Double Lead 12-28 Thread Question

[mwebster51]

I was considering making some 12-28 double start/lead threads on a rod. I see sources for double start taps, but am having trouble finding a "double start" die. I assumed I would need a "double start" die for the "double start" thread. Is that not the case? Does a single start die work with a double start tap?
I suppose another way to pose my question is: Can one buy a 12-28 double start die?

 

[MrWhoopee]

I've never heard of a double-start die. That doesn't mean they don't exist, I'd never heard of a double-start tap either. 12-28 is pretty uncommon to begin with, double-start would make it "doubly" so. You will probably have to single-point it on a lathe. Good learning experience.

 

[mmcmdl]

Does a single start die work with a double start tap?

No . Completely different animals .

 

[mwebster51]

I am having trouble finding any double-start dies no matter the size. I see the taps i.e. https://www.icscuttingtools.com/catalog/page_206A.pdf . I don't have a metal lathe. My background is woodworking. I restore old hand planes and I often run into uncommon threads. this just the latest.

 

[mwebster51]

No . Completely different animals .

That was my thought, but I can't seem to find available (not custom made) purchasable double start dies. Seems if sellers sell the taps they would likely sell matching dies but..... I thought I was missing something...

 

[RJSakowski]

I was considering making some 12-28 double start/lead threads on a rod. I see sources for double start taps, but am having trouble finding a "double start" die. I assumed I would need a "double start" die for the "double start" thread. Is that not the case? Does a single start die work with a double start tap?
I suppose another way to pose my question is: Can one buy a 12-28 double start die?

A double start thread requires a double start tap and die. The thread depth of the double start differs from that of a single start so even though you could in theory cut a double start thread by clocking the tap or die 180º out of phase witha second thread, the thread geometry would be wrong and unusable.

 

[mwebster51]

A double start thread requires a double start tap and die. The thread depth of the double start differs from that of a single start so even though you could in theory cut a double start thread by clocking the tap or die 180º out of phase witha second thread, the thread geometry would be wrong and unusable.

 

[RJSakowski]

Presumably, taps are made because there are instances where a tapped hole can't be cut on a lathe ot with a thread mill. However, there are fvfew instances where a rod can't be cut on a lathe by single pointing; hence much reduced need for a die.

 

[Janderso]

That’s a very fine thread for a double start/lead imho

 

[mwebster51]

Presumably, taps are made because there are instances where a tapped hole can't be cut on a lathe ot with a thread mill. However, there are fvfew instances where a rod can't be cut on a lathe by single pointing; hence much reduced need for a die.

Guess that makes sense. Thanks