# Bore Measuring



## JimM

What do you guys use to measure the internal diameter of a hole when boring. 

Is it simply a question of of using the 'back' jaws on a digital caliper or would a set of gauges such as these be a better idea

http://tinyurl.com/o9wztx

I know they're only cheap but I'm just getting 'tooled up' so every penny counts at the moment

Cheers

Jim


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## cobra428

That's the bore gauges I use. Smaller holes I have a set of pin gauges I got from Enco also helpful in setups.
Tony


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## Metal Butcher

I insert an {expanding hole gage} or {telescopic bore gage} in the hole or bore, Then after being locked in on the inner diameter they are removed and measured accurately. I measure using a micrometer.

The import gages are not very expensive, there are other more expensive ways and tools used to measure holes/bores.

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=94873

I have-and-use a small set, and a large set, of hole/bore gages.

This is what they look like;
 Large Set- http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=5649

Small Set- http://jjjtrain.com/vms/measure_transfer_inst/measure_trans_06.html

Remember this If you search on the internet, "Gage is a widely used alternative spelling of the word gauge."

Heres a link to some really nice stuff! http://catalog.starrett.com/catalog/catalog/PLH2.asp?NodeNum=22078&Mode=PLIST


-MB


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## 90LX_Notch

Turn your own gauge(s) for the required diameter. 



Make one smaller then what you need and gauge to it first or use drill bits depending on the diameter. Then take light cuts until the final gauge fits. 

I did this recently for a project for my neighbor. I roughed the bore checking with my calipers. Then I used a drill bit as gauge to get within .004. Then I used a shop made gauge for the final diameter as I machined the last .004.


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## kvom

I recently got a set of expanding bore gauges. They showed that the inner jaws of my digital caliper were off by .003.


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## Noitoen

90LX_Notch  said:
			
		

> Turn your own gauge(s) for the required diameter.



Just an idea :noidea: Turn a gauge a little longer to the correct size and in the last few mm or in, make 2 or 3 steps of smaller diameter to aid in the last fit. scratch.gif


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## mklotz

The inner jaws of most dial calipers have minute flats on them which means that, while they can accurately measure the separation of two flat parallel surfaces, when used on a hole they acutally measure the distance between two very small chords of the circle. This ensures that they will always read low. If you own one, try measuring the ring standard for your inside mike with your calipers and you'll see what I mean.

True bore gages are hideously expensive and overkill for most home shops. The split ball and telescoping rod types shown in previous posts are very usable though they do require some practice to develop the right procedure and "feel" for using them. A set of pin gages is a worthwhile investment for any small shop since they can be used in more jobs that checking bore diameters.


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## Stan

Unlike Marv. I haven't been able to develop a good feel for bore gauges after thirty years of practice. Getting an accurate bore measurement is the toughest measurement I have to make. Consequently, I always make the bore first and then make the piston to fit the bore. It is much easier to polish down the piston than to enlarge the bore to fit.


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## tel

Noitoen  said:
			
		

> Just an idea :noidea: Turn a gauge a little longer to the correct size and in the last few mm or in, make 2 or 3 steps of smaller diameter to aid in the last fit. scratch.gif



For important bores that's what I do, with 0.005" and 0.002" undersized steps on the nose.


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## JimM

Thanks for all the replies guys, I've ordered the set from Chronos as it sounds like it will be useful

Also taken on board the other suggestions and no doubt will be trying them out as well in the weeks/months/years to come !

Jim


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## rake60

For small bore sizes I prefer my ball gauge set.

Here's a link to Enco's offering. *Small Hole Gage Set* 
It works and feels very much like a telescopic gauge but takes less
of a _feel_ to master.

Rick


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## Tin Falcon

I have used a variety of tools for checking bores. 
AF tech school I learned with 'T" Gauges 
I have a good small set of "T"gauges and small hole gauges the prices on the HF set are very tempting but have not tried them. 
When I worked as a pro machinist We used dail bore gauges and bore mics and air gauges very precise. But very pricey and overkill for the home shop although I do have an air gage to set up one of theses days. Like Dave said when the order of Round tuits finally shows up. 
Most recently Mrs falcon got me a .2-1.2 inside mic for my birthday. 
And last but certainly not least . I have a set of Moore and Wright Sheffield hole gauges this is a set of 7 gauges that are adjustable transfer tools that have balls extending from the sides near the end so they will gauge from .125 to .500 inch . 
Tin


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## BobWarfield

If it really has to be precise, dial bore gage. These are available for less money than you might think via eBay, but more money than you probably want to spend!

