inertia sanders and the like

[neil mackay]

This to all the wood theorists, rocket scientists, and deep thinkers out there and for that matter anybody who has an opinion on the matter.

Now we have all heard that we must sand down through the grits and never miss one http://www.woodworkforums.com/images/smilies/no.gif tis a cardinal sin of wood turners everywhere to miss one.

Now when I started out a few years back I could not afford to buy all the grits within the brand I was using, namely Noritake Astra dot. So I took a punt and bought a range at the same time got a inertia sander and a few power sanding heads.
Love technology http://www.woodworkforums.com/images/smilies/actions/2thumbsup.gif so couldnt help myself. http://www.woodworkforums.com/images/smilies/happy/biggrin.gif

This sort of sanding produces very fine results a few grades down the range than the grit being used and so jumping a few grits works, well for me any way. http://www.woodworkforums.com/images/smilies/smile.gif

So my question is, Why? http://www.woodworkforums.com/images/smilies/standard/confused.gif Why does this sort of sanding produce the result it does.

[Dan Hintz]

What grits are you using? The rule of thumb is do not jump more than 50% of the prior grit. If you do, you're forcing the smaller grit to compensate for what the previous left behind... and if you jumped, it's a lot, which wears out the smaller grit more quickly (more work is needed out of it).

For me, a good progression is 80, 120, 180, 240, 320, 400, 600... I either skip the 400 and go straight from 320 to 600, or skip the 600 and stop at 400. Notice how each jump is (roughly) 50% more than the last.

[neil mackay]

its not so much the grits, but rather why the rotary sanders punchs above thier weight by producing a finishing greater or finer than the same grit by hand.

[Tom Wilson66]

If I remember correctly, it was explained to me that hand sanding leaves parallel scratch patterns in the wood. Power or inertia sanders leave a somewhat random, non-parallel scratch pattern, which is harder to see, therefor it looks smoother for the same grit. In other words, the scratching is still just as deep, but harder to see.

[Dan Hintz]

Ah, I didn't realize what an "inertia sander" was, just thought it was odd talk for sanding. The question makes more sense now...

[neil mackay]

Here you go a inertia sander DIY, handle is 12" long the head on this one about 1 1/4" with a velcro patch to attach the sand paper