Tight bore tolerances, Are Dial bore gages the only choice?

I never got properly set up for measuring tight tolerance bores yet. Generally got by with telescopic gages, pin/plug gages (or making my own) and sometimes testing with the mating bearing when provided.

Now I have some crazier stuff coming up with +/-.0001 on bores(it gets crazier)

Just wondering whats out there. Lasers seem no good at doing ID's if its a blind hole.
Are Dial bore gages still where its at? I saw sunnen has a few very special bore gauging systems with incredible accuracy but they cost a fair bit and are really meant to do high quantity parts that you can take to the measuring system which stays on the table, you can't hold that set up in a lathe to measure your part.


Range I need is usually from just under .500 " to about 2" but if it goes a little bigger it doesn't hurt.
Current budget ideally under 1K but could go to 2K if its really worth it and can't be questioned as to the readings it gives me.


If it has to be a dial bore gauge(or maybe digital bore gauge by now?) who currently makes the best ones? Mitutoyo or what else should I look at?

Measuring bores +/- .0001 from under .5 to 2.0 for under $1K or so is a challenge.

Mitutoyo makes a good dial bore gage. Etalon makes a good bore micrometer, with B&S and Mitutoyo not too far behind and Bowers still way better than the new round of cheap imports. You could get a decent used set for under $1K. However, reliably measuring to .0001" with either a bore gage or hole micrometer is asking a lot, short of systems like the Sunnen you noted.

Pins might still be your best bet, especially if bore straightness and roundness are issues. Probably worth understanding how your customer will check these. As you know, whatever you read immediately after boring or lapping these holes on a lathe will likely be more than .0001 different when the part cools down.

A shop I worked at in around '77 or '78 used an air bore gauge system for tight tolerance bores in some valves we were making for the military, Navy I think. I don't remember a lot about how it worked, but it seems like we would slide a pin in the hole and read a gauge that was calibrated in .00001. The gauge was calibrated off the air leakage around the pin. The inspection area was hospital clean and temprature controled. I've never seen this system used since and have no idea where you would buy it. I do remember that it was supposed to be big $ though.

We do a lot of work as you describe and although it is somewhat unorthodox, we use a small high end digital height gage. The machinist places a small precision ground plate on the lathe ways and sets the height gage ontop to allow for dimension checks without removing from the machine.

Here is the gage we use:

Fowler Sylvac Z-Cal Height Gage

I couldn't believe that is what they use, but it seems to work pretty well.

The stated accuracy for that height gage is .00024", which is allready out of his tolerance range. Interesting idea though.

Air gage is the only way to go for under .0001 tolerances. Mahr / Federal products makes- or made them. Most plugs are custom made and you need a setting ring to set the gage. There has to be tons of surplus ones on the market.
Here is one link for more info:Willrich Precision - Chatillon, Digital Force Gage, Mitutoyo, Starrett, Mahr, Federal, thread gages, force measurement, surface roughness gage.
Dan

Dan from Oakland said:

Air gage is the only way to go for under .0001 tolerances. Mahr / Federal products makes- or made them. Most plugs are custom made and you need a setting ring to set the gage. There has to be tons of surplus ones on the market.
Here is one link for more info:Willrich Precision - Chatillon, Digital Force Gage, Mitutoyo, Starrett, Mahr, Federal, thread gages, force measurement, surface roughness gage.
Dan

Click to expand...

agree with that, air gauging is the way to go, not too expensive, and custom plugs and ring setting gauges need making for each size, but repeatability is second to none.

I was forgetting about air gauges. Never saw one, so never used one. Could be a bit of a pain in the butt to measure with that in the lathe no? and when the part is a blind hole then you need custom setting rings surely with same depth and all that as you may not get exactly the same air leakage as if it was a through hole, but I suppose as long as you have the ring gauge you can make a blind hole sleeve with an o-ring to back it up and go from there? Oh and you'd probably need to be really darn close to finished size, how much range does one of those have? maybe a thou?

One problem I have with pin gauges is that for one thing its not a true reading, and usually it takes a few tenths above pin diameter before it really goes in, feels that way anyhow.

SND
No matter what gage you use, they all have some advantages and some disadvantages... what matters is reliability...

Is your shop temp and humididity controlled? 24 hrs a day, every day all night, all year??... If not, and your grinding equipment for OD's and ID's not in real good condition? Then talking about .0001 is living in fantacy land...

Air gage is the best. I've used Edmunds with good success. They make special plugs for blind holes and just about anything else you can think of. It's just a probe on a small hose, so it's no problem to use on the lathe or anywhere else. They work good with honing machines because the oil doesn't matter.

CH

air micrometer

Yeah, we've got an edmunds set up here and it is a real nice tool for measuring our precision bores. Cost is about 5K including custom tooling for measuring parts of same dimension. Could be used on a lathe between cuts if you wanted.

