Cutting a very small pivot

[bobolink]

I have successfully made several pivots to repivot some damaged ones.  But am having trouble making the smallest so far.  I need to make a .14mm pivot.  Im using blue pivot steel and carbide gravers.  They cut fine in the beginning.  I am chucking the steel in a collet and once it gets cut down to about .18mm it becomes so springy to apply even the slightest cutting pressure snaps it.

I am now trying to not square off the pivot until it gets to the size needed to give it more beef to hold onto then gradually taper back on the steel.

Does anyone have any suggestions on best way to cut a pivot this small?

Thanks,

bob 

[nevenbekriev]

Can You please draw a sketch  with pencil of what You are trying to turn, as I am not sure what I understand from the text. Do You try to turn very long and thin object? What the length is?

[bobolink]

Very simple straight plug to replace a broken pivot. It needs to be  .14mm wide and .90mm long. 

[Neverenoughwatches]

Can you support it from behind ? Or finish the diameter at the tip before turning towards the headstock. 

I think you need more meat that fits into whatever the arbor is as well.

Finish the pivot thicker, do you have jacot to finish the diameter off.

[bobolink]

Yes I have Jacot.  I started last night to size the end and work towards the meat  rather than doing even cut.  Yes the end going into the pivot will be bigger but am still uncomfortable that once in the pivot hole and I work to size the pivot end it will break.  Ouch. But I am thinking to taper it so only the minimum amount needed on the .14 end. 

[nickelsilver]

Just made a staff today, 0.115mm pivots, on the large end for me. Noticed the steel was resisting the cut, touched up my (carbide) graver and got them to 0.12+ no issue, Jacot, done.

 

The grit of the grinding wheel makes a huge difference. I use 14 micron for most stuff (rough out at much higher grit). 7 micron when I'm feeling fancy. If you are sharpening on diamond plates, even the finest grit is "rough", it will cut and you can get to "pre-Jacot" diameter but will it need frequent touch-ups. The rough surface from aggressive grits breaks down quickly When the carbide approaches polished, the edge retention is an (or) order/s of magnitude more than from a rougher finish.

 

I frequently turn pivots to 0.07 to allow 0.01 in the Jacot for a final 0.06mm. I'd there's any resistance to free cutting off to the grinder. If you don't have fancy grinding machines, a lap made from brass (ok), acrylic (ok), or bronze (great) with cheap 3 micron diamond paste will give you a polished face in seconds.

[caseback]

What diameter blue steel are you starting with? 

Edited January 28 by caseback

[nickelsilver]

2 hours ago, caseback said:

What diameter blue steel are you starting with? 

Not sure who you're asking, but when I make anything  it's standard full annealed steel. For a staff I turn everything with a slide rest and leave what will become the pivots a couple hundredths less than the next diameter up and then hand turn the pivots post heat-treat. The deviation in diameter is the length guide. Get them 0.01 oversize, cut the rivet, cut the roller table and hub tapers (also post heat-treat), stake to balance, Jacot, hit the pivot ends in the lathe and boom.

Edited January 28 by nickelsilver

[caseback]

7 hours ago, nickelsilver said:

Not sure who you're asking, but when I make anything  it's standard full annealed steel. For a staff I turn everything with a slide rest and leave what will become the pivots a couple hundredths less than the next diameter up and then hand turn the pivots post heat-treat. The deviation in diameter is the length guide. Get them 0.01 oversize, cut the rivet, cut the roller table and hub tapers (also post heat-treat), stake to balance, Jacot, hit the pivot ends in the lathe and boom.

I was asking the OP. Your response came in while I was typing .

In my limited experience, cutting blued steel with carbide freehand down to 0.12mm is no problem. However, If you start out with a thin wire with too much stickout (and no slide or steady rest), I imagine that it could be difficult.

Edited January 29 by caseback

[nevenbekriev]

I would advice no to turn insert for the pivot hole from blue steel rod but use thin guitar or violin string. This will be 0.2mm. I will show how to thin it slightly tapered to fit the hole. I do it using diamond disk or plate, pin wise and wooden plank. The string piece in pin wise protruding 1cm, supported in a notch on the plank, one hand with the plate grinds it while the other hand rotates the pin wise. This method will not guarantee the insert to become fully round in cross section. That's why I drill bigger hole and insert thicker pivot wire, then turn it to size in the lathe

[Neverenoughwatches]

1 hour ago, nevenbekriev said:

I would advice no to turn insert for the pivot hole from blue steel rod but use thin guitar or violin string. This will be 0.2mm. I will show how to thin it slightly tapered to fit the hole. I do it using diamond disk or plate, pin wise and wooden plank. The string piece in pin wise protruding 1cm, supported in a notch on the plank, one hand with the plate grinds it while the other hand rotates the pin wise. This method will not guarantee the insert to become fully round in cross section. That's why I drill bigger hole and insert thicker pivot wire, then turn it to size in the lathe

whats the idea of not having a uniform pin Nev ?  To grip the hole better ?

[nevenbekriev]

18 hours ago, Neverenoughwatches said:

whats the idea of not having a uniform pin Nev ?  To grip the hole better ?

There is no such idea. This is just hand method that can not guarantee the pin will be uniform.

[Neverenoughwatches]

10 minutes ago, nevenbekriev said:

There is no such idea. This is just hand method that can not guarantee the pin will be uniform.

Ok thanks Nev, i wondered if there was a reason for doing it this way besides not having a lathe with which to turn it. Interesting that you mention a groove in wood, in a watchmakers tool lot I bought was a small 1 inch piece of very hard wood with lots of grooves in in. I've used it a few times for making the brass taper pins for the hairspring stud.

[nevenbekriev]

Yes, this is the way to make tapered pins for all places they are needed in watches and clocks. If the material is soft like brass or soft iron, then fine file is better to use.

[bobolink]

 Thanks everyone.  I was able to cut it on the lathe but leaving a slight taper that I will finish after its installed.  That will give it enough strength for now so it didnt break.

I did find that the gravers had to be soooooo sharp with this small size, that I both switched gravers along the way to be sure, and also rehoned along the way.  They were carbide gravers.  I dont have any attachments for sharpening so only do it by hand.  Except for a new blank that needs alot of grinding then I just use diamond plate on my drill press to get tbe bulk off, then hand grind the rest.

Now lets see if I can get the hole right and get it installed.