# Need help with measuring internal diameter



## devils4ever (Sep 6, 2019)

Newbie here practicing making internal and external threads. For the internal thread, I've been making nuts for the external threads. I've been getting inconsistent results trying to measure the internal diameter of the nut. I started using my digital calipers, but was getting readings all over the place. 

So, I bought a set of Mitutoyo Telescoping Gages hoping to get reliable consistent results. Well, I'm not. The bore is about 0.600" and I'm getting readings from 0.595" to 0.605". So, I'm looking for advice on how to use these accurately.

Thanks.


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## JimDawson (Sep 6, 2019)

There is a trick to it.  You have to ''rotate'' the gauge through the bore.  Hard to explain, but easy to do.  Does require some practice to get consistent results.


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## Karl_T (Sep 6, 2019)

With practice, you'll do better than 10 thou accuracy with telescoping gauges. Still, its one of the most troublesome things to get accurate readings on bores. I won't use them when extreme accuracy is needed.

I've bought inside micrometers, they work quite a bit better. A bit expensive for a set to go down to 0.500".

I sprung for bore gauges, got them at auction. they are extremely accurate but you'd need DEEP pockets to buy them new.

Another thing to consider is pin gauges, great for small bores. If you only have one small job, you can make your own pin gauge, then fit your bore to the gauge.


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## C-Bag (Sep 6, 2019)

I've been using telescoping gages for decades and they are just like using a micrometer or anything else. It's all about feel and technique which only comes with practice. The major problem with them is it is a dual stage process because you have to have good feel to get the gage right, then good feel with the mic. I have thought a mic stand would help measuring the gage as that can be cumbersome to hold both leading to inaccuracies. But I'm so used to the whole thing I get well within .001 with my cheapo dial calipers and my gages. I was also shown the basics over 40yrs ago by an old oil field wildcatter. He basically showed me how he did it and what I was looking for in less than 5min. The rest was practice on that VW cylinder until I got the same reading several times on top and bottom to check for taper. Been good to go ever since.


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## benmychree (Sep 6, 2019)

You insert the telescoping gauge in the bore, with the spring released at an angle of perhaps 10 degrees off being straight across the bore, lock the lock and push on the handle to rock it over center in the bore, remove it and check for size with the mike, carefully feeling for the maximum size of the gauge; with practice, you should be able to measure a size within a few tenths of a thou easily.


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## mickri (Sep 6, 2019)

Newbie to newbie here.  I had this same problem.  I got all kinds of advice from the pros on here and I watched more videos than I can count.  Then I started noticing in some of the videos that the person had their thumb at the bottom of the hole keeping the bottom of the telescoping gauge in one place.  This was never mentioned anywhere. 




 As soon as I started doing this my readings got more and more consistent.  Using a micrometer stand helps too.  I don't have one so I used a small vice to gently hold the micrometer.  Another thing that I discovered was that outer edge of the hole tended to have small burs.  Removing the burs also helped with getting consistent measurements.  And practice and more practice.


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## mickri (Sep 6, 2019)

And another thing.  When you rock the telescoping gauge you start at a small angle and rock it to vertical as you pull the gauge out of the hole.  It is one fluid motion.   The thumb helps to keep you from going past vertical.  If you don't get the gauge to vertical you will get a larger reading.  If you rock the gauge too far past vertical you will get a smaller reading.


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## mikey (Sep 6, 2019)

devils4ever said:


> Newbie here practicing making internal and external threads. For the internal thread, I've been making nuts for the external threads. I've been getting inconsistent results trying to measure the internal diameter of the nut. I started using my digital calipers, but was getting readings all over the place.
> 
> So, I bought a set of Mitutoyo Telescoping Gages hoping to get reliable consistent results. Well, I'm not. The bore is about 0.600" and I'm getting readings from 0.595" to 0.605". So, I'm looking for advice on how to use these accurately.
> 
> Thanks.



Just to be clear, you do know that using a telescoping gauge to measure the ID of a nut with existing threads with a telescoping or ball gauges is not going be consistently possible, right? Not trying to be facetious; just making sure you understand this. These gauges require a clean consistent surface in order to work properly.

