius on the 0.75 inch face both on the leading edge (knife edge) and trailing edge of the scarf. (I did this with the 12 inch disc sander, the table set as low as possible and the scarf starting just inside the outer edge of the disc.)

Is this unavoidable on the disc sander? Would the radius be minimized if I tried to get the point of the scarf as close to the disc's center as possible (as opposed to its edge)? Would raising the table increase or decrease the radius?

Btw, I was able to do a similar set up on the belt sander and got a nice straight scarf joint. So that may be the solution.

Does this represent your task?

[ATTACH]25636[/ATTACH]

anmius · Post by **anmius** » Wed Jul 16, 2014 11:57 am

algale wrote:I am joining some narrow strips of cedar for my long-delayed canoe project. The strips are 6 to 9 feet in length by 0.25 inches thick by 0.75 inches wide with bead and cove on the long edges. The scarf is supposed to be across the 0.25 inch thickness of the strip and is about 2 inches long (1:8 ratio).

The canoe book shows the scarf joint being made on a disc sander with a temporary fence set up at a shallow angle. The blunt ended strip is simply fed along the fence into the disc standing on its 0.25 inch edge with the 0.75 inch face pressed into the disc.

Looked easy in the book, but when I tried this on my Shopsmith, the result was a scarf with a very pronounced radius on the 0.75 inch face both on the leading edge (knife edge) and trailing edge of the scarf. (I did this with the 12 inch disc sander, the table set as low as possible and the scarf starting just inside the outer edge of the disc.)

Is this unavoidable on the disc sander? Would the radius be minimized if I tried to get the point of the scarf as close to the disc's center as possible (as opposed to its edge)? Would raising the table increase or decrease the radius?

Btw, I was able to do a similar set up on the belt sander and got a nice straight scarf joint. So that may be the solution.

Could there be a little confusion between the "sanding disc" and the "conical sanding disc?"

JPG · Post by **JPG** » Wed Jul 16, 2014 12:01 pm

anmius wrote:Could there be a little confusion between the "sanding disc" and the "conical sanding disc?"

Hmmmmmmmmmmmmm!:eek:

algale · Post by **algale** » Wed Jul 16, 2014 1:22 pm

JPG40504 wrote:Bingo I think!:)

And I also think the belt sander is the method of choice!

Sorry, I'm not using the Velcro sanding disc.

algale · Post by **algale** » Wed Jul 16, 2014 1:24 pm

anmius wrote:Could there be a little confusion between the "sanding disc" and the "conical sanding disc?"

Nope. Using the 12 inch flat steel sanding disc. No Velcro and no conical disc are involved.

algale · Post by **algale** » Wed Jul 16, 2014 1:25 pm

dusty wrote:Does this represent your task?

[ATTACH]25636[/ATTACH]

You are correct!!! Oops. Except the piece is only 0.75 tall not 2 inches tall!

algale · Post by **algale** » Wed Jul 16, 2014 1:29 pm

beatnik wrote:If the belt sander works for you, go with it.

I think that's where I am going to end up. At this point I am just curious if this can be done on a disc sander as shown in my canoe book.

reible · Post by **reible** » Wed Jul 16, 2014 1:32 pm

My guess is that you have wood movement while sanding.

I would use sandpaper as a backing, make sure backing is at least as tall as the work piece. Clamp as close to cut as you can and last but not least the sandpaper should come to the wood, not the wood to the sandpaper. You might have to play with the location where paper and wood meet or even resort to double sided tape to hold the wood in place.

I've done this before but never with that thin of wood. If I get time in the next day or so I will give it a try. In theory it should work but sometime it takes a bit more missing with then would seem necessary.

Ed