Best option for bore measurement?

Jlel12 · Aug 19, 2013

Hi all,

My office has run into issues with bores on parts coming in under/oversized, and have decided to increase our in-house inspection capacity. I've been tasked with sourcing the equipment, and I'm currently trying to parse through the different options available to us - I was hoping to get some feedback and suggestions from the experts.

Here's our situation:
- We're a small engineering firm, and all of our parts are made by outside shops. We have some people with varying degrees of machining/metrology experience on-staff, but no dedicated machinists/QC folks, so we can't necessarily trust that the use of the tool we get will have the accumulated experience and "feel" of a professional machinist.
- Bores in our parts fall in one of three ranges: small (30-60 mm), medium (80-150 mm) and huge (around 250 mm - only a few parts this size, and all within a fairly close range). The aspect ratio of these bores is always less than 1, and is typically very small (shallow bearing recesses, for example). Finest tolerances that we call out are +0/-0.02 mm (basically +0/-.0007"). Walls around bores are rarely thinner than 2.5 - 3 mm.
- The purpose of these tools is a) to have a leg to stand on when we argue with our machinists that they've goofed ("I checked this +0/-.02 bore with my dial calipers" really doesn't hold water), and b) be able to determine, with reasonable certainty, whether bores are comparable across lots of parts. We don't want - and don't need - to spend a gazillion dollars to get a complete set of equipment.

The tools I'm looking at include (images in titles, for clarity):
- Telescoping spring gages: I personally have always been nervous about using telescoping gages (although that may be because I goofed while using them my freshman year of college, and blew a 3" tap). However, I've only had crappy gauges historically, and the surface finish on most of our parts is quite good (we call out 1.6 microinches on most parts). We have OD mikes that are good enough to measure these, and can get length standards.
- Internal calipers: I'm concerned that these will suffer the same issues as measuring with regular calipers - compliant arms, heat sensitive, prone to cosine error (I think it's a cosine error, at least - if the measurement isnt taken perpendicular to the bore axis). Not a fan, but can be convinced.
- Rod-type & tubular inside micrometers: Better than the calipers, but I'm still concerned about them not being perpendicular to the hole axis.
- Bore gage set: I've seen some of these with supposed "self-centering" wheels on one side, but I'm a little skeptical. The price point is attractive, though.
- Three-point bore micrometers (120-120-120): These seem like the best option, especially since they claim to be self-centering and self-aligning. Conveniently, they're also the most expensive.

Options beyond these are going to be excessive (i.e. Etalon 135-135-90 bore mikes, differential pressure gages, etc.). Regarding what sorts of errors we see/are likely to see on our bores (ovaline vs. 3-lobed) - I unfortunately don't have a good sense. It's about a 50-50 split between turned and milled parts (which I assume are interpolated and then finish-bored), for what that's worth. Let me know if there's any additional information I can provide to help clarify my situation.

Finally, apologies if I've goofed on terminology. I've read through a whole host of threads on this subject, and all the different names are starting to run together at this point...

Toms Wheels · Aug 19, 2013

Ease of operation with Normal employee, no background in machining etc. would be Go/no-go gages in the sizes you need. Green end fits red end doesn't. Not cheap but cost much less than a person who would know how to use any other real measurement tools. Less expensive are scissors type dial bore gages, These would need to be set by someone who knows what they are doing, and some training of the user in the technique of getting a good reading.

So much depends of how many parts you use and percentage of bad parts and the cost of lost time, labor etc, vs the cost of inspection. Do the bad parts cost you more than the cost of inspection. Or are the bad parts just a PITA without much cost.

5 axis Fidia guy · Aug 19, 2013

Dial bore gauge would be my first choice, once you set it up its a no brainer, give several guys telescoping gauges and you will get all different readings. With a go no go gauge its impossible to tell if the bore is actually round or not, a hole can easily be out of round if milled.