I wanted to add to what the other guys have said:

Telescoping gauges can potentially measure precisely. How precisely depends on what you use to read them with. For bore work a micrometer is suggested, not calipers.
Aside from technique, one of the main causes of inconsistent readings is human error. Trying to hold the telescoping gauge in one hand, the mic in the other and then trying to turn the barrel of the mic while holding both ends of the gauge in the dead center of the anvils and parallel to the axis of the mic is extremely difficult. A mic stand or small padded vise eliminates all of this. If you get serious about boring holes I suggest you buy a mic stand or set up a small vise to help you.
In order to read accurately, the convex ends of the gauge need to touch the mic contact surfaces pretty much in the dead center of those contact surfaces. If the gauge is off kilter then you will not get an accurate reading. The simplest way to assure accuracy is to get the handle of the hole gauge perpendicular to the axis of the mic spindle and then make sure the contact surfaces of the gauge are in the center of the mic contact surfaces. Again, a mic stand makes this easy.
When you assess the accuracy of your technique or your gauges, you need a known standard. I suggest you buy a ring gauge that is hardened, ground and calibrated to read in tenths. They are available on ebay and the precise size is not important, although you should have one to fit your telescoping gauges and one to fit your smaller small hole gauges. If you can consistently read those ring gauges with your tools then you know that your technique and the way you are reading them is proven and you can rely on them on your project.
When you measure a bore it must be clean - no debris or chips and no oil. Clean the bore and clean your tools before sticking them in the hole.
With all of that said, most hobby shop projects do not need tenths accuracy; that includes nuts unless you are going for a class 3 fit. I would guess the vast majority of boring needs would be met with a inside micrometer accurate to 0.001". For practical use, this is just fine; they are very accurate and easy to use with the part in the lathe. Mitutoyo, Starrett and any of the Swiss makers would work well.


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## ericc (Sep 6, 2019)

Are you trying to measure a nut's minor diameter, or are you trying to measure the hole before the threads are cut?  I recommend doing neither.  Try to look up a minor diameter in a handbook (like Machinerys Handbook).  Or, easier, get a tap drill size and just drill to that size.  A drill should be close enough.  If you are boring, you are measuring a straight bore, not threads.  Use a plug gauge, homemade if necessary, to test the fit.  Use thread wires to test the gauge.


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## Bob Korves (Sep 6, 2019)

Good posts above.  

A couple more things.  Using a telescoping bore gage is much more repeatably accurate when we can hold the gauge as square as possible to the bore axis, and rocking it through the diameter as square as possible and as centered as we can eyeball it.  Side loading create errors.  Using a bore gage while leaning way over, down, and sideways while reaching to make the pull is just asking for inaccuracy.  Try to get in a comfortable position when you can clearly see straight down the bore how you are doing.

The other thing is not overtightening the telescopic gage.  Doing so allows excessive forces to cause offset inaccuracies.  Tighten it just enough to mic it reliably afterwards and without being able to squish the measurement with the mic.  Over tightening also damages the gage, see the next paragraph.

Another thing is the telescoping gage itself.  If it is an old cheap one, with rust on the parts, inside or outside. you are much more likely to have errors.  If you gronk down on the screw and pull hard to get the gage through the bore, you are very likely galling the gage, which will make it less accurate for any user from then on.  Beware of used telescoping gages, and ones with visible rust.  I am not a tool snob, but my quite old Starrett telescoping gages still work like new and slide smoothly and evenly through the bore.  I would never trade them for anything else, the newer ones are not as good as an older set used by a real pro regularly and cared for properly.  Good work can be done with less good gages, but is not as repeatable and is more frustrating. 

After using good gages carefully for some time to get used to them, it is quite possible to get consistent readings repeatable to a couple tenths on work that is easily accessible.

Practice makes perfect.  I do not use telescopic gages regularly, so I practice for a bit to ensure repeatable results before measuring the money part.

Anybody can do it if they work at it and pay attention.


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## benmychree (Sep 6, 2019)

The way I described using my gauges is the way that I have done it since the 1960s, same Starrett set, and they still work fine.  I also have a B&S set that uses one handle for all the gauge sizes, it is longer than the Starrett models, and they also offered an accessory handle about twice the length, very handy for deep holes.  The tightening knob on the Starrett model is so small that it would be difficult to over tighten them.


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## devils4ever (Sep 6, 2019)

Okay, I'm getting a lot better results now. The video helped a lot. I thought the gage was placed in the bore and was slightly tightened, removed, tightened fully, and then measured with a mic. Now, I'm tightening the gage more and rocking it in the bore and I'm getting under a 0.001" variance now! More than enough for me.

