bridgeport mill accuracy

Anybody here could do that within 5 tenths

I don't know about the accuracy but as long as the tool/toolholder length is at least six inches, using the quill is not necessary. Unless I'm missing something, it could be chucked in a rotary table and turned, raising the knee or lowering the quill after each pass is taken.

Yeah, I could probably do it within 5 tenths of an inch..

A Bridgeport EZ Track could do this nicely, but I doubt your friend has one in his garage. If he does he's a lucky guy!

Chris

I'm confused. Do you mean that you want the EZ Trak to interpolate a 4.250"

I think the quill travel on an EZ Trak is even less than a regular B'Port due to the readers, drive...

I think on a knee mill, the reasonable way to assure success may be to ue a boring head with a rigid boring bar installed at 90°, lower the quill all the way and bore by raising the knee. You'll get your extra one inch of effective travel because the boring head head will extend below the quill.

Maybe not. Reading quickly I had missed the "6 inches long" bit. I used an EZ Track for making recesses maybe 1/2" deep (can't remember exactly) for bronze bushes and it worked nicely.

Chris

I *think* you're tolerance is probably incorrect, or at least incorrectly stated.

Indeed, actaully nailing a +/-.001" tolerance on a 6" long bore would be difficult using a very rigid lathe, let alone a flimbsy knee mill.

Do you actually need the diameter to be within +/-.001" for its entire length? What about the straightness of the hole in relation to either the round faces of the tube, or the outside diameter of the tube (or both?)

Your friend may tell you he can make the part you need correctly because he understands its appliction. If you actually need +/-.001" over 6", you'll probably have to pay a *lot* more than your friend is charging you...

Regards,

Robin