Cuttings an 8tpi thread in free cutting silver steel

[Ken RatcliffeParticipant @kenratcliffe25229]

" Also, the cutting tip should be aligned exactly to match the helix angle of the thread."

That now makes sense as to why the cross slide needs to be angled at 14.5degrees – I think

I have one more piece of free cutting steel, so will give a whirl with all the suggestions (many thanks), but have also ordered one (Thanks Martin)

[David Davies 8Participant @daviddavies8]

Ken

setting the topslide ar 14.5 deg is not the same as making the tool match the helix angle of the thread. The leading edge of the tool must have its clearance angle increased as the helix angle increases. If not the tool will foul the work. The trailing edge of the tool does not need the same treatment as the helix is going away from that edge. The treason for the 14.5 degrees is so that the cut is only applied by the leading edge, the trailing edge merely follows.

hth

Dave

[Tim StevensParticipant @timstevens64731]

How about making it a different way ? Try wrapping a spring made of square wire round a central wire? And then, if necessary soldering the ends away from the working area?

Or grind the thread away instead of cutting it?

Cheers, Tim

[Nigel McBurney 1Participant @nigelmcburney1]

I have seen a similar worm drive on a very early hard drive actuator and that was ground,only one company succeded in producing it. As its to drive a clock why not change material and used leaded mild steel,the finish will be far better than silver steel,a poor finish on silver steel may cause a lot of wear.

[Steve RParticipant @steverichardson2]

Think I have some old gramaphone parts with worms on like that.

not sure how you would use the rear tool post support without having to reset it and the tool for each cut, as the tool post would move if you moved the cross slide.

tailstock support, travelling steady set well, and fine cuts…

[andrew mcleishParticipant @andrewmcleish96372]

Hi ken i might be able to help phone me on 01628 473140

[Ken RatcliffeParticipant @kenratcliffe25229]

Hi Andrew, I ended up getting one from Carlo Groce (two in fact because I dropped one !). Manythanks though

[bernard towersParticipant @bernardtowers37738]

Would a live tooling approach work, still using a travelling steady as well??

[John HaineParticipant @johnhaine32865]

This is an initial attempt at milling a 4-start "helix lever" gear by CNC using my 4th axis on the Novamill. With some attention to supporting the blank it should be possible to do 1-start helices – the Victorian era clocks that used these had 1-start pinions so they could do large reductions in one step. Though milled with an ordinary slot mill (1mm) it is possible to do angled flanks by some careful offsetting of the cutter relative to the blank axis.

[Dave HalfordParticipant @davehalford22513]

Posted by Tim Stevens on 03/11/2020 17:21:19:

How about making it a different way ? Try wrapping a spring made of square wire round a central wire? And then, if necessary soldering the ends away from the working area?

Or grind the thread away instead of cutting it?

Cheers, Tim

Verdict do something similar in their indicator, a coarse spiral of hard polished wire.

And yes I do know this is nearly a year too late

Edited By Dave Halford on 15/06/2021 14:21:43

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