I'm using it on a smooth bore. It's not threaded. I'm boring so I can put threads in it for practice.

I'll try the thumb technique, too! Sounds like a mic stand is in my future. Any plans for one? I'd like to practice making one.

I am using Machinery Handbook to set the minor diameter.

My gages are new from Mitutoyo. I assume a very good brand?


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## epanzella (Sep 6, 2019)

I measure the hole by rocking the gauge like the others have said but use the mike a little differently. My left hand is partially disabled so it's difficult for me to hold the gauge and the mike. I have a small toolmakers vice that I use as a mike stand. To measure the telescoping gauge, I preset the mike  a bit oversize and rock the gauge thru just like I did with the hole. I then tighten the mike a little and rock the gauge thru again. I do this untill the gauge drags slightly on the mike anvil. I can get within a few tenths that way. It's slow but it's the only way I can be accurate given my situation.  Obviously I just do this near the finish line and use dial calipers until I get close.


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## mickri (Sep 6, 2019)

I was going to make a micrometer stand and looked for DIY plans.  The simplest that I found used a plastic clamp.  Never got around to making a stand.  Too easy to put the clamp in the small vise on the work bench next to the lathe.


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## mikey (Sep 6, 2019)

The only real advantage of a mic stand is that it tilts, allowing you to read the barrel of the mic without having to bend over or twist you neck. A Panavise with a swivel base works just as well.


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## darkzero (Sep 6, 2019)

HF used to sell a micromter stand. Not sure what they are a copy of but it looks similar to the Mitutoyo one. Surprisingly it works pretty well, stable, holds a micrometer securely, & it's padded so it won't leave a mark on a micrometer.

I rarely use it though, I only use it when I need to measure multiple parts at a time. But it's good to have around for what they were selling them for. Best $7 or $8 I have ever spent there.


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## T Bredehoft (Sep 6, 2019)

Just a side note...


mickri said:


> . If you rock the gauge too far past vertical you will get a smaller reading.


Not so.

First off,  it will not get smaller than the hole is, never.

Second, the tightness of the gage is such that the telescoping action can operate, but not slip once it has been compressed. 

Third, if it's too tight you run the chance of breaking the handle when trying to _*slide *_the gage through the bore. pivoting on one end.

Lastly, never, never rock the gage through the bore more than once.


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## mickri (Sep 7, 2019)

I have been playing around with different stand ideas this evening and came up with these two using stuff I had on hand.







My lathe has a long bed.  36" between centers with room to spare.  The end of the bed is always clear.  The way protector that I use when changing chucks pretty much lives back there.  The first stand is two clamps with a hose clamp holding them together.  The second stand is a magnetic base that I rarely use because it doesn't have an on/off switch and collects chips like crazy.  And it doesn't have a way to lock the arm in place. Impossible to get accurate readings on the DI with the arm able to move.  It has a small plastic clamp held to the base with a hose clamp.  This is going to be my go to stand in the future.  It will probably live on the end of the ways.

Tom, you have forgotten more about machining then I will ever know.  And my measuring skills are not the best.  So you are probably right that going past vertical doesn't give a smaller measurement.  Still I had to go out into the shop and give it a go.   I found that if I only went a little past vertical my measurement did not change.  But if I rocked the gauge past where the edges touched the bore my measurement was anywhere from .0005 to .002 smaller.  Chock that up to really poor technique on my part.   Before I started using my thumb as a guide I routinely rocked the gauge way past vertical.   Been a learning experience for me.  Thanks for sharing your knowledge.


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## darkzero (Sep 7, 2019)

mikey said:


> A Panavise with a swivel base works just as well.



Oh that's a good idea. I never thought to use a Panavise but I got my Panavise after the HF stand. I love my Panavise but sadly it doesn't get used much anymore after I stopped messing with electronics. 

I also have a  Craftsman Panavise knock off with the suction base. Been sitting in the same spot on my desk for years. Lol. Maybe I should take em both to the garage so they get used again.


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## mmcmdl (Sep 7, 2019)

darkzero said:


> . Lol. Maybe I should take em both to the garage so they get used again.



Anything I take to the garage gets LOST again !


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## darkzero (Sep 7, 2019)

mmcmdl said:


> Anything I take to the garage gets LOST again !



