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Kevin E
Kevin E
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A hand-held micrometer requires the operator to simultaneously hold the part, hold the micrometer, and operate the spindle, while a bench micrometer eliminates at least one, and sometimes two, of these. It's not that hand-held micrometers can't be accurate, it's that bench micrometers allow the operator to concentrate all their attention on the actual measurement itself. So, rather than the hand-held style of micrometer tool Goodson sells I'm making the equivalent of a bench micrometer.

With the above in mind, the 1" micrometer I will be using allows setting the cutter over a 2" range of diameters. So, I designed the instrument to cover the range of diameters from 1" (i.e. a smaller seat pocket than I can imagine ever needing) to 3" (larger than I can imagine ever needing). I want it to be as accurate as possible, but since it only will be rarely used, I didn't want to spend a lot of time on aesthetics. Basing it on a repurposed chuck of Al satisfied these requirements.

For no good reason (I mean it, for no good reason) some time ago I bought a used Black & Decker valve grinding set, and with that set came a number of duplicate pilots. One of those duplicates would do quite nicely, so I picked one that the cutter tooling fit over with no perceptible play (so, probably less than 0.001" clearance, although there was no reason to take the time to measure it).

The first photograph shows the large diameter micrometer head I won't be using along with the bracket it came with.

[Linked Image]

I decided to repurpose the bracket rather than make something from scratch, so that only required making a sleeve to match the smaller OD of the 1" micrometer head to the ID of the hole in the bracket. Conveniently, the OD of the head is an Imperial ⅜" so it was an easy matter to ream it for a snug fit, shown in the next photograph.

[Linked Image]

The sleeve was thick enough that I could have tapped it for a setscrew, but I decided to slit it instead and rely on gentle clamping pressure to hold the micrometer, as shown in the next photograph.

[Linked Image]

With the micrometer portion done, I turned to making the base from a large Al bracket in the scrap bin. The next photograph shows it after I had roughed it to size with a saw and then faced it to the desired thickness on the mill.

[Linked Image]

I ran out of time at that point, but the final photograph shows that what remains to do is to tap two holes in the side to hold the micrometer bracket, and drill a hole the depth of the Al block to hold the pilot.

[Linked Image]

The pilot I've chosen is for a guide that is +0.010" over ⅜", so I can drill the hole for it as deep as possible with nearly-inflexible ⅜" carbide tooling. Although I'll have to finish drilling that hole with an extra-long ⅜" HSS bit, the earlier portion of the hole should keep it quite straight. I'll then remove the remaining ~0.01" with the Sunnen hone for a tight push fit.

Making a 1.000"-dia. standard to fit over the 0.375" top of the pilot will let me zero the micrometer (actually, any accurately-sized standard that is 1" or larger would do).

NYBSAGUY and I were laughing about it earlier today, but this new precision instrument will be yet another inscrutable object in the garage for my daughters to puzzle over when settling my estate sometime in the (far distant, I hope) future, before tossing it in the trash and moving on to the next of the thousands of unidentifiable objects.

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The specific reason we were laughing was the repeated use of the phrase "from a deceased gentleman's estate" in the Bonhams Stafford auction. Seems the closer I get to being that gentleman, the more often I see the phrase in use.

Since I will, at some far off point, fall off the perch, it will be my daughter's responsibility to get rid of all the crap in my garage. "It says 59GS head complete, but I don't know what that means. You can have it for $5."

Multiply that by 1,000 for the expensive crap in MMan's garage and you can see the issue his two brilliant daughters will face.

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Originally Posted by NYBSAGUY
Multiply that by 1,000 for the expensive crap in MMan's garage and you can see the issue his two brilliant daughters will face.
Triggered by the fact two of my Gold Stars came "from a deceased gentleman's estate," I assembled a 'Black Book' containing a flash drive and paper copies of files listing the tooling (and my estimate of prices) for my lathe, mill, hone, precision tools, etc., plus each of the bikes, as well as other information that could be of great use in sorting out the disaster I'll leave behind (e.g. bibliography of my 3000+ motorcycle books, magazines, etc.). However, I expect my daughters will dutifully go through, at most, the first page of the Black Book before losing patience and hiring a dumpster.

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I almost finished the setting micrometer yesterday before again running out of time. While the base does not have to be perfectly flat for it to be completely functional, slight rocking would be annoying. So, I accurately clamped it in the vise and faced it, as shown in the first photograph.

[Linked Image]

I then reset it in the vise and tapped two holes for attaching the micrometer assembly, as shown in the next photograph.

[Linked Image]

A third accurate repositioning allowed me to drill the hole for the pilot. To do this I carefully positioned the center of the drill 0.500" from the end of the fully-extended micrometer head and on its centerline. It turned out the ⅜" carbide drill bit I have is long enough that I didn't have to extend the depth using an ordinary HSS drill bit. The only remaining task is to hone the hole for the ~0.01"-larger diameter of the bottom of the pilot.

The last photograph shows a mock-up of the final tool.

[Linked Image]

The bottom of the pilot is tapered so it sits in the ⅜" hole.

The base could be ~1" shorter so I'll have to decide after I finish making it, whether I'm finished making it. There's no functional reason to shorten the block so I'll probably leave well enough alone.

Before someone raises the question, yes, I agree, this is quite a bit of trouble to go to for a tool that I'll rarely use, and that my daughters will throw out sometime in the future because they don't know what it is. But, arguably, it will be easier to use and more precise than the commercial version, and it didn't cost $450. However, the real reason for making it is that I have a love of precision instruments, wanted to make it, and could make it. So, I did.

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With only one item left on my to-do list I thought I'd get it finished... wait, what's this, my list has a second page?.... oh, no, , it's an entire notebook!! Damn. Oh well, I wanted to get at least one item crossed off my way-too-long to-do list.

I honed the hole in the base to fit the bottom of the guide, ending up with a fit that required light taps from a small hide mallet to insert the guide in the base. So, the clearance is zero and it has full contact with the base over ~2½" providing excellent alignment. I then measured the ID of the ball driver for the cutter at 0.0001" over ⅜", and the OD of the exposed section of the pilot to be 0.3744", so the clearance between them is 0.0007", i.e. ±0.00035".

[Linked Image]

Of course, the clearance between the ball driver and the specific pilot that would be used when machining a given head wouldn't necessarily be the same, and in operation the side thrust on the cutting tip might or might not take up some or all of whatever clearance there is. But, the measured clearance on the setting tool itself means I can set the cutter to an accuracy of ~0.0005".

Given that this setting tool is capable of accuracy in the tenths, a round setting standard for it would only introduce unwanted uncertainty due to the additional clearance it would have. In any case, when accuracy is needed, gauge blocks are the gold standard. The measured diameter of the pilot is 0.3742", for a radius of 0.1872". This means a 0.3128" stack of gauge blocks next to the pilot would extend out 0.5000" (1.000" diameter), which is where I want to 'zero' the micrometer head. This is shown in the next photograph.

[Linked Image]

With the micrometer head accurately calibrated with gauge blocks, the tool is now ready to use, as shown in the final photograph.

[Linked Image]

With luck, I'll never have to install another valve seat, but I'm now ready in case I ever need to.

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Anyone who is interested in the technical details described in this Ariel rebuild also might find interesting a thread documenting my complete restoration of a Vincent Black Shadow.

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