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Advice on lathe Threading tools

Looking for some advice on tooling for lathe threading

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Martin Connelly03/06/2020 16:18:58
1369 forum posts
159 photos

Have you considered a drill and file for the keyway? Lathe gears trains are low power applications so it does not need to be perfect. There is also the option of using the lathe as a shaper for this.

For the drill and file method make a plug for the hole in the spacer. Drill the plug and spacer with a drill of diameter the same as the keyway width at the plug spacer interface. Remove the plug and file the semicircle cut out in the spacer into a keyway. For the lathe as shaper do the same for drilling the semicircle then make a HSS tool to mount on the lathe and use that to cut the keyway. There should be videos on the web.

Martin C

old mart03/06/2020 16:42:38
1756 forum posts
138 photos

I didn't even bother to produce a keyway in a spacer I made when I made some extra gears for the S & B model A. The gears needed to be displaced axially in some configurations, so a spacer was needed to go one side or the other. Originally, the spacer would have had a key like the gear, but I just filed down the half of the key which was under the spacer, and turned the key round in its slot depending whether the gear was inboard or outboard.

Jim Beagley03/06/2020 16:44:02
75 forum posts
41 photos

Hi Martin.
no I’d considered neither of those options.
is shaping in the lathe normal practice? I assume you would use the apron to move the tool across the work and the cross slide to adjust the cut? If the work is in the chuck how is this held fast?

if I opted for the drilling option, could I drill the keyway hole prior to drilling the main bore? I suppose reaming could then be tricky.

Martin Connelly03/06/2020 17:24:11
1369 forum posts
159 photos

Example of keyway cutting.

Martin C

Nigel McBurney 103/06/2020 19:41:09
708 forum posts
3 photos

Jim The work is held in the chuck with the spindle locked or if no lock the lathe is left in back gear, the apron is moved by HAND using the saddle hand wheel,, Where I first worked any keyways in gears and pulleys were cut in a 8 inch Willson lathe and it can be hard work,on smaller lathes care should be taken to avoid strain on the saddle gearing, a lever type attachment is far kinder to the small lathe. When cutting the keyway feed is put on with the cross slide,after taking the cut,wind the cross slide forward so that the keyway tool does not rub on the return stroke, on a big lathe with rigid tooling if you do not withdraw the tool on the return stroke it will take the edge off the tool right across. I was warned about this when I cut my first keyway ,after cutting a couple of keyways I forgot to withdraw the tool and took the front edge clean off,the work is not damaged but the tool needs a regrind. Hence the reason for clapper box toolholders on planers and shapers,but I was given an American book machine shop practice,in later years written by someone who knew his trade, he recomended when cutting internal keyways on a shaper to lock the clapper box tight to avoid tool chatter. Now this goes against what I was taught when cutting keys on the lathe,but when I aquired a 14 inch shaper I had trouble with cutter chatter and it worked and I did not damage the cutting edge of the tool,now both machines were not toys but I cannot see any reason why the tool edge breaks when using the lathe but is ok with the shaper box locked up,

Jim Beagley04/06/2020 15:34:43
75 forum posts
41 photos

Thanks all.

I only have a carbide insert boring bar right now - perhaps I need to get an HSS one.
I like Old Marts solution as well.


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