Rich P63 · Aug 19, 2013

For what it is worth...I have been a mechanical inspector since 1997 with 5 years before that as a machine setter for coinng presses and secondary honing machines for 6 years before that.

The only tool in your list I would consider checking a .0007" tolerance band with is the tri-bore mics. They also show standards in those kits which you can verify the tri-mic's against as well as develop some touch to get repeatability and reliability in your measuring.
Remember the "Rule of Thumb" or 10% rule
Your gage resolution should be 1/10 of your tolerance. For example, if your tolerance is .002, you need discrimination of .0002
the bore mic's like you are showing that I have used only had .0002" discrimination. Not sure these will even qualify for that but I have had good success and repeatability in the past with tri-mics like those shown; these could be your "last word" on those type of measurements. You also need to have a reputable tool manufacturer here to have faith in your equipment. You get what you pay for.

greggv · Aug 19, 2013

I also would go with the dial bore guage, for the same reasons as the Fidia guy.

Gordon B. Clarke · Aug 19, 2013

Jlel12 said:
Hi all,

My office has run into issues with bores on parts coming in under/oversized, and have decided to increase our in-house inspection capacity. I've been tasked with sourcing the equipment, and I'm currently trying to parse through the different options available to us - I was hoping to get some feedback and suggestions from the experts.

Here's our situation:
- We're a small engineering firm, and all of our parts are made by outside shops. We have some people with varying degrees of machining/metrology experience on-staff, but no dedicated machinists/QC folks, so we can't necessarily trust that the use of the tool we get will have the accumulated experience and "feel" of a professional machinist.
- Bores in our parts fall in one of three ranges: small (30-60 mm), medium (80-150 mm) and huge (around 250 mm - only a few parts this size, and all within a fairly close range). The aspect ratio of these bores is always less than 1, and is typically very small (shallow bearing recesses, for example). Finest tolerances that we call out are +0/-0.02 mm (basically +0/-.0007"). Walls around bores are rarely thinner than 2.5 - 3 mm.

I'm looking at your "problem" differently.

All your parts are made by outside shops. Unless those outside shops were chosen based on the cheapest offer I suggest you demand parts delivered to spec. Has anyone visited any of your suppliers to see how they measure and what they use to do so? As has been mentioned in another post the measuring equipment that should be used should preferably be 10 times as accurate as the tolerance and some of your tolerances are small.

You don't write how many parts you get delivered at one time but ask (no, demand) that each part has written on it what the measurement is. Find a company that has the necessary measuring equipment to verify if the written measurements are correct or not. You don't need to verify 100% as all you want to determine is how reliable your suppliers are.

If they aren't reliable then dump them and find others that are.

I'm also wondering what criteria was used to select your suppliers. Feeling you have to carry out inspection yourselves to get in spec parts is madness. Your supplier should be working for you - not you for him.

My advice? FIND RELIABLE SUPPLIERS. They might cost more initially but I'm certain you'll end up saving money.

Gordon

racen857 · Aug 19, 2013

- Three-point bore micrometers (120-120-120):

If you are talking about .0007 tolerances that is the only way to go and have any good proof of bad bore size.

Teleascope gages were great in the 50's and the tublar mics are good in good hands, but hard to get to .0007 on a regular basis.

Next thing would be give the testing of parts to 1 or 2 guys in the shop NOT everybody who walks in and thinks that it would be fun to measure parts once in awhile.

Mud · Aug 19, 2013

5 axis Fidia guy said:
Dial bore gauge would be my first choice, once you set it up its a no brainer, give several guys telescoping gauges and you will get all different readings. With a go no go gauge its impossible to tell if the bore is actually round or not, a hole can easily be out of round if milled.

