Bore gages

I got a few bore guages at an auction. They are nice, accurate and fast. The set that uses three points to measure diameter are cool. But, not worth the price if you had to buy new unless you were running production on the same part all day long. Or, grinding a bore to a couple tenths tolerance.

I don't like telescoping guages - too putsy and easy to make an error of a thou. Of course, inside mikes don't go below 1", and you get a lot of need to measure in this range. You didn't mention gage pins, I like them for under 1" bores.

Karl

I'm looking at things like the Mitutoyo series 526. They *seem* to be basically like telescopic guages, but with a dial. The set I'm looking at goes from 1.4" to 6". I know that Mitutoyo makes them to work in holes as small as .240" diameter, but this one won't go anywhere near that small.

I've had good luck with them, but certainly they are not without their flaws. At the very least it sucks to have to keep measuring them - the bore gages should be a lot faster, if nothing else.

I think 1.5" is the smallest I've seen.

I use small-hole gages and telescopic gages pretty much exclusively at this point, but I'm considering broadening my horizons. 8-)

If you need the accuracy, they are great. We've got at least 30 Mohr gage kits here at work. Our kits can cover everything from .128" all the way up to .500". Kits consist of a digital head, various extension pins and the necessary ball ends and check rings. Takes about 30 seconds to set one up. When you have to do hole diameter checks on

500-600 holes in a single installation, it makes for fast inspection. Don't know what the kits cost, but I believe that you can start with just the head and one size set up.

Craig C. snipped-for-privacy@ev1.net

I don't think so! My experience is the low to mid price bore gauges have poor repeatability, and the higher quality ones are just too expensive to justify! I tried a couple of dial bore gauges out a few years back. I ended up returning them and went back to telescoping gauges. Greg

Good god man, you've never lived.

I've only used

Bore gauges are a must have if you do a lot of accurate i/d work. I have three sets. The main one for engine bores is a Mercer 2" - 6" which reads to a tenth of a thou. It does that fairly repeatably too. It's actually fairly scary putting it down most production bored and honed blocks and watching the needle move so far round the dial with taper and ovality. Most engine builders use a 1 thou gauge which makes a badly bored block look a lot less wrong. That gauge made me get my own boring and honing perfect though because it exaggerates small variations so much you feel like you've cocked a job up if the gauge moves at all.

The other two sets get used a lot less. One runs 0.75" to 2" and the other goes down to 0.5". They are both pretty old sets and read to a thou. The Mercer looked brand new and still does because I've taken care of it. I picked the lot up several years ago for 200 quid at a metrology establishment with a 0-1" dial gauge and a 3" to 4" Moore and Wright mike thrown in for free. I only went there for the Mercer but he kept bringing out stuff I thought would "come in handy sometime" and he made me an offer I couldn't refuse for the job lot :) Those places often have good second hand stuff for sale which they've rebuilt and calibrated. What my lot would cost new these days I shudder to think.

I only use the telescoping gauges for measuring valve seat insert bores in cylinder heads when I'm fitting unleaded inserts or bigger inserts. With a shallow hole bored down to a flat base there often isn't enough depth to get a bore gauge in and still be able to rock the pins over centre. I hate using the telescoping ones though. Slow and fiddly and you get a different measurement every time you use them. A colleague reckons you'll always measure slightly big with those and he tends to knock half a thou off whatever the micrometer says when you measure the gauge. Especially in soft metals like ally where the ends dig in a bit as you rock them over centre. One of these days I must have a play with a through bore and see how a T gauge reads compared to the Mercer.

For through bores like engines and especially long bores the dial gauges are the only way. You can take a reading in a couple of seconds and know it's right. You can map out a bore from top to bottom measuring taper and ovality to a tenth or so in no time. With T gauges it'd take forever and not be accurate anyway.

The three pronged gauges are very expensive and supposedly very accurate but no good for meauring ovality of course as you aren't just reading across a diameter. I've never found the need for one. I couldn't manage at all without the Mercer though.

Dave Baker - Puma Race Engines

You find somebody to love in this world you'd better hang on tooth and nail - the wolf is always at the door. (Don Henley - In A New York Minute)

Ah. There are two basic kinds of these things.. they really do mimic the small hole gages (with the ball-end) or the telescopic gages. The ones that you use are the small-hole-gage type. I'm looking for something to do up to

6" or larger bores. That would be a big ball. 8-)

You normally buy the ones of that style sized for a particular range, like 0.100" to 0.250", that kind of thing. There are a few sizes listed in my catalogue, running up to about 1.5", where the telescopic-gage-type takes over.

You're not the first to say that. 8-)

For the 2-6", in tenths, from Mitutoyo, brand new retail price down the street is $408.50 Canadian. The .750-2" would be about $310 (no perfect match in ranges; that's an average of the prices of two reasonable matches). The last one would be around $380. No perfect match there, either. So those three sets would run you around $1100 Canadian, which is still a fair bit when converted to pound sterling.

The sets at work have been through the wringer. Too many apprentices with no brains using them, I guess. The ends are worn flat. Probably tightened up too hard before rocking them.

