Hands on with the Watt Micrometer (1776)

After bugging the Science Museum, London, several times for information on the James Watt Micrometer I was eventually put in touch with Ben Russell, curator of mechanical engineering. After a very interesting email exchange with him over a year or so I was invited to view the micrometer out of the case and partially dissassemble it with him next time I was in London. There have always been questions as to whether Watt made it himself and so this was a great opportunity to gather more evidence.

Since I published this I've become inclined to side with the people who think the rear hammer marks were to knock the rear pins in and out. What do you guys think?

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What is a read pin? The pins I see in the picture look like ordinary steel or brass taper pins that were commonly used in clock movements for centuries, and certainly in 1776. I think a careful workman would drive them in with a pin punch, leaving no hammer marks on the plate. So perhaps you have evidence of a not so careful workman, and such have been around for millennia.

Larry

I just watched this from another email and thought I should post the link, but this is better. It is your video. I too have held this thing, I’m just not sure what it is or who made it. I also got to go through Watt’s workshop which I will admit is full of strange contraptions.

It is such a shame there is nothing linking this to Watt prior to when the museum got it.

The mysteries continue.

Nice job on the video - thanks.

typo! fixed it to 'rear pins'

But yes, I agree this appears to have been built by someone who either a) wasn't that skilled or b) was in a hurry because this was for fun or a prototype or some other reason. But even if in a hurry I would think using a punch to hammer the pins in wouldn't have been a big deal to do.

It supposedly was also built relatively early in Watt's career, though he had been an instrument maker by this time, where as many of the smaller items that we know can be directly attributed to him are from his retirement. I look forward to hearing more from Ben and his research.

Those pins may have originally been knocked in with a punch by a skilled person and have looked beautiful, but how many times over the years has it been dismantled and re-assembled by someone with lesser skills?

You can't just assume that what you see in the way of blemishes was there from day one.

An excellent and valuable video presentation.

Ben Russell and I have aired some aspects of this instrument, and one of the things that came up was the possibility of it being hastily made to test a concept. However, Mr Francis has noted wear on the moving anvil, which seems to suggest that it wasn't just tried and quickly abandoned.

If it was made to test a concept, then it was presumably not intended to 'sell' the idea to anyone else. Otherwise it would surely have been given more user-appeal, by putting numbers on the dials, and having just a single pointing hand on each dial. More likely that it was made as a prototype to allow the designer to identify the pros and cons.

Even if the workmanship had been very good, rather than very poor, it would have disappointed as a precision measuring instrument. Too much friction, no sensitivity, too much scope for lost motion. Bizarre anvil shape - poor even for measuring flat plates, useless for round items.

And the workmanship is poor. And not because it was made in a rush. If that was the case, why go to the trouble of making the frame U-shaped? Much easier to have square corners. Why bother putting a decorative radius on the top corner of the frame and the gib? It’s hard to see how any moderately skilled worker could have turned out such work, unless he was ‘not himself’ at the time.

From what I’ve seen of Watt’s commercial instrument work, and in truth I haven’t seen much, the standard of workmanship is by no means pleasing to the eye. A bit slapdash in places, but far better than we see in this micrometer. Also, it is known that Watt was capable of doing precision instrument work. He made a dividing engine in 1772, and by 1774 had improved its screw to the extent that it ‘did not err the 1/200th of an inch’ in 9 inches [Letter from Watt, quoted in Richard L Hills’ ‘James Watt’ Vol 1].


What was the designer’s motivation? Presumably to provide an instrument for end measurement, in which the use of dials offered the possibility of rapid readings with reduced chance of ‘operator error’ (compared with the alternative of sliding calipers with a tiny vernier). What items it was intended to measure is another question.

The idea that the instrument might have been made in the 19th century as a ‘spoiler’ to imply priority over Palmer’s micrometer can be dismissed out of hand. This is a bench instrument, bearing no meaningful resemblance to the familiar pocket micrometer.

In passing, Palmer’s concept was brilliant: a small highly portable instrument with the ingenious concept of putting all the graduations on a compact sleeve and thimble. My impression of the quality of Palmer’s early micrometers – admittedly only from photos – makes me doubt that they could have reached the standards of accuracy that we expect now, and in fact were achieved very early on by Brown & Sharpe

Is there any update on Ben's findings? Has he published anything yet? Or is he still working on it? Would love any info anyone has.