What he said. A good Dial bore gage takes all the feel out of measuring, all you have to do is watch the gage dial as you manipulate the gage correctly, so it's more sure for less than completely experienced people to get reliable measurements with. Plus you can cover a wider range of size with one tool than a tri mike. I recommend Sunnen bore gages and setting equipment. There are cheaper alternatives but once you use a Sunnen all the rest seem like toys.

juergenwt · Aug 19, 2013

Toms Wheels said:
Ease of operation with Normal employee, no background in machining etc. would be Go/no-go gages in the sizes you need. Green end fits red end doesn't. Not cheap but cost much less than a person who would know how to use any other real measurement tools. Less expensive are scissors type dial bore gages, These would need to be set by someone who knows what they are doing, and some training of the user in the technique of getting a good reading.

So much depends of how many parts you use and percentage of bad parts and the cost of lost time, labor etc, vs the cost of inspection. Do the bad parts cost you more than the cost of inspection. Or are the bad parts just a PITA without much cost.

I kind of agree with Tom. Without willing to hire qualified people (if you can find them) I would go with a set of "GO-NO GO" gages. Since you are designing in metric does your engineering department follow ISO standards? I am talking about ISO/DIN 286 tolerance tables or do you just assign a plus/minus tolerance on your own? If you use ISO tolerance - like 30H7 - than you should be able to buy off the shelve gages at a reasonable price. If you do not use ISO than most likely the smaller sizes will be off the shelve items. For the larger size - 250mm - a local grinding house should be able to supply them. Google "Metric Round Plug Gages".
A word of caution: If you work in metric than buy your gages in metric. If you work in inch than buy your gages in inch. Do NOT mix the two systems - ever. Mistakes happen when you have skilled people doing it. With unskilled people - forget it.
Buying expensive measuring equipment and having unskilled people use it is a sure way to disaster.

The real Leigh · Aug 19, 2013

Gordon B. Clarke said:
You don't write how many parts you get delivered at one time but ask (no, demand) that each part has written on it what the measurement is.

Permit me to suggest a more formal approach...

Specifically, that each delivered part have a serial number stamped into it, i.e. by a metal stamp hit with a hammer, not an ink stamp.

By doing so you can track not only incoming conformance to spec, but also potential failures in service, correlating each back to the source.

Quality goes into a product before any metal is removed. It cannot be added as an after-thought.

- Leigh

PeteM · Aug 19, 2013

Another option would be an adjustable diameter/groove gage, such as those made by Mueller (and others):

High Quality Precision Dimensional Inspection Gages

These have a few advantages for your wide range of shallow bores:

1) A single gage can cover the entire range (as can dial bore gages).
2) These can rest at the top of the bore, which usually helps inexperienced operators get a good reading (unlike dial bore gages).
3) They are relatively easy to set and check.
4) The indicator typically reads to .0001"

I wouldn't expect actual accuracy (after various setting and measuring errors) to be .0001, but it sounds like this may be good enough. In addition, these would be clumsy to use if your bores have out-of-roundness issues. You'd have to approximate things by taking several measures across the bore -- and really a three point bore mic would be better. Be advised that bore mics typically come in standard and bottom-reading models. You might need the latter of you go that route, given the shallowness of your bores.

juergenwt · Aug 19, 2013

Gordon B. Clarke said:
I'm looking at your "problem" differently.

All your parts are made by outside shops. Unless those outside shops were chosen based on the cheapest offer I suggest you demand parts delivered to spec. Has anyone visited any of your suppliers to see how they measure and what they use to do so? As has been mentioned in another post the measuring equipment that should be used should preferably be 10 times as accurate as the tolerance and some of your tolerances are small.

You don't write how many parts you get delivered at one time but ask (no, demand) that each part has written on it what the measurement is. Find a company that has the necessary measuring equipment to verify if the written measurements are correct or not. You don't need to verify 100% as all you want to determine is how reliable your suppliers are.

If they aren't reliable then dump them and find others that are.

I'm also wondering what criteria was used to select your suppliers. Feeling you have to carry out inspection yourselves to get in spec parts is madness. Your supplier should be working for you - not you for him.

My advice? FIND RELIABLE SUPPLIERS. They might cost more initially but I'm certain you'll end up saving money.

