Since those measurements all look nice neat mm integers, and it is a scientific instrument, it could well be metric. Try measuring surrounding metalwork to see if you obtain predominately mm or inch values.

The rack and pinion might not necessarily be Module, though, even if metric.

I’m certainly no instrument maker, but I wonder if using two racks might be advantageous.
Allowing one to offset slightly, would allow an effective backlash adjustment, other than just depth of tooth engagement.
Comment is only up for a discussion, rather than a recommendation.

Bill

To be honest, my biggest concern is that the damaged rack doesn’t look entirely convincing anyway.

If this and the Lantern Pinion are both original parts, then I suggest that you do some experimentation and then jump-in with DiY manufacture to your own design

… it could be a considerable improvement.

MichaelG.

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P.S. __ Forgot to mention: Your photo of the little pinion is excellent ! … do you have a diameter measurement for the pins [to compare with the rack] ?

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Edit: __ With thanks to Charles … please ignore that question ^^^
< blush >

On 14 May 2024 at 21:22 Charles Lamont Said:

Michael – I think it is your assumption that it is a lantern pinion. It does not look like one to me.

Ah! … that’s interesting

… I mis-interpreted the two bearings !

mea culpa

MichaelG.

May I suggest trying the rack fitted the other way round. It might just be that the worn part of the rack is all at one end and this will restore use, albeit as something of a bodge.

Regards   Brian

PS    I was rather taken with Old Mart’s more permanent solution of reforming the rack and then displacing it towards the pinion.

A good look at the rack illustration shows (to me at least) that the rack was cut in stages, starting with a narrow plain metal-saw-type blade. Some of the cuts are deeper than others, eg 8 from the far right shewn, which hints at hand-work. Then, I suggest, the tops of the slots were widened with eg a triangular file (or a double-conical rotary saw cutter). In this case, making a replacement rack should be easy if a little time consuming.

It becomes a different matter if it is needed to measure the movement caused by the rack etc, rather than using it just to achieve good focus. In this case, the pinion knob is going to be marked with one or more scales in fractions or decimals of a unit, perhaps with a vernier scale, and this makes the choice of the ‘right’ rack easier, as we must finish with calibrations which are true to the original. This also makes it necessary for every tooth shape to be identical along the whole working length, and this rules out hand filing.

So, can we have some more detail on the purpose of the rack & pinion, please? And a note of any calibrations or scale on the body or the knob for the pinion?

It is helpful that the pinion (whether a lantern or otherwise) appears in very good condition, so it should be re-useable. So, job ‘only’ needs a new rack.

Hope this helps – Tim

Tim/John

I think the pertinent point is that this microscope has been identified as a Powell and Lealand from 1865

I posted a link earlier, which covers the P&L microscopes of that general vintage rather well … and although it has not been explicitly confirmed, it currently seems a reasonable assumption that this statement is applicable:

By 1865, as shown in the example in the Billings collection(left)

MichaelG.

On 15 May 2024 at 12:33 Brian Wood Said:

Having looked again at the information provided, the pinion details indicate that this is 70 DP, almost exactly. How much this helps with restoration is rather debateable.

 

Regards   Brian

It does until you apply the long-addendum rule for 12 teeth then it comes out at 76.5DP. The 1mm pitch of the rack is very, very close to 80DP, as in 0.0001″

That rack was clearly hand-cut though, either that or someone has tried to re-cut it by hand. It’s probably ‘that’ll do’ spec.

On 15 May 2024 at 17:48 Tim Stevens Said:

A good look at the rack illustration shows (to me at least) that the rack was cut in stages, starting with a narrow plain metal-saw-type blade. Some of the cuts are deeper than others, eg 8 from the far right shewn, which hints at hand-work. Then, I suggest, the tops of the slots were widened with eg a triangular file (or a double-conical rotary saw cutter). In this case, making a replacement rack should be easy if a little time consuming.

…

This is indeed quite do-able, in a non-measuring situation such as this one. I remember my old man making a new rack on the push-button klaxon horn on his 1923 Harley by the same/similar method, back about 1970. It is still working today. And it takes a lot more strain than a microscope focuser. You have to push the button down hard with your palm to spin the high-ratio gearing inside the klaxon to make it bark. A source of fascination to three generations of kids. `

[ footnote ]

For the rack, the first part of this video can obviously be simplified to just turning a cone … but it’s beautifully done:

MichaelG.

https://youtu.be/6M2yAUEmJbE?feature=shared

I would suggest a grinding-wheel would rapidly lose form while clogging with brass particles, but really we need know what tooling Penninelad has available, to be able to advise him usefully.