On Fri, 13 Apr 2012 13:18:27 -0700, Bob La Londe wrote:

"Lloyd E. Sponenburgh" lloydspinsidemindspring.com wrote in message
. 3.70...
"Bob La Londe" fired this volley in
:


Ok shiny was probably not the best term. Smooth is more important. It
will have a low pressure pneumatic seal with am o-ring and piston. The
raw tube works ok, but I was thinking with a better than mill finish
the o-rings might last longer.

So far I have not worn out an o-ring with the existing units, but I
would like to make future ones "better."

How long are these tubes, Bob?

Finished working length may vary from 10-12 inches.

It takes darned near forever with a long boring bar, but with the right
speeds and the right rake on an HSS boring bit, you can get a pretty
nice finish.

Yeah, I thought about a round face boring bit, but supporting and doing
a 12" internal finish is beyond my skills and equipment. I was just
hoping to improve the finish "some"

Get it turned to "round" (sans weld), then use a small flap hone if you
want to clean it up.

I may "just" do a flap wheel down the bore and see how that works out.
perfectly round is not super critical. it's a low pressure o-ring fit
after all.

Remember, I went through this recently with a customer's project, and
finally ended up buying an aluminum air cylinder long enough to cut
what I needed. But mine was 18" long and 6" i.d. That made it kind of
hard to bore with a conventional setup, and I didn't have the time to
jig the lathe to mount the work on the cross-slide, and the bit in the
spindle, supported by the tailstock.


I recall your project. I read quite a bit on that thread. Glad you got
it worked out.


Bob

I think that if the seam on the inside is very big, doing your flapwheel
alone is going to be very disappointing.

I would either try to do a boring bar mounted on the cross-slide, with
center rest to hold the tube in place, or mount the tube on the cross
slide and run it past a boring bar that's spinning on the lathe, with
center rest fixed to the lathe base somehow, or I would make a boring bar
with a pilot that runs down the inside of the current tube (avoiding the
seam) and shaves everything evenly.

I suspect the piloted boring bar would be the closest to being within my
abilities, and it certainly matches the drawer full of 50-year-old ball
bearing sets that I inherited from my uncle. I don't know what would
work for you.

I'd bore it out, then look at polishing it with whatever 'soft' tools
came to hand.

But first, I'd look for seamless tubing.

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com