Help Wanted – Rack operated tailstock specifications.

[Anonymous]

Posted by Chuck Taper on 01/07/2023 22:45:22:

…but in this world I'm not that skilled (etc).

Here's an opportunity to start acquiring the skill.

I take the tolerance on the shaft to mean the shaft should be 0.873" to 0.874". It's a rather old school way of specifying a tolerance, and tends to be frowned upon these days. Ideally a tolerance is specified as zero to a smaller/larger number, or as a plus/minus tolerance around a nominal value.

For the application I don't think backlash adjustment is needed. Presumably it is for a tailstock or capstan so the important movement is always in one direction.

Andrew

[Kiwi BlokeParticipant @kiwibloke62605]

Andrew. Backlash might encourage drill bit 'grabbing' in awkward materials, but I don't suppose many machine quill feeds have any such adjustment, so it can't be much of a problem in practice.

Thanks for explaining the tolerance spec. style; certainly odd…

Jason. The mental agility I meant was that required to read the dial, swapping between sixteenths and decimal inches (or mm!).

Edited By Kiwi Bloke on 02/07/2023 11:25:51

[Michael GilliganParticipant @michaelgilligan61133]

Agreed, Andrew

0.874 +0.000/-0.001 would be my preferred way of expressing it

… or in plain English

“seven eighths … less one or two thou, so that it slides nicely in the hole”

MichaelG.

[david bennett 8Participant @davidbennett8]

Just a reminiscence –

Many years ago, before I had a computer and when ebay wasn't invented, I acquired a very sad looking cast iron Unimat sl. One of the many things missing was the lever pinion. I could see what was required by looking down the hole. As i was unlikely to find one, I decided to make it. The only dimension I had was the hole diameter. I knew nothing about gear forms, and the only likely cutters I had were for clock wheels. I picked the most likely cutter and a piece of bronze and set out to make what you see in the pics. (with a real one for comparison) It is still doing the job perfectly well to this day.

dave8

Edited By david bennett 8 on 02/07/2023 19:13:44

Edited By david bennett 8 on 02/07/2023 19:15:02

[Ian PParticipant @ianp]

Which begs the question…why not use the existing pinion?

The picture in the very first post of this thread looks to have an eminently reclaimable pinion and shaft, just needs some gentle work with file.

Its for feeding drill etc, not a precision measuring device

Ian P

[Nigel Graham 2Participant @nigelgraham2]

A good point, and I returned to the photos for a closer look.

The question seems to say the damage causes the rack to foul the barrel but I'd am inclined to think, no it's more likely the damaged teeth jamming in the rack.

Since the teeth are all still there, just a bit chewed up perhaps with raised patches on them (somehow!) simply dressing their profiles with a file may well be all that's needed.

Certainly try that first.

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