Joey

I think you (or your customer) is definitely living in fantasyland wanting bores that are +/- 0.0001" and be able to read them for $1K-$2K for 1.5" of range.

Here's how we break down bore gauges here.

At the top of the list is dirt simple plug gauge. Don't use them for anything under +/- 0.002" and won't check for out of round.

Next is a dial bore gauge. Can be used successfully down to about +/-0.0005" (maybe 0.0003" with good operator). Are fairly versatile and can be setup fairly easily with a set of gauge blocks.

There's also a guage some refer to as a Holeshot gauge. It has three little feet that go out from the center of the gauge until they all seat in the bore. Then you just read the number on the gauge. Don't have much experience with these. Haven't found them reliable for horizontal measuring applications.

Next is a twist on a dial bore gauge. Mahr's term for them is Dimentron. They're basically just a fancy dial bore gauge mounted inside of a plug that eliminates any "rocking" action of the gauge. Put the gauge in the hole, read the number on the indicator on top. They read as good as the indicator you put on them. We use them with indicators that go down to 10 microinches. They have some range (+/-0.015" is advertised). Definately need a master ring to have much repeatability. The last ones we bought were about $500 for the plug and then you had to get an indicator too.

The top of the list is an air gauge. Microinch repeatability. Simple to use and accurate. Will need a plug for each size you are boring. Will need a master ring for each size. You can use them on the machine (provided you connect the plug to the amplifier with a hose). My #1 choice for bore measuring because of operator ability. Not very mobile though. A new one won't be in your budget either. The amplifiers run $2k-$3k new and then you'll need money to buy plugs and master rings.

I'd go visit some local hone shops and see what kind of instruments they have. It'll likely be Sunnen though. And I second the comment about seeing how your customer will measure them. For all we know he'll be checking a +/-0.0001" bore with a set of import calipers.

+/-0.0001" bores ain't cheap to make and ain't cheap to measure.

You are correct, Catman, they aren't normally cheap (they are for us, but we make basically a commodity product), and gauging IS expensive.
An air pin alone will generally set you back in the ballpark of $600-$1200 or so, depending.....

But, back to the OP, for that tolerance, air gauging is the only sensible way to go.

These two gages will handle most of your sizes;

844 K - Mahr Metrology

844 N - Mahr Metrology

You can use a micrometer to set them but a master ring is preferred.

Of course air gages are the best way to go but takes time and money to build a good library.

Athack

The Gods have answered you . looks like a great tool and cheap.

http://www.practicalmachinist.com/vb/tooling-parts-accessories-sale-wanted/precision-air-gage-f-s-212043/

Firstly, thanks everyone for the messages, I'll investigate further some of the possibilities.

This work definitely isn't worth investing any crazy amounts of money into. It's often 1 or 2 of parts, there's only a few types I do with with the .5000 bores and we are allowed to use the mating bearing for those. there's some A-286 stuff 40mm bores that I'd like to be able to check accurately(+.0004, -.0000) but again $300part that I may do 2-3 of in a year, so far they got accepted however I did them, and a few other random things like that. I just have no way to really certify 100% that it is right, even just being able to get a decent number might be fair enough for me. Reality is I don't know anybody around here really set up to inspect the crazy tolerances they put on drawings, some do think their CMM's are good to .00005" even if the spec sheet says +/-.0002"... but most times it either goes together or it doesn't, problem is if it fails and they decide to try to find someone to blame it on(which hasn't really happened yet either with any of the shops I know making the same/similar parts)

Right now there's 1 particular part (qty2) I'm looking at and is the reason why I thought to look further into getting some type of bore gauges even if I know there will be no way to even hold the craziness on this part. The problem here is engineering/drawing related, most dimension on thickness, OD, parrallelism, you name it is all +.0000/-.0001, and maintain a 8 finish on both sides doing so, in bronze. +/-.0001 is the bore tolerance. It has slots milled in with +.0005/-.0000 and 16 finishes on the walls, holes through, thing is gonna wanna move like a worm. Supposed to get roughed, stress relieved and finished, try holding that thing after stress relieving... All designed over 25yrs ago. I get the feeling the engineer was playing tricks as he was a very good smart guy from what I heard, so maybe this was the joke copy and there's probably the actual working copy hidden somewhere else. No current employee was there back when this stuff was being designed initially as they all retired and now a new unit got ordered. Due to its use I want to cover my butt as much as possible, and its possible other people will be doing it as I may No quote it, even if they are even less likely to hold that tolerance than I am. Sure would be nice to know what the heck they did first time around cause its still in service...