Gordon

Gordon - we tried having a group of "Preferred Suppliers" and relied on them to deliver the perfect part so we did not have to check. Success rate was around 50%. At one time we had Japanese owners and they greatly promoted this way of doing business. They also promoted "Just In Time" delivery. Just like in Japan. It worked there so why not here? Well it did not.
I must say they where great in trying to find out why it did not work as in Japan.
The answer was not surprising once you took a close look at our "Preferred Suppliers".
Their preferred supplier in Japan employed a ratio of 20% unskilled to 80% skilled or semi-skilled workers. Here in the US it was just about the other way around. Mostly a short "On The Job" training period or just a short "load, push button, un-load". Some places with just a handful of skilled people mostly in "Set Up" and tooling. Not even in inspection (for the most part).
The 50% ratio for reliable vendors was a direct result of this.
We still used the "Just In Time" delivery and with bad parts coming in - guess what? Production suffered badly. It does no good if the parts come in just in time and than you have to stop everything. A "SORRY" from the vendor is not going to help.
Finding other vendors helped some times. First lot was OK, after that - forget it. A lot of re-work. OK we charged them but our production schedule went to hell.
So we went back to at least a partial inspection of incoming parts and a somewhat earlier delivery to give us a little cushion.
Ps.: It was not just our US suppliers given us a headache but also suppliers in Taiwan, China and Vietnam.

gbent · Aug 19, 2013

I'm with Mud on equipment. Sunnen bore gages and setting fixtures. The simplest, most versatile, and most cost effective method I know of to make .0002 accuracy measurements in the size range mentioned. IIRC, the large gage is 2" to 10"+, and the setting fixture is 2 to 8". The next smaller gage is about 1.2" to 2". I don't recall if it uses a different setting fixture or not.

Gordon B. Clarke · Aug 20, 2013

juergenwt said:
Gordon - we tried having a group of "Preferred Suppliers" and relied on them to deliver the perfect part so we did not have to check. Success rate was around 50%. At one time we had Japanese owners and they greatly promoted this way of doing business. They also promoted "Just In Time" delivery. Just like in Japan. It worked there so why not here? Well it did not.
I must say they where great in trying to find out why it did not work as in Japan.
The answer was not surprising once you took a close look at our "Preferred Suppliers".
Their preferred supplier in Japan employed a ratio of 20% unskilled to 80% skilled or semi-skilled workers. Here in the US it was just about the other way around. Mostly a short "On The Job" training period or just a short "load, push button, un-load". Some places with just a handful of skilled people mostly in "Set Up" and tooling. Not even in inspection (for the most part).
The 50% ratio for reliable vendors was a direct result of this.
We still used the "Just In Time" delivery and with bad parts coming in - guess what? Production suffered badly. It does no good if the parts come in just in time and than you have to stop everything. A "SORRY" from the vendor is not going to help.
Finding other vendors helped some times. First lot was OK, after that - forget it. A lot of re-work. OK we charged them but our production schedule went to hell.
So we went back to at least a partial inspection of incoming parts and a somewhat earlier delivery to give us a little cushion.
Ps.: It was not just our US suppliers given us a headache but also suppliers in Taiwan, China and Vietnam.

Thanks for the detailed reply but it raises more questions than answers. If the parts are critical and/or expensive I certainly agree with Leigh that each part should be identifiable although I wouldn't recommend "marking" a thin walled bushing with a hammer. I'd have them laser marked if marking is necessary.

That you have "suppliers" from so many countries suggests that large quantities are involved. I simply can't get into my thick skull that you can't find American suppliers that can't deliver parts to spec unless price is the predominate factor. You are prepared to offer time (your employees checking incoming parts) and buying expensive measuring equipment (and gauges expected to measure tolerances down to 0.02mm will cost) just because you have at present suppliers that can't (or won't) deliver what you order.

Try a simple experiment. Give the quantity and specs for some of your most common bushes here in PM and see who responds with what. You can also demand to know what their measurement capabilities are. Of course this information from potential suppliers needn't be made public here in PM but it'll let you know your possibilities and options.

