Making Pivots

[david]

This is a video showing the pivot turned to .01mm over the finished diameter and "burnished" down to the final .1mm diameter. This is not the only process that is used  to get the pivot to the final diameter, but removing almost all of the material in the turning operation will help maintain the concentricity of the staff. Tempering  steel to a spring hardness will help ensure that the cutter pressure has less chance of pushing the pivot out of concentricity due to pressure from the cutting tool. This is because the pivot has the ability to spring back after the cutter pressure is removed. A higher yield strength gives the pivot a higher resistance to strain.  An extremely sharp tool and a light touch will reduce  cutting pressure on the pivot but the steel will have less ability to spring back to its original concentric position.

There is also the element of microscopic warping due to heat treatment after the part is turned. If the heat treatment and normalization is done before  turning, the warpage  of the metal will be negabile in the final product.

In the end everyone has a different perspective on this subject but this is my perspective based on my background and  the many failures I had when I was learning how to do this. 

david

Here is the video:

https://www.youtube.com/watch?v=mkGygB7BMsQ

Edited March 4, 2017 by david

[szbalogh]

14 hours ago, david said:

https://www.youtube.com/watch?v=mkGygB7BMsQ

Thank You David!

Completely forgot this video. Just prepared a steel piece yesterday. Hardened to glass hardness but did not anneal it. Will do it today before start turning. I will turn it in a collet and grind between centers. 

I am curious how things will turn out

[adiorio110]

14 hours ago, david said:

This is a video showing the pivot turned to .01mm over the finished diameter and "burnished" down to the final .1mm diameter. This is not the only process that is used  to get the pivot to the final diameter, but removing almost all of the material in the turning operation will help maintain the concentricity of the staff. Tempering  steel to a spring hardness will help ensure that the cutter pressure has less chance of pushing the pivot out of concentricity due to pressure from the cutting tool. This is because the pivot has the ability to spring back after the cutter pressure is removed. A higher yield strength gives the pivot a higher resistance to strain.  An extremely sharp tool and a light touch will reduce  cutting pressure on the pivot but the steel will have less ability to spring back to its original concentric position.

There is also the element of microscopic warping due to heat treatment after the part is turned. If the heat treatment and normalization is done before  turning, the warpage  of the metal will be negabile in the final product.

In the end everyone has a different perspective on this subject but this is my perspective based on my background and  the many failures I had when I was learning how to do this. 

david

Here is the video:

https://www.youtube.com/watch?v=mkGygB7BMsQ

Thank you ..Video explains a lot

Anthony

[szbalogh]

What is YOur opinion? 

[szbalogh]

Well, the my mistake, started cutting the left pivot before finishing the balance rest. Then the staff was braking from the collet before finishing the left side. It was a good practice

But the other pivot was turned to 0.14mm. Here a 0.2mm drill is put next to it as reference.

[ppod]

I realize this is an old thread but it comes up as one of the top results in some of my searches on the topic.  So I just wanted to say that, although I am a complete beginner in using a lathe of any kind, I've been able to make pivots on the order of 0.1 mm on a Sherline with no problem.  As far as I can tell, at this tiny scale, any steel can be cut on the Sherline, it's just a matter of having the right cutters (e.g. carbide).

I think my choice of materials and my technique is all wrong, so I am not in a position to recommend anything specific.  But I wanted to mention that very cheap diamond disks (something on the order of $3 on AliExpress, grits go up to 3000, in my case mounted on a Foredom M.BL with a custom adapter) work well for grinding the tiny carbide tools that I've been making out of 1 mm carbide rod.

I also wanted to mention that I've had miserable time with Sherline-made WW collets -- maybe (probably) I am not doing something right but (even if so) I feel increasingly confident in saying that they are unusable expensive garbage.  But I've been quite happy with the lathe itself.