[Newbie] Question about interchangeability of DTI tips

jmx66

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Assuming the thread size matches, how interchangeable are tips? What are the advantages of ruby-tipped?
Here's the dumb question: what does length do to readings?. I would assume a tip that is twice as long would make the dial move half as much. I.e. if you want the dial to remain accurate, you must use the correct length tip?
Thanks all.
-John
 
A longer tip will have more movement at the tip than
a shorter one to travel the same distance ( .001 )
Your indicator is geared , So .001 will always be .001
 
A longer than specified stylus will introduce cosine error and would have to be factored in to the reading.
If you want to avoid the math or other problems, just buy the stylus specified for your DTI. Ruby is used as a non marring
tip. Every DTI comes with a contact point designed for that model. Thread sizes, length, ball size, material. There is a ton of information
here: http://www.longislandindicator.com/p69.html
 
I don't see how it will always be a .001 movement when the tip is out further from the axis point. If you have a tip that is 3 times longer then the original the tip will move 3 times the amount as the shorter one. The gears can not make up for that difference.
 
Cosine error is introduced when the tip is at the wrong angle to the work. Usually indicators are calibrated for a 15° angle.

Longer tips require a correction factor if you care about the absolute numbers. However, usually a dti is simply used to adjust things for a null reading, in which case it doesn't matter. Zero difference is zero difference, no matter what you multiple it by.

It's possible to have gearing in the indicator you could use to compensate for tip length, but I've never seen or heard of such a thing.

Sent from my Pixel XL using Tapatalk
 
Test indicators translate a linear movement into an angular movement. Assuming there is no cosine error, the DTI will only read correctly with a tip the same length as the original tip. Doubling the length will halve the angular travel for the same linear displacement.

The primary reason for using a longer tip is to reach locations which are not accessible with the shorter tip. Using one will decrease the sensitivity of the DTI by the inverse ration of the tip lengths. If you can live with the decreased sensitivity, it isn't a problem if you correct for it or are using the DTI to indicate zero as sptemari stated.
 
When indicating a hole for center the length difference would probably not matter. But if you were using the indicator to check a step or length you would need to either calculate the difference when using a longer tip or use the right length tip.
 
Thank you all for this informative (and surprisingly lively) discussion. :cool:
 
Cosine error is introduced when the tip is at the wrong angle to the work. Usually indicators are calibrated for a 15° angle.

Longer tips require a correction factor if you care about the absolute numbers. However, usually a dti is simply used to adjust things for a null reading, in which case it doesn't matter. Zero difference is zero difference, no matter what you multiple it by.

It's possible to have gearing in the indicator you could use to compensate for tip length, but I've never seen or heard of such a thing.

Sent from my Pixel XL using Tapatalk

Actually, Mitutoyo makes a custom stylus for it's DTI's that nullifies the cosine error. The stylus can be used at any angle.
 
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