Need some advice on measuring inside diameters

I'm about to start on a project that will require me to measure the inside of a bore to an accuracy of about 1/2 a thousandth. The bore will be some- where between 2 and 3 inches.
Can someone tell me what the most cost-effective tooling is to do the measurememt? I've tried the cheap Enco telescoping guage sets and I can't get a repeatable measurement from them.
I don't have an unlimited budget so I'd appreciate a solution that won't make a major dent on my budget.

Do you know why you aren't measuring the bore to the same dimension? The telescoping gauge set should do the job if you are careful with it. Inside measurements are rather difficult to master for most people without somebody to show them when they are doing the job wrong.
-- Why isn't there an Ozone Hole at the NORTH Pole?

says...
  Quoted Text Here  
You could buy a dial bore gage but that will probably bust your budget. I would say that you should practice with the telescope gages and a good micrometer, without too much effort you *should* be able to do a half thou with those.
Find somebody near you who has used them a lot, and practice checking bores with them, and see what kind of numbers they come up with, vs what you come up with.
You might also consider a pair of spring leg ID calipers, you might not have good luck with telescope gages but maybe have a better feel with the spring calipers.
Another approach would be to purchase an ID micrometer, those work well in the range you are working in. In between the telescope gages and the dial bore gage in cost.
Jim

  Quoted Text Here  
    I agree with this. The main trick is to develop the right feel. Start by letting the telescoping gauge expand within the hole tilted slightly. Tighten the knurled knob at the end just enough to give a little drag, and rock the gauge through the point of maximum drag. Snug the knob down a bit more and check whether the gauge feels the same rocking through that point again. (If it doesn't, you've disturbed the setting while tightening.)
    Once you get it locked with a known drag, then take it to a micrometer. In the size range you are talking about, I would suggest a bench mount for the micrometer, so you have your hands free to do other things than support the micrometer. slowly tighten the micrometer until you feel the drag as you rock the gauge through the point at which the gauge rods are parallel to the spindle. Repeat this until you get consistent readings.
    Go back to the bore, and try again. Keep doing this until you are getting repeating readings.
    Note that the feel as it passes through center will be different in the bore and between the micrometer anvils, as the surface finish of the two is different (unless you are lapping the bore to an amazing finish. :-)
    And I have not used the cheap Enco sets. I first learned on a set sold by Sears (as Craftsman) which is not self-centering, and have since acquired a smaller set of self-centering ones by Starrett. Given who made the Craftsman micrometers and combination squares at the time, I suspect that this, as well, was made by Scherr Tumico, but I don't know for sure.
  Quoted Text Here  
    Good advice -- if you can find such a person.
  Quoted Text Here  
    Perhaps so.
  Quoted Text Here  
    There are two basic styles. The more affordable ones have a micrometer thimble with a range of 0-0.500", and a set of shanks which screw on to add precision distances in half-inch increments. The feel for this should be similar to the telescoping gauges. But it is harder to use deep into the bore. While there is a handle to hold the gauge down there, getting a fingertip down to turn the micrometer thimble is a problem.
    Much better -- but expensive new, and each covering a limited range (e.g. 2.4-2.8") are the various flavors of tri-mikes. There should be a setting ring with each one. The larger ones read in steps of 0.0002" IIRC. The smaller ones in steps of 0.0001"
    Most of mine (including sets) are made by Tesa, and sold under the Brown & Sharpe label.
    The only one I find on a quick search of eBay is too big for your project, and is a newer one with a digital head as well, so it is going for a rather steep price -- $350.00. But it will show you what I am talking about. The auction number is "3872855627", and the URL (pared to the essentials) is:
    http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item872855627
The big ring in the second picture is the standard. You measure the ID of this to calibrate the micrometer.
    When measuring, three arms extend outward at 120 degree angles, so it is self-centering in the bore, and gives excellent repeatability.
    And I can tell you that I have gotten a set of four of the smaller ones (0.400" to 1.200" IIRC) with two standards (the standards are sized so they are the maximum size of one micrometer and at the minimum size of the next), plus an extension handle for reaching deeper into a bore to take your measurement, for less than this one is currently selling for. (But mine were standard micrometer thimbles, not digital readouts.)
    Since each covers only a fairly narrow range (the bigger ones a wider range than the smaller ones, as this one in the auction is 5.000" to 6.000"), you do need to know your size a bit more closely, unless you get lucky, and wind up with a set covering the range and with a full set of standards for zeroing these micrometers.
    These are my own favorite way to measure IDs.
    There are also, getting into the *very* expensive ones, gauges which depend on feeding compressed air into a gauge plug which puffs it out in several directions, and precisely measures the bore diameter by measuring the change in air pressures. These are used in production testing, and I believe that they have a very limited range.
    I hope that this is some help,         DoN.

