# Thread: Design for a Height Gage Centre Finder?

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## Design for a Height Gage Centre Finder?

I was thinking about how you can measure a hole location using a surface plate and height gage, and a lot of the info and videos I found were people using a CMM-level height gage that electronically measured the top and bottom of hte holes and computes the centre. Very nice and very expensive.

I guess you can use a pin gage set, put the right pin in the hole, find the top height and subtract 1/2 the diameter, but that requires a pin gage set and doesn't sound like quick work.

I saw Fowler sells "Centering cones" which seem like a visual approximation method at best, so I came up with this idea:

The ball solves the angle problems presented by a cone. A spring keeps the hinge balls in place under tension. You roughly set the height and push the ball into the hole, then you adjust the height to zero out the DTI. Read the height gage reading and you're done. Measuring holes less than 1" from the surface plate may be tough but that's not a new problem with height gages.

I haven't decided how the ball at the front will be held on. I was thinking maybe a magnet so that balls could be swapped depending on the target hole diameter.

Something to play with. I may 3D print the design to try and get a confirmation the idea is sound.

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A conical hole?

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So you have to rely on the reading of one dial to get your reading from the height gage, correct??

To me, it sounds like there is too many contact points to amplify the error.

I like the gage pin method, that's how I do it.

Once in a while I'll measure the hole dia. and then the bottom of the hole and calculate it from there.

JL.............

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It would seem that the accuracy is dependent on the edge of the hole (same problem with a cone, but maybe less so, depending). And the perpendicularity of the face that defines the edge of the hole.

Gage pin, or just measuring top and bottom, neither of those are affected by the face and/or edge.

The ball depends on contacting the edge, if the edge is tilted, then the ball either does not register right, or else tilts the block, distorting the reading. How much is dependent on the degree that the face is off perpendicular, or the degree of "issues" with the edge.

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Just use a height gauge with a DTI. Zero out the DTI on the plate, and sweep the bottom of the hole till the DTI reads zero again Then add half the hole dia. No pins req'd, works for holes of varying sizes and is quick. I prefer using pin gauges, as we have quite a few sets at work, but the direct DTI works too. That adds to much complexity and error (Burr, or off center/mishapen countersink on the hole throws it off) for little to no gain.

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I didn't notice it explicitly stated, but I think the objective is finding the centre of a tapered hole. Short of making a matching tapered end on a pin, i'm not sure how I'd do this....but also can't recall a time when I had to. Is this just an exercise, or is there some practical instance where its needed?

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Originally Posted by Bented
A conical hole?
The part about the cone was referring to the centering cones that Fowler and others offer as a product for locating holes with a height gage.

http://www.fowlerprecision.com/Produ...565-105-0.html

Originally Posted by JoeLee
So you have to rely on the reading of one dial to get your reading from the height gage, correct??

To me, it sounds like there is too many contact points to amplify the error.

I like the gage pin method, that's how I do it.

Once in a while I'll measure the hole dia. and then the bottom of the hole and calculate it from there.

JL.............
Originally Posted by J Tiers
It would seem that the accuracy is dependent on the edge of the hole (same problem with a cone, but maybe less so, depending). And the perpendicularity of the face that defines the edge of the hole.

Gage pin, or just measuring top and bottom, neither of those are affected by the face and/or edge.

The ball depends on contacting the edge, if the edge is tilted, then the ball either does not register right, or else tilts the block, distorting the reading. How much is dependent on the degree that the face is off perpendicular, or the degree of "issues" with the edge.
You're right, the face and edge are problematic.

Originally Posted by Dan Dubeau
Just use a height gauge with a DTI. Zero out the DTI on the plate, and sweep the bottom of the hole till the DTI reads zero again Then add half the hole dia. No pins req'd, works for holes of varying sizes and is quick. I prefer using pin gauges, as we have quite a few sets at work, but the direct DTI works too. That adds to much complexity and error (Burr, or off center/mishapen countersink on the hole throws it off) for little to no gain.
You're right.

Originally Posted by Mcgyver
I didn't notice it explicitly stated, but I think the objective is finding the centre of a tapered hole. Short of making a matching tapered end on a pin, i'm not sure how I'd do this....but also can't recall a time when I had to. Is this just an exercise, or is there some practical instance where its needed?
That is an interesting idea, I think possibly it would work for finding the centre of a tapered hole. Ideally if it was only contacting inside the tapered bore and not where it meets the face.

It's become an exercise now, as the possibility for errors is outlined above. The DTI on the height gage is much more sensible as it avoids some major sources of error.

I'm printing it out now as I'm interested in seeing it work, but it won't go beyond that. I'll post a picture when it's assembled.

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Originally Posted by mattthegamer463
The part about the cone was referring to the centering cones that Fowler and others offer as a product for locating holes with a height gage.

ah ok, so you are trying to measure a straight bore regular hole's height above the plate while its laying parallel to the plate. I cry foul on the Fowler rig, depends too much on the edge that could give a false reading. I thought you were trying to measure a tapered hole location.

If you need accurate, its very easy - put the dti tip in bore, sweep to find the lowest reading then compare to a gauge block stack. If less accuracy is need or you don't have blocks, zero the height gauge with the tip on the plate, note or zero the indicator reading, move the tip to the hole, sweep to find the bottom, move the height gauge until the indicator is in the same spot and read the height gauge

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After rummaging my drawers I made some tweaks and printed this out. It works but it is very flimsy. Aside from the error sources pointed out, it appears to work as expected. Without a surface plate I was able to get hole centres within a few thou of what the digital calipers showed with conventional methods.

Sent from my SM-G960W using Tapatalk

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This seems to partially solve the second thing that I was going to bring up, the angle of that top surface in the original drawing would make the readings less sensitive and would therefore make the hole height measurement a lot more inaccurate. Your change to a vertical surface for the DTI to read against is a great improvement.

But it illustrates my first problem with this idea. You can plainly see the chamfers on the holes in the 1-2-3 or 2-4-6 block. Your set-up is reading the height of that chamfer, not the height of the hole. Chamfers are not always concentric with the hole. I fear that anything that relies on the "edge of the hole" is going to be limited to an error of several thousandths. If that is good enough, then go for it. But for accurate measurements you will need a better method. Note below.

Just thinking about it, I would go for a couple of small probe arms, one for the top and the other for the bottom of the hole. Their tips would be directly above/below each other. They would have a common pivot point and a linkage on the outer end that averages the two readings. When that average is brought to the preset zero by adjusting the height gauge, that reading (+/- an offset) would be the height of the hole. This would allow you to quickly sweep side-to-side and in and out to find the best zero reading so it would allow for the finish on the inside of the hole. And if properly constructed it could read holes that are somewhat close to the surface plate the height gauge and part are standing on.

Note: I said you are reading the chamfer but that is not strictly true. Depending on the size of that chamfer and the diameter of the ball, you may be reading one of three things:
1. The intersection of the chamfer and the hole
2. The surface of the chamfer
3. The outer edge of the chamfer
Each of these three has it's own set of problems that interfere with the accuracy of the measurement.

Originally Posted by mattthegamer463
After rummaging my drawers I made some tweaks and printed this out. It works but it is very flimsy. Aside from the error sources pointed out, it appears to work as expected. Without a surface plate I was able to get hole centres within a few thou of what the digital calipers showed with conventional methods.

Sent from my SM-G960W using Tapatalk
Last edited by Paul Alciatore; 07-16-2019 at 05:11 PM.

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