Screw Thread Measurement Utility

The three wire method gives very accurate figures for the true size of screw threads by measuring from the flanks of the V rather than from the crest of the threads. As the crest are normally truncated, measuring across them gives a false reading. The problem with the three-wire approach is the complex trigniometry involved! We are please to bring subscribers a utility that saves you all the headaches, allowing you to input just a few parameters and giving a direct readout.

Pete Worden has produced the program to assist in the measurement of screw threads by the 'three wire method' of placing three wires of the correct size across the thread to be measured, two on one side and one on the other, in the 'V' of the thread and measuring across the wires with a micrometer.

www.model-engineer.co.uk/news/article/screw-thread-measurement-utility

Neil

Windows Subscribers only

MichaelG.

Vista gives this error:

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Paul

Why Do I Have OCX Errors?
OCX / ActiveX / Tabctl32.ocx errors generally occur because your web browser or program  attempts to load a corrupt or missing ActiveX control. Also, these problems may occur if some ActiveX-related subkeys are missing from the Windows registry.

Edited By Oompa Lumpa on 19/06/2014 03:02:07

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

.

Lofty,

That doesn't do the same job

The three-wire technique is for measuring the diameter of the thread, not for checking the pitch. ... See here.

MichaelG.

Edited By Michael Gilligan on 19/06/2014 08:03:34

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

If you buy a thread wire measuring kit with accurate wires, most quality sets come with a chart and a formula for working out the correct wire size for the pitch of the thread and thread angle.

If you have an engineers hand book or access to a standards book, there you will find the effective thread sizes that are used , so you can make the correct class of thread required.

But recently I purchased a thread mic that has different anvils, and the spindle does not rotate. The down side is the cost of the anvils. But worth it to me from a time saving point of view. You still need to know the effective thread diameter and have some form of reference for zero when the mic is larger than a zero to what ever.

I wonder how I managed to put up with wires all these years.

Neil

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

Ahh, many thanks for the 'heads up' I had a chat with our calibration people today and they have used the method in checking go-no go thread gauges.

Seems a bit excessive for normal workshop use, what sort of applications would use it?

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

Or, you can buy Marlco thread measuring parallels which are so much easier to use than wires, but regrettably at a considerable cost .

chriStephens

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.

Surely measuring a thread is something most of us will need to do only rarely, in which case the 3-wire solution is cheap and effective?

Neil

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

?

If I was using the three wires I'd either do it by winding as you suggest, or if it was too stiff to wind, I'd just use a bit of sellotape and card to hold the three wires together at their far end.

Neil

Rubber band/s.

Hi,

A bit of sticky grease will hold the 3 wires with no problem.

Tony

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,

Nigel,

I disagree, if you are contemplating using the 3 wire method of screw measurement there is plenty of information freely available on the net. You do not need first class carbide inserts to make this viable but of course it makes it easier. With a piece of HSS, off hand grinder & thread gauge plus patience you can produce a perfectly satisfactory screw cutting tool.

Any type of screw cutting needs careful setting up like all metal cutting procedures, I’m afraid that is what engineering is all about.

Finally, yes I was taught all this “stuff” as an apprentice and used 3 wires regularly to check threads when a gauge was unavailable or uneconomic to use, as for trigonometry I still use it on a regular basis.

Tony