<snip good stuff>
I'd want to hear from someone who gages bores every day before commenting on the practicalities of this, but I sat through a lecture by a real expert on the subject back when Mitutoyo (then my client) introduced their first digital bore gage. I had a lot of questions for him, and, if I recall correctly, these were some of the things I learned:
In an engine cylinder, if you're measuring a newly-machined or Sunnen-honed cylinder, the three-legged bore gages are great. The cylindricity of those bores is quite good and what you're measuring is variations in bore diameter from the top to the bottom of the cylinder.
OTOH, if you're measuring a worn cylinder, they may not be so great. These cylinders may be elliptical at the bottom, and the three-legged gages won't tell you the amount of ellipticality [is that a word?]. The important point is that they will undervalue the maximum diameter, thus misleading you about how much metal you have to bore or hone to restore cylindricity. Once you machine the bores, though, and you've restored the cylindricity, the three-legged gages are, again, great.
To measure an elliptical bore you need something that will gage specific diameters at specific radial angles around the bore (primarily parallel-to and perpendicular to the crankshaft centerline), and the practical way to do that is with a two-legged gage. Of course, using one and getting accurate results with it is tricky. But according to that lecturer, that's the way to do it. I have a set of B&S telescoping bore gages, and he told me that I should practice with those, since it was engine cylinders that I was most interested in. He said that's the way he does it, and he can get his hands on any kind of gage he wants.
Again, this guy is a gaging expert, not an engine restorer or builder. His point may be more academic than practical. But he sure knew his bores.
-- Ed Huntress

  Quoted Text Here  
Well, not every single day but on a pretty regular basis. Two main types of bores; engine cylinders and counterbores for valve seat inserts.
before commenting on
  Quoted Text Here  
on
Sunnen-honed
diameter
Hmmm. On an engine production line it may well be that they take a statistical view about ovality and use three-legged gauges to just check for average diameter but I don't think you'll find many engine reconditioners or race engine builders doing that. The ovality is one of the main things you want to check for, even on a freshly bored and honed cylinder. Most engine bores I've measured, and that includes brand new OE manufacturer ones, are bigger perpendicular to the crank axis than parallel to it.
  Quoted Text Here  
won't
point
about
do
to
The only way to get both speed and accuracy is with a dial bore comparator. Telescoping (T) gauges are slow and fiddly at the best of times and generally over read slightly. They work better in hard materials and with fine surface finishes. In soft materials like aluminium they make a slight indentation as you rock them over centre. I have to use them for measuring valve seat counterbores in aluminium heads because there isn't enough depth to get the dial bore gauges in without fouling the bottom of the bore. I'd say at best I can work mine to about half a thou. That's within the tolerance I need for machining the inserts to to get the correct press fit but if I could use a dial bore gauge I still would.
If the OP needs half a thou accuracy then get a dial bore gauge. If he has to use T ones then get the best quality he can afford because cheap ones tend to stick and grab. However top quality T ones can set you back as much as a good second hand dial bore gauge. To get any repeatability with T gauges you need to practice on a known bore or a micrometer.
A good way is to get two mikes and set one up in a vice at a given size. Practice rocking the T gauge over centre across the anvils and measuring the result with the second mike. You can either aim to get the correct reading or to get a consistent over reading. The latter is probably easier. -- Dave Baker - Puma Race Engines (www.pumaracing.co.uk)

snip------
  Quoted Text Here  
comparator.
I agree. To use them properly takes time.
and
  Quoted Text Here  
depth
If you can't make them work in aluminum and hold a couple tenths, it's not the fault of the telescoping gage. They're certainly capable. I've done it and had perfect results time and again, and holding .0002" tolerance. Mind you, my work was always inspected by an impartial third party, so there was no escaping the truth.
Success in using telescoping gages is all in how they are applied, and experience. I propose to you that you have too heavy a hand. That's curable.
Harold

