Sunday, March 18, 2012

Hemingway Set-Over Centre: Making the 1/2 Centre - Part 2

A little time was spent in the shop before preparing for church (yes, we attend 2 services per week - with my mum & mum-in-law on Saturday for either the Hokkien or Mandarin Service and on Sunday for our English Service).

I finished the arbor with a thread hole to mount the partially completed 1/2 centre and fastened the threaded end of the 1/2 centre in it. This is what I have:

It wobble like no tomorrow. I therefore declared this to be good for the scrap bin.

I do not have another piece of silver steel in my stash bin and thought of using the piece of silver steel meant for the 2 adjustment screws that came with the kit. The 5/8" diameter silver steel rod supplied is slightly longer than 5". Each adjustment screws is only slightly longer than 1". Then it struck me that the extra length is meant to be use to make the arbor... Argghhh... I'll cut a short section of 1.5" to make the 1/2 centre.

The much trusted 3 jaw chuck is now in use.
Facing the end square to prepare to turn slightly under 1.5" length to 0.5" diameter.
The finishes came as a surprise. It was so rough and looks the textual on a diamond file...
I stop work right away, not wanting to carry on till I figure this out.  The silver steel was turned with the HSS tool from Proxxon.  I tried turning with and without oil, spindle speed of 330 rpm and 660 rpm, advancing the tool 0.1mm to 0.4mm radius, feed slow, fast, and with autofeed.  The rough surface remains...

Anyone can provide me with a solution to this and the reason why this occur?  Appreciate any help.

- Posted using BlogPress from my iPhone


GeneK said...

Wong, two things to cover. First the wobble in the collet. How much of the rod was inside the collet? Just a comment about how I was taught on the watch makers lathe. Put the part into the collet and lightly tighten on the part. Run the lathe in reverse and using a piece of wood touch the part until it runs true and then grab the draw bar to tighten the collet and check if it was still running true. Even with the four and three jaw chucks I get everything running true from end to end before the final tightening of the chuck.
Your second problem of the rough finish it appears to be tearing, not cutting. Check the tool for a good sharp well honed cutting edge and that the geometry is correct for the metal you are cutting. I can't see just how the tool is shaped, make sure you have enough back rake to make it shear off the metal not scrape and tear.


Wongster said...


I'll check the 2 things you pointed out in my next session.

On the rough finish, I've no problem when facing. Should I use my carbide insert instead?