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How to read Interapid 312B-1?

CalRon

Iron
Registered Member
#1
I recently purchased an Interapid 312B-1
https://www.mscdirect.com/webapp/wcs/stores/servlet/product/details/06442800

It is a .0005" indicator with range of .060"

Initially, I thought each line was .0005", but there are only 60 lines on the dial. This would mean one full revolution is .030", not .060". Does it take two full turns to equal one revolution?

This is a popular DTI, so I'm sure plenty of you have experience with it.

Thank you
 

chips&more

Active User
Active Member
#2
The dial is marked correctly. Each graduation/line is 0.0005”. One complete revolution is 0.030”. And that’s a very nice indicator. The best of the best. You did gooooooood!...Dave
 

JR49

Active User
H-M Supporter-Premium
#3
I recently purchased an Interapid 312B-1
Each line = .0005" , every other line = .001" , each revolution = .030" . It must make 2 complete rev. and equal .060". The smaller needle to the right of the big needle tells you what rev. you are on. Happy machining, JR49
EDIT wow, you're a faster typer than I !!
 

CalRon

Iron
Registered Member
#4
Thank you very much for your help. I was so confused by the .060" range.

So far Ive used this to check the tram on my new mill and used Jacobs super chucks. Good news is, everything I've been testing is twice as good as I originally thought!

I'm as green as green can get when it comes to machining so I have a lot to learn.

Thank you!
 

Doubleeboy

Active User
Active Member
#5
You have the Sherman tank of precision dial test indicators. While a delicate and very accurate instrument, they are very durable. I have had mine for 15 or so years, dropped it on mill table a few times, twice it bounced and hit concrete floor. It works as well as day I bought it and is the equal of some other Swiss made indicators that cost double what a 312-b costs. If mine broke tomorrow I would buy a new one immediately while I waited for Long Island Indicator to repair the 312-b. By visually splitting the difference between the lines you can easily dial in to a tenth or two. Mitutoyo and Starrett both make fine instruments, but for dial test indicators that are accurate, small, and durable the 312-b is the winner in my book.
 

CalRon

Iron
Registered Member
#6
Good to know these are built so well because I bought mine used. It looks like it was barely used but I can tell it is older because the white face on the dial is slightly yellow. Pretty cool knowing this thing is still going strong after all these years.
 

TakeDeadAim

H-M Supporter - Premium Content
H-M Supporter-Premium
#7
age really does not matter with these indicators. I have two, one I bought over 30 years ago and another I bought used a couple years ago. My older one was a bit sticky so I sent it to an instrument repair guy and all he needed to do was clean off the old sticky lubrication and re lube it. There was a lot of use on that tool and I expected it to need a part or two. The repair man said they are very well built and rarely need more than cleaning unless damaged. You have a tool your grandchildren's children can use.