Sounds like you have to turn into a Cal lab. Have two. Measure with one
and see what the other says. If it matches - try the extremes (of the scale)
and back to central region. If the TBD version isn't matching - slightly flex
the pointer to see where it does - then the length of the next version is that of
the first plus the air gap. Test Test Test.

Martin

Dave Martindale wrote:

writes:


How long are the pointers supposed to be? Perhaps Ive had a stroke
or its a case of brain fade..but doesnt the length of the pointer make
a difference as to the actual measurement displayed on the dial?


Yes, the scale will be calibrated properly only for the correct length
of probe/finger. (I think of the "pointer" being part of the dial, not
what touches the work).

If you can't find what the correct length is for this particular DTI,
you can make one of any length. Then figure out how much deflection you
get on the dial when you move the point 0.001". You can do the latter
by clamping the DTI so it touches the spindle of a mike held in a vise,
or use a micrometer head if you have one. Something like a Height
Master would be even better.

Basically, you must have *some* way to move the measuring finger
reliably a known distance. Then see how much the pointer on the dial
moves. The ratio gives you a "calibration constant" for your DTI - now
you'll know that it reads 1.2 times the actual displacement, or whatever
the value actually is.

If you're really fussy, once you know this value, make a new probe whose
length is equal to the length of the first one multiplied by the
calibration constant above. (Measure from pivot bearing to contact
point on the ball). Now you'll have one that's just the right length.

If you're less fussy, just live with the first one you made.

Dave


--
Martin Eastburn, Barbara Eastburn
@ home at Lion's Lair with our computer
NRA LOH, NRA Life
NRA Second Amendment Task Force Charter Founder