On 14 December 2023 at 22:31 felis concolor Said:

How does one use this this for measuring and reading an actual bore diameter?

The first thing to do would be to read the instructions.

In short, you don’t use it for direct measurement.

It is a comparative instrument only.

You zero it out at your chosen size using a ring gauge (or gage – I think one is metric, the other imperial). Make sure Berel is in a good mood before you attempt to rotate her.

Poking it up your chosen hole then tells you the difference from your ring.

I always wonder what instruments like this are for exactly.   The set-up procedure and limited range suggest repetition work to me – a need to measure many bores with good but not exceptional accuracy.   The accuracy is better than needed for threading, unless something special is being done.

For my purposes taper gauges are ‘good enough’ to identify nominal diameters.  Cheap, quick, and not very accurate:

I don’t sneer at spring calipers either – applied carefully they work surprisingly well, though plenty of practice is needed:

On the lathe, I mostly bore to match an existing part, which is offered up as it’s own gauge – not measured accurately.  I occasionally use the lathe dials, checked with a digital caliper.  Similar on the mill – fitting is preferred to accurate measuring.

When measured accuracy is needed I switch to a set of telescopic gauges.  They’re more costly, take longer to use, require care and a digital caliper to take off the actual measurement, but are OK in the range I work too – rarely better than ±0.02mm.   The sets cover large and small bores.

I often make simple plug gauges on my lathe, for example to make sure by fit that a hole bored on my milling machine matches that on another part.

No doubt Fells’ dial instrument would get measurements faster than my T-gauges, and I think it could also detect ovality, but for pro accuracy it’s not in the same league as a 3-point internal micrometer, or production GO/NO-GO gauges.   Gut feel is they’d be ideal in a shop refurbishing engines or hydraulic machinery.  Fells’ example is too small for most engine cylinders, and better instruments are available for that, but it would do valve ports, injectors, & spark plugs etc.   Hydraulic and pump repairs too.   Can anyone confirm what sort of work a dial on legs would be first choice?   (Don’t think I need one myself, but I’m often wrong!)

Dave

It will indicate the difference in size from the gauge (Ring, Micrometer, etc) to which it was set to Zero.

Hence, it compares the bore being measured with that usewd to set the Zero.

In used it will need to be be gently rocked to and fro in both planes to show the minimum reading, oe. when perpendicular to npth both axes, (diameter and longitudinal)

It might take a while to become used to this procedure, but practice makes perfect!

Howard