DTI vs DI

[GlennW]

Since I was using mine today I figured I would add this.

To eliminate some confusion when using a DTI that doesn't have constant clockwise rotation in a mill spindle:

Just work with the point on the back side of a pin.

And work with the point on the front side of a bore.

Doing this will result in the needle indicating in a normal clockwise direction.

[earlgo]

Good tip Glenn. You must have some experience with this.
--earlgo

[GlennW]

Thanks Earl!


I was gifted a box of things last week from a friend, and in it is a small DTI with a 1" face made by Lufkin that is graduated in .0001" and has a total travel of .032"

It is .004" per revolution with a revolution counter that counts eight revolutions. I've not seen anything like it before, as most .0001" DTI's have fairly limited travel!

He also gave me a very nice indicator stand that he made that is for use on a surface plate. I'm restoring it now.

[ctwo]

Glenn, not sure I understand the confusion over needle movement, but then I generally am using a BesTest. I guess the needle always swings clockwise (auto reversing?). I have several types of DTI's, many with manual reversing levers and my favorite is a Teclock with a 1" 90° face.

[GlennW]

Glenn, not sure I understand the confusion over needle movement

For some it can be a bit counter intuitive at first for the needle sweeping clockwise to be indicating the lowest point. Especially if you are used to using a BesTest DTI.

[Cary Stewart]

A comment. Starrett Last Word DTIs have a switch on the side which changes the direction of needle rotation. I have a Federal .0001" vertical that I inherited and it also has a switch on it. Some modern DTIs will rotate the needle only one way regardless of the direction of the contact arm movement. Others will automatically change direction of needle movement. You pays your money and gets your choice.
Cary

[Glenn Brooks]

Steve,

So just thinking about keeping track of .99619469809 convinces me to stay with my DI!

Glenn

[John Hasler]

A comment. Starrett Last Word DTIs have a switch on the side which changes the direction of needle rotation. I have a Federal .0001" vertical that I inherited and it also has a switch on it. Some modern DTIs will rotate the needle only one way regardless of the direction of the contact arm movement. Others will automatically change direction of needle movement. You pays your money and gets your choice.
Cary

It doesn't change the direction of needle movement with respect to lever movement. In one position clockwise rotation of the lever results in clockwise movement of the needle away from it's position against the stop. In the other position counterclockwise rotation of the lever results in counterclockwise movement of the needle away from it's position against the stop.

Thus clockwise movement of the needle always means clockwise movement of the lever. All that the switch changes is which way the spring drives it as it tries to get back to the stop. Reading ODs or IDs, clockwise rotation means motion away from center.

[ctwo]

I never bothered to think about correlating needle rotation with the indicator arm movement. Often I'll just touch the indicator to tell which way the high spot is - or it just stops moving and reverses direction at the high/low spot.