MetalworkingFun Forum

Needed to make a 55 x 2 mm nut for a hay rake. How do you measure an internal thread? The shaft wasn't available so I had to make a test shaft that I used the 3 wire method to measure then cut the internal thread using the test plug to check the PD. Is there a beter or easier method? In this case he needed the part, none available in north america and an unknown delivery time from Germany.

Greg,

To do it properly you would need a go-no-go thread plug gauge, but one that size would probably cost you $300 or more. The way you did it will work fine. I usually make my gauges to the upper extreme of the tolerance to ensure that the internal thread ends up large enough.

Tom

Thanks Tom, thought there might be gauges that were thread specific. A pain to machine a test plug for a one of nut but guess thats the business.

C'mon Greg, you know the rules: It didn't happen without pictures!

Oops, he picked it up still warm off the lathe, needed to get back to being a farmer out standing in his field. or something like that.

I recently cut a special thread using this very technique. It was a .900-32 3B thread, so I calculated the pitch diameter of the external thread and made a gauge to the high side of the 3A tolerance, then cut the internal thread using the gauge to size it. Worked like a champ.

Tom

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ones things for sure once you make the gauge you will have it for the next time.

Not me, it went right back into the scrap bin. If I ever need to make another .900-32 thread, I'll just crank out another gauge. It might be nice to have some standard sizes on hand though, maybe even a go-no-go version of them.

Tom

The nut is off making hay but here's the test plug.



As per Tom its back in inventory.