Inside Micrometer or T-Bore Hole Gauges?

[ltlvt]

Omitting cost and made in the USA I use gage blocks to verify my O/D mics then I use what is being referred to as T type snap gages. of course, taking more than one measurement. And using the proper method of using the T Type snap gauges. {Rocking them inside the bore} Practice and repeatability will tell you if you are using them correctly. If I am trying to meet a critical dimension, then I use these to verify. My personal opinion is you cannot put a price tag on practicing. In my case I was looking for confidence in myself and it only comes from verification.

 

[benmychree]

With telescoping gages, technique is everything; Insert in the hole at a slight angle radially, tighten the lock firmly and lever the gage over in the bore and withdraw it and measure it with the micrometer, the result will be consistent readings. At least they work for me after about 60 some odd years of use.

 

[pontiac428]

After collecting increasingly better telescoping gauges and practicing my technique ad nauseum, I retired them once I bought a "zero" to 6" bore micrometer. The bore mic is very repeatable and tenths sensitive (well, mine is metric, but 25.4 is a non-repeating decimal that gives the same precision whether measuring parts or galactic parsecs). I think mine came from Shars, so it's not exactly Swiss, but I feel it gives vastly superior results to the plunger bobs, and passes any cal standard I can throw at it.

 

[Dabbler]

Both snap gauges and inside micrometers take lots of practice to get an accurate reading. Like any tool in your shop, better quality makes it somewhat easier to get better accuracy with less skill.

The easy answer is "both". but that tells you nothing.

Start with a quality set of snap gauges (telescoping gauges, T gauges - whatever you call them). Make some or purchase standards with very nice polished measuring surfaces - surface finish matters a *lot* with snap gauges) and practice a couple of times per month, You make them by cutting a slot in a piece of steel, lapping the slot and using that as a standard. Make 3 or 4 that are about .001 different from one another (and mark them on the back). This avoids several kinds pf predictive measurement errors. *Dont* look at the answer until after you have made your measurement...

When you can afford it and can measure accurately with snap gauges, you can then learn the completely different technique of measuring using a bore gauge or inside micrometer. Stick with your 4 standards until you get repeatability, then accuracy.

 

[Ischgl99]

I have a cheap set of snap gauges and after watching ToT’s video, took them apart and understood why they were difficult to use. They needed a lot of refinement. I recently got a set of Mitutoyo gauges and they are much nicer and I find easier to use.

I use bearing rings to practice on, the bores are very accurate, so you know how close to the right measurement you are getting.

 

[projectnut]

In my opinion, I think you'll find a bore gauge is the most accurate. Second in accuracy would be the inside micrometer, and the least accurate would be the snap gauge. A bore gauge can be accurate to .0001". Inside micrometers are usually good to .0005", and snap gauges are good to .001". Having said that the most difficult to calibrate is the bore gauge.

I have 5 bore gauges in all that measure from .040" to 8.000". I have 3 sets of Starrett inside micrometers that go from 2.000" to 12.000", and a single set of snap gauges that go from .500" to 6.000". The most used are the bore gauges, and the least used are the inside micrometers. It seems I either need a high level of accuracy or relatively little accuracy.

All styles can be purchased used for pennies on the dollar compared to new. The nice thing about the bore gauges is that they can be used for both metric and imperial measurements by just changing out the indicator head.

Here are some pictures of bore gauges I purchased from a local used equipment vendor. These go from .040" to 6.000"

 

[epanzella]

Snap gauges are accurate but are the hardest to use accurately because feel is the deciding factor. This applies to both measuring your bore and then measuring the snap gauge with a mike. On a critical measurement, I put the gauge in the bore at an angle, let it expand, lock it, and then let it go perpendicular to the bore as I retrieve it. Next I set my mike to a little bigger than the expected measurement and sweep the snap gauge thru it. I close the mike a few tenths at a time until it just contacts both anvils and I have my measurement. If you can get the same answer thee times in a row you have the thing knocked.

 

[twhite]

Snap gauges are accurate but are the hardest to use accurately because feel is the deciding factor. This applies to both measuring your bore and then measuring the snap gauge with a mike. On a critical measurement, I put the gauge in the bore at an angle, let it expand, lock it, and then let it go perpendicular to the bore as I retrieve it. Next I set my mike to a little bigger than the expected measurement and sweep the snap gauge thru it. I close the mike a few tenths at a time until it just contacts both anvils and I have my measurement. If you can get the same answer thee times in a row you have the thing knocked.

That is my basic way also. Feel is SOOOOOO important for good measurements. All measuring tools for that matter.


Cutting oil is my blood.

 

[ErichKeane]

I do basically the same thing, though my Starrett set clamps hard enough I can lightly clamp the micrometer on it without changing the measurement.

 

[jbobb1]

With telescoping gages, technique is everything; Insert in the hole at a slight angle radially, tighten the lock firmly and lever the gage over in the bore and withdraw it and measure it with the micrometer, the result will be consistent readings. At least they work for me after about 60 some odd years of use.

I've always used telescopic gages this way. Feeling the same "resistance" from bore to mic is also important.