  Quoted Text Here  
with
slight
measuring
I'd
fit
there
I think my hand is fairly capable but my T gauges aren't. Mine are not the best set in the world and need to be nipped up a tad tighter than I would like before you rock them over centre or they slip. A Moore & Wright or Mitutoyo set would be nice but they cost over £100, or $200 in your funny (and rapidly diminishing in value) money. My T gauges are Draper Expert ones which cost about £20 and work well enough to get me within the tolerances I need for the specific job they were bought for.
For anything else I can get a dial comparator into I use those instead. I have three sets which cover the range from 0.5" to 6" and cost me only £100 for the lot second hand from a metrology lab. The nicest is the 2" to 6" Mitutoyo which reads to 0.0001". The other two are fairly old ones with 0.001" dials. For under 0.5" I have an expanding small hole gauge. A split ball end with a tapered expander inside which opens the two sides as you turn the adjusting screw. Adjust until it just rubs in the bore and then mike it up across the ball ends.
As I said to the OP, if he wants precision with T gauges then buy the best he can afford but they'll cost as much as a good second hand dial comparator and still be slow and fiddly to use. Frankly they aren't state of the art technology anymore and there are better ways of measuring things.
Not that I doubt you but using T gauges to 0.0002" is stretching my credulity a bit. That's close to the limits you can repeatably use a micrometer to for an o/d measurement and well beyond what most people would claim they can do for i/ds with T gauges. However perhaps you are a measuring god with abilities beyond those of us mere mortals. -- Dave Baker - Puma Race Engines (www.pumaracing.co.uk)

On Sun, 13 Feb 2005 15:07:04 -0000, "Dave Baker"
  Quoted Text Here  
THese are rips of the old Standard gage design, but not only do not address the problems inherent in the Standard, they're not as well made. I had a set of them, from .750" to 6", figure I was lucky to get the $20 I sold it for. (I also told the sucker, ummm, customer not to bring them back if they started to stick, I won't fix them.) The footpiece on the Mitutoyhoho is aluminum, galls if not kept lubed well, and temperature sensitive beyond any use in a non controlled environment. Standard is bronze, better, but the cause of most of the problems we had. Tool steel would be better, but probably more prone to corrosion and even worse problems.
Greybeard

wrote:
  Quoted Text Here  
I've always liked Standard gauges. Not as good as Sunnen though. I had problems with several Standard gauges being sticky. Part of the problem was wear from being used by the hone dept. There were scratches on the moving parts as well. After sleeving (with aluminum nickel bronze) and polishing out the scratches they were once again accurate enough to measure to .0001". But before repair you really had to be careful. ERS

snip----
  Quoted Text Here  
That would make a huge difference. I've handled such gages and they do make measuring more difficult.
I'm partial to the sets that telescope from both ends, keeping the handle towards center. My Starrett gages are so built, and the lock is made to function properly. I trust them for close work and don't get let down.
A Moore & Wright or
  Quoted Text Here  
ones
I
Yet you claim they won't work to .0002"? My expectations from my tools are much higher, and I"m not disappointed.
  Quoted Text Here  
£100
I, too, own several dial bore gages, all of which are Sunnen. Lovely tools, but limited for use in shallow bores.
I have an expanding small hole gauge. A split
  Quoted Text Here  
I have a similar set, again, Starrett, but mine are the half ball, so they are affective in very shallow bores. My claim to fame was in producing small work when I was in business, so I tooled up appropriately. Again, I trusted my small hole gages when working in tenths. They are as good as the hands in which they are placed. If you learn the procedures, they are capable.
  Quoted Text Here  
comparator
Perhaps, but are these better ways in the future for many of us? It's like a CNC versus manual machines. Knowing how to run manual machines and having the skill to do it properly is something that will serve you for ever, and will serve one well without spending huge amounts of money. That, to me, is far more attractive as a home shop type, which I now am.
  Quoted Text Here  
You can't be serious! When I worked as a grinder, I was expected to read a micrometer within .000050", and did so routinely-----and could verify my readings with a Sheffield Shadowgraph. I recognize that the surfaces involved were far better than machined surfaces, which makes a huge difference.
and well beyond what most people would
  Quoted Text Here  
I claim nothing more than having mastered my trade, at a level that allowed me to survive in the world I knew, which I did. If one can't read T gages to .0002", it's a lack of skill, or poor gages. Decent gages are capable.
Understand that there is a huge difference between building race engines and producing tooling for the aero-space industry. That's not to diminish in any way the importance of your work, nor the level of skill involved, but they are two very different arenas. In order for me to have been successful (which I was) I had to master certain things, and master them well. You, no doubt, have skills that I have yet to master, and may never. I wouldn't expect an automotive machinist, *any* automotive machinist, to step in and do the work I did, no more than I'd expect to step in and do the work they did. We are not trained in the same way, and in many instances the work bears little resemblance when compared.
Harold

