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

[Technical Ted]

You can’t use a cheap inside caliper to make a transfer measurement?


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I have had very good luck using calipers was winegrower posted. They can be surprisingly accurate! Well, let's put it this way... they will be as accurate as the person using them.

Ted

 

[dbb-the-bruce]

I have had very good luck using calipers was winegrower posted. They can be surprisingly accurate! Well, let's put it this way... they will be as accurate as the person using them.

Ted

And @Winegrower

I did try this method also.
It was definitely better than using standard dial/digital calipers, but still fussy. In addition to getting the diameter points exact, the outward spring of the calipers makes it hard to determine exactly where you have diameter and NO spring.

Too be clear, it's the shallowness of the hole that is the problem here. Inside calipers typically have a radius end that exceeds the .05 depth or at least makes so you are trying to accurately engage the top .01 or less of the walls. I guess grinding the tips to be pointier would help but then it's harder to make the transfer measurement from the tips.

I'm really fighting the shallowness of the hole and lack of wall to measure.

 

[Technical Ted]

Here's a trick I've used. Leave the part longer than needed on the end so you can bore a deeper hole. Leave it enough longer than needed so you can measure the bore more easily. When finished with the bore, face off to desired finish length.

Ted

 

[ChazzC]

There's a couple on eBay right now: one for $90 (eBay item 274670776150) and one for $140 (eBay item 193858684259), both plus s/h.

 

[BGHansen]

How about an inside micrometer? You can pick up an import 0.2" - 1.2" for around $50.

Bruce

 

[Iceberg86300]

Here is a three pronged, i.e. "Tri-mic" / "Tri-mik" / "Intri-mik" / "Holtest"

I really love these for repeatability b/c it's tough to screw up. Not all will bottom though, so be careful of that fact.

(Photo is brown sharp NOT the spi in link)

https://www.mscdirect.com/product/details/00342865

And here's one of the type Bruce posted a pic of:

https://www.mscdirect.com/product/details/38169108

Edit: for your specific application I'd go with the latter. The tri mics are awesome but it's gonna be tough to find one that will go within .05" at anything approaching reasonable cost. Their main use is repeatable measurements deep & DEEPER with extensions, like feet deeper, into bores.

The latter style is generally for the top portion, say ~1/4"-1/2" deep max, of bores less than 1" in diameter, and ~1"-2" deep max in bores larger than 1" in diameter. Depending on brand, of course.

Regards,

Steve

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