disc sander runout.

[Dave Bureau]

I have a powermatic 12" disc sander. I noticed that there is a little runout while spinning. is there a way to fix this or do i need a new plate? any know where to get a new disc plate or a fix for the old one? runout is barely noticable but there is some runout.
Thanks
Dave

[Bruce Page]

Dave, I wouldn’t worry about it if the run out is barely noticeable. If it’s more than you are willing to live with then you have two options; A, purchase a new platter from PM or B, take your platter to a machine shop and have it re-machined. The A option is probably the cheaper way to go.

[Chip Lindley]

Unless the disc is so bad that only part of your sandpaper does the work, No worries! Not sure about the PM, but my Rockwell disc is attached to the hub with recessed bolts. If yours is also, determine the side with least runout and shim the disc with some very thin metal. This would be trial and error, but much less expensive than re-machining or purchasing a new disc. AND, this won't work if the disc is BENT. To fix a bent disc, remove it and see if you can't get it back in shape with some judicious blows of an adequate hammer on a wood block!

[Bruce Page]

Unless the disc is so bad that only part of your sandpaper does the work, No worries! Not sure about the PM, but my Rockwell disc is attached to the hub with recessed bolts. If yours is also, determine the side with least runout and shim the disc with some very thin metal. This would be trial and error, but much less expensive than re-machining or purchasing a new disc. AND, this won't work if the disc is BENT. To fix a bent disc, remove it and see if you can't get it back in shape with some judicious blows of an adequate hammer on a wood block!

Yeah, if shimming is an option, that is the way to go. My 12” Delta Sanding Station disk mounts onto a shaft with set screws. It had an unacceptable wobble when I picked it up used so I set it up in my engine lathe and took a light clean up cut on it.

[Faust M. Ruggiero]

Dave,
I bought an old Rockwell Delta 12" disc sander at a auction. It had quite a bit of run out at the edge of the disc. The run out did not affect the quality of my work. I used it to touch up miter joints and to remove saw marks from concave curves. The problem was the machine vibrated so much I could dance with it. It moved better than I could. I experimented with shims to no avail. Then I noticed the disc itself seemed out of center on the hub, thereby throwing off the balance. I tried to correct this with counter weights. That didn't work either. Finally I sent it to a young and talented machinist. He immediately determined the motor was spinning true but the hole drilled in the flange for the motor shaft was ground to a slight funnel shape. He repaired this by adding tapped holes for set screws at specific points in the hub of the flange and using them got the flange running true.
Then he found the holes drilled in the disc itself were not drilled in locations that centered the disc on the hub. His intent was to true the disc to the hub. Prior to doing that, he checked the flattness of the disc and found it to be warped. The easy fix for that problem is to send the hardened disc out to a shop that will grind it on a machine that holds the disc down with strong magnetic force. This disc had already been ground and it's thickness was compromised. That meant when the magnet was applied, the disc would distort, making truing impossible. He purchased a blank for a new disc, drilled new holes and sent it out for flattening and hardening. I now have a wonderful machine that cost half of a new floor stand model and is true.
It is easy to say I should have just bought a new machine knowing what I went through to make the old one work well. However, this is the chance we take when buying second hand machinery. It is good but not usually without effort and money.
I thought you might enjoy the story.

Faust M. Ruggiero