Why can one not use their thread gauges to cut thread?

[benmychree]

That is the point I was tying to make as a hobby, resources can be better applied on things you need. A thread mic can be a big outlay for something that may not be used often even thread wires can be pricey. You may not always have a small drill or rod laying around to gauge threads but most everybody has access to some kind of wire, with it and a little imagination you can get the job done. I would rather buy something I'm going to use on a regular basis.

I remember many years ago, a old machinist friend brought me a threading job to and had measured the part to be duplicated with wires; as you mentioned, everyone has access to some kind of wire; in this instance the three wires were baling wire! RIP Bill Hesse.

 

[mcostello]

Yes but when You get tired of messing around holding wires...............

 

[Firestopper]

I'm a simpleton when it comes to cutting threads. I use a nut or bolt as a gauge. It's worked for years. Another thing I do often is use dies for final cuts (if I have the correct size) for smaller threads. I also have a decent assortment of taps. For gunsmithing, I use the counterpart as a gauge for the best fit.

Paco

 

[benmychree]

Most of the time I use a nut to gage the fit of a thread, nearly never do I use a die to fit a thread, except possibly in the case of a very small size; where I want a particularly nice fit, I use thread mikes, all of which I bought fairly cheap on EB.

 

[magicniner]

Thread wires are a little more practical for the home machinist.

Well for those for whom thread wires work better than adequate work holding solutions I say go at it, but I was just pointing out that there are other practical options and that that which was alluded to as being impossible is not ;-)

 

[benmychree]

One important thing is to spread a rag under the area being measured with wires to catch them when they are fumbled, (nearly inevitable) to keep them out of the chip pan and getting lost.

 

[RJSakowski]

If using a wire or three wires to measure the pitch diameter, be aware that any error in the actual diameter is multiplied be three in the pitch diameter calculation. For accurate measurements, it is important that the wire be round to within a tenth or two of a thousandth. To that end, baling wire would probably be a poor choice, at least without pre-qualification.

Secondly, the wire diameter should be between 60% and 90% of the thread pitch. If it's too small the wire won't stand above the crest of the thread and if it's too large, the wire won't be making contact within the flanks of the thread.

 

[RJSakowski]

I gave some thought to using nuts as a gage. In particular, I was concerned that an interference at the top of the threaded piece might give a false indication. In reviewing the situation, if the rod is turned to the major diameter prior to threading, there will be no interference at the crest as an internal thread is cut deeper. There could be interference at the root of the threaded piece but this would only occur if the cutting tool had a larger radius than for the thread being cut.

If using nuts as a thread gage, I would turn the rod to the major diameter and my threading tool would have a radius of 14% or less than the thread pitch. If those conditions are met, the nut will contact the thread properly.

As the threading progresses the test nut would go from not starting to threading with difficulty to threading easily to being noticeably loose. The subjective part is to determine how loose you wish the thread to be. Comparison to another thread will aid in that.

As a final comment, go/no go thread plug and ring gages are commonly used to determine progress and/or suitability when threading.

 

[magicniner]

As a final comment, go/no go thread plug and ring gages are commonly used to determine progress and/or suitability when threading.

And they're often cheaper than you'd expect

 

[benmychree]

If using a wire or three wires to measure the pitch diameter, be aware that any error in the actual diameter is multiplied be three in the pitch diameter calculation. For accurate measurements, it is important that the wire be round to within a tenth or two of a thousandth. To that end, baling wire would probably be a poor choice, at least without pre-qualification.

Secondly, the wire diameter should be between 60% and 90% of the thread pitch. If it's too small the wire won't stand above the crest of the thread and if it's too large, the wire won't be making contact within the flanks of the thread.

As to the diameter of thread wires, that is why they are sold in sets, with a specific pitch for each different set of wires; the set that I use (occasionally) was made at the Mare Island Navy Yard during WW-2 with a purpose made pouch with compartments for each wire set with the pitches marked with an fountain pen.