Nevertheless, deals are out there. I use these for bearing fits. 

For everything else, I have the telescoping gages. 

The advice to make a plug gage for your bore is excellent advice. It's easy to do and quite convenient to have one.

Cheers,

BW


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## gbritnell

As has already been stated, a bore gauge is great if you can justify the cost versus use. I served my apprenticeship using telescoping gauges (snap gauges) for most small to medium holes. I always had good luck with them but I developed a technique for using them. Measure once and check the size. Measure twice and see if that measurement matched the first. If it did you were generally good to go but if not, measure a third time to verify your measurement. I also bought a set of Starrett small hole gauges. These work but take a 'feel' to use them. After awhile I made a tool that would be as accurate as a telescoping gauge if not more. I made this around 1969 so there's possibly something out there similar today. It's not complicated, just a round bar with a square key along the bottom and a small dovetail cut into the end to hold one of my indicators. The moveable arm has a small ball tip made from drill rod and hardened and screwed into the arm. The arm is reversible giving me a range from .187 to 4.25 inches. The bar could me made longer but if would get a little unweildy. Usually when working up to my hole size I just put the ball on the moveable arm against my bore or slot and with the lock screw just snug I pinch the arm so that it slides out till my indicator reads. I then take a mike reading and adjust my cut. When I get close to size, .003 for example, I set the tool with my mike to zero first and then use it as a snap gauge. I find this is as accurate as what my machines will cut. Here's several pictures of my tool.
gbritnell


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## 90LX_Notch

gbritnell - Damn, that's cool. If I ever get a mill that's a definite build.


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## BobWarfield

Indi-calipers!

Or is it a Dial-Test-Caliper?

Ingenious!

BW


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## bob ward

gbritnell, that is GDF brilliant.


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## John S

I like it, that's really neat and far better than the kludge i have used over the years.






JS.


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## gbritnell

Hi John,
Similar idea, just a different way of getting there. I thought about making a fine adjust screw for mine but it would need to be released whenever the jaw was turned around for long or short measurements. Maybe I'll look into it a little farther.
gbritnell


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## ozzie34231

Beautiful Britnell.
I assume you broached the internal keyway???
Ozzie


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## gbritnell

Hi Ozzie, 
Yes I broached it. Through the years I have purchased several different size broaches for making key slots for my model engines, .062, .094 and .125. They come in handy for other projects like this one. 
gbritnell


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## IanN

Hi,

While Marv is correct in stating that if you measure an internal diameter with the inner jaws of vernier calipers there will be an error due to the fact that the jaws do not come to a knife edge, this error is not usually a problem.

My calipers have flats on the inner jaws that are 9 thou wide (call it 10 thou to make the sums easy). This gives the following theoretical errors:

Using these calipers to measure a one inch hole will give an error of two tenths.
Measuring a 0.5 inch hole the error becomes four tenths.
The error only really becomes an issue when you get down to hole less than 0.5 inch diameter - at 0.25 in dia. the error is eight tenths.

If you are worried about fractions of a thou, you will not be using these types of calipers to make the measurement anyway.

The real problem with using the vernier jaws is that you cannot assess bore taper.

Despite over thirty years in the business (15 as a machineshop instructor) there are still situations where I find it difficult to compare sizes with bore gauges. This is often due to the difference in "feel" due to the difference in surface quality between the bore and the reference (for example, comparing a turned bore with the surface of the micrometer anvils). To get round this inconsistency I made a DTI based gauge similar in concept to the ones shown earlier in this thread which removes the requirement to match the feel of the bore by relying on the DTI stylus spring to provide a constant pressure.

A further requirement that I had on the gauge was that it should have a reach of 1.5 inches to allow bore taper to be assessed.

My gauge is based around a design published in Model Engineer magazine in the 1980s and is designed to work from 2 inch bore (where my "stick" micrometer stops) down to under 0.4 inch.

By machining the contact pad on the swinging arm in-situ the tool reads accurately to one thou over the whole range of the DTI (0.25 inches).

