thread size

[blockmanjohn]

Hi, When using a die, say 3/16 24, should the stock size be exactly 3/16 or a little smaller? I'm asking this because I have been threading some 3/16 x 24 on 3/16 tool steel and it is so tight that it is almost impossible to keep the stock from spinning in my lathe's 3 jaw chuck. I have been taking off about .005 and it becomes just doable. Is it normal to have to turn down the stock to a bit below the thread size, or am I missing some thing? Thanks, John.

 

[dnalot]

Hi

Most thread dies are only intended for chasing an existing thread. I'm not very good and cutting a thread on the lathe but I can get close. That's when I drag out my threading die and chase the thread to its final form.

Mark T

 

[GailInNM]

I will be fine to take off 0.005 from the major diameter. The ANSI thread specification for 3/16-24 shows it to be a NS (National Special) so it does not show up on a lot of thread charts, but the 0.1875 diameter of your stock is the absolute max size for that thread.

a quick calculation shows that a major diameter of 0.181 would be least diameter that would fit in the ANSI specification for 2a or 3A class of threads.

In the US, 10-24 threads are commonly used on 3/16 stock. It's major diameter is 0.190 and the 0.1875 diameter falls into the upper end of the major diameter specification for it. If you are making the mating part also you might consider using the more common 10-24 thread.

If your heart is set on the 3/16 24 thread and you happen to have a 10-24 die, you can also thread with the 10-24 die first and then follow with the 3/16 24 die and it will only have a few thou to take off.
Gail in NM

 

[blockmanjohn]

Thanks for the great information. I only wish that I had posted this before I started making the parts. From now on it will be 10- 24 on the 3/16 rod. Thanks, John.

 

[Wizard69]

Thanks for the great information. I only wish that I had posted this before I started making the parts. From now on it will be 10- 24 on the 3/16 rod. Thanks, John.

This is a good time to suggest getting a handbook of some sort. You also download the standards that float about the net. The standards have a military document number that escapes me at this moment. Idiot that i am i spilt Come Zero on my laptop where that stuff is stored so i cant help you with precise information.

In any event there are a number of issues to consider including the class of fit, the roundness of the material and its hardness. In any case it often makes life easier to machine a lead in taper to get the tap started. Also mic ip the shaft before starting to assure yourself, stock an oftentxz