Funny lathe machining problem....
Proctologically Violated©® wrote:
Awl--
I'm sure I can "solve" this by being more vigilant, but that it happens at
all seems sort of strange.
Briefly, I'm drilling a 3/16 hole 3/4" deep in 1/4" round brass: face,
c-drill, then a 3/16 drill (tailstock/drill chuck, 5C collets).
Then, I'm turning down a piece of 1/4" round brass to 3/16" OD, for about a
3/8" insertion into the other piece w/ the 3/16 hole, for a "nice" fit.
Using a live center.
Have DRO, Aloris tooling, good for half a thou, I'm pretty sure--at least
the DRO says so!
Problem is, the 3/16 OD pc gets in only about half way before it hits some
kind of "step"!!!
To achieve the full 3/8" insertion, the fit winds up being far too sloppy!
Still works, but annoys the hell out of me.
Seems like a simple no-brainer, and I'm sure I could solve it w/ sequential
drill sizes, reaming, etc., but it doesn't seem to me like this should be
necessary, as there is nothing complicated or exotic here.
I would have anticipated any other type of problem--holes too big, holes too
small, ragged/jagged sides, holes off-center, etc.
But an invisible step??
Any idears?
Mebbe on my next have-at-it here, I'll test the female portion w/ a 3/16"
dowel, to at least try to identify the offending piece/operation.
It's pretty clear what the problem is (diameters!), but puzzling as to *why*
this problem is occuring.
That's 4 diameters deep, quite a bit. Probably the chips are scoring up the ID
somewhat. Maybe you should take Harold's oft-offered suggestion and rough the
part out and don't try to do a finish bore 4 diameters deep in one push?
Also, another idea is maybe there's a spot on your tailstock ram which isn't as
tight as the rest, and maybe your drills are grabbing a little in brass, trying
to pull themselves in, like they do, and maybe when it gets to that spot on your
tailstock ram, it "jumps" a little so you have a little bulge.
I normally machine brass dry, so I agree it likely isn't a lubricant issue.
You can also try a brand new 3/16" drill bit and see if you still get the problem.
GWE
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