ID micrometer, is it worth buying one?

[Black Forest]

When I broke my boring head I was boring a pocket for a 47mm outside diameter bearing just like the one in your picture. Now that you talked about how to measure and the various methods I am on the hunt for a good quality bore gauge size 35mm to 50mm. They are quite proud of these type of instruments!

[oldtiffie]

Here is the OP:

I am currently making seats for 8 bearings, like the ones below. Made the first one, but really struggled with measuring using my caliper. I needed to spend several minutes seating the caliper properly, getting the right feeling about the caliper position and reading the dimension. This first one ended up being a nice tight fit.

So my question is, will buying an ID micrometer make things easier? Based on how those look, it seems I will still need to spend several minutes positioning the mic to the hole, getting that right feeling and making the measurement.

My answer is that a good inside micrometer is a very handy tool and accurate too, but I suspect that the bore depth will be too shallow for the body (diameter) of inside micrometer.

I'd suggest that you use a standard outside micrometer and a telescopic bore gauge - with practice you should be able to accurately and consistently keep to ot hold 0.01mm (0.0004") and with further practice 0.005mm (0.0002").

I normally opt for spring calipers as I can hold 0.01mm easily and 0.005mm with a bit of prior practice and care.

[Jaakko Fagerlund]

Calipers are good scribing lines, scratching your back, or when a scale isn't handy. Using them for precision bores is just guess-work at best.

But with an outside mic they do precision work, as I previously explained. No guess work, they provide the same accuracy as the telescoping gages. Only disadvantage is that you are only able to measure up to a depth of the jaws length.

[Black_Moons]

Make your own go-nogo or multi step/tapered gauge outta some scrap steel if you don't do precision inside jobs often and need to do the same job over and over.

ie: if you need 4" exactly, make a gauge with 3.990" 3.995 3.998 3.999 3.995 3.998 3.999 4.000 4.0005
Or similar steps. (or more then one guage, one for sneaking up on the size, another for the last few thou, if you need that kinda accuracy)

[Carld]

taydin, for bearing race pockets your better off using telescopic gages. The shallow pocket is hard to measure with a dial mic or inside mic. It's even hard to measure with the telescopic gage sometimes. You need to practice using them a lot to get the right feel and the right size of the bore.

[MaxxLagg]

*snip*

I prefer telescope gages for bores under 6 inches. They are quick to use and once you've become practiced very repeatable, holding repeat readings to 0.0002" if employed with care. I can take telescope gage reading in about 1/4 the time of inside mike readings.

I strongly suggest telescope gages and a little practice for all bores less than say 6" dia. And learn the correct technique in using them.

How to: Extend the telescoping ends a bit larger than the bore. Snug the clamp. Insert the gage to the level you wish to check. Sweep the handle ONCE through a radial plane. You will meet increasing resistance then a sudden release as the axiis of thegage passed the radial plane. Withdraw the gage without bumping it and check. Repeat until you've sufficiently explored the size profile of the bore. Practice on a known inside diameter like a bearing race over a few days until you attain muscle memory and consistancy in reading. The knack of using a telescope gage like many other skills can be perishable. If months or weeks have elapsed since you last used one better practice a few readings before you moving on to the real work.

Machine shop tip of the century: NEVER look at the mike thimble while you're taking a reading. You can unconsciously fudge as much as 0.001" one way to another, easy as pie.

+1 on all this, especially the bolded portion. Dial bore gages are the way to go if you can swing the expense for a quality one. Once set to the proper size they do a superb job of showing you the size and condition (i.e. bellmouth, out of round, etc) of a bore. However, too many people, through lack of technique and the resulting lack of confidence in their results, dismiss the accuracy of telescoping gages. If used properly, they're capable of .0002 accuracy, all day. They're cheap and with just a little practice just about anybody can achieve these results. You've got to use the right technique, as noted above and, just as importantly, you have to be able to master measuring with a micrometer to tenths accuracy and repeatability for telescoping gages to be of any value as a precision tool. The best way to develop micrometer "feel" is to get a set of gage blocks in the tenth range, blindly grab one and measure it with your micrometer without looking at the thimble and keep doing this with different size fourplace gage blocks until you can measure them, without looking, and get it right every time. Of course, you have to have a micrometer capable of measuring to tenths. Once you can do this with an aught-to-one mic you can build up bigger stacks of gage blocks and get the right feel for your bigger mics. They'll ALL have their own feel. Calipers are good scribing lines, scratching your back, or when a scale isn't handy. Using them for precision bores is just guess-work at best.

[oldtiffie]

It looks like I can get the Asimeto dial bore gauge (50 - 160mm range) for a not so bad price here: Below is the link:

http://www.asimeto.com/Products/Holt...p?ProductID=89

But looking at the tip of this, I am confused. Will I be able to use this and my 50 - 75mm micrometer to measure the bearing seat? Or do I need a reference ring with 52mm ID to compare against?

Your "reference ring" can be the outside diameter of the bearing/s you are using. Use your micrometer to check it. Now use your outside micrometer to set/check the bore gauge/micrometer.

Look up the bearing manufacturers catalogue for bearing sizes and limits as well as the tolerance/limits of the hole you are boring. These are very close tolerances.

The "fit" is also part of the bearing ultimate performance as the outer race is compresed slightly and the inner race is expanded slightly so that when combined they give the optimum fit between the rollers and the balls.

"Class of fit" is very closely related to "class of finish".

