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Rare unusual b&s #24 dual adjust knobs micrometer ebay

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Dec 4, 2019
Brown & sharpe #24 crazy dual knob micrometer. Its in great shape on ebay item # 164297594393 if your into cool rare tools this thing might make you smile.
 
The fact that you have only one post to promote a micrometer that happens to be in the same state as you is just a coincidence.
 
Cool. How does it work?

I can't wrap my head around how you would use it, the ratchet thimble is throwing me off. I'm guessing you start by ratcheting onto the part like normal, but then what effect does turning the tenths dial have? Is it trial and error?... turn the tenths dial a little at a time until you get a reading with the marks lined up?
 
Cool. How does it work?

I can't wrap my head around how you would use it, the ratchet thimble is throwing me off. I'm guessing you start by ratcheting onto the part like normal, but then what effect does turning the tenths dial have? Is it trial and error?... turn the tenths dial a little at a time until you get a reading with the marks lined up?

You probably set the thimble to size, then use the second thimble to back off the barrel to line the mark up exactly with a thousanths mark and then you read the vernier to determine the tenths.

If you think about measuring something that is on the half a thou, the mark will be half way between thousanths ticks. Rotating the barrel will rotate it half a thou so that the 5 on the vernier will like up.

Steve
 
You probably set the thimble to size, then use the second thimble to back off the barrel to line the mark up exactly with a thousanths mark and then you read the vernier to determine the tenths.

If you think about measuring something that is on the half a thou, the mark will be half way between thousanths ticks. Rotating the barrel will rotate it half a thou so that the 5 on the vernier will like up.

Steve

You think so? Maybe. The reason I doubt it is that unlike the Starrett 221, the tenths thimble here does not appear to be geared to the main thimble. First the literature says it's not geared, also the uneven graduations suggest that the tenths thimble operates a cam. If that's correct, then backing off the tenths won't have any effect on the main thimble, so you can't just back it off until some marks align.

Edit: looking at this a little more closely and I think you're right, the tenths thimble operates a little arm that turns the barrel. Cool design.
 
Looks like a similar design (in precision..?) to one of these -

Starrett T221XL High Precision Micrometer 0-1" Range Carbide

I worked with a guy that had one, but I didn't quite grasp the concept over a regular tenth vernier reading mic.

The thimble at the end is geared to the thousanths thimble and spring loaded. Once the work piece is contacted by the anvil the thousanths thimble stops, but the tenths thimble continues until the lines on the thousanth thimble like up (so if you were measuring 1/2 thou, you would continue moving the tenths thimble until the thou moves have a graduation, then read the tenths off the red markings).

You can see it in operation in this video. The first 30 seconds shows how the two thimbles move once the anvils contact at zero and gives you an idea what does on a workpiece.

Starrett 221 Micrometer - YouTube

The advantage over a regular tenths mic is that you are reading it in one place and don't have to turn the mic, which is useful when you want to get the reading when the mic is on the part and you can't move it.

Steve
 
I looked at the video, I think that guy has the expansion measurement wrong. Yes the 1.0000" gauge block will expand as per his calculation (I'm assuming he is correct) but the micrometer will also change as temperature changes as he stated in the reason he is using the holder. So both the Mic. and the gauge block is at 80 degrees.
For precision work I use the Starrett 238 1" and 239 for 2"+ having a set up to 7". Carbide faced with tenths vernier on those up to 5". I use the 1 and 2" the most, sometimes the 3" but found a few really nice ones up to 7" on ebay that look good in my Oak tool chest.
 
You probably set the thimble to size, then use the second thimble to back off the barrel to line the mark up exactly with a thousanths mark and then you read the vernier to determine the tenths.

If you think about measuring something that is on the half a thou, the mark will be half way between thousanths ticks. Rotating the barrel will rotate it half a thou so that the 5 on the vernier will like up.

Steve
Steve, you are absolutely correct according to the inventor's patent application where he lays out this mike's advantages and how it operates.
I would agree that it is very similar to how the Starrett 221 operates. However, by the time Starrett began to use this idea, I guess the B&S patent had expired.
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