I have one of the Harbor Freight 7 x 10 lathes.
I have a bicycle seat post that I want to reduce the diameter by 0.025".
The spindle head is to small to accept the post, the bed is to short to
use the tail stock.
Any clever ideas how I could use this lathe to do the job. The post is
I took it to a machine shop, he laughed and said, "I've already spent
more time on this than the part is worth."
You need a steady rest (Google "lathe steady rest"). For a one-shot
that doesn't sound at all critical, cutting aluminum, you can make one
out of plywood that will do the job.
You may find a plan or idea for one online, or maybe someone here can
tell you how to jury-rig one.
However, if the bed is too short to use the tailstock, it raises the
question of how long this thing is and how much of it you want to turn
down. A long, thin aluminum tube is going to present a deflection
problem, in which case you may have to rig a follow rest in addition
to the steady rest. You can look that one up, too.
It sounds like this lathe is just the wrong tool.
Clamp the seatpost on allthread in a drill with some nuts and a washer.
Run that with the left hand with the end of the allthhread on a block of
wood. Angle grinder with flap disc in the right hand. Take passes back and
You'll be done in a few minutes for quick and dirty OD removal.
Get an extended bed from Little Machine Shop and turn it into a 7x14?
If you are comfortable with it you might be able to make an adjustable V
support to go on in place of your tail stock. Then turn a tapered mandrel
in the chuck, and drill and thread a hole in the middle. then gentley tap
the post onto the mandreal, run a piece of all thread thru it, and put a
washer and a nut on the end. Now adjust your V support to hold the post
straight, and turn the end that's on the mandrel with light passes until its
the correct size.
Of course then it will be weaker and might break on you moving up the
schedule for your next rectal exam.
Yes, as I wrote the question, I thought, I could make a holder for the
live center out of wood and bolt or clamp it to the end of the bed.
I did see a steady rest someone built for their mini lathe, it was
very nice but quite a project.
It's about 12", 11" of it I need to reduce. I'm not to worried about
deflection, it just needs to slide in my bike frame tube, nothing
precision about it.
It's a seat post with a spring in it, I want a little more protection
for my compromised spine.
Well, you may want to rig a center, or just a steady rest. If you
have room for a center, that would allow you to turn the whole length
The issue with deflection in this case is not accuracy so much as the
ability of the tool to cut, if the work springs away. Or, much worse,
especially with alumimum, is a positive-rake tool digging in, pulling
the work toward the tool, and wrecking the work.
Cutting aluminum is pretty easy, and skating of the tool is not
generally a problem, but use a sharp tool and try zero rake to avoid
I always try to figure out what is the real requirement. In this case I th
ink the real requirement is to have a shaft of some diameter 12 inches long
. Does it need to be a tube? Can you buy a tube or shaft of the right dia
meter? Could you get the right diameter by using a threading die to take o
ff some of the metal and use the depth of the thread as a guide to removing
the necessary amount of metal. Maybe using a drill press to spin the post
and a file to remove the metal down to where the threading disappears.
Is it hollow, or solid? And if hollow -- how thick are the
walls? If you remove 0.025" diameter, will it be strong enough?
How long is the post? I presume that you mean that it will fit
into the chuck, but not into the spindle. If it under 10" OAL, can you
mount it between centers?
Or do you have a steady rest for the lathe? If so, you might be
able to hold it in the chuck and support near where the diameter reduces
and turn that which sticks out.
Or -- find someone local to you who has a larger lathe as a
hobby operation, rather than for income. (A clue as to where you live
-- general region, not street address -- might get someone nearby
responding. You may need to at least offer a non-spam-proofed address
in your posting to allow direct communications.
That's the problem with a commercial shop which has plenty of
business. If times were slow, they might have taken it on, just to keep
When they grab the tool and climb up it, they'll often spring out of
the centers up and back -- right for your head.
We don't hear as much about that danger today for several reasons, one
of which is that, unlike the early days of manufacturing, our primary
workpieces aren't power-transmission shafts, as they were in the early
And, of course, there aren't a lot of lathes doing production work
with an operator standing in front of them, and without a protective
We once did a job similar to this. Make a "center rest" out of
plywood and a section of 2 x 4. Mount a drill bit of some sort in your
chuck and slide the "center rest" along the ways and mark the center.
Bore that to match the present diameter of the seat post. Stick the
seat post through the Center rest, clamp the center rest to the ways,
and chuck the last 1/4 - 1/2" in the chuck with the seat post clamp,
if any, hanging out past the center rest. Turn the post to diameter
and cut off the small original diameter section where you had chucked
Depending on what your time is worth it is likely cheaper to just buy
the correct size (at least that is what I ended up doing :-).
[but it's a 12" post}
One out-of-the-box suggestion: turn a tapered steel mandrel that
goes from x inch diameter to x - 0.027". Get a honkin' big hammer
and drive it down the seat tube. Use lubricant, and start at the
narrow end of the mandrel, of course.
I used a piece of 3/4" plywood, cut the shape of the ways on the
edge, then I bolted a piece of 2" angle iron to both sides to ride on
the ways. I then drill one angle iron to except the original tailstock
I put a bit in the chuck and slid the plywood assembly against the
drill to make hole to accept the live center.
It worked. I got it turned down to slide in the tube.
Because of the extra length above the seat post to accommodate the
spring and hardware, the new post puts the seat higher than the original
seat. I need look into the best way to reduce the height. It's out of
simple height adjustments. Might need to cut the spring length.
Thanks all, Mikek