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...and notice how his screw-cutting-lathe has an accurate lead screw in it? :) https://www.ssplprints.com/image/100286/henry-maudslays-original-screw-cutting-l

...and notice how his screw-cutting-lathe has an accurate lead screw in it? :) https://www.ssplprints.com/image/100286/henry-maudslays-original-screw-cutting-lathe-c-1800 https://www.ssplprints.com/image/100286/henry-maudslays-orig... https://www.gracesguide.co.uk/Henry_Maudslay:_Machine_Tools https://www.gracesguide.co.uk/Henry_Maudslay:_Machine_Tools I've never actually seen a detailed explanation of how he cut that first accurate lead screw! Like I say, as far as I can tell it took an iterative variety of processes that made a variety of screw threads, with no one method alone being enough by itself.

mauvehaus 6y ago
The top two pictures of the gracesguide.co.uk page show a screw originating machine, not a screw cutting lathe. And that's the machine you need. AIUI, it's used to cut a lead screw in relatively soft material by holding a cutting tool to it at an angle. Once you have that, you can generate a screw in harder material from it (carefully, one has to assume).
- petertodd 6y ago
  Ah, I see what you mean. I was aware of those machines. But IIUC they by themselves don't generate accurate enough screws, as the blade doesn't track the material exactly, so errors build up over the length of the screw. Getting those errors out in subsequent generations of screws is the hard part.
  - yetihehe 6y ago
    You can average out errors over thread by repeately sliding a long nut over your screw while using lapping compound. Each part of nut will contact only highest (in direction of travel) parts of thread and slightly cut them. You will need to cut off about the same length as nut from both ends of your screw. Nut will have to be made from two parts so that it can be slightly tightened on rod.
Accujack 6y ago
Wrap a triangle around a cylinder. Adjust the angles of the triangle to govern the pitch of the resulting spiral. Use the resulting spiral as a master guide for screw threads being cut on a metal cylinder.

mauvehaus 6y ago

The top two pictures of the gracesguide.co.uk page show a screw originating machine, not a screw cutting lathe. And that's the machine you need. AIUI, it's used to cut a lead screw in relatively soft material by holding a cutting tool to it at an angle. Once you have that, you can generate a screw in harder material from it (carefully, one has to assume).

petertodd 6y ago
Ah, I see what you mean. I was aware of those machines. But IIUC they by themselves don't generate accurate enough screws, as the blade doesn't track the material exactly, so errors build up over the length of the screw. Getting those errors out in subsequent generations of screws is the hard part.
- yetihehe 6y ago
  You can average out errors over thread by repeately sliding a long nut over your screw while using lapping compound. Each part of nut will contact only highest (in direction of travel) parts of thread and slightly cut them. You will need to cut off about the same length as nut from both ends of your screw. Nut will have to be made from two parts so that it can be slightly tightened on rod.

Accujack 6y ago

Wrap a triangle around a cylinder. Adjust the angles of the triangle to govern the pitch of the resulting spiral. Use the resulting spiral as a master guide for screw threads being cut on a metal cylinder.