Telescopic Gauges - Technique?

Ref #3 from OP For shallow bores and grooves, like Bill I use Dial calipers and a mic to check over the ends when the dial reads as the bore/groove indicated.
Sometimes it's better to set the mic to the dimension required and check the reading on the caliper dial so you have a target to get to.

As Bill said these do come up for sale fairly often and are well worth the investment as they are also useful to check any bore is parallel.

For smaller than 12mm diameter holes/bores I find ball type gauges and a mic give accurate readings but only with practise as is the case with telescopic gauges.

Several other useful methods for measuring bores can be seen in my Photo Album. (Internal Measuring Devices)
https://www.model-engineer.co.uk/albums/member_album.asp?a=35959

Emgee

Edited By Emgee on 30/08/2022 11:42:00

i still use them from time to time. (The old spring calipers, not vernier or digital.) Actually handy for the question in hand about measuring the diameter of a shallow recess, then measure the calipers with a micrometer.

We were issued with them as apprentices in the 70s but I rarely remember ever using them much. But prior to about WW2 or a bit after, much reasonably precision work was done with calipers and six inch rule, as you say. Final fit and finish would be done by direct comparison with the mating part. I know they were my old man's go-to measuring tool on the lathe. He was an apprentice of the 1940s.

Lots of useful advice on techniques for telescopic gauges in the posts above. In one of his books Tubal Cain gave some advice for using spring calipers ( plain ones, not the screw adjusted ones) which he regarded as potentially very accurate. He was writing 50 odd years ago but the advice still seems relevant for those using plain calipers.

First adjust the calipers to roughly the size needed. Then try for fit.

If the caliper opening is too large, hold caliper by one jaw, near the pivot, and tap the other jaw on the vice, and try again.

If the opening is too small, hold caliper vertically by one jaw, jaws up and pivot down, and tap the pivot vertically downwards on the vice, and try again.

It really works and makes it fairly easy to make tiny adjustments with a very simple piece of kit..

Rod