bridgeport mill accuracy

i have a cast iron tube that is about 6 inches long with a id of 4
inches. i need to enlarge the id by about a quater inch . my friend who
has been a machinist for fifteen years says that he can do it on his
mill in his garage as he does not have a lathe. he says that he can jig
it up to make it work without much trouble eventhough the quill travel
is only five inches. he is a good friend and all but he is well known
for overstating sometimes.i need the final id to be within 1000th of a
inch. what do you think?
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Anybody here could do that within 5 tenths
Reply to
Tom Gardner
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.
Reply to
Yeah, I could probably do it within 5 tenths of an inch..
Reply to
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!
Reply to
Christopher Tidy
I'm confused. Do you mean that you want the EZ Trak to interpolate a 4.250" +/-.001 hole that is 6 inches deep? Sorry, ain't gonna happen that way. Your interpolated hole will not be round to the tolerance specified.
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.
Reply to
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.
Reply to
Christopher Tidy
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...
Reply to
Robin S.

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