As things stand at the moment, if you start measuring yourself then "just in time" will also have to include having the time to return defective parts and getting new ones that also have to be checked and that isn't exactly what "just in time" is about

If, no matter what, you insist on measuring (and doing what the supplier should be doing) then there is a relatively inexpensive method to measure bore diameter. Have a set of 0.001mm external micrometers (they are available up to 275-300mm) and one 0-25mm 0.001mm micrometer with a ball on the stationary anvil. Measuring the OD is simple and then just subtract 2 times the wall thickness. Not quite as accurate as expensive internal measuring options but certainly good enough to weed out the dodgy suppliers.

Having Taiwan, China and Vietnam as alternatives to the USA suggests price is what's giving the problem as I can think of a number of European countries that could give you what you want with one hand tied behind their back

Once you get a steady supply of "to spec" parts then you can start looking at price.

Gordon

Just after I posted this I took a look at what you've previously posted in other threads and I got very mixed signals as to who you work for and what you do.
Of course you don't have to tell me or anyone else but as said, mixed signals.

Halcohead · Aug 20, 2013

If you can afford tri-mic's, the additional cost of a dial bore gauge doesn't seem unreasonable. Those are certainly the two choices I'd make. You can do side-by-side comparisons for one size, and then use that to decide what preferred measuring tool might work for additional features as they come up. One thing of note--temperature, especially on aluminum parts, is important to control when measuring to those tolerances, especially on the larger sizes. I've never loved internal mics, and they are nearly as susceptible to feel as telescoping gauges.

Gordon B. Clarke said:
My advice? FIND RELIABLE SUPPLIERS. They might cost more initially but I'm certain you'll end up saving money.

Gordon

This is silly. Prototype/R&D engineering involves designing things that are frequently outside of or at the limit of the capabilities of any 1 given supplier, in quantities that do not justify the development of carefully controlled processes (or the drawings and documentation which that process may require). Furthermore, mistakes are inevitably made, either in drawings, design, or out of spec vendor work. Having in-house capability to inspect critical features allows an engineering company to take at least one of those variables out of play, while saving both the company and the vendor plenty of time. When doing R&D, the ability to nimbly identify and solve mistakes and errors is /far/ more valuable than depending on a supplier to be perfect every time.

Nick Mueller · Aug 20, 2013

Telescoping spring gages: Best chance to measure wrong. Transfer one dimension to an other and then try to measure that. -> crap!
Internal calipers: Not precise enough. -> crap!
Inside micrometers: Well, not the best option
Bore gages: Well, they are precise, but a pain to calibrate. You would need a set of calibration rings or gage blocks together with a clamp to stack them. -> Not for untrained people
Three point bore micrometers: That's the way to go. Quick and relatively easy to use. Unfortunately the most expensive way. especially if you have a lot of different diameters to check.

Re the argument that you need better suppliers:
How can he decide that his supplier is reliable, if he can't verify it?
Either buy the metrological equipment, or shop out measuring to an other unreliable source?

Nick

Halcohead · Aug 20, 2013

Well-said, Nick. Also a set of gauge blocks (and pin gauges) are in general quite useful for verifying and checking both parts and measuring tools. Case in point, a stack of gauge blocks plus two gauge pins can provide a quick and dirty check of bore size under desperate circumstances. Easy to feel oversize, and things just don't go together if they're under.

iMillJoe · Aug 20, 2013

Jlel12 said:
Hi all,

My office has run into issues with bores on parts coming in under/oversized, and have decided to increase our in-house inspection capacity. I've been tasked with sourcing the equipment, and I'm currently trying to parse through the different options available to us - I was hoping to get some feedback and suggestions from the experts.

