"Bob La Londe" wrote in message
...
"Jim Wilkins" wrote in message
...
"Bob La Londe" wrote in message
...
"Jim Wilkins" wrote in message
...
"Bob La Londe" wrote in message
...
"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.
Nice!
http://precisionmatthews.com/PM1440BLathe.html
My 10" lathe is fine for a hobbyist but the 15" lathes I used in
company shops were better for commercial jobs. I tend to make one-off
prototype parts whose design I refine while machining them so I never
used the CNC capability.
The optional accessory I like most is 5C collets. Right now there's a
chuck like this in the collet holder:
http://www.ebay.com/itm/like/3910061...&ul_noapp=true
I can move the 5C-mount chuck and work to the milling machine to drill
holes, mill slots or add wrench flats and then return it to the lathe.
When making repair parts I can test the fit on the machine without
losing registration in the chuck. For most jobs this is enough to hold
and index it on the mill:
http://www.ebay.com/bhp/5c-collet-block
I have a nearly complete set of second-hand collets but only the sizes
that accept my supply of ground drill rod and shafting stock get much
use.
Machined brass pipe fittings run much truer than iron ones and are
very handy to chuck and modify other fittings.
I still use my small lathe at its higher speed to drill deep holes
such as grease passages in axles and for polishing.
--jsw