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Someone check my thread measuring math

BoydAllen

Simplifying it down as far as I can, for an 18 pitch thread to get pitch diameter from over the wires, I subtract .1441
 
.04789 is the number to subtract from your measure over the wires to get the pitch for 18 threads per inch. And the wire size is .032
 
Be very careful using thread dimensions found on the internet!!! I against instructions drilled an older very nice Remington 22 target rifle for a scope. I bought a drill and tap according to the numbers on a machining website that sold taps and dies. The number drill was 2 digits too big and the tap barely touched the sides of the hole. The very helpful tech guy at EGW sent me a set of # 8 crews and told me the holes in the base were already big enough for the # 8 screws and all worked out in the end. But it could have been disaster. Trust but verify!
 
I print out the specs, put them in a plastic sleeve then into a 3 ring binder along with drawings for various actions. Several manufacturers have their own binder.
 
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If I'm duplicating a thread, and don't have a receiver to check it on, I don't even worry about actual PD once I have a thread to measure. I can simply measure in the thread with a caliper and duplicate that measurement on the new barrel. This providing I trust the thread on the old barrel. If the thread measures the same, it is the same. Caveats: You have to be sure to stay in the same thread and you have to use the same caliper. The knife edges will vary on different instruments. If starting from scratch, you have to use the wires to establish true PD. Once you have a good sample though, the caliper method will work fine. It won't give you actual PD, but it will give you a valid comparison dimension. WH
 
Referring back to my original post, it was based on bad information from a search. The second time I looked, I got a number that corresponded to Cloudrepair's. AI can bring us mistakes that sound reasonable if we do not know better. Thanks to everyone for the help.
 
Will Henry said:
If I'm duplicating a thread, and don't have a receiver to check it on, I don't even worry about actual PD once I have a thread to measure. I can simply measure in the thread with a caliper and duplicate that measurement on the new barrel. This providing I trust the thread on the old barrel. If the thread measures the same, it is the same. Caveats: You have to be sure to stay in the same thread and you have to use the same caliper. The knife edges will vary on different instruments. If starting from scratch, you have to use the wires to establish true PD. Once you have a good sample though, the caliper method will work fine. It won't give you actual PD, but it will give you a valid comparison dimension. WH
Click to expand...
A caveat..or warning is that if the old thread and new thread have any variance in tool cutter angle when threaded, it can cause erroneous readings by that method. I agree that it is generally fine but when dealing with finer threads is where it'll be more consequential, as a little can go a long way with finer threads.
 
gunsandgunsmithing said:
A caveat..or warning is that if the old thread and new thread have any variance in tool cutter angle when threaded, it can cause erroneous readings by that method. I agree that it is generally fine but when dealing with finer threads is where it'll be more consequential, as a little can go a long way with finer threads.
Click to expand...
As in almost there to "WHAT THE HELL HAPPENED"
 
gunsandgunsmithing said:
A caveat..or warning is that if the old thread and new thread have any variance in tool cutter angle when threaded, it can cause erroneous readings by that method. I agree that it is generally fine but when dealing with finer threads is where it'll be more consequential, as a little can go a long way with finer threads.
Click to expand...
This is true when using wires as well. If the angles are wrong, the measurement will also be wrong. I'm assuming one knows how to set his cutter angle etc. By the way, I sometimes use a threading insert but I'm just as happy grinding a steel cutter. In fact, I find I can get a better finish with a steel cutter. WH
 
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