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Paul

Wouldn't a proper thread gauge be easier to use, **LINK** most decent tap/die sets seem to come with them.

Hi Lofty
Sorry mate Those gauges measure the pitch ie TPI you can get whit , metric . ba etc
Nobby

A bit of plasticine or blue tack helps with wires. unless you have 3 hands.

Page 12 here is a good guide to the method and the various errors that can affect the result.

**LINK**

Regards
John

Martin Cleeve in "Screwcutting in the Lathe" seems to suggest that for "production" runs you'd probably use gauges, but for "special" ie non standard threads or short runs then wiring might be used as the cost of gauges would be excessive. Also you can use wiring for QA/QC as the tools used for it are easily checked against standards, whereas gauges could be more difficult to check – how do you check for wear on an internal thread? Probably the main use in the "home" shop would be if you were copying the spindle nose thread of a lathe for example, for making a dummy spindle either as a gauge or as a means to mount a chuck or faceplate other than on the lathe spindle, and you want to ensure an accurate and faithful reproduction. The usual way of using a faceplate or chuck as a gauge can have problems if the said faceplate or chuck thread isn't exactly correct. You might just wind up with a dummy that fits the particular faceplate but not others.

Martin also points out that without a go/no-go gauge of some sort, wiring is really the only way of checking the thread being cut while it is still in the lathe and thus still machinable.

Keith

Just as a point of interest, there was a device sold on ebay recently (item no. 121360098886). To me it looks like a home-brew job but it should make holding the wires in place less of a problem.

Tony.

Hi Neil,

What a sheltered life you must lead. Although in fairness I lean more to the John Stephenson end of the spectrum than some here.

Three wires are a nightmare and if parallels are not available then wrapping copper wire of correct diameter around the thread and measuring across that is far easier.

ATB

chriStephens

Rubber band/s.

I do wonder about this discussion ,lots of chat about 3 wire measurement,but no mention about thread angles, ,unless the thread has a perfect angle a three wire measurement is not much use , The work would need to be machined with top class carbide inserts ,or finished with a thread chaser both of which must be set at exactly 90 dergrees to the work axis, HSS tools would need to be checked with a shadow graph. All of which is out of the realm of the model engineer. I would expect three wire or improved variants to be used when checking precision ground threads, ie threaded lathe spindles, checking or calibrating gauges,and the three wire would only be a part on the check. the vast majority of threads produced industrially are checked with go/no go gauges, Three wire checking was always part of the technical training curriculum ,and the use of trigonometry, the vast majority of engineers who learnt about it never heard about it again,