Any special techniques for using disc sander

[ClintO]

When using a 12" disc sander to sand a long article , by passing it across the face, is there a special technique to getting flatness?
I am concerned about the huge differences in the speed of the grit at the edge of the disc when compared to the centre grit.

I know when trying to file a large flat surface you can get an indentation in the centre because it gets more attention than the edges.

I am probably worrying too much but I always like to try and understand these things

[glenn k]

I use a saw, plane or thicknesser to get things flat and sand latter to get it smooth. Maybe it wouldn't work in your circumstances.

[derekcohen]

Any special techniques for using disc sander

Clint

In one word, the answer is "no".

Keeping a sanding disk flat is near-impossible in my experience. But then someone probably can do it, although I wouldn't recommend it.

A better sanding method for flatness, rather than just surface removal, is to use a drum sander. A decent 3"x 3" sanding drum is available from Carba-tec for about $40. Use it in a power drill or, better still, in a drill press. You can make a jig/machine for this quite easily.

The essence of the jig is to set up the drum to turn vertically. Either pointing up through a table top, powered by your power drill, or pointing down if powered by the drill press. Allow the drum to lie a few mm below the surface of the table top (so you can sand to the bottom edge).

The next component is a movable fence. The can be as simple as a straight edge clamped to the table. My preference would be to bolt one end through the table, using this as a pivot. The other end is movable (in- and outward) and just secured with a clamp.

In operation the board to be sanded must run between the sanding drum and the fence (i.e. it is sandwiched). Sand small amounts progressively, moving the fence towards the sanding drum by parts of a mm.

This set up will enable you to surface 6" wide boards (turn the board over after each pass). The PROVISOR is that the underside is flat to begin with (as you will be following these contours).

Regards from Perth

Derek

[Ben from Vic.]

I know when trying to file a large flat surface you can get an indentation in the centre because it gets more attention than the edges.

I don't see how this can happen, I may be way off here, and I don't own a disc sander, but I'd figure that the outside of the disc would potentialy remove more stock because of greater speed, except it can't because the disk is flat (unless you push one corner harder that the other), but you could never end up with a hollow. :confused:

Sorry ClintO, I know this doesn't help at all. :o

Just curious. :)


Ben

[Sturdee]

I have a disk sander and I would not use it to sand long boards. Whilst it does not matter that the speed on the outside and inside of the disk is different there are other problems to overcome.

Firstly you would need to build a suitable fence, secondly auxiliary infeed and outfeed tables to support the work and finally you would have to worry about the uplift factor when the work passes on the right side of the sanding disk.

I therefore support Derek's suggestion which seems both simpler and safer.


Peter.