Thread Wires.

I am surprised this many people use thread wires in the home workshop. Why? Is the conventional thread depth calculation plus a bit of "try and fit" at the final stages not precise enough for some types of home shop work? Or is it simply for the joy of knowing that it's "spot on"?

As I see it, they are only useful for situations where good thread engagement is required but the two interacting parts cannot easily be test-fitted with each other.

I know not! Plenty of examples on here of people chasing 2/10 of a thou when 2 thou or sometimes even 12 thou would be perfectly acceptable. I imagine there must be a lot of shadow graphs tucked away in strictly temperature controlled garden sheds and the calibration bills for measuring equipment must be horrendous.

Paul.

Even then, I'll usually make a "test bung" and turn the thread to fit that. EG, if turning a chuck backing plate, make a male threaded plug that fits one of the existing chucks nicely, then screwcut the new backing plate until the threaded plug is a nice fit.

There is usually ‘more than one way to skin a cat’, but if one already have the wires, why not use them? Making plugs regularly for several one-off jobs may not be as efficient as measuring with wires, for those that do more than the occasional hobby job.

In my limited experience, backplates are one item that definitely does not need a really tight fitting thread, it may even hinder the registration faces contacting squarely, if too tight. I would sell mine, as I simply haven’t used them and, like you, would make a threaded plug for the few and far between jobs that required that level of precision.

Agreed, NDIY. I was thinking more along the lines of those without a large and comprehensive set of thread wires. To use them properly you really need different sizes for different pitches, and different thread angles. But if you have them, yes might as well use them. Providing the other thread (eg chuck body etc) was made to the correct standard and has not worn over the years.

As you say, chuck is probably not the best example as a looser than normal fit is actually a good thing, allowing location on the register. Just front of mind at the moment as been helping a mate do one for his rather large lathe. He is of the "tighter is better" school, but hey it's his lathe - and will be him wrestling a 16" diameter screwed-on chuck on and off the spindle at every change!

I had a male thread to make for a friend when done I will post it, I’ve not got the mating part to use as a test fit , so I cut it to tolerane I’ve done my bit, that’s where the wires come in, I understand what every one else is saying, but why have something if your not sure how to use it, I had a slimier response when I asked about metric threading on my metric lathe, I was told don’t use the thread dial as you don’t need to just reverse it, my thoughts were and still are if its made for the lathe I want to use it, now I figured it out it’s great.

Alan.

When i was in the training school at RollsRoyce we were taught to do and check everything the proper and accepted way, that included thread cutting etc and the use of wires and micrometer to check them, in later years I realised that it was not always needed to use wires but in my opinion it is always best to know how to use them and not need them than to need them and not know how to use them.

.

Wise words of the week award for you, Bill

MichaelG.

What if you only have one piece of material to make the part, and the female thread is firmly attached to an aeroplane 3 miles away? Or the matching part is too awkward to fit onto the lathe?

Surely the whole point of owning a thread cutting lathe is so you can make parts that don't use readily available threads? I wouldn't dream of screwcutting an M12 thread for instance, but an M24x1(Russian fuel system) is a totally different matter!

I always use thread wires for threads and worms simply because it removes the 'cut and try' method, I know what I trying to achieve, so measure it, make a precise adjustment and its right - job done.

The only benefit of 'cut and try' method is a scrap bin full of nearly right bits!

Just had a look on the Arc Eurotrade site and see for about 10 quid you can buy a very comprehensive set of thread wires that cover metric and US threads from 48tpi/.5mm to 3tpi/6mm. Plus a handy little holder for the pair of wires on t'other side.

At that price, yes why not use them/play around with them? Far cry from the old days when such equipment was super exotic and expensive. I might have to get me a set.

EDIT, actually not just the old days. There's a set of Mitutoyo thread wires on eBay right now for A$950! Yikes.

Edited By Hopper on 06/12/2018 05:38:50

If you are into thread wires, what do you do about thread radius and truncations etc ? For small threads, I tend to use thread chasers if I have the right size but of course, even with these you still need to measure the correct 'diameter'.
BobH