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Cuttings an 8tpi thread in free cutting silver steel

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old mart02/11/2020 21:25:04
3185 forum posts
201 photos

The bush idea would work well as long as the assembly could be separated after each pass to completely remove all traces of swarf. Grinding the ACME form is not enough, it should be honed for the sharpest possible edge. Also, the cutting tip should be aligned exactly to match the helix angle of the thread.

Dennis Pataki02/11/2020 21:27:54
10 forum posts

Would milling that thread be a better process than trying to single point cut it?

speelwerk02/11/2020 21:28:38
397 forum posts
1 photos

This is similar, silversteel, diameter 2.8 mm, core 0.9 mm, pitch 1.10 mm and 8 turns if it becomes more slender you make an extra support. Nikomilling worm.jpg

Baz02/11/2020 21:43:07
533 forum posts
2 photos

Milling would certainly be my chosen method of manufacturing.

Ken Ratcliffe03/11/2020 09:52:42
25 forum posts
2 photos

" 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 803/11/2020 14:14:45
avatar
146 forum posts
9 photos

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 Stevens03/11/2020 17:21:19
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1430 forum posts

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 103/11/2020 19:29:44
avatar
894 forum posts
3 photos

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 Richardson 222/11/2020 09:44:01
26 forum posts
3 photos

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 mcleish14/06/2021 11:17:18
7 forum posts

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

Ken Ratcliffe14/06/2021 12:40:10
25 forum posts
2 photos

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

bernard towers14/06/2021 21:32:40
215 forum posts
73 photos

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

John Haine15/06/2021 06:58:29
3940 forum posts
227 photos

pxl_20210427_095641473.jpg

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 Halford15/06/2021 14:20:59
1590 forum posts
16 photos
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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