Measuring an internal thread
#1
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.
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Greg
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#2
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
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#3
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.
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Greg
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#4
C'mon Greg, you know the rules: It didn't happen without pictures!
Hunting American dentists since 2015.
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#5
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.
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Greg
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#6
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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#7

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#8
ones things for sure once you make the gauge you will have it for the next time.
dallen, proud to be a member of MetalworkingFun Forum since Apr 2012.

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#9
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
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#10
The nut is off making hay but here's the test plug.

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As per Tom its back in inventory.
Free advice is worth exactly what you payed for it.
Greg
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