Brown and Sharpe Digit-mike

Topics include, Machine Tools & Tooling, Precision Measuring, Materials and their Properties, Electrical discussions related to machine tools, setups, fixtures and jigs and other general discussion related to amateur machining.

Moderators: GlennW, Harold_V

Post Reply
User avatar
refinery mike
Posts: 623
Joined: Sat Jul 02, 2011 1:54 pm

Brown and Sharpe Digit-mike

Post by refinery mike »

I just bought a Brown and Sharpe mic off EBay. "Digit-Mike 599-10-1" First off i might say that i am totally pleased with it. I checked it against gage blocks and it has an error of less than half a ten-thousanth All the way through it's range. It is also like totally easy to read. Even for me and i sometimes struggle with mic accuracy.
But i have a question if anyone knows. The dial that spins in the little window. It seams to do the impossible. The dial in the window goes from 00.0 to 100.0. If you turn the knob one full revolution then the dial goes from 00.0 to 20.0. In effect you have to turn the knob 5 full turns for the dial to go from 00.0 -100.0. The thing is that the dial in the window always turns with the same RPM as the knob. There is never any hint of the dial shifting or another dial shifting into place, or anything like that. Yet the knob turns 5 times around for the dial to go one full revolution. Yet you can easily see that the knob and the dial are turning at the same RPMs. I know this makes no sense at all but i can assure you that is what happens. Any one have an explanation.
Attachments
Copy of IMG_6814.jpg
John Evans
Posts: 2366
Joined: Tue Jan 20, 2009 9:33 pm
Location: Phoenix ,AZ

Re: Brown and Sharpe Digit-mike

Post by John Evans »

Spindle 10 thread per inch rather than 40 like a regular mic? I have the same mic and that's my guess.
www.chaski.com
User avatar
refinery mike
Posts: 623
Joined: Sat Jul 02, 2011 1:54 pm

Re: Brown and Sharpe Digit-mike

Post by refinery mike »

actually the spindle thread is 50 threads per inch. Fifty turns of the knob will get you one inch. but fifty turns of the knob will only give you ten compleat turns of the inside dial. Yet the dial and the knob turn together at the same rate. So the inner dial appears to turn at the same RPM as the nob, but also turns five times slower at the same time. It appears impossible.
spro
Posts: 8016
Joined: Mon Feb 20, 2006 11:04 pm
Location: mid atlantic

Re: Brown and Sharpe Digit-mike

Post by spro »

It is Swiss made so anything is possible. Definitely interesting!.
John Evans
Posts: 2366
Joined: Tue Jan 20, 2009 9:33 pm
Location: Phoenix ,AZ

Re: Brown and Sharpe Digit-mike

Post by John Evans »

Well I was wrong as I was thinking of my Etalon Rapid Mic that is 1 turn per .100 ,it's scale is on the outside of thimble. The B&S must have a gear train to the dial. I have a set of NSK mechanical digit style and they have a gear train that works kinda like a car odometer.
www.chaski.com
spro
Posts: 8016
Joined: Mon Feb 20, 2006 11:04 pm
Location: mid atlantic

Re: Brown and Sharpe Digit-mike

Post by spro »

Hi. Yes. This has something else going on in there.
User avatar
refinery mike
Posts: 623
Joined: Sat Jul 02, 2011 1:54 pm

Re: Brown and Sharpe Digit-mike

Post by refinery mike »

Brown and Sharpe claims that there are no gears involved, but i can not find any pictures of inside that thing. And no way do i want to try to take it apart. Sure enough it would never go back together right. Anyway you got to see this thing. two cylinders of similar diameter, about 1/8 inch apart. Both turn at the same rate, side by side, apparently on the same axis, But the silver ring has to go around 5 times before the inside dial with numbers goes from 0 to 100, One apparent revolution. Impossible yes. What magic do those Swiss have up their sleeves.
User avatar
refinery mike
Posts: 623
Joined: Sat Jul 02, 2011 1:54 pm

Re: Brown and Sharpe Digit-mike

Post by refinery mike »

I looked all over the web and could not find anything. Today i met a Machinist i know and he had the answer. The dial does in fact turn at the same RPM as the knob. But the tiny little numbers are separate from the wheel and the numbers are changed each time the wheel goes around. Off course they are changed out of view of the window. They are so small and perfect that you need a magnifying glass to see the deviding lines where they change. It is like a Swiss watch maker made the thing or something.
Big Rack
Posts: 21
Joined: Sat Jan 11, 2014 12:55 pm

Re: Brown and Sharpe Digit-mike

Post by Big Rack »

I have one in black it directly reads to .0002 and it's fascinating.
IRACO
Posts: 1
Joined: Sun Jun 03, 2018 11:11 pm

Re: Brown and Sharpe Digit-mike

Post by IRACO »

I have the metric version 0-25 mm. 599-10-100-1 Someone has already said that B&S states that there are no gears inside. The only other way of doing this then is with a planetary (NO gears) system involving an outer cylinder with a race machined on the inside and balls placed in the race, and then a shaft through the middle of it all, and tightly held together, the shaft being driven by the balls, which are in turn driven by the inside of the drum. This arrangement does two things for us, input to output 'gear' ratio. Mine is about exactly 2:1 and will, also provide the slipping friction clutch at the same time. The rest is simple and straight forward, as it's no great feat to get 00-99 markings on the drum that's viewed through the window. Hope that this helps as to how it's made to work.
Post Reply