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dmartin
05-05-2016, 11:16 PM
Last week I got as a retirement gift a nice Starrett inside micrometer set. It was a very nice gift and I'm not complaining at all but I do have some questions. I have always used the telescoping type and then measured them with an outside micrometer. If I am boring to a close tolerance for an interference fit or for any other reason. I take many measurements until I am satisfied that I have an accurate measurement. For me an accurate inside measurement is tough and I am very careful to repeat the reading a few times until I am confident it is an accurate reading.
Having never used an inside mic it seems to me that the telescoping type would be just as accurate or maybe more so than the inside micrometer.
I guess my question really is what is the advantage of using an inside micrometer vs the telescoping type, is it more accurate and are there any tips on using it properly as I have never used one before. Thanks and have a good one.

Dwight

J Tiers
05-05-2016, 11:42 PM
I have never seen a telescoping gage for a 36" bore, but maybe they exist.

Then also, the sectional type have been used for aircraft manufacturing and the like, as a distance measuring device, typically measuring up from reference points to something like a point on the wing, etc. That type can be had in long versions, like screw-together sections to 10 feet. I've used them to measure the bore of armatures on generators.

What you probably have is the smaller variety, with a 2" or so basic unit, and extension rods to 12" or so. Still useful. For one thing, they can be set/calibrated to a size, and then easily adjusted around that size to check progress on a bore with less hassle than telescoping gages, since you only need to handle one tool, not two.

If calibrated, so the extension rods give the true size at zero, they are as accurate as their marks allow. Most only go to a thou.

bobw53
05-05-2016, 11:48 PM
Tubular style? Like this? http://www.ebay.com/itm/Vintage-Craftsman-Inside-Micrometer-/252372737995?hash=item3ac2965fcb:g:66kAAOSwE6VXI~T Y

I usually use them more as a go/nogo. When I first used them I used to try and adjust them inside the bore... NO!!!..

If it still goes jack it up a little, if it don't go, bring it down a little... 1000X easier and quicker, (and more accurate, at least for me) than telescoping gages..

Running a pile of parts, having two of them is great, Go and a NoGo. Piece of green electrical tape on one, red on the other.

LKeithR
05-06-2016, 12:23 AM
... When I first used them I used to try and adjust them inside the bore... NO!!!..

If it still goes jack it up a little, if it don't go, bring it down a little... 1000X easier and quicker, (and more accurate, at least for me) than telescoping gages...

That's the proper way to use them...at least what I was taught--try the fit, adjust, rinse and repeat. More like an adjustable gauge--check'em against a mic or a standard for accuracy. Generally more accurate than telescoping gauges...

Mcgyver
05-06-2016, 08:14 AM
If I am boring to a close tolerance for an interference fit or for any other reason. I take many measurements until I am satisfied that I have an accurate measurement. For me an accurate inside measurement is tough and I am very careful to repeat the reading a few times until I am confident it is an accurate reading.


Same here. As for differences, depending on which one it is, an obvious one is it can cover a much large range. There is probably an argument as well that eliminating a step eliminates sources of error. I've found as the diameter increases telescoping gauges become more difficult to use and the inside mic slightly easier, in that you can play around with it to catch the greatest distance, being the diameter.

Still, with every kind of bore measurement thingy, I still grab for the telescoping gauges 90% of the time, quick and easy.

Carm
05-06-2016, 09:06 AM
"I guess my question really is what is the advantage of using an inside micrometer vs the telescoping type, is it more accurate and are there any tips on using it properly as I have never used one before. Thanks and have a good one."

The advantage is you have a number/graduation to look at. Whether it has greater accuracy than a 'scope is moot, since they need verification.
I set them to a mic, and if I need to get anal, Jo block the mic. That way the inside mic has the same feel as a 'scope.
That avoids the caution Chili Bob warns about, adjusting in the bore. Easy to force a screw. Just like a 'scope, you still have to feel the true diameter.

I had a set of Scherr-Tumicos, similar to the Starrett kit in the link. There was a rod that screwed into the head to give greater reach on small bores that also insulated from heat of hands, and gave perpendicular reference.
Inside mics are quicker for many duplicates vs. one-offs.
The Go/ NoGo is a great idea if you have two.

J Tiers
05-06-2016, 11:12 AM
Tubular style? Like this? http://www.ebay.com/itm/Vintage-Craftsman-Inside-Micrometer-/252372737995?hash=item3ac2965fcb:g:66kAAOSwE6VXI~T Y

I usually use them more as a go/nogo. When I first used them I used to try and adjust them inside the bore... NO!!!..

If it still goes jack it up a little, if it don't go, bring it down a little... 1000X easier and quicker, (and more accurate, at least for me) than telescoping gages..

Running a pile of parts, having two of them is great, Go and a NoGo. Piece of green electrical tape on one, red on the other.

No, not like those, that is the usual small style.

Tubular are for longer measurements. These go from 8" to about 36" or so. The sections, and the nose pieces screw together to allow any distance between, with the 1" adjustment length of the basic 8" to 9" section.

