Threads "cracking" on flanks?

[pacifica]

Of course artists mix with linseed oil, the absolute best coverage,adherence and opacity of white paint.Do not touch or inhale fumes.

 

[pontiac428]

That's a nice fine thread, looks like a precision tool.

Usually when I get that kind of "orange peeling" on threads, I blame my speed, or my DOC, or my tool grind. It's always a fine line between too much or too little RPM in my mind.

I don't know that I would start slathering lead paste all over my shop. Lead contamination spreads like vermin, and if you have young kids around, expect their IQs to drop before the real toxic avenger side effects start showing. I agree that lead dust works; there are a lot of toxic products that work better than any alternative. Since I just reviewed the toxicology of Tap Magic, I can tell you they've added graphite as a solid lubricant, so you probably don't have to go after a can of slow-acting poison in order to make satisfactory threads.

 

[benmychree]

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

It usually came mixed with linseed oil, when I find some, I pour off any oil on top and replace it with machine oil and mix it up with the lead, so the lead will not dry out and harden in the can with exposure to air. If one bought the artist powder pigment use machine oil to make a thick paste.

That's a nice fine thread, looks like a precision tool.

Usually when I get that kind of "orange peeling" on threads, I blame my speed, or my DOC, or my tool grind. It's always a fine line between too much or too little RPM in my mind.

I don't know that I would start slathering lead paste all over my shop. Lead contamination spreads like vermin, and if you have young kids around, expect their IQs to drop before the real toxic avenger side effects start showing. I agree that lead dust works; there are a lot of toxic products that work better than any alternative. Since I just reviewed the toxicology of Tap Magic, I can tell you they've added graphite as a solid lubricant, so you probably don't have to go after a can of slow-acting poison in order to make satisfactory threads.

I have had lead exposure most of my life, and have managed quite well; I once asked my doctor to test for lead several years ago, and the result was negative; use toxics intelligently and carefully, and wash your hands.

 

[benmychree]

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

I have tried lard oil, and was not impressed with the results, TapMagic is worlds better for cutting oil and does not get rancid and stink like lard oil. I think lard oil was the thing for threading brass pipe back in the day.

 

[mikey]

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.

The tearing is occurring on the leading flank, which suggests this is possibly a tool geometry problem. Assuming you ground your threading tool, what side relief angles did you use? Was the tool M2 steel or did you use a cobalt tool? Was the tool honed well before cutting your threads?

EDIT: Did some thinking about what this could be and wondered what your depths of cut were, especially as you got closer to your finished thread. There is a lot of flank engagement as you get close to your finished pitch diameter and you should be taking very light cuts, in the neighborhood of 0.001-0.002" deep per pass. Too deep a cut can cause rough cuts like that.