My workspace is small so I'm pretty good with knowing where everything is. But I "lost" a 5/8 endmill that I never even got to use yet for over 2 yrs. I finally found the damn thing in my other good box of acid brushes, how it got in there I still have no clue. I quoted lost cause I didn't lose it, it was the damn gremlins!


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## mikey (Sep 7, 2019)

darkzero said:


> Oh that's a good idea. I never thought to use a Panavise but I got my Panavise after the HF stand. I love my Panavise but sadly it doesn't get used much anymore after I stopped messing with electronics.
> 
> I also have a  Craftsman Panavise knock off with the suction base. Been sitting in the same spot on my desk for years. Lol. Maybe I should take em both to the garage so they get used again.



Yup, a Panavise will work fine. I used one before I got a Mitutoyo mic stand. I didn't think parallax could affect how you read a mic but it can when boring at the tenths level; the stand/Panavise helps with that part. 

The other thing a stand does is help to tell you if your technique when using a telescoping or small hole gauge is correct. If you have a ring gauge then you know what the telescoping gauge should read. If you put the telescoping gauge in the mic properly, with the contact points in the center of the mic's anvils and the handle of the gauge is perpendicular to the mic spindle axis, then you know what that gauge should read when the mic juuust touches the gauge. If it does not read what the ring gauge says it should then the problem is with the way you are using the telescoping gauge and you need to brush up on your technique. 

A ring gauge and mic stand is to a telescoping gauge what a cylinder square is to a precision machinist's square. When it takes you two hours just to get to the boring stage of a project, you best have your technique down pat or you'll be boring that project all over again. Ask me how I know.


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## mmcmdl (Sep 7, 2019)

My space is actually pretty large being a garage and 2 basements , but my " work " space is still non-existent . Way way way too many projects going on !  I'm getting caught up slowly but it sure seems that every time I get an empty space , it's occupied with a new project within 72 hrs .


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## dpb (Sep 7, 2019)

I believe I read the following in one of the Gunsmith Kinks books from Brownells:
Take a junk bowling ball and cut a flat on it.  The flat does not need to be perfect.  Mount a small vise of your choice on the flat.  Get a short piece of large diameter pipe, and set the bowling ball on it.  The ball can now be rotated any way you please, to access the part in the vise.


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## francist (Sep 7, 2019)

That was and still is a very common method for hand engravers as well, the ball in question often being the size of a lawn bowling ball and of lignum vitae. Instead of a piece of pipe, a small pillow or doughnut of leather accomplished the same function as a cradle for the ball. 

In practise, the piece to be engraved was adhered directly to the flat on the ball using pitch, wax, rosin, etc and then popped off when done. The lawn bowling ball was just the right size to nest comfortably in the holding hand, but not so large as to not be able to grip.

-frank


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## NortonDommi (Sep 7, 2019)

mickri said:


> And another thing.  When you rock the telescoping gauge you start at a small angle and rock it to vertical as you pull the gauge out of the hole.  It is one fluid motion.   The thumb helps to keep you from going past vertical.  If you don't get the gauge to vertical you will get a larger reading.  If you rock the gauge too far past vertical you will get a smaller reading.


Sorry I have to disagree Mickri.  You can measure a bore at any point and the aim is to move the telescoping gauge from a position off perpendicular to the bore wall to perpendicular and then to an angle.  As soon as the gauge is nor perpendicular to the wall again it is free and this allows its removal for measuring.  Tension on the screwed in handle holds the setting though it pays to lock solid before measuring.  Trying to remove the gauge by sliding it out of the bore without altering its setting is impossible.


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## mickri (Sep 7, 2019)

I think that you misunderstood what I posted above.  I start with the gauge at an angle which you describe as "not perpendicular to the bore."  Look at the picture I posted above.  Then I rock the gauge to vertical which you describe as "perpendicular to the bore".  For me once the gauge is vertical (it could be just past vertical) the gauge slips out of the bore.  It is one fluid motion from start to finish.  So what are you disagreeing with?  My terminology?  Or????

One of my projects is swapping a Toyota 3 TC engine and 5 speed into my 66 MG Midget.  This requires that the drive shaft from the Toyota (2 7/16" ID) be mated up to the drive shaft (1 3/4" OD) on the Midget.  Spend part of the afternoon turning a bushing that slips inside the Toyota drive shaft and over the outside of the Midget drive shaft.  I wanted a very tight fit.  Lots of micrometer readings.  My new micrometer stand with the magnetic base got a real workout and preformed better than my expectations.


