measuring threads

[wellman]

I work for a pump maufacturer and we do a lot of threading of shaft , tubing and pipe also some custom component parts.
what is the best way to measure threads so that i know each part will go together smoothly without spending a fortune on thread gages. Also, If i make my own thread gages on a engine lathe what kind of hardening if any do i need to try?

 

[BillPSU]

Any thread gage is normally traceable to some national standard and are made to very tight tolerances. I would not recommend making your own thread gages as they are precision ground thread forms. Who ever decided to make the custom parts should have known thread gages were required.

 

[enginebob]

You can use special thread mic's, and the good old mic'ing the 3 wires or pins technique. Internal threads you will need some kind of gage. In the long run the gages will pay for themselves. Way better than scrap parts and wasted time.

 

[funnelguy]

Be careful about relying on solely on thread mics or snap gages on the shop floor without using ring gages on external threads. A defect in the thread root (chipped or worn insert or wheel or wrong insert) will not show up unless functionality is assured by the use of the GO ring gage on external threads.

I've seen an entire lot of centrifugal compressor casing studs that somehow passed QC with thread root defects. The problem wasn't detected until the shop tried to drive the studs into the lower casing half. Not good.

Making your own gages is asking for trouble. We've all done it, I suppose. At some point you'll need to prove that your gage is correct, calibrate it and maintain records. I think I'd sooner order the gage from a specialist. Maybe I'd take the risk on soft, temporary gaging on a rush order IF I was confident of the part, operator, and had experience with the thread form. But I would get REAL gages in-house ASAP.

 

[jbel]

Let's talk $$$ here.

Make your own thread gages -> $

Buy thread gages --------------> $$$

Make parts that gage
correctly on your in-house
gages but will not gage on
a certified standard,
don't realize mistake until
customer calls and says
"whole shipment is scrap and
how could you possibly
make all these parts
wrong?" -------------------------> $$$$$$$$$$$$$$$$$

Penny wise and pound foolish I always say......

 

[EdDanzer]

The method of measuring the thread will be determined by the accuracy required and the actual ability to machine. Thread gauges for large diameter tubing can be machined from steel and work quite successfully if properly handled and checked. I doubt anyone would buy a hardened and ground 12”-4 thread ring gauge to do a few threads per year when a ±.005 tolerance is acceptable. Thread wires work well for small lot quantity parts with medium tolerances, thread mics are great for small diameter threads.
If you are going to make thread gauges, this should be done with proper inserts, and a rigid accurate machine and checked carefully before each use, just as a hardened and ground gauge would be.

 

[unclesyd]

EdDanzer brings up a point about the needed accuracy and sizes.
I have seen a lot the supply houses that have refurbished gauges for what I would consider bargain prices. I never looked into the certifications on same but there must be some guarantee of accuracy. I think this could be one approach for your gauge problems.