Measuring Internal Angles

J Skeleman · Mar 26, 2019

Hello Everyone,

I'm looking for a new method of measuring internal angles like the one in this picture. (The 12° ±3)

Right now we're using a molding putty to take an impression and make this inside feature into an outside feature. Then we toss that on a comparator and take our measurements. While this works, it's a lot of time wasted waiting for the putty to set, and it really doesn't seem like it produces the most accurate results. This is a deep hole measurement, not a through hole.

Is there some type of gauge that might make our putty process obsolete?

btw
I'm fairly new to QA, and entirely hopelessly lost when it comes to machining and manufacturing, so please keep the engineer jargon to an understandable level. Lol.

Thanks in advance.

Larry Dickman · Mar 26, 2019

what do you have to work with? CMM?

You can check the angle with a sine plate. The diameter you could check by calculating a gage point and use a tooling ball

J Skeleman · Mar 26, 2019

We have three very ancient manual optical comparators, and a Keyence IM-6010, which is one of the older models, it might have been cutting-edge about 15 years ago.

I'm unfamiliar with sine plates and tooling balls, I will have to do some research on how to work with them. These measurements will be taken for first and last article inspection.

Thank you for the suggestion.

MichaelP · Mar 26, 2019

An ID taper micrometer (if you had one) would work here.

EDIT: O-ops! Sorry, I missed the diameter of the hole.

michiganbuck · Mar 26, 2019

If you have repeat angles I think best to make a Go/nogo gauge..that is a quick and easy check once the gauge is in hand.

optical comparator with a straight pin held to the angle often gets 1/2 degree and better a quick as a wink.

For a mile like 3* a hand protractor should be OK.

Small bevel protractor is handy for +- 1*

Precise Universal Bevel Protractors - BP-301 - Penn Tool Co., Inc

loop is handy to set such.

J Skeleman · Mar 26, 2019

michiganbuck said:
If you have repeat angles I think best to make a Go/nogo gauge..that is a quick and easy check once the gauge is in hand.

optical comparator with a straight pin held to the angle often gets 1/2 degree and better a quick as a wink.

For a mile like 3* a hand protractor should be OK.

Small bevel protractor is handy for +- 1*

Precise Universal Bevel Protractors - BP-301 - Penn Tool Co., Inc

loop is handy to set such.

I've thought about getting a series of go/nogo gauges made, but we have so many different parts and sizes that it might end up being more trouble than it's worth.

Thank you for the link, once I figure out *how* to use something like that with my parts (Like I said in the OP, my experience is near zero for this sort of thing) I might have to pick one up.

mc3608 · Mar 26, 2019

I would also use a Sine Bar

MichaelP · Mar 26, 2019

I'm trying to think how to use a sine bar to measure a taper of a .152"dia hole.

J Skeleman · Mar 26, 2019

MichaelP said:
I'm trying to think how to use a sine bar to measure a taper of a .152"dia hole.

I'm glad it's not just me. Lol

michiganbuck · Mar 26, 2019

The part set on a surface plate perhaps in a V block at the specification angle as assured with a sine bar under the V block and strike the angle with an indicator perhaps held with a surface gauge or height gauge is a common method. looking for zero-zero in this case.
Receiving inspection very likely to use the method..

Set a surface gauge or a indicator holder on a sine bar and strike the part angle with the part held horizontal in a V block. (not so common method.)
Yes, just checking the angle not the size with both methods.

.152/ .162 likely checked with a digital caliper.

Conrad Hoffman · Mar 26, 2019

Two balls, one sized to fit near the top of the taper, one sized to fit near the bottom. Measure heights one at a time and calc the angle. Should be quite accurate.

RJT · Mar 26, 2019

Yep, Conrad beat me to it.

J Skeleman · Mar 26, 2019

Conrad Hoffman said:
Two balls, one sized to fit near the top of the taper, one sized to fit near the bottom. Measure heights one at a time and calc the angle. Should be quite accurate.

Is there somewhere I could find an example of this being done, or a formula?

