Screw cutting an internal Acme thread.

Struggling to find time to edit videos - this job was done in December '22 (hence the long sleeves & background noise from a space heater) & I can't remember exactly what it was for! The original brass block was completely worn out & the screw was pretty worn also so I tried to just make the new block(s) to suit the old screw.
The blocks were machined to size & drilled in the centre in a milling machine, before being held in a four jaw chuck on our Colchester Triumph 2000 lathe for threading using the Ainjest rapid screw cutting attachment.

[GardenTractorBoy]

This was an interesting job, I enjoy watching projects like this. Thanks

[chrisstephens]

When cutting trapezoidal threads I could never decide whether to grind the tool to perfect dimensions and keep cutting deeper till the thread fits or grind the tool narrower, go to spec depth and then lengthen the cut, decisions decisions 🤔
I did design a special jig to grind the perfect angles for trapezoidal tools that could be used either on my surface grinder or using a cup wheel on the mill, perfect results every time, hopefully😂😂😂😂
If all goes according to plans it will be on the SMEE stand at the Midlands show next month, along with a 60 degree threading tool version.

[oggpete]

Nice job and thanks for the interesting videos.
Bearing in mind that it’s the male part of the leadscrew thread that’s worn away; surely the width of the thread grooves in the new nut need to get narrower (thus leaving wider lands to fit into the worn grooves of the screw) to accommodate that wear… perhaps that’s what led to the loose fit

[HaxbyShed]

Much more confident than me. Straight in. Did you reduce the audio on the squeal 😊?

[cdrive]

I watched this twice to insure I wasn't missing something and I don't believe I did. Your fitting segment confirmed typical ( none linear ) thread wear along the length of the screw. Resulting in the same none linear fit along the screw's length. IE: Good fit here or there but sloppy elsewhere. In the end you removed a little more stock to compensate for the badly worn lead screw. Logic would seem to confirm that lead screw Nut and Lead Screw should be machined as a matched set. Yes, I realize that Lead Screws are hard as hell and will probably need annealing before machining but what other choice do you have? Maybe turn a new one? Works for me cause I'll get to see another enjoyable video. Thanks! 👍💌
Wakodahatchee Chris