Any tricks for measuring the inside dia of a shallow bore or pocket?

D

dbb-the-bruce

Dave
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I'm stumped. There must be some tricks to that make it easy (or easier) to get an accurate inside diameter of a shallow bore.
I've got a part that I want to turn a shallow 1" dia. bore into. The depth is only about .050 and it's too shallow for the telescoping bore measuring tools.

When I try to use the pointy tips of calipers I get readings that vary +/- .003 because it's hard to find the true diameter with the caliper tips.

Is there some special tool or a clever trick for getting an accurate measurement in this case?

I did try a short piece of 1" drill rod and was able to use little bits of plastic shim to determine that I over shot it to 1.003, but there has to be a better way to do this while turning it.
 
Three prong mics . They are quite expensive but they can measure bores almost as accurate as dial bore gages . They may show up as tri mics on the Bay sometimes . You should be able to get within .0005 with a good set of calipers though .
 
mmcmdl said:
You should be able to get within .0005 with a good set of calipers though .
Click to expand...
I find using a typical dial/digital caliper is just way to fussy in regards to position and not loosing the measurement. It's really hard to get a repeatable measurement.

I didn't have much luck searching for "three prong mic or indicator" there must be a better name for them.

I did find dial bore gages, Mitutoyo has a special probe tip that can measure with in 2 mm of the bottom of a hole. Also pricy and limited range. The other speciality thing I found was shallow bore gages - very expensive and seems like they are for large 12" holes at the smallest.

The shallow bore gage gave me the idea of two pins, one fixed on movable in a slot and lockable that I could make. The pins would be used to transfer the measurement and make it easy to measure with calipers.

I'll keep looking.

I did recently by a full set of pin gages from .25 to .06 - They have made checking and matching smaller holes *MUCH* easier. really glad I got them.

Maybe I'll splurge on and inside dial caliper.

Thanks for the suggestion.
 
You need it ? $75.00 It's called an indical . I'm holding one in my hand .
 
Stay put . I'll get a pic ! You do have a dovetail indicator , correct ?
 
OK , hold on a minute . Pics to follow .
 
Turn a piece of rod to a couple of dimensions, like .998, .999 & 1. Take your time and get them perfect. When the .999 goes in and the 1 is hard to start, then you are there. Basically you are making gauge pins. If you have money to burn, you could buy a set or use a 1" round gauge block. My round gauge block came from Ebay in a junk assortment. The Indicol mentioned above took me a couple of months to get at $60. New is around $180.
 
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