My attempt at screw jacks and ACME...

[metalmagpie]

What is an accurate way to measure the width of the blunt end you need to grind on the end for a given thread?

The right way is with an optical comparator.

[Jaakko Fagerlund]

You can get pretty much good measurement with a micrometer and a lttle patience, but with trapezoidal thread it doesn't matter if the tip is a little bit narrower/longer, it just makes more extra space at (or outside) the threads major diameter.

What I have done external trapezoidal threads, I made a HSS bit that was narrower than what was needed and just moved the cutter with the top slide to get the thread width correct.

[T.Hoffman]

Any chance of a few shots of the internal threading bit?

Here's what I used for internal and external. I ground the 3/16" internal bit from a hss blank, and then used my dremel cutoff wheel to chop the length so it fit nicely in the bar with nothing sticking out the back.
The very tip of the internal bit may be hard to see because it still had some residuals left on there from the process.
The larger boring bar on the bottom is the one that proved to be too big in my bored hole for doing this job.

[RussZHC]

Thanks, now this

The right way is with an optical comparator.

makes a ton of sense.

Attempting single point threading is on this spring/summers list of things to do and I am still trying to wrap my head around grinding such small/fine surfaces...start large I guess and work my way down

[loply]

Outstanding.

Had on my list for a while a 2-stage (telescoping) set of these to make... Just like yours but where the thing screws into a bigger one.

I struggle to make work that neat though, and would probably end up giving up if I tried to cut an acme!

What kind of knurling tool did you use to allow you to knurl such size stock? Been looking out for a larger one for a while, mine limits me to about 18mm dia.

[T.Hoffman]

I struggle to make work that neat though, and would probably end up giving up if I tried to cut an acme!

What kind of knurling tool did you use to allow you to knurl such size stock? Been looking out for a larger one for a while, mine limits me to about 18mm dia.

Start out on something easy to cut and give it a try a few times before going for the real thing. You'll learn a lot, and once you get the process down it isn't bad. Don't expect perfection right away, but learn from it as you go. You'll never cut an acme thread unless you try to cut an acme thread....

My knurling tool is a homemade scissors type, made by an older machinists and given to me after he made an improved version. I think I could do up to 3" diameter, but never checked for sure.