# Measuring a Tapered Hole?



## kcmillin (Feb 25, 2011)

I have a few projects in mind involving tapered holes. I have made er32 collet chucks in the past and never bother measuring the hole because the collet itself provided a measuring device, also the size of an ER tapered hole is non critical, but what if it is?

How do I ACCURATELY  measure a tapered hole? 

Kel


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## mklotz (Feb 25, 2011)

I presume you want to measure the taper angle...

Measure the diameter at two locations separated by a known distance. Do the trig and solve for the angle.


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## kcmillin (Feb 25, 2011)

Marv, I should have explained better.

What I want to know is how to measure the major diameter of the hole. It Is kind of a guessing game with an inside micrometer.


Kel


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## peatoluser (Feb 25, 2011)

If you turned up a male plug gauge of a known diameter, insert into bored hole, and measure the sticking out bit with depth mike, should be able to calculate diameter of bore with trig.
If you need to bore to a known dia., make a couple of gauges of different diameters to check progress.
I usually make 3 - nearly there
             spot on &
             oh bugger ;D
the 3rd one seems to get used alot :


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## 90LX_Notch (Feb 25, 2011)

Kel, 

Without knowing the size of the hole-

If I were checking it in a qc environment, I would drop a sphere in the hole and throw it up on the comparator and measure across the points of intersection. With that being said, in the home shop I would do it with a sphere and a drop indicator. Measuring from the top of the sphere to the plane that the hole is in. From that measurement the diameter should be able to be calculated. Or draw the measurement in a cad program and dimension the intersection of the sphere and hole. 

Hope this makes sense.

Bob


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## kcmillin (Feb 25, 2011)

Bob, I like the sphere method. I will search for a good quality ball bearing. 

Also, I have since been doing research and found what is known as a "Chamfer Gage" Is this used to find the diameter I am looking for? They are quite expensive though.

Kel


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## 90LX_Notch (Feb 25, 2011)

Kel,

It's been so long since I used a chamfer gauge. Even then, I rarely used it. If I remember correctly, they're for measuring the depth of the chamfer not the diameter.

Bob


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## woodchip85 (Feb 25, 2011)

Without knowing the size of the hole-

If I were checking it in a QC environment, I would drop a sphere in the hole and throw it up on the comparator and measure across the points of intersection. With that being said, in the home shop I would do it with a sphere and a drop indicator. Measuring from the top of the sphere to the plane that the hole is in. From that measurement the diameter should be able to be calculated. Or draw the measurement in a cad program and dimension the intersection of the sphere and hole. 
Hope this makes sense.

Bob Thm:

Yep that's how I'd do it you can even measure the size of a parallel hole this way by sweeping a DTI to the high point then moving to the surface and zeroing back in, then just work back using trig, (or cad)


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## mklotz (Feb 25, 2011)

Sorry for the delay, Kel. Friday is my regular sushi-for-lunch day and I had to rush off before the chef could lose patience and cook the fish.

The only thing I can think of off the top of my head is the same as Bob suggested - use a tooling ball or ball bearing and a height gage, then trig to derive the hole diameter (or use my CSEG program).

The problem with this approach is that you're at the mercy of the condition of the hole edge. If it has any irregularities they will affect the measurement. You never specified numerically what you meant by "ACCURATELY" so we'll leave the error analysis of the edge influences as an exercise for the reader.

It may be worth your while explaining what you're doing and why you need this measurement. It's possible that there may be alternate ways of accomplishing what you want without the need to make this measurement.


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## kcmillin (Feb 25, 2011)

Marv, I really don't have a specific use at the moment. I do plan on someday making morse taper attachments and taper lock hubs for flywheels. I am sure that these do not require high tolerances like + or - .001", but something might. Keep in mind I will be doing all measuring while the part is is the lathe.

I want to learn as much as possible, and thought that someday I might just need to make a tapered hole to within .001" 

I can get incredibly anal about measurements, and methods used to acquire said measurements. I get great satisfaction when things turn out dead on. Weather the job requires it or not. :shrug:

Kel


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## DaveH (Feb 25, 2011)

Kel

Here is one way

2 steel balls one must be twice the dia of the other.

Measure how far each ball goes into the bore (depth mic)

From the two measurements and the dia of the balls you can calculate the distance between the centres of the balls.

Double this distance you calculated between the centres of the balls. This is the hypotenuse.

Now Sin = opposite divided by the hypotenuse 

The opposite is the radius of the larger ball (Because it is at a tangent to the taper )

This will give you ½ the included angle.

You can do this whist the taper is still in the lathe.

Try it with cad.

Dave


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## mklotz (Feb 25, 2011)

OK, being German, I can understand curiosity and compulsive accuracy.  

Normally, with tapers, both male and female, we're more concerned with the taper angle than with the exact diameters at either end of the workpiece. Typically the taper is measured by making diameter measurements at two locations separated by a known distance and then trigging out the angle. We don't "gage" the taper from a measurement of the end diameter.

With tapers, I've never encountered a situation where the diameter of the end opening was critical. I admit the possibility that such situations may exist but I doubt that they are common.

Self-locking tapers need to be *very* accurate to work well but, again, that concerns control of the angle and not the hole sizes.


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## kcmillin (Feb 25, 2011)

Ah yes, German. A part of me is German, along with Norwegian, and I am told Bohemian, although I am not sure what/where that is.

Thank you for shedding light on this. 

So far (knock on wood) I have had good luck making angles on the lathe by using angle blocks and a DTI to set the compound. Two ER32 collet chucks were made first try, and checked with Engineers Blue. 

I guess a rule of thumb would be that the large end of the Male Taper HAS to be larger than the opening on the female taper.

Kel


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## mklotz (Feb 25, 2011)

kcmillin  said:
			
		

> I guess a rule of thumb would be that the large end of the Male Taper HAS to be larger than the opening on the female taper.



Desperately resisting the temptation of numerous sexual innuendoes, I will say that that is an excellent rule of thumb (or other body part).

And remember, there are only Germans and those who wish to be.


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## kcmillin (Feb 25, 2011)

mklotz  said:
			
		

> Desperately resisting the temptation of numerous sexual innuendoes, I will say that that is an excellent rule of thumb (or other body part).
> 
> And remember, there are only Germans and those who wish to be.



 :big: :big:

Kel


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## peatoluser (Feb 25, 2011)

For those following this site and wondering what a chamfer gauge is or how to measure a hole using a steel ball check out this website
http://www.brunswickinstrument.com/dsart.htm


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## 90LX_Notch (Feb 25, 2011)

Kel,

Here is a post I did awhile back on making Morse Tapers. Sparky's reply is excellent advice. I have since made other adapters and the last one I did I used Sparky's method. I used two indicators to set the taper per inch. Doing it this way is pretty much "dead nuts" accurate.

http://www.homemodelenginemachinist.com/index.php?topic=4925.0

Bob


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## tel (Feb 26, 2011)

> What I want to know is how to measure the major diameter of the hole. It Is kind of a guessing game with an inside micrometer.
> 
> 
> Kel



The Tel Rough As Guts method is this;

Tightly plug the little end of the hole with a wad of newspaper.

Melt some sulphur.

Pour molten sulphur into hole (large end) until it is a little proud of the top.

When the sulphur soldifies, file or scrape it back flush with the top.

Gently push the sulphur plug out of the hole (No! From the small end!)

you can now _GENTLY_ measure the big end with an ordinary mike.


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