As to grinders in this area, never heard of anybody doing such work around here. Probably gotta go a 1000miles north/west before I'd find someone still doing any of that work holding a tenth and who's able to prove it, chances are they'll say " sorry but the auction is tomorrow ". There's probably a couple facilities near me with the equipment, usually government funded from long ago an it just sits there collecting dust while others play cards or something, but can't touch that... One customer had a nice full sunnen set of bore gauges with setters and all, but some temp employee put legs on it and it ran away, I just wish he had offered it to me.


I can say my shop is about as temperature controlled as it gets in my area, but I have no systems really in place for it(thought about it), its just super well insulated and stays around 68F +/-2F most of the year, it did get a little warm this summer(climate control eh?) but I wasn't making any parts that really made me care about that. Most of it is small stuff under 1", but this particular part is just under 3" which is about as big as things get for me.

I'll look further into the Mahr gauge as to pricing and all, and maybe just a plain dial bore gauge, it would do a fair bit of what I need. I think air gauging is way overkill for my needs and budget now, even if I could measure it to .000005 and prove its on size, if their bearing doesn't fit, I'm still the dummy who made it wrong.

My experiences with the size range and tolerance you specified: it's at the limit of a dialbore, requires a good gage (I've used Standard and Mahr) and a ring very close to size. Alternatively, a Marposs column with LVDT probe, again with a xx master ring sized at one tolerance limit.

This won't meet your tolerance requirement, but it will come close. Sunnen has a series of small bore gages along with a setting master micrometer. I think 3 gages cover from about .5 to 2.0. For one-off parts they are probably the most bang for the buck.

Sunnen also has their PG "parking meter" series gages that are more accurate than a bore gage, but require the parts to be taken to the gage.

They never learn........

Some times tight tolerances are needed, however.......

It was the early 80s and I was the new guy in R&D. Wasn't up to making waves, recession back then and all.

There was some raised voices and the problem seemed to be the .00003 tolerance given on a hole.

The old machinist wanted to know why he needed it"That €$¤÷ing close"

It" has to be" the edict came down. This from a designer who put numbers on a print so they looked "balanced", even amount of ink all over. Function and readability was secondary.

The old machinist, being an old machinist, went and made the part, a smile on his face. Took a while to finish the part, still smiling.

Part done, waits till several people were around(this was a running feud), and gives the man the part.

The machinist says" the hole is wrong........"

" Well fix it then" said the voice from on high.

"I will when you tell me if it's oversize or undersize......." As he walked away.

Needless to say, he didn't have to fix it. And I knew I found a home and a mentor.

Miss you Chickenfoot.......RIP

So far I've een suggestions for equipment for taking 0.0001" qualified readings but no mention of how to set them, calibrated setting references, or even comparison references.

If you have gaging equipment, you need a way to set it or calibrate it to the feature size. Most small shops have a set of Jo blocks. Some even have a set in current calibration. Few will have ring gages or if they do they are not in the range of the current bores to be checked. Fewer will have the gage block accessory kit that makes gage setting much more convenient. 0.0001" resolution readings requires equipment senstive enough to register 0.000025" (25 millionths bi-laterally. Most 0.0001" reading dial indicators in good condition will do that.

Air gaging equipment if set correctly will do it in a breeze (so to speak) but the various orifaces, gaging probes etc. have to be selected correctly and the fine adjustments made with two possibly three (for checking linearity over the range) setting rings for the size under consderation. Generally speaking air gaging equipment is only ecconomic for multple part checking and then if the correct apparatus components for checking the size range is already on hand. Air gaging can get fearsomely expensive in time and cost.

I'm asuming you're referring to 0.0001" readings you can take to the bank, that is, readings a metrology lab can confirm if necessary.

0.0001" range absolute meaurements that are repeatable by a third party with different measuring equipment are very difficult to perform reliably outside of a measuring room. You also need apparatus whose calibration is tracible to NIST standards.

Comparative readings where you seek a size deviating in 0.0001" increments from a mating part serving as a reference tandard is far simpler task. Here you don't care about absolute sizes; only deviation from the size you are using for a comparatve standard. Most any small shop can do that with fairly simple equipment including dial bore gages with good indicators with careful temperature control and compensation, and especally, repeat zero technique.

Will the budget stretch to calibrated gaging rings? If so a good 0.0001" bore gage set will perform the comparative readings for you.

Not mentioned so far is electronic gage heads and gage amplifiers. These use LDVT (linear displacement variable transformer) techonology and will register with complete reliablity down to 0.000005" (5 millonths) The probe type LDVT has a 3/8" dia barrel and will install as a direct replacement for an AGD dial indicator. Most have about 030" measuring range and the display is switchable in 3 to 10 ranges from 0.000005" to 0.0005 per graduation. A lucky shopper can find such apparatus for $200 to $500 on eBay. This would be the solution to your bore gagng problem provided your bore gage itself was up to snuff particularly in the linkage translating radial movement of the gaging probe to axial. The best employ frictionless design but you might discover a simple axle and bell-crank in the budget stuff.