Here's our situation:
- We're a small engineering firm, and all of our parts are made by outside shops. We have some people with varying degrees of machining/metrology experience on-staff, but no dedicated machinists/QC folks, so we can't necessarily trust that the use of the tool we get will have the accumulated experience and "feel" of a professional machinist.
- Bores in our parts fall in one of three ranges: small (30-60 mm), medium (80-150 mm) and huge (around 250 mm - only a few parts this size, and all within a fairly close range). The aspect ratio of these bores is always less than 1, and is typically very small (shallow bearing recesses, for example). Finest tolerances that we call out are +0/-0.02 mm (basically +0/-.0007"). Walls around bores are rarely thinner than 2.5 - 3 mm.
- The purpose of these tools is a) to have a leg to stand on when we argue with our machinists that they've goofed ("I checked this +0/-.02 bore with my dial calipers" really doesn't hold water), and b) be able to determine, with reasonable certainty, whether bores are comparable across lots of parts. We don't want - and don't need - to spend a gazillion dollars to get a complete set of equipment.

The tools I'm looking at include (images in titles, for clarity):
- Telescoping spring gages: I personally have always been nervous about using telescoping gages (although that may be because I goofed while using them my freshman year of college, and blew a 3" tap). However, I've only had crappy gauges historically, and the surface finish on most of our parts is quite good (we call out 1.6 microinches on most parts). We have OD mikes that are good enough to measure these, and can get length standards.
- Internal calipers: I'm concerned that these will suffer the same issues as measuring with regular calipers - compliant arms, heat sensitive, prone to cosine error (I think it's a cosine error, at least - if the measurement isnt taken perpendicular to the bore axis). Not a fan, but can be convinced.
- Rod-type & tubular inside micrometers: Better than the calipers, but I'm still concerned about them not being perpendicular to the hole axis.
- Bore gage set: I've seen some of these with supposed "self-centering" wheels on one side, but I'm a little skeptical. The price point is attractive, though.
- Three-point bore micrometers (120-120-120): These seem like the best option, especially since they claim to be self-centering and self-aligning. Conveniently, they're also the most expensive.

Options beyond these are going to be excessive (i.e. Etalon 135-135-90 bore mikes, differential pressure gages, etc.). Regarding what sorts of errors we see/are likely to see on our bores (ovaline vs. 3-lobed) - I unfortunately don't have a good sense. It's about a 50-50 split between turned and milled parts (which I assume are interpolated and then finish-bored), for what that's worth. Let me know if there's any additional information I can provide to help clarify my situation.

Finally, apologies if I've goofed on terminology. I've read through a whole host of threads on this subject, and all the different names are starting to run together at this point...

I work with bores about that size alot. I would sport for the 3 point mics.

Just DO NOT buy Spi, they are junk. They need there calibration checked before every use, and recalibrated every other use or so, even though they live in a climate controlled inspection lab.

Nick Mueller · Aug 20, 2013

Case in point, a stack of gauge blocks plus two gauge pins can provide a quick and dirty check of bore size under desperate circumstances.

That's an option of a machinist. But not for an untrained person. A three point bore micrometer with a ratchet/friction mechanism is something repeatable and easy to use. With the calibration rings that come with them, he has an object to train with and get reliable results.

The Mueller gages mentioned would be nice (and I personally would prefer them), but in my eyes are too demanding.

Nick

Gordon B. Clarke · Aug 20, 2013

Nick Mueller said:
Re the argument that you need better suppliers:
How can he decide that his supplier is reliable, if he can't verify it?

Nick

This is what I wrote in post #6

"You don't write how many parts you get delivered at one time but ask (no, demand) that each part has written on it what the measurement is. Find a company that has the necessary measuring equipment to verify if the written measurements are correct or not. You don't need to verify 100% as all you want to determine is how reliable your suppliers are."
I didn't suggest or imply that the "measuring source" should or would be unreliable.

Other than that I agree with what you wrote.

I've been in the situation a couple of times as described by the OP (although not quite as bad) and the solution was more focus on finding reliable suppliers and they were found.

Gordon

Best option for bore measurement?

Plastic

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Diamond

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