[Newbie] Question about interchangeability of DTI tips

the angle of the tip really doesn't matter. the pivot point will still move the same distance. It is the tip length that changes the accuracy. As long as the tip is the same length as the original the indicator will read properly at any angle. If you don't believe me try it with size blocks and tip at different angles.
 
the angle of the tip really doesn't matter. the pivot point will still move the same distance. It is the tip length that changes the accuracy. As long as the tip is the same length as the original the indicator will read properly at any angle. If you don't believe me try it with size blocks and tip at different angles.
Just to clarify a little, the tip's angle to the DTI body at the pivot point doesn't matter, that's true. But, the tip's angle to the piece being measured does matter. A tip at 15 degree angle to the measured surface will read differently than a tip at a 45 degree angle to that same surface, due to cosine error.

Tom
 
Depends on the model:
From LIIS website:
Unlike other test indicators, Interapid indicators do not have serial numbers on them. Perhaps someday the manufacturer will remedy this situation but for now you'll have to assign your own unique serial number to each indicator if you intend to keep track of their calibration. It's easy to scratch a number into the painted body using a sharp tool. A permanent marker with a super fine point will also work. Do not use an electro-engraver because it creates sparks which have been known to damage the pinions on the gears.
cosine1a1.gif

Interapid series 312 test indicators are designed to permit a true reading when the angle between the stylus and the reference surface is 12° as shown in A and B (to the left).
In the rare cases when axial measurement is required with the stylus at 0° with respect to the reference surface as in C and D in the illustration, (for instance: small diameter bores) the readings must be multiplied by a factor of 1.022 (See further information on cosine error.)
It also follows that incremental calibration discrepancies can be corrected by adjusting the contact point angle.
 
Actually learning the finer points of how things work and should be used is very much a part of the enjoyment i get from this hobby. I can be concerned about and dwell on any aspect of anything regardless of how trivial it might be to someone else. That is what defines a hobby to me.
 
.... But if you were using the indicator to check a step or length ...

I'd hesitate to use a dti to measure a step, unless it was in conjunction with a stack of gage blocks on a surface plate. It's possible, but getting the angle just right is going to be trickier than using a drop indicator or a mic.


Cosine error is over rated. If one knows enough to be concerned about or calculate it. Then it is not a hobby.

Well, in that case you would probably be using the wrong tool for the job. I'm trying to think of some case where the numeric reading actually matters and another technique wouldn't be easier and more accurate. About all I can come up with is measuring the depth of a shallow groove or shoulder inside a hole that's too small for a telescoping gage or groove mic to get into.

Sent from my Pixel XL using Tapatalk
 
Back
Top