12" steel sanding disk runout?

tsmccull · Post by **tsmccull** » Sun Jul 26, 2009 1:04 am

It's been 20+ years since I've used my sanding disk and I noticed that I could see a slight wobble on the edge as it's slowing down (this is without any sandpaper on it). How much edge runout should I expect from a properly setup system? If I lightly touch a pencil held stable on the table to the disk near the edge when it's running, I get a pencil mark roughly halfway around the disk, which seems to indicate that about half the disk isn't coplaner with the rest. Is this normal and nothing to be concerned about, or is it possible my disk has either warped or gotten bent sometime over the years? Thanks for any advice.

dusty · Post by **dusty** » Sun Jul 26, 2009 6:10 am

The 12" sanding disk is well known for not being perfectly coplanar. Even without having been mishandled in any way, I believe it is hard to find a disk that is perfectly flat.

However, quill bearings can be the cause of the same symptoms that you describe.

Do you witness the same phenomena with a blade and arbor installed. I consider run out that is <= .005" to be acceptable.

tsmccull · Post by **tsmccull** » Sun Jul 26, 2009 10:41 am

Thanks for the advice. I checked a blade and see much less edge wobble, even considering the smaller diameter, so I think the quill is ok. I cut a hole in a block of wood to fit the sanding disk's arbor, marked the high and low spots as I turned it on the machine and persuaded the disk to bend slightly using a rubber mallet. After much trial and error, I seem to have minimized the runout. Looks about the same now whether I use the primary quill end or the opposite power takeoff end, so I think I've probably got it as good as it's going to get. It's too bad Shopsmith doesn't machine the arbor-disk assembly flat once it's assembled. I wouldn't think automating that process would be too tough - mechanics do it with brake rotors all the time!