[taydin]

It looks like I can get the Asimeto dial bore gauge (50 - 160mm range) for a not so bad price here: Below is the link:

http://www.asimeto.com/Products/Holt...p?ProductID=89

But looking at the tip of this, I am confused. Will I be able to use this and my 50 - 75mm micrometer to measure the bearing seat? Or do I need a reference ring with 52mm ID to compare against?

[rohart]

For cylinder bores. over 1 1/2", I have a nice dial bore gauge, and I'd like a couple of inside mics, but for everday boring I made myself (and continually add to) a set of gauges. I've now got one each for 8mm to 22mm in 1mm increments, and to 40mm in 2mm increments, plus most imperial standard sizes.

Each gauge is about 20mm long, with 4mm each of dead on, -.05mm, -.1mm, -.2mm and -.5mm, with a 1mm groove between the lands. They're threaded to take various lengths of handle.

The only problem is using them in shallow holes when you can't use the centre sections.

I bore fast using a caliper to 1.5mm undersize, and then capture one of the parts of the smaller gauge with a fine feed.

That lets me hit just under dead on my target quickly, with whatever cut will give me a good finish. Then I can finish to the fit I want with abrasive paper.

Sometimes I'll bore a shallow ledge wider till a gauge fits, so I know where I am. If I do this 1mm undersized, I know I can clean the ledge right out before I'm anywhere near the final bore.

I suppose this kind of bore gauge set is available commercially, and then it would be more accurate and hardened. I do admit to having to mike up each gauge I use beforehand to check its size before use.

[Forrest Addy]

I've bored lots of bearing seats of all sizes in many materials.

Bore gages are nice and very accurate but expensive.

I've used inside calipers and transfered the measurement to an outside mike but this is tedious and almost impossible unless you are practiced. I never do it unless ther'es an obstruction like a line bar in the way.

Inside mikes are probably the best bets for all sizes even it they are slow. They have the advantage of the micrometer collar graduations for repeatability in multiple readings but I still ignore the the inside mike reading and check the size with the OD mike I used on the race to be fitted. Thus all measurements are comparative and temperature changes from handling the inside mike are neutralized.

I prefer telescope gages for bores under 6 inches. They are quick to use and once you've become practiced very repeatable, holding repeat readings to 0.0002" if employed with care. I can take telescope gage reading in about 1/4 the time of inside mike readings.

Don't dismiss import bore gages. The quality can be variable but if you stumble on a set that one a day when they were making them right you might get a good deal. Remember it's a comparative iinstrument. Ultimate accuracy depends using repeat zero technique with a jo block stack or OD mike.

I strongly suggest telescope gages and a little practice for all bores less than say 6" dia. And learn the correct technique in using them.

How to: Extend the telescoping ends a bit larger than the bore. Snug the clamp. Insert the gage to the level you wish to check. Sweep the handle ONCE through a radial plane. You will meet increasing resistance then a sudden release as the axiis of thegage passed the radial plane. Withdraw the gage without bumping it and check. Repeat until you've sufficiently explored the size profile of the bore. Practice on a known inside diameter like a bearing race over a few days until you attain muscle memory and consistancy in reading. The knack of using a telescope gage like many other skills can be perishable. If months or weeks have elapsed since you last used one better practice a few readings before you moving on to the real work.

Machine shop tip of the century: NEVER look at the mike thimble while you're taking a reading. You can unconsciously fudge as much as 0.001" one way to another, easy as pie.

[Jaakko Fagerlund]

Dial bore gauge and an outside micrometer to set it. Takes 30 seconds to adjust it and 5 seconds to measure. Also reveals out of roundness and tapering just as fast. And i remember a Mitutoyo set once cost around 450 EUR that covers 18-125 mm, but we made extension tubes so the set covers up to 250 mm now (the extensions are 50 mm each, accuracy in length not needed).

Cheap, fast and reliable method is (vernier) calipers and outside micrometer. Only requirement is a locking thumb screw on the calipers, so you can lock it while in the bore and then remove it without messing the measurement. Accuracy easily down to the 0.01 mm, I use this almost daily at work, especially when making bores for bearings. Just practice with a known diameter hole, like the bearings you have to get the feel.

[oldtiffie]

You should be able to hold +/- 0.0005" or better with:

- spring or friction internal calipers and telescopic bore gauges:
http://i200.photobucket.com/albums/a...easdevice1.jpg

- digital internal bore gauge:
http://i200.photobucket.com/albums/a...l_caliper1.jpg

- internal micrometer:
http://i200.photobucket.com/albums/a...c50to300_1.jpg

http://i200.photobucket.com/albums/a...ic25to50_1.jpg

- or make a "stick" gauge (using a normal external micrometer) - the principle on which it operates is the basis for all of the above:

http://i200.photobucket.com/albums/a...auge1-Rev1.jpg

All of these require a very good "feel" to accurately transfer and measure a distance (includes diameters) - and is a "manual" skill which may take some time and learning to be accurate and consistent.

If it were me I'd opt for the spring or friction caliper and the outside micrometer (option 1) or make a "stick" and use that (option 2).

[KiddZimaHater]

A quality set of Inside mics is the way to go.
Get a 0-6" set of either STARRETT or MITUTOYO.
Once you get the "feel" for them, they are dead-nuts accurate.
_

[jimsehr]

I just looked at ebay and inside mics are going for cheap. You can always get a reading and then check the reading with outside mics. So I would buy one in a second. I think they are a real time saver.
jimsehr

[RLWP]

I already have the bearing sleeve itself. I didn't really understand how such a gauge would help in this case?

When the bearing sleeve will drop in, it is too late. Turn up a plug that is slightly smaller and go on boring until that falls in and the bearing sleeve doesn't

Richard