How would you finish this bore?

[GlennW]

Glenn, the spindle is polished with crocus cloth. It just needs to be smooth.

"Smooth" doesn't necessarily mean that it is round and straight! Especially if it is to fit into another part at close tolerance.

[Greg_Lewis]

Glenn, the spindle is polished with crocus cloth. It just needs to be smooth.

"Smooth" doesn't necessarily mean that it is round and straight! Especially if it is to fit into another part at close tolerance.

Yup. But it's the best I can do with the tools and talent I have (please note avitar and sig line ). As far as I can tell, it's straight and round to within a half a thou.

[BadDog]

You generally need (at least) 3 points of contact to measure roundness because of the very common "lobing" problem. For example, a v-block micrometer is often the reference. If carefully done, you can also use a v-block to support and rotate the bar under a tenth DTI. But depending on number of lobes and contact points separation for the reference, you can still miss tri-lobing (or more). It's quite the challenge as you get more and more dependent on roundness. Straightness is a completely different problem.

It all boils down to, how close is close enough? I pretty much never have to worry about such things, tool makers have different goals/requirements, as do people making critical parts (like Glenn does, Harold did, etc).

[Greg_Lewis]

Yes, Russ, I learned that the hard way. Many years ago I needed a 7/8 dia. piece of shaft that was right on the dia. In my innocence I thought a piece of drill rod would do it. The catalog spec claimed that it was within .0003. So $35 later I cut off a piece and was working with it and something wasn't right. My mic said it was right on the diameter, but things just weren't working out. Only when I set it up on V-blocks as you describe did I discover that it was tri-lobed by over .003. I should have bought a piece of ground shafting. I've still got the rest of that piece of junk in the stock rack.

[Harold_V]

Why the mill rather than the lathe?

He commented that the bores are not the same diameter because of wear in his lathe. That wouldn't be a problem if he bored with his mill.

H

[Greg_Lewis]

Why the mill rather than the lathe?

He commented that the bores are not the same diameter because of wear in his lathe. That wouldn't be a problem if he bored with his mill.

H

Unfortunately my mill is a little Clausing 8530 and the quill just barely fails to have enough travel. The only options there would be to reset either the toolbit, the work or the table and none of those would insure the accuracy I was aiming for.

[John Hasler]

Have you considered altering the design? If the quill has nearly enough travel you could shorten one of the bearings slightly.

[Greg_Lewis]

Have you considered altering the design? If the quill has nearly enough travel you could shorten one of the bearings slightly.

Yeah. I should have thought of that. At this point I've got the bearings pressed in and bored to minus .001 so the Sunnen hone is looking like the most expedient solution. Setting the block up in the mill to take off .0005 from each wall of the bearings isn't something I can do. But thanks for the idea anyway.