I am usually dealing with short bores, but I'm still seriously considering picking the set up.

I bought a couple of Federal dial bore gages at work for some finicky bits. They are worth every penny.

Best is if you can set them with ring gages, I've been making do with micrometers. Not right but they still show variation at the 0.0001 level.

Jim

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That's definitely the best way I agree, not that I have any and have to make do with the mike for setting. It compensates for any error in how perfectly the gauge lies across a true diameter of the bore it's measuring which is down to the accuracy of the two contact feet on the measuring head. For engine work a few tenths is neither here nor there really when most pistons have a tolerance of -0/+0.001" on the bore size and plenty of production engines don't even get within that 1 thou range.

For comparison work on bore taper and ovality, knowing the true size isn't so important. For high precision engineering if you're trying to hit a tenth on diameter I'm sure ring gauges play their part.

Dave Baker - Puma Race Engines

You find somebody to love in this world you'd better hang on tooth and nail - the wolf is always at the door. (Don Henley - In A New York Minute)

Just a warning for using the mike. You will get to small readings (about 1..2/100 mm) if you don't put a load on the mikes anvil (pressing slightly outwards; 10 N force is about right to make the mike's ratchet work) when adjusting it. Don't forget to lock the mike's anvil under load.

I once cross checked a inner mike, a ring gauge and a mike and always got that error, so I doubted the ring gauge. But the ring gauge was only 0.5/1000 mm below size (I took it for calibration). The error came from the minor blacklash of the outer mike. Remember that mikes do have a ratchet, some backlash and need a defined load to be accurate.

Jo blocks and a special fixture or ring gauges are the only reliable way to set bore gauges. I do have only one ring gauge and use the mike.

Nick

I was going to mention Jo blocks also. I've got one of those cool racks to stack & clamp them in. Can't justify buying ring gages, especially with the Jo's already in hand. Have never bought a bore gage either. A few of us have a borrow club sorta thing. If ya need it, and the other guy's got it, go get it. Saves us some coin.

michael

I made my own ring guages. Piece of cake, just a little lathe work. After they are ground on the ID, you just need someone with a very accurate tool to measure them. Then stamp this reading on your homemade guage. In my case, I traded a favor with Joe Way (seen on this NG)

Karl

I can see how the 'dial' aspect of them would be very important when looking for the condition of a bore... when looking for bulges, waisting, out of round, etc. I'm primarily looking for a fast and accurate way to see where I am in the boring process so that after I take my final 40 thou cut, I'm where I want to be.

The set that I was looking at was an import, but looks pretty much like Mitutoyo. Would you agree with a previous poster who suggested that a bore gage isn't worth having if it isn't a big name?

I'd *like* .5" - 6", but what I see available for a reasonable price is

1.4" - 6".

Well ... I've never used one of the dial bore gauges either, but I do have a pretty complete set of Intrimics now -- in the range from the smallest to about 1.8", and a few in other sizes. This is thanks to haunting eBay for a while. One of the best buys was when two identical sets of four were up for auction at the same time, and the one closing second had a really splashy fancy description full of images, while the one closing first was just good enough. I opted to bid on the one closing first, since its price was a lot lower. I got it, and at the time that it closed, the other lot was already higher. One interesting thing is that the higher-priced lot did not have the proper wrenches needed for calibration and for installing/removing the (include) extension tube set. I think that I got the better deal by far. (The other one had current calibration stickers, which they made a big thing of, but both came with two setting rings (each ring covered the high end of one mic and the low end of the other).

So -- if you're not in a hurry, you might try tracking eBay for the sizes which you need most.

Good Luck, DoN.

There are two more things to consider. First, if you are looking at used ones, there is the issue of how accurate the movement is. Secondly, if the gage does not come will all the extension points, buying them can get expensive (If even available.). Extension can easily exceed $25 each, and sometimes it requires as many as 7 extensions to give a full range for a given bore gage. So a $50 Ebay 'buy' may not be such a good deal.

Hmmm. Most dial bores, or their electronic versions thereof, have a small range from the setting, usually less than 20 thou. Federal make some with a longer range, but they're three point, won't show out of round.

Again, this depends on what you want to do with it. I've seen some pretty decent homebuilds, and I've seen junk with big names on it. I'll admit a strong preference to Standard, I like the way the indicators are made, but the Federal, I think they called them the "500" series are good too. Both pricey as hell, hard to justify if you don't have need for .0001" accuracy or enough pieces to make it worth while. (The indicators on the Standard are shockproof, and they don't mean maybe. You could destroy the gaging foot, but the indicator wouldn't be hurt.)

Let me look through my junk, I had a bunch of them but I've also sold a bunch, don't really know what I have left, and you may have to learn to cut 3/8"-40 threads to make tail pins for them. I'll send an email when I look them up, might be a day or two, rebuilding a Boyar-Schultz surface grinder, and the owner wants it. Think there's a few Intrimikes down there too, but metric, and not a complete set. I know I don't have anything below 1", maybe not below 2", but I've got so damn much, I don't know what's down there.