The DTI reads "backwards" due to the operation of the swinging arm so I remarked the dial - in the case of the main dial this involved changing a 5 to a 15 and a 15 to a 5 which was quite simple. Reversing the numbering on the small turns counting dial was too fiddly and I produced a new paper scale.

The DTI shown can be replaced with a metric DTI. 

Gauge set to maximum







Gauge set to minimum






Gauge parts





















Ian.


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## gbritnell

Ian, that is a very neat gauge. It's not like I need another one but I'll probably make one like yours also. The only thing I would make a little differently would be to machine a little drill rod hemisphere with a stem, harden it and insert it into the end to give a finer feel to the high point if you know what I mean. I see you have somewhat of a radius formed on the ends of your levers.
gbritnell


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## IanN

Hi,

I agree the anvils should be machined to a better finish and hardened.

As I hinted in my previous post, I cheated when making the gauge anvils and the pad that touches the DTI stylus.

I simply filed the gauge anvils to a radius that ensured they would work within the minimum diameter the gauge was designed to measure (they ended up about 1/16th rad.) then machined the pad to suit using the following method:

Assemble the gauge without the DTI and set the unit in the mill with the DTI axis vertical.

Set the gauge jaws at maximum open and measure the distance between the jaws with a mic.






Clamp up and run a little end mill across the pad.






Close the mic by 20 thou and raise the end mill by the same amount and repeat.

Do this until you reach the minimum open setting for the gauge jaws.

You end up with a series of very small facets which are reduced to a smooth curve with a few strokes against some very fine emery paper held on a glass plate

This process compensates for all the lumps and bumps due to the imperfect shape of the anvils.

Ian.


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## gbritnell

Aha! just like when I make my camshafts.
gbritnell


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## Deanofid

Boy, there are sure some good ideas in this thread! Thanks George, John, and Ian, for sharing your methods.
I've become very used to using tele gauges to measure inside diameters over the years, and am even half-way good at it, but what you fellows show here would be a great addition to my shop without breaking the bank on buying an inside mic.

Dean


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## joegib

Hi,

I've read this thread with interest but I don't think I've seen an inside micrometer mentioned:






I picked up this Mitutoyo unit secondhand on EBay about a year ago for around £20. Although I have T-gauges and small-hole gauges I've never really got the right "feel" for them so I thought the ratchet action of the micrometer would compensate for that. TBH I haven't had the chance to use it on a serious job yet but testing it with various standards suggests it's accurate. The only obvious problem I can see with this device is that it only measures bore diameter near the entry  taper in the bore wouldn't be detected. Are there any other disadvantages?

Joe


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## pete

Joegib,
For even more accuracy you can set the I.D. mic. and measure across the anvils with a rachet equipped .0001 micrometer. No it still won't measure bore taper, But lapping would take that out.

Pete


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## joegib

Thanks for the tip.

Joe


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## Jan_Rune

Maybe an old post, but i have something similar to those great shop made tools in this thread. Its called an Unimeter. Even though this one is branded S.P.V i have one that is identical made by C.E. Johansson (CEJ) that i cant tell apart except the branding. 

Very usefull tool. I also have a similar type to measure from the outside that is made by Helios Preisser, Germany.

The smallest diameter you can measure with this one is 28mm. The SPV is cut down. I use this one for holes up to 60mm. Theere is also a extension shaft so you can measure bigger holes. For smaller holes i use a Mitutoyo 12-20mm bore gage or pin gauges if i can find the right diameter. I have two boxes full, maybe around 200-300 CEJ pin gauges. One day im gonna sort them. Atleast thats what i tell myself


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## lohring

Another idea for a cylinder guage is below.  You would need one for a particular diameter, but it is very accurate.  It would be especially useful for people making a multicylinder engine.

Lohring Miller 

View attachment 4bidg.pdf


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## Tin Falcon

Lohring : interestig article on the bore gage build. I like that it shows the theory behind it so one can make whatever size they need. 
Years ago I worked at a shop where we used federal Air coparators. I ended up buying one on e bay never got around to making probes for it. 

somthing like this. 
http://www.threadcheck.com/technical-documents/mahr-dimensonair-air-gage.pdf
Tin


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## petertha

Some really interesting gadgets presented here. 