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## NortonDommi (Sep 8, 2019)

Well clearly I have misunderstood what you wrote and it seems not the only one.  I read that  "start at a small angle and rock it to vertical as you pull the gauge out of the hole" as meaning start with the gauge extended a bit, rock it to vertical,(square to the bore),and pull it out.   No offence meant!  You did state that if you rock it too far you will get an undersize reading though and that is impossible as once rocked 'over center' the gauge then becomes free.
  You are mad driving a midget!  Speedway is for motorcycles, I've seen those midgets and they are dangerous.


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## devils4ever (Sep 8, 2019)

Wow. A lot of great responses. Seems like we all are learning.


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## mickri (Sep 8, 2019)

I don't think that my 1966 MG Midget will ever see a race track of any kind let alone a speedway race track. 




Even with the Toyota engine it will only have around 85hp.  I have been slowly resurrecting it since I drug it out of field 2 years ago.


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## C-Bag (Sep 8, 2019)

devils4ever said:


> Wow. A lot of great responses. Seems like we all are learning.


I didn't want to get to deep into technique as writing about it is just going to confuse further. I wanted to give encouragement to practice and point out this is one of the many places you don't need more tools, just attention to technique and feel. I don't use my gauges everyday even though total experience is over decades. So it takes more attention than usual if I've not done it for a while as I'll forget all the details that have been pointed out. But once I'm "warmed up" it all comes back. Metrology is frustrating at first because we're dealing with such small tolerances and it can be hard to tell if it's tools or technique are the problem. No way to get around it except adapt and overcome.


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## epanzella (Sep 8, 2019)

Using tools with "feel" is a funny thing. I'm a retired contractor and I remember teaching a greeny how to cut rafters exactly the same with a circ saw. At first they'd be a 16th off this way or that but after  a few months  most would be right on. When asked what they learned to go from "off" to "on" they had no answer. They just magically got better with apparently no more information than they had before. It's the same way with mikes and other gauges.  You could know nearly all there is to know and not be very consistant, but as you do it day in and day out your brain, eyes and fingers get used to working as a team and you just start to get better. It's magic!


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## Bob Korves (Sep 8, 2019)

epanzella said:


> You could know nearly all there is to know and not be very consistant, but as you do it day in and day out your brain, eyes and fingers get used to working as a team and you just start to get better. It's magic!


That is indeed true!  

The problem is that many/most of us are HOBBY machinists, who never do it full time, and may not go back to any given technique or skill until the next time we need it for a somewhat similar project, which can be years apart, and quite possibly never again.  So, we have to get our game brain on, prepare and refresh our memories, learn it from written text from a H-M posting or a YouTube video, new and outright if it is our first go at it (and hoping the advice is correct,)  and all of this by ourselves much of the time.  And that is quite a different thing than practicing it every day after being shown how to do it right by an experienced pro.  We are doing well to at least get ourselves properly prepared for any dangers that come with the operation, much lest try to get it perfect on the first try or the first try in 10 years.  Much of the advice we get is not even correct, and the genuinely inquisitive, curious, and cautious will have a lot better "luck."


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## epanzella (Sep 8, 2019)

Bob Korves said:


> That is indeed true!
> 
> The problem is that many/most of us are HOBBY machinists, who never do it full time, and may not go back to any given technique or skill until the next time we need it for a somewhat similar project, which can be years apart, and quite possibly never again.  So, we have to get our game brain on, prepare and refresh our memories, learn it from written text from a H-M posting or a YouTube video, new and outright if it is our first go at it (and hoping the advice is correct,)  and all of this by ourselves much of the time.  And that is quite a different thing than practicing it every day after being shown how to do it right by an experienced pro.  We are doing well to at least get ourselves properly prepared for any dangers that come with the operation, much lest try to get it perfect on the first try or the first try in 10 years.  Much of the advice we get is not even correct, and the genuinely inquisitive, curious, and cautious will have a lot better "luck."


You're so right Bob. I must have leaned to weld 20 times over my life but between stick, TIG and MIG, and the fact that I don't do this for a living, considerable time could pass between doing certain welding processes. What usually happens with me when I'm using some process that I haven't done in a while is I start out like a total hack and by the time I get decent again the project is finished!


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## NortonDommi (Sep 8, 2019)

Looks like you need some windy roads.  The midget I was thinking of was one of these:


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