Die size

[Howdya do that]

Some one please slap me if I am missing obvious:doh:

I have a steel rod the I wish to thread and put a nut on, how do I work out what size would be best?

I found heaps of charts that tell you what size hole for a certain tap but not what rod size for a certain die.

[pipeclay]

The size of the die in general terms will be the same as the diameter of the piece you want to thread,1/4 rod = 1/4 die,6mm rod = 6mm tap.
You will have a difference if you wish to do pipe threads though,die size does not equal rod size.

[malb]

1/4 rod = 1/4 die,6mm rod = 6mm tap.


For 6mm tap read 6mm die.

If you can refer to a thread chart for the drill size, you may find that the chart lists the major diameter of the thread. This is the overall diameter of the stock used to cut the thread, and the measured diameter of the stock you want to thread.

This works because when you cut the thread with the die, the die is removing material to form the thread, so the root or minor (deepest part of the thread) diameter is smaller than the overall diameter.

When cutting an internal thread (nut etc) the drilled hole through the material needs to be at the root diameter, and the tap then cuts the thread into the wall of the hole.

Exceptions are:

Pipe Threads - pipes are often listed by the internal diameter rather than overall diameter e.g. 1/2 inch pipe is 1/2 inch bore and the overal diameter is closer to 0.825 in. If you know the pipe size, there is a die with a matching label to suit, i.e. use a 1/2 in pipe die to thread 1/2 in pipe.

Oddball threads - BA (4BA) and American numbered threads (0-80, 2-56, etc) are based on different rules.

The pitch of 0BA is 1 mm and the diameter is 6mm. The pitch of each higher numbered thread is obtained by multiplying the pitch of the lower number by 0.9 so K-BA has a pitch of p = 0.9K. The major diameter is given by 6p1.2 and the spanner jaw size as 1.75 times the major diameter.
The angle of the thread is 47.5 degrees which is different from that used by other threads (55 or 60 degrees) so BA fasteners are never interchangeable with Whitworth/Metric ones even when the pitch and diameter seem similar (except 0BA - 6 mm) .Thread range is 0 BA to 16 BA, but normally only even numbers are used.

American Unified threads are based American wire guage sizes. The first number (smallest) refers to the AWG diameter of the fastener, and the second number refers to the pitch of the thread in Threads Per Inch (TPI). Sizes range from 0 (.0600 in dia) to 12 (0.2160 in dia) (not all commonly available). From 1/4 in diameter they use the fractional size for designation e.g. 1/4-20 is 1/4 inch diameter 20 TPI.

Hope this helps a little

[joe greiner]

When cutting an internal thread (nut etc) the drilled hole through the material needs to be at the root diameter, and the tap then cuts the thread into the wall of the hole.



Strictly speaking, this applies where the male and female materials are of substantially different strengths; e,g. steel bolt/screw in plastic or aluminium. Where the two materials are near identical, a reduced engagement is advisable. This is why nominal tap drills are somewhat larger than the root diameter. Machinery's Handbook, 24th edition, p. 1699, has a lengthy discussion on this. The gist of it is that about 60-75 percent engagement is satisfactory. And when the length of engagement is more than 1.5 times the nominal diameter, even 50 percent engagement can be sufficient. Adherence to such guidelines usually reduces the likelihood of broken taps, although specifications for a particular project may require more engagement and should be followed.

Joe