"Jim Wilkins" wrote in message
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"Bob La Londe" wrote in message
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"Jim Wilkins" wrote in message
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"Bob La Londe" wrote in message
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"Doug Miller" wrote in message
. ..
I needed to shorten the tailpiece for a bathroom sink drain:
chrome-plated brass tube 1.250
OD with 0.030" wall. Obviously the tool of choice would be a tubing
cutter, right? Except that
my tubing cutter has a maximum opening of 1.220", despite being
labeled as "1-1/4". Grrrr.
OK, no problem, I'll chuck it up in the metal lathe and part it off.
Should be easy, right?
No sooner does the parting tool start removing stock, than the tube
begins slowly but
inexorably sliding out of the chuck. Not crooked or anything like
that, still concentric, just
creeping slowly in the direction of the tailstock. OK, maybe I didn't
tighten the chuck enough.
Stop the lathe, reseat the tube in the chuck, make sure it's darn good
and tight, try again.
Same thing. I get maybe 0.0005" (that's right, half a thou) removed,
before the tube begins
sliding again.
I tried low rpm, high rpm, slow feed, rapid feed, lots of oil, no
oil -- no difference that I could
see.
After 45 minutes, I finally got it turned down far enough to slip it
into the tubing cutter, after
which it took about 45 seconds to complete the cut.
Why is this happening? And, more importantly, how can I prevent it?
This was number 1 of
two pieces that I have to shorten by the same amount.
Which way was it creeping? If out, then just set the lip on the tube
up against the back of the chuck jaws, and use a bullnose center in the
end. If slipping in, put a block of wood inside the chuck behind it,
and tighten down the screws of your spider to keep the block from
moving. If you don't have spider bolts on the back of your lathe
spindle it might be time to add them. Never know when you might need
to do some turning on a rifle barrel next.
I would suspect it was slipping in because the end with the lip would
be more rigid effectively making your tube into a cone with the large
end at the lip when you clamp down.
Personally I would have probably cut it on the bandsaw or with a
hacksaw, and then debuirred it with a file, or deburring tool depending
on what was handy. There is a huge amount of overlap in the joints of
that type of fitting, and it doesn't have to be very precise at all.
Lots of tools could have done the job. Tail pipe cutter. Pipe cutter.
Tubing cutter. Hacksaw. Bandsaw. Abbrassive saw. Dremel tool.
Jigsaw. Sawzall.
That style fitting and assembley is designed with ease of use in mind.
Hence the huge overlap. As long as it reaches past the geasket, and
doesn't have any burrs to catch hair and clog its fine.
http://www.autozone.com/loan-a-tools/tail-pipe-cutter
That is an option I never think of. Its a good one too. I've used my
tail pipe cutter maybe a half dozen times in 25 years, and most of those
times I could have used something else. The one or two times it was
really the right tool for the job I could have just borrowed one from
Autozone. Doh!
Tubing is difficult to part with a larger lathe too, because it flexes too
easily. I sometimes score it with the lathe bit and then saw along the
groove with a 24 TPI or 32 TPI hacksaw.
Whenever you are turning wood on the lathe you could make a pair of cones
with holes through the center for threaded rod, to hold hollow tubes. Just
don't try parting work held at both ends because when it becomes flexible
enough to deflect away from the cutting pressure, the near side will close
and grab the bit.
--jsw
I've gotten spoiled in a very short time. Last month I took delivery of a
new 3HP PM1440. It does things.
For the last decade or so all I've had is a small lathe (8x18) and a mini
lathe (7x14), and I have found quite often a hacksaw is the right tool for
the job. For a lot of materials the mini lathe just doesn't have the
horsepower or the rigidty to use a parting tool or a parting blade. I've
often scored a groove and used the hacksaw to make the cut. Just have to
remember to move the saw back and forth to get the chips out from between
the teeth.
Now on the new 1440 I can actually use a parting tool. First thing I did
was waste a foot or so of 1018 I had laying around being amazed at what the
new machine would actually do. I put knurls on impact sockets just to see
if it would do it. Threaded things in one pass to see how hard it would
push. LOL.
My very first actual part on it worked the very first time when I took it
off the machine. Almost never had that happen with the mini lathe. LOL.