And the other problem is that I need this to work for many different sizes, so something less specific would be preferable. This is a nice fall back though.

Thanks again!

Clive603 · Mar 26, 2019

With that wide open tolerance you don't have to use balls a rod with a very short 12° taper on the end would do OK.

I'd be thinking in terms of having two caps to sit on the end of a depth micrometer. Part tight against one side of a suitably thick plate, depth micrometer on the other. Measure how far down your small end test cap, a ball or rod slightly larger diameter than the internal bore, goes down. Swop for the large end test cap, slightly smaller than the exit end, and measure how far that goes down. Subtract second reading from first and refer to a pre-calculated table of values to see if its in tolerance.

A spring loaded electronic probe would be way faster. I made something of that ilk about 35 years ago using an Heidenhain nanometre reading probe.

You will need to dig out the CAD program and do some grunt work drawing out the effect that tolerances on the internal bore and end hole have on the measured size of the angle as well as the variation in angle itself so you know what sizes to make your caps. You will need more than one pair of caps, select according to the outer diameter.

If you are sure your process produces a straight hole one measurement somewhere on the slope will suffice.

Clive

Gordon B. Clarke · Mar 26, 2019

Had a quick look to see if anybody has mentioned this but if so haven't seen it.

Do you really have to measure (it's a large tolerance) or do you really just want to know if it's OK? What I'm suggesting should have been done before even starting to machine parts.

1. Measure the angle on whatever is making the angle.

2. Have a bushing (or similar) made for the operator to stop at the depth giving the correct finished "diameter".

3. Have a machinist try that out on a piece of softish material, cut in half and measure, if you really have to measure.

I'm getting the impression you are trying to shoot sparrows with guided missiles and giving it too much thought.

If what you have is made by a supplier then as QA ask how it's done. I'm in fact surprised that you haven't asked someone at your place of work.

michiganbuck · Mar 26, 2019

Gordon's pretty much nailed it for the angle in #15.
Check perhaps the fixture or what ever holds the part and makes the angle, angle is a given (has to be that angle).

Simple hand slip gauge, or a go and no go gauge for the .152- .162, or a caliper.

Still: Receiving inspection very likely to check the part as mentioned in #10 to be sure you checked when making the part..

QT Gordon: [to know if it's OK?] One should not get so close .00002 to such a wide tolerance as that part has.

CarbideBob · Mar 26, 2019

The drawing shows me a max of .002 error front to back blows the tolerance.
Sort of rules out protractors.
Checking very short tapers suck, I'm in the use two balls camp.
Problem with that being the very open dia. tolerance so more than one set would be needed.
Sine bar/plate also sounds good but you have to kind of search for the low reading which is frustrating in a dia. this size if using a dti/surface gage.

Don't let the drawing fool you , this is not a big feature.
Bob

machinistrrt · Apr 5, 2019

If the only objection to your current method is the time involved in making the casting, then switch to a low temp casting alloy like cerrosafe, the casting is ready in seconds. I used this stuff when working in a header die shop, easy and quick to do.

Luke.kerbey · Apr 9, 2019

If all the parts have the same angle with different diameters you could get a tapered gauge made with a range that covers all required parts and simply blue out the part and test with the gauge.
Not the easiest way but it’s one of many solutions

Mike1974 · Apr 9, 2019

CarbideBob said:
The drawing shows me a max of .002 error front to back blows the tolerance.
Sort of rules out protractors.
Checking very short tapers suck, I'm in the use two balls camp.
Problem with that being the very open dia. tolerance so more than one set would be needed.
Sine bar/plate also sounds good but you have to kind of search for the low reading which is frustrating in a dia. this size if using a dti/surface gage.

Don't let the drawing fool you , this is not a big feature.
Bob

Nothing to really add here, just wanted to note this. I often program parts that are less than 2" square, often times 1" and under. Sometimes I am taken aback when I go to machine to look at a part I programmed and see just how small it is!

Especially when I zoom in on a .015" endmill during verify and it is taking up the whole monitor. :crazy:

Measuring Internal Angles

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