Lathing long narrow objects

[Titanium]

Lately I’ve been trying to make pins for a strap and to do this I need to lathe a bit of metal down to 1.3mm wide and it has to be 20mm long. To do this I place a live centre at the non-chuck end then slowly lathe the rod down. The problem I’m having is the diameter of each end can be up to 0.12mm thinner than the middle. I’m using an Emco Unimat 3 to do the work.

 

Is there a way to get better results or is it a difficult thing to do?

[khunter]

You're probably experiencing flex in the work piece, and without a steady rest on the back side of the work you'll get that. I would try turning shorter sections at a time, it might take longer but the results should be more uniform.

[jdm]

You can buy 1.30mm ready pins

https://m.cousinsuk.com/sku/watch-straps-bracelets-fittings/parallel-tapered-watch-bracelet-pins/parallel-tapered-watch-bracelet-pins/P1209

[teegee]

6 hours ago, Titanium said:

.. each end can be up to 0.12mm thinner than the middle. I’m using an Emco Unimat 3 to do the work.

Such a thin and long piece will definitely flex with any significant tool pressure. You could try with an extremely sharp cutter (so not some carbide insert), or with a very sharp hand graver. Or try to stone/sand the 0.12 mm center error away..

[oldhippy]

Use a fine needle file. That is what I used for making pins. Don’t have too much sticking out of the chuck.

[measuretwice]

There are many ways to come at this.  Easiest is to machine it in sections, like oldhippy suggests, have a little sticking out of the chuck, machine some, pull more out etc.  Sort of a manual Swiss lathe (with a swiss lathe tool stays still and the material advanced out of the chuck).

Does your lathe have collets or just the three jaw?  I don't think too many of those had collets so if its just the three jaw, carefully maintain the same radial position of the material - this will minimize the affect of scroll error as you reset the position.

You can get a less than a perfect finish this way but there is a neat toolmakers trick for that.  take two pieces of wood and glue some fine emery to them - roughing maybe 600 or 1000 grit, then 2000 grit.  Ideally flat little slips of hardwood, but two popsicle sticks might work (better if its harder).  pinch them over the revolving work, abrasive side to the work obviously, and bring to size.  Unlike holding the abrasive cloth by hand, the firm backing gives some control an makes it possible to end up with a reasonable good and smooth cylinder.  Make sure you protect the bed with paper towel, any abrasive paper gives off lots crap you don't want on the ways.  Now if you're ever called upon to make 1mm taper lap you know how lol

[Titanium]

3 hours ago, measuretwice said:

ou can get a less than a perfect finish this way but there is a neat toolmakers trick for that.  take two pieces of wood and glue some fine emery to them - roughing maybe 600 or 1000 grit, then 2000 grit.  Ideally flat little slips of hardwood, but two popsicle sticks might work (better if its harder).  pinch them over the revolving work, abrasive side to the work obviously, and bring to size.  Unlike holding the abrasive cloth by hand, the firm backing gives some control an makes it possible to end up with a reasonable good and smooth cylinder.  Make sure you protect the bed with paper towel, any abrasive paper gives off lots crap you don't want on the ways.  Now if you're ever called upon to make 1mm taper lap you know how lol

This is a good tip. I guess I could put the wood in a vice and that should give me better control.

I have a weird ER chuck for the Unimat that attaches to the spindle but it does not normal ER16 collets properly. I think it's for ESX 16 collet which are apparently ever so slightly different. Today I ordered this collet chuck so I'm looking forward to using that. I'm still trying stuff. I'll report back if I find a good way of doing this.

[Titanium]

Sherline Lathe Follower Rest #1090 seems to have been designed for this. I might be able to adapt one for the Unimat.