Advice on lathe Threading tools

[old martParticipant @oldmart]

I have several digital calipers, three cheap Chinese 150mm/6" size and my old 150mm/6" Mitutoyo and the heavyweight 300mm/12" Mitutoyos. I can trust the Mits to measure exactly, inside or out, but not the cheapies, especially not inside.

A set of tee shaped rocker gauges is worth getting, and getting to know well. For bores, if you don't have the means to measure inside accurately, the safe way is to make a plug gauge. Say, if your bore was to be 50mm, then a double ended plug gauge with one end 50mm and the other 49.95mm would work quite well. When the small end fits, you are close and the full size should not quite go in. Size for size will not fit without force.

It is worth gradually building up a few good make second hand micrometers, they are usually easy to judge from their cosmetic condition whether they have been abused.

[Jim BeagleyParticipant @jimbeagley46363]

That's all useful information – thanks.
My digital calipers (you're quite correct that they aren't verniers of course Martin) are actually Mitutoyos and I'm quite happy with them.
I will look at getting some second hand mics as suggested. M&W I guess is the go to, but are there any other recommended makes?
I'll get some of the cheap internal gauges and see how I get on with them.

[Tony Pratt 1Participant @tonypratt1]

Mitutoyo do some very nice tools, but if buying new get from a proper tool dealer [RS/Cromwell etc.], beware of counterfeits.

Tony

[Martin ConnellyParticipant @martinconnelly55370]

Jim, the Model M Mk2 has a cone and cup clutch in the apron to engage the drive to the carriage or cross slide. It also has a torque limiting clutch on the carriage to limit the drive as well. It was the torque limiting clutch I was referring to for driving up to a stop. I don't think the Sabel has this torque limiter, it is a spring loaded ball in pocket system and makes a loud noise when it operates. If you look at pictures of the Mk2 apron it sticks out of the side and the drive shaft passes through it.

Martin C

[old martParticipant @oldmart]

Before buying mechanical micrometers, you need to make up your mind whether to choose imperial or metric. I have both types and have no bother which I use, the lathe and the Tom Senior are imperial, but the drill mill is metric. That is only a suggestion, as converting one to the other is easy, you can use your digital calipers as a converter any time. The last time I bought a micrometer, I got a bargain, a NOS 25-50mm with a length bar in a nice box with instructions, quite old as it is made in the DDR.

[Jim BeagleyParticipant @jimbeagley46363]

Once again, all good advice.
Mart, most of the lathe is imperial, although it now has a metric cross slide.
I suppose metric is more natural to me so that’s probably what I’ll get.
The verniers I have seen seem to do both as well.

I was lucky enough to find a 100T/127T Boxford gear wheel which fits the Sabel perfectly and I also now have a 36 and 40T stud gears so I can cut some metric threads!

Can anyone broach a key way into a spacer for me if I send the spacer? I need one to move the 56T screw gear in and out to meet the metric conversion gear and it’s missing.

i also just picked up another well abused Sabel from eBay which has an original cabinet and some other parts missing from my machine which is great news. I’m currently removing 70years of grime from the cabinet in prep of paint.

[Martin ConnellyParticipant @martinconnelly55370]

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 martParticipant @oldmart]

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 BeagleyParticipant @jimbeagley46363]

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 ConnellyParticipant @martinconnelly55370]

Example of keyway cutting.

Martin C

[Nigel McBurney 1Participant @nigelmcburney1]

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 BeagleyParticipant @jimbeagley46363]

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.

Jim

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