How about initial setup of boring heads? Do you guys have a favourite method or 'pre-measurement' jig that facilitates knowing what the cutter tool sweep (=diameter) is accurately right from the start? I do the cut + measure method, but I thought it would be handy to 'know' the value with higher degree of accuracy beforehand & correlate that to the dial setting when its more of a finishing operation vs. progressively enlarging a bore. I've gotten tricked by cutting tool spring back or burr/finish giving me a false bore measurement. My crude method is clamping an old set of verniers in the mill vise & making contact at two max X-deflections. I envisioned a jig like attached sketch, but maybe there is a better method?


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## MachineTom

I generally set the boring head and then measure. Take an edge finder to the fixed outside edge of the mill vise. Zero your reading, then set your boring head to the radius of your hole to be.
Now adjust the cutting tool to just touch the vise jaw. Bore the hole. 
Just remember set the radius distance, not the diameter.


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## Richard Carlstedt

I have used a simple method for bore measurement for years
It requires a good mike, and a good set of adjustable parallels 
Cheap parallels are not consistent in corner construction ( radius/chamfer) , smoothness, or parallelism.
Insert the parallel and expand it, then read across the diagonal corners.
The parallel will center itself and also tell you the bore is tapered or bell-mouthed  by movement.
(That is, it will be tight inside and yet pivot at the bore entrance.) 
Works great and does not require special tools....although I do like Georges' measuring tool approach as well
Rich


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## gus

Gus is very ham-fisted when it comes measuring i.d. when boring engine cylinders. Digital Caliper gave me inconsistent readings. Bought a set of M.I.C. aka Made in China 20-----40mm, 3 point HoleTest Micometer from ArcEuroTrade,UK. Came with Ring Gages too. So far so good. Mitutoyo and Starrett cost me a bomb. With a price of one Mitutoyo Inside Mike ,I bought a set of 4. Tried asking for a 5--10% discount but Mitutoyo dealer won't budge. $$$$ came from Dividends. Retirees must watch their savings.


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## Jan_Rune

I just liked gbritnell's tool so much i put together one myself. Hope he dont mind


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## petertha

Jan_Rune said:


> I just liked gbritnell's tool so much i put together one myself.


 
That's really nice!

- the black bits look like maybe off a commercial accessory? Did you make it or modify it? Can you elaborate?

- I didn't have much luck finding a tiny dovetail cutter, but maybe I'm looking in the wrong place. Did you make the cutting tool or buy it?


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## Jan_Rune

petertha said:


> - the black bits look like maybe off a commercial accessory? Did you make it or modify it? Can you elaborate?



I cant really say i made it. Its just put together with stuff i had laying around. Yes, the black bits are from some kind of measuring rig made by CEJ. Came with a lot of tooling i bought sometime ago. 
















The 8mm hardened rod was drilled out with a carbide spot drill to fit the 4mm shaft of the Mitutoyo dovetail mount. The Mitutoyo mount was pressed into the hardened rod. Here is how the mount looks:






The rod mount for the "adjustable" contact point was bored out. So it fits around the dovetail thumb nut. Everything else was just put together for setting up the tool. Its really easy to use and i can measure holes down to 19.70mm. 


...


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## gus

Tin Falcon said:


> Lohring : interestig article on the bore gage build. I like that it shows the theory behind it so one can make whatever size they need.
> Years ago I worked at a shop where we used federal Air coparators. I ended up buying one on e bay never got around to making probes for it.
> 
> somthing like this.
> http://www.threadcheck.com/technical-documents/mahr-dimensonair-air-gage.pdf
> Tin[/QUOTE


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## tornitore45

Lohring,  I suppose the 4 ball gauge must be held on axis or it gives a cosine error.
What technique you use to keep the gauge on axis or the base perpendicular to the bore axis?


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## lohring

That error would apply to most of the bore measuring techniques.  It is very small even with a several degree misalignment.  The ball gauge measures over a small range.  If the cylinder holding the balls has a small clearance in the nominal bore that error will be almost non existent.  The article I posted suggests a tapered ring around the cylinder.  Look at the picture.  That completely solves the problem.  

Lohring Miller


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## tornitore45

Did not associate the tapered cylinder with its function.


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## fencer

I have a vernier caliper with rounded jaws on the outside edge allowing the measuring of bores.These have limitations as you can't detect a taper in the bore.I made a set of differet size size tapered parallels with round edges on the staight side ,used in different formats measuring with a mike gives an accurate reading .I will still make one of the guages shown.
Frank


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