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I have a small job that requires threads be cut on the OD of a round rod. I have looked all around for a chart that indicates the outside diameter a rod should be when using a die to cut threads. Something along the lines of a tap drill chart, but for dies? Any takers?

TIA - Ryan

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The same size as the hole they are going into.

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The diameter of the rod should be the nominal dimension of the thread. So if you wanted to cut 1/4 x 20 threads you would start with a 1/4" rod. In actual practice the diameter of the rod should be a few thousandths of an inch smaller than the nominal dimension.

What size threads do you need to cut?

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Thanks Roger Shoaf, that makes sense. I need to make it 5/16 x 32. Sounds like that might workout because the diameter of the rod is .311 right now.

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Roger Martin wrote: The same size as the hole they are going into. ^^^^^^^^^^ I believe that dies are sized so that they will cut proper threads on rod whose OD is the nominal thread size. ie, if you are threading 1/4" rod, and use a 1/4-20 or 1/4-28 die, you will get a proper thread.

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If the top of the thread is slightly truncated because the diameter is a little less than the nominal diameter, the strength is almost the same and the effort to cut the threads is greatly reduced. The Machinery Handbook has tables with dimensions for various classes of threads.

Dan

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Another point is, it's a lot easier to avoid drunken threads from a die, if the stock is turned way undersized for a length equal to about one diameter or so. This allows the die to start cutting true, and in most cases the first bit of undersized stock can be trimmed off afterwards.

Jim

================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ==================================================

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And if you're wondering how to find out them wee diameters with numbered machine screws, a number 0 is .060" diameter, and every number is .013" more.

Regards,

Robin

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That should work OK, just make sure there is a lead on the end of the rod and use cutting oil. Stop and reverse to break the chips every 1/2 turn. Be sure to start the threads using the large side of the die.

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The bolt or rod size for threading is given by the formula:

nominal diameter - (0.216/pitch)

Where: nominal diameter is the stated diameter expressed as a decimal, such as 1/4 is 0.250, etc. Pitch is the number of threads per inch.; for example an 18 pitch would be 1/18 or 0.056, a 20 pitch would be 1/20 or 0.05, etc.

For a worked out example, consider the rod or bolt size to thread 3/8 - 24. The bolt should be:

0.375 - (0.216 / 24) this equals 0.366. For a 1/4 - 20 thread the bolt should be: 0.250 - (0.216/20) which equals 0.239.
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Does that mean a 00 is 0.06060, and a 000 would be 0.0606060?

:)

Jim

================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ==================================================

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Nope. Consider 00 as -1 and 000 as -2.

It never ceases to amaze me how frightened a lot of people are of negative numbers. My youngest son's grade 6 teacher thought numbers less than zero were "imposible". The UTM coordinate system, while much more convenient for most things than Lat/Lon, puts a false reference of

500,000 in the middle of a zone to avoid dealing with minus signs. Accountants somehow figure placing a number in parentheses makes it easier to understand than preceding it with a minus sign. Bah!!

Ted

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According to my late father, (an accountant) this was much easer to spot on a ledger page than a minus sign.

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Red ink?

Jim

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