I'll add my ignorant question

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 aluminum. I took it to a machine shop, he laughed and said, "I've already spent more time on this than the part is worth."
Mikek
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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.
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Ed Huntress

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On 1/12/2016 4:10 PM, Ed Huntress wrote:

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.
Thanks, Mikek
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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 at once.

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 digging in.
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The issue is not cutting but keeping it cool so when you cut you don't cut expanded metal or shrunk metal when measuring...
Martin
On 1/12/2016 7:38 PM, Ed Huntress wrote:

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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 it.
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 :-).
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On 01/12/2016 4:10 PM, Ed Huntress wrote: ...

Just heard this afternoon a lathe operator was killed when the bar was turning bent and hit him in the head...spinning things unsupported can do nasties.
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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 days.
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 enclosure.
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I'd grind it myself with fluid. Light touches. That is a tool post grinder.
Martin
On 1/12/2016 9:28 PM, Ed Huntress wrote:

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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 forth.
You'll be done in a few minutes for quick and dirty OD removal.
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On 1/12/2016 4:49 PM, Cydrome Leader wrote:

Yes, it's not the right size tool, but it only cost me 10 lbs of shrimp!

I'll keep that in mind if a wooden steady rest or live center support doesn't work out.
Thanks, Mikek
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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.
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On 12/01/16 21:59, amdx wrote:

If you have a press available you could turn up some sizing dies and push the seat post through those to reduce the diameter.
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On 1/12/2016 7:39 PM, David Billington wrote:

Hmm, it's internally threaded, so maybe not a good idea.
Thanks, Mikek
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On Tuesday, January 12, 2016 at 4:59:13 PM UTC-5, amdx wrote:

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.
Dan
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    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 doing something.
    Good Luck,         DoN.
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amdx wrote:

Chuck up one end, Pull the tail stock and bolt it to a riser block so it is centered. Chunk of 4X4 would likely do the job. Turn to the mid point. Reverse the post and turn the remainder.
--
Steve W.

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On Tuesday, January 12, 2016 at 1:59:13 PM UTC-8, amdx wrote:

[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.
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Why not make the hole larger ? Might be easier to find a reamer that is the size you want. Not a drill.
Martin
On 1/12/2016 3:59 PM, amdx wrote:

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On 1/12/2016 3:59 PM, amdx wrote:

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 clamp. 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
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