Threading via Machinist Handbook (measuring)

@mickri my 3wire set has a booklet with it. I was doing 2 threads per mm so I just take the whole value (M) and subtract 1.7mm (it was actually something like 1.698) and that number should fall within the allowance of the pitch diameter. I almost want to pop for a thread micrometer, if I can find one that covers a large range and isn't a grand.
@JRaut it does make sense to at least consider the minor diameter last for sure. I have threading down but my technique could use some cleaning up, hence the metrology.
 
Thread micrometers are nice but just like a regular micrometer each thread micrometer only covers 1". You need a 0 - 1, 1- 2, 2- 3, and so on. With the wires there is no limit to the diameter that you can measure. My set of wires also came with an instruction card. The instructions work off of the pitch diameter which you either have to calculate or look up in a table. Using the formula in my old Machinery's Handbook all you need is the major diameter. Both methods will get you to the same place. I just find the old formula easier to use because it gives me the measurement over the wires and that is what I shoot for.

Holding the wires is a pain. I found using rubber bands really helped to keep the wires in place.

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Yeah, that rubber band method looks better than the form block I was using, what a pain.
To clarify, you’re just comparing the number you get from measuring with wire against the books Major diameter? I was taking that number, subtracting the constant from the wires cheat sheet and comparing that to the pitch diameter in the handbook. As long as I was within the allowance I was good (?)
 
What we are both doing will get us to the same result. I have some odd ball threads that I need to cut where there is no table where I can look up the pitch diameter. I would have to calculate the pitch diameter. So it is easier for me to use the major diameter. Both methods get the same measurement over the wires. 24.400 mm. When I am cutting a thread I keep cutting until the micrometer measurement equals the calculated measurement over the wires. I don't do the math to see how the micrometer measurement over the wires compares to the major diameter. If you really want to know if your are within the min/max pitch diameter range I would do the calculations at the min and max diameters. Using your numbers that range would be 24.231 mm to 24.400 mm based on the min/max numbers in the table you posted.

I invariably overshoot my target diameters. To try to avoid this I have started doing two things. One thing is that when I get within 0.010 to 0.015 of my target diameter this is where I take my cleanup/spring cuts. Then say I am still 0.008 over diameter for example. I now take two 0.004 cuts and just two 0.004 cuts. I have found that by doing this I am spot on to 0.0005 larger than my target diameter. The other thing I am doing is instead of taking my cleanup/spring cuts at the last position of the tool bit I back the tool bit out 0.005 to 0.010 for the cleanup cuts.
 
If you use full profile threading inserts, each insert is only for one tpi(for example 13 UN). With this type of inserts it is hard to cut too deep of a thread. the downside is you need a separate insert for each TPI.
 
mickri said:
Thread micrometers are nice but just like a regular micrometer each thread micrometer only covers 1". You need a 0 - 1, 1- 2, 2- 3, and so on. With the wires there is no limit to the diameter that you can measure.
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Just guessing here but a 0-1" and 1-2" thread mic will cover maybe 99.9% of the threads most of us cut. Above 2", just use your wires.

Thread mics are faster, quite accurate enough for a hobby shop and are direct reading so no calculations to do or mess up. Plus, you spend zero time looking for the wire you dropped in the chip pan or that rolled under the lathe.

Nowadays, import thread mics are so cheap and come with changeable anvils to cover a wide range of threads. Shars sells some for a decent price.
 
mickri said:
I have been trying to use the 3 wire method too. My 1915 Machinery's Handbook gives formulas for metric, imperial and whitworth threads. Simple to use because it gives you the micrometer measurement over the wires. The formula for metric threads and imperial threads is the same because they are both 60 degree threads. The formula is M = D- 1.5155P +( 3 W). M is the measurement over the wires. D is the outside diameter of the screw in inches ( major diameter). P is the pitch of the thread in inches. For metric threads you have to convert the metric diameter and pitch to inches. W is the diameter of the wires. Plugging your numbers in M = .9449 - 1.5155 * .0787 + (3 * .045). M= .9606 or 24.4000 mm. This is the measurement over the wires.
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Finally found someone with an older version than mine.
My copy of M.H. is a 6th edition, 1924.
 
Man...I respect the old/vintage tools....but guys, a lot has been invented and changed since the 1920's! :D
Seriously though, I would dig having an old piece of history like that.
 
mikey said:
Just guessing here but a 0-1" and 1-2" thread mic will cover maybe 99.9% of the threads most of us cut. Above 2", just use your wires.

Thread mics are faster, quite accurate enough for a hobby shop and are direct reading so no calculations to do or mess up. Plus, you spend zero time looking for the wire you dropped in the chip pan or that rolled under the lathe.

Nowadays, import thread mics are so cheap and come with changeable anvils to cover a wide range of threads. Shars sells some for a decent price.
Click to expand...
For sure, after trying to do it by the book, I REALLY want a thread mic. Wires are so frustrating. I have no idea how long I fiddled with those to get a solid, repeat reading
 
Because I do everything manually I specifically wanted an older version of the Machinery Handbook. Those guys were just as smart as today's machinists. They just didn't have all of the newfangled equipment. I have do things like they did. My copy is a pdf. I would like to have a hardcover because I could keep it out in the shop rather than having to go back and forth to look something up on the computer.
 
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