Threads "cracking" on flanks?

[SmokeWalker]

I’m getting this mysterious cracking on my threads in C37 alloy steel bolts I was single point threading on my manual lathe. Any ideas why? Tools were HSS and cutting fluid was used. Changing the sfm didn’t make much of a difference. The thread looks pretty good until you get close.

 

[benmychree]

It looks more like tearing; was the tool sharp? Was the tool perfectly on center? What cutting fluid was used?

 

[benmychree]

I went on the internet to look at specs for that material, supposedly it is a medium carbon steel, heat treated to Rockwell C 37, which is hard enough to require a cutting speed that is not too high to avoid dulling the cutting tool, but at that hardness, it should not be tearing, and should finish fairly well. If I had a problem like that I might make a mixture of TapMagic with some white lead mixed in.

 

[Janderso]

Can you still buy white lead?

 

[benmychree]

Can you still buy white lead?

No, but I have a several lifetime supply! Want some? It is the very best thing for press fits; the yard superintendent at Kaiser Steel, who had formerly been a machinist and shop superintendent, said " you could shove a telephone pole up a fly's ass if you used white lead"

 

[Janderso]

PM sent.

 

[pacifica]

You can buy lead white as an artist pigment: https://www.naturalpigments.com/lead-white-4-oz-vol.html .

 

[Ed ke6bnl]

You can buy lead white as an artist pigment: https://www.naturalpigments.com/lead-white-4-oz-vol.html .

would you mix that artist pigment with oil or grease to make a paste?

 

[pacifica]

If you're going to use it you should get: -D-lead hand soap- removes heavy metal dusts.

 

[pacifica]

I believe with something like lard-an old machinist favorite, or crisco is readily available . Lard oil: https://www.mcmaster.com/1308K4-1308K4 .