How to measure an Acme thread

[DavidB]

HI guys I need some advice on how to measure an Acme thread.

 

Here are the sizes

 

Effective Dia 37.26 - 37.75mm

Minor Dia 33.54 - 34.32mm

MD 40.95 - 40.92

Pitch 4 TPI

 

These sizes are Pre plate sizes.

 

I assume a wire is needed, where can I find some info on the wire diameter I need and the size to measure?

 

Thank in advance Dave

[Radical1]

Hi Dave, you could use the 3 wire method of measuring the pitch dia. there is lots of info on this method including the calculation for the best wire size to use (this depends on the type of thread and pitch) and the correct measurement over the wires in the machinist handbook. A quick look in the book suggests the best wire size is 0.12911 but your size callout (dia.) is metric and your "pitch" is in TPI (inch) the dia. should be converted to inch. After getting this info you can then calculate the proper measurement over three wires. There is some info here about using the one wire method for ACME threads http://www.neme-s.org/Shaper%20Books/Square%20Threads/TMT%20Square%20Thread%20Info.pdf