  Quoted Text Here  
I've used these, I have a small selection of them. I get the impression that they are somewhat less accurate when fully expanded. For example, the .3 to .4 inch one seems like it's really opened up too far at .400 and that the ability to measure at that limit might be impaired.
Also the finish on the ball ends seems so-so.
Did you ever polish them to improve their function?
What other tricks can you suggest for using them to the fullest accuracy?
Jim

Harold and Susan Vordos says...
  Quoted Text Here  
they
Again, I
  Quoted Text Here  
as
are
I've never touched mine aside from using them, Jim. What it takes is considerable practice, and something against which you can verify your readings until you know the feel. Plug gages are quite helpful if you have them at your disposal, something like a set of Deltronic pins, graduated in tenths.
Regards how they often are somewhat wrong for the bore at hand, I agree. When you have them at the top end, you become *very* reliant on the feel, which is very light. You must transfer that same feel to the mic when making your reading, and that takes considerable practice. Again, it's a matter of doing it until you know when you're there, or not.
I'm of the opinion, especially now, after reading some of these comments, that some people are just plain too damned ham handed to ever get it right. Doing fine, precision work involves more than just understanding how to run machines. It's something that comes from within. I've worked with some good hands that struggled with tough projects, yet were fairly good on the machines. They seemed to lack that killer instinct that sorts out those that can from those that can't.
Some time ago one of the readers here posted that they had spent a half day in the shop of a guy that was a toolmaker, watching him grind the ways of a machine, if I recall. His comments rang true. It's not what a good machinist/toolmaker does, but *how* he does it that makes the difference. It is that quality that many lack, and will likely *never* have it. You don't learn it, *it comes from within*.
Harold

  Quoted Text Here  
LOL.
When I worked in production, that was the inevitable result when a new guy was hired on. He would invariably measure the ODs on parts as too small, and the bores would be measured larger than they really were.
The amount of error told one how long they would last working at that job. If it were a thousanth or less, they would be long-term candidates. If it were three or more, they would be gone inside a month.
They had the feeling that the outside micrometers were some kind of clamping device, crank that sucker down till you get the reading you need.
The bore mikes were treated like some kind of elaborate tailpipe expander. If the bore wasn't big enough, you *make* it big enough!
This is one reason I semi-jokingly suggested to the original poster that he *try* a spring-leg caliper. Those things teach *feel* more than anything else. Old time machinists didn't even measure a number when fitting a shaft, they just used an ID caliper to check the bore, transfered that to an OD caliper, and used that to check the shaft as it was being turned.
I keep a set of inside/outside spring leg calipers here at work. It's suprising to see how there are certain jobs for which they are still ideally suited.
Jim
Jim

  Quoted Text Here  
What do you mean, "old-time machinists"? <g>
-- Ed Huntress, Never a new-time machinist

  Quoted Text Here  
Hmmmm. I have inadvertantly trod a toe. <gg>
Seriously, though, if you suggested fitting a shaft like that, without even using a micrometer, to most folks in the trade right now, they'd look at you like you were crazy. And listened to that old fogey music....
Jim

Ed Huntress says...
  Quoted Text Here  
I know. That's exactly how I do it, or did it, when I actually had time to play in my shop.
I have about 15 spring-leg calipers, all Starrett, including a few hermaphrodites. My uncle rarely used anything else, and I inherited them.
I once had a pretty good feel for using them, but I don't know if I still have the touch.
-- Ed Huntress

snip----
  Quoted Text Here  
That's the key to success. Becoming familiar with how it feels and applying it consistently, and often, is the way it works.
It's like riding a bike, Ed. You may be rusty, but it's still there-----just needs some salt and vinegar! <g>
Harold

  Quoted Text Here  
    [ ... ]
  Quoted Text Here  
    While I have a Starrett set, I also have another set which I prefer. They were made by Lufkin (now out of that business, unfortunately), and are better in really shallow holes than my Starrett ones. The Starrett go beyond the maximum diameter point, so really shallow holes are difficult to measure properly. The Lufkin ones are ground down to the precise half way point, so they will measure anything which has a sharp ridge at all.
    Were the Starretts ever made that precisely? Do I just have a later version which is not as nice?
    Enjoy,         DoN.

  Quoted Text Here  
you
then
they
Again, I
  Quoted Text Here  
as
are
My Starrett set was made in the early '50s, and it's very nice and smooth. However, I've used them so seldom that I can't testify to their accuracy.
Most of the stuff they made then was really good quality.
-- Ed Huntress