Yes, you CAN adjust them while inside the bore. You just have to be extra careful that you are not trying to make a screw-jack out of them. Much the same as with outside mics, don't try to make them a C-clamp.

http://img.photobucket.com/albums/0803/jstanley/tooling/mic%20tubular%20inside%201_zpsykxul7nb.jpg (http://smg.photobucket.com/user/jstanley/media/tooling/mic%20tubular%20inside%201_zpsykxul7nb.jpg.html)

http://img.photobucket.com/albums/0803/jstanley/tooling/mic%20tubular%20inside%202_zpspupwfffn.jpg (http://smg.photobucket.com/user/jstanley/media/tooling/mic%20tubular%20inside%202_zpspupwfffn.jpg.html)

Forrest Addy
05-06-2016, 12:26 PM
Inside mike for less than 4" are to me a PITA especially if the hole is deep. You have to feel around tweaking the barrel one handed. Meanwhile the tool is warming under the heat of your hands expending and reading a smaller diameter than the true size. That's why I usually treat inside micrometers as transfer tools, never taking their reading as Gospel without confirmation by an outside mike in thermal equilibrium with the work environment.

I've use them up to 10 feet iD's. Most of the large adjustable inside mikes in my career shop were of brass construction and as I was on the large machine tools I quite often used inside mikes to progress my work. Warmth from heaters, the sun through the clerestory window, my hands, cold drafts from open doors, downdrafts from the windows on cold days made accurate measurement a crap shoot especially where thousandths tolerances were specified over tens of feet.

Anyway, inside mike were always a source of problems. I've seen a circle of very competent shop people and white hats passing around an inside mike taking readings in turn and disputing the results. Most of the time these controversies could be resolved by considering thermal expansion also affected measuring tools. Inside mikes have low thermal mass and using them requires considerable handling. So long as your are aware of the effect of heat and follow-up sensitive measurements with comparison to outside mikes, you will take reliable readings.

That said, inside mikes are valuable tools in their place. I've spent weeks crawling around inside naval propulsion dear cases (4 per ship) taking 12 point readings in the bearing fits. All with inside mikes. I'd call out the actual reading and my note taker would apply the previously determined thermal correction. Nope, Inside mikes are essential tools but you have to be aware of their sensitivities.

I suggest you keep using your telescope gages because you are used to them but phase in inside mikes. You will discover each has strengths and weaknesses. There will come a time where you reach for one or the other without thinking about it.

You never stop learning this damn trade. That's probably why so many retirees set up home shops. Hell, I know doctors and lawyers who spend their spare hours in their home shops.

old mart
05-06-2016, 12:41 PM
See if there is a threaded hole in the side of the barrel, for screwing in a handle. It makes it easier to hold.

J Tiers
05-06-2016, 03:11 PM
See if there is a threaded hole in the side of the barrel, for screwing in a handle. It makes it easier to hold.

THIS.

Not only is it easier, but it keeps the heat of your hand away.

Forrest, I an surprised you don't suggest to use the handle, for all the reasons you mantion.

Carm
05-06-2016, 04:28 PM
THIS.

Not only is it easier, but it keeps the heat of your hand away.

Forrest, I an surprised you don't suggest to use the handle, for all the reasons you mantion.

Mebbe 'cause it was mentioned in post #6. Mebbe not.

Forrest Addy
05-06-2016, 08:54 PM
THIS.

Not only is it easier, but it keeps the heat of your hand away.

Forrest, I an surprised you don't suggest to use the handle, for all the reasons you mantion.

Handle or no handle you still have to manipulate an ID mike and that transfers heat onto it. Also the better mikes 12" and over have plastic insulators on the rods. If you are careful to handle the tool via these insulators you can keep heat input to a minimum. I never sweat that part anyway. I try to have a good OD mike handy to transfer the measurement to. Far as I'm concerned an inside mike is a screw adjusted telescope gage.

Those handles are often an interference in congested work accesses, proximity of boring tooling, other components, etc. That said the handles sure work and I've used them many a time for convenience in deep bore.

My only complaint is if you drop a handle equipped inside mike 30 feet to a steel deck and a forklift runs over it before you can run the length of the gallery and down a ladder to get to it there is no guarantee the handle won't break off. Even Starrett's finest won't hold up in every work-place situation.

dmartin
05-06-2016, 09:09 PM
Thanks for the replies, I understand the proper use of it now. I was thinking, how am I going to adjust this inside while keeping it centered and square. It did come with a handle and now that I understand that you make small adjustments and keep checking the bore until you get it right it makes more sense. Here is a picture of the set and it was a nice retirement gift. I will probably use it at times to double check measurements. Who knows maybe I'll get to like it and trust it and use it a lot.
Have a good one.

Dwight

http://i1346.photobucket.com/albums/p686/dmartin109/Inside%20Micrometer_zpser7uxo8z.jpg (http://s1346.photobucket.com/user/dmartin109/media/Inside%20Micrometer_zpser7uxo8z.jpg.html)