Heh! That it has worked brings to mind the saying "hold my beer, and watch
I've experienced a length of 3/4" CDS that was hanging out the back of a
headstock that got off center at speed. Once you've seen that, you don't
take chances. If, for any reason, that pipe got away, and it can, you
could expect as much as the tractor being tipped over---and people in the
vicinity killed. No way in hell I'd do that unless there was a restraining
cap, so the pipe COULDN'T get started off center. Like a steady rest of
sorts. Even then I'd have reservations, but then I quite like life. I'd
also run it much slower-----there's no need to run at high speed if you have
propulsion for the abrasive material as has been suggested.
Check out the following couple of web sites for info:
www.euro-inox.org - find the PDF entitled "The Mechanical Finishing of
Decorative Stainless Steel Surfaces". It's a good read.
the whole site has good info about what you want to do.
Also, I gotta tell you that I agree with others that spinning the work when
it's not secured is a recipe for disaster. When you try to apply the force
needed to polish or finish the material, I think the opportunity for a real
problem is going to be very real.
You're still asking for trouble.
*IF* the pipe crawls over a wheel, good chance you bought the farm.
In order to do this safely, the setup should include a third restraint that
prevents the pipe from leaving the cradle of two wheels, even when a bearing
in one or more of the wheels seizes.
It SEEMS safe, sure - but if that pipe gets out of balance and jumps
off the wheels at that speed, IT CAN AND WILL KILL ANYONE IN THE
VICINITY. It can easily get out of balance and start jumping around,
finally it starts whipping vertically like a lasso and has the power
to cut a tree in half.
What you have lashed up here is a classic "Here, Hold my beer and
Watch This!..." situation. Please rig up a video camera at a safe
distance at least 2X the length of the pipe away, and preferably
behind a Lexan barrier, so the Coroner's Inquest is a lot simpler.
And after the hubbub is over, your next of kin can sell the footage to
America's Funniest Home Videos.
We have seen what happens, and it is not pretty. Machine shops
regularly feed long sections of bar and tube stock through a hollow
lathe tailstock, turn it at machining speeds, and occasionally the
free end gets away - and with a sufficient application of horsepower
it'll destroy anything within range. I'll bet a dozen participants
here can provide "After" pictures of bar-feeder whipping stock
runaways that will curl your toes.
You just built a lathe with triple the stock length, triple the
horsepower and torque available to spin the stock, and far less
intermediate support. And you wonder why we are concerned...
The idea is fine, but you are turning the pipe way too fast. 10 to
30 RPM is plenty fast enough - set the PTO at the slowest speed and
let the tractor run at dead-slow idle, the rotation only has to go
fast enough to keep exposing all sides of the pipe as you clean up the
And have a volunteer come out and stand by to hit the Kill Switch
and call 911 just in case you get tangled up in the pipe - it happens.
Bring an umbrella, buy them a pitcher of lemonade, let them read a
book - as long as they are close by when the screaming starts.
To knock off the mill finish and start exposing the nice metal
underneath you need bulk cutting - I'd start off with either a
right-angle grinder and a metal-cutting wheel held with the face flat
against the pipe, or a belt sander and a rather aggressive belt like
30 or 50 grit. Have the grinding wheel cutting face or the sanding
belt face travel going /against/ the rotation of the pipe.
For the final finish you'll have to experiment - You can use a
running belt sander with various grit belts, a power drill with a
flap-wheel, ScotchBrite abrasive nylon finishing buff wheel, or a
heavy wire brush, or a right-angle grinder with a wheel or wire brush.
We can't get more specific than that without knowing what finish you
want, and you probably don't know exactly what you want yet either.
Knock off the big chunks on one length of pipe, and then experiment
with various sanding brushing or grinding techniques on short sections
till you get a look you like.
If the power tools are electric you have to do the work dry - even
with a GFCI protecting you from getting shocked, water will wreck the
tool unless it's designed to be waterproof. If you use air tools
applying water may help, this is another part of the "experimenting to
see what works best" phase.
All the 'tractor lathe' is doing is to keep exposing the bottom side
of the pipe you are buffing up, Period.
--<< Bruce >>--
Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here.
All logos and trade names are the property of their respective owners.