Looking for smartphone app to determine hole size with 3 gauge pins...

# Thread: Looking for smartphone app to determine hole size with 3 gauge pins...

1. Diamond
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## Looking for smartphone app to determine hole size with 3 gauge pins...

As the title says, an app to determine an unknown hole size by use of three gauge pins.

For instance, suppose you have a hole larger than your largest gauge pin. You put two pins in the hole, then by trial and error you find the third pin that tightly fits in. By the pin diameters the app calculates the hole size.

A while back someone mentioned such an app to me. Anybody know of such a thing? In my younger years I would take it as a challenge to develop the algorithm, now I'm satisfied to accept one already written.

2. That's actually a good idea for an app. Think I'll play around with excel and see if I can't come up with something.

3. Plastic
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Just made an Excel sheet to do this.

PM me if you'd like it. It's nothing pretty, but it works. Verified it against Solidworks drawing of a 3 pin circumscribed circle.

Pin A must be the largest pin, B must be less than or equal to A, and C must be less than or equal to B.

4. Cast Iron
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What's wrong with using 2 pins to find the diameter?

5. Diamond
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If the first two pins are the same diameter it makes life easier. I'll probably come up with it tonight.

6. Plastic
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What's wrong with using 2 pins to find the diameter?
You can't guarantee they are lined up perfectly to gauge the diameter.

7. Plastic
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Here's a screen grab of the excel calc I made

8. Aluminum
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Originally Posted by Buttpoop
Just made an Excel sheet to do this.

PM me if you'd like it. It's nothing pretty, but it works. Verified it against Solidworks drawing of a 3 pin circumscribed circle.

Pin A must be the largest pin, B must be less than or equal to A, and C must be less than or equal to B.
Buttpoop, I reproduced your your formula, and it is correct. However, your restriction, A > B > C, is not needed. Just put in any 3 values and you get the right output.

Jacques

9. Plastic
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Originally Posted by jariou
Buttpoop, I reproduced your your formula, and it is correct. However, your restriction, A > B > C, is not needed. Just put in any 3 values and you get the right output.

Jacques
Looks like you're right, it's not needed lol.

10. Aluminum
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One interesting note to add here.

There is a particular case that is easy to remember, if the pin sizes are 1, 2, and 3, the bore size is exactly 6, i.e. exactly the double of the largest pin.

So, for example, if you are targeting a bore of say 0.900 and you have pins up to 0.500 as I do, no need to fumble around to test a bunch of pins. Just grab pins that are half, one third, and 1/6th of the bore, i.e. 0.450, 0.300, and 0.150 and Bob is your uncle.

Of course, this works cleanly like this only when the targeted bore is divisible by 6. But you can still use this fact to do some quick check by rounding up or down to a multiple of 6 and you have the first 2 pins determined. You can narrow the search for the last pin pretty quickly, and then plug in the formula to see where you are.

Jacques

11. Cast Iron
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Would you guys be interested if I made a simple web app for this and hosted it so anyone could use?

I've been building things like this using python/flask for internal use and this seems like a fun exercise for the portfolio.

12. Diamond
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Originally Posted by g-coder05
That's actually a good idea for an app. Think I'll play around with excel and see if I can't come up with something.

OK G-coder, and what angle will you be using for them pins in that excel sheet?
180 deg for 2 pins?
120 all around or 180 + 90 in-between for 3 pins?
Any angle between 3 pcs of XX pins + the nominal +/-?

13. Diamond
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Originally Posted by carbonbl
Would you guys be interested if I made a simple web app for this and hosted it so anyone could use?

I've been building things like this using python/flask for internal use and this seems like a fun exercise for the portfolio.
Sure, definitely I'd use it. Thanks for the offer.

Python/flask...????? I never got beyond programming in Visual Basic. VB was a natural for me being so similar to Fortran and assembler used in my only "real" job as a mathematician at Boeing. When I started the machining business CAM was pretty expensive so I wrote my own CAM plugin for Visual CADD. It was dirt simple you highlighted a cutter path and called the CAM plugin to generate a snippet of Gcode. Part of my intention was to market the plugin. Gave up the marketing idea after the local developers sold VC to the Turbo CAD folks.

14. Originally Posted by Buttpoop
You can't guarantee they are lined up perfectly to gauge the diameter.
If they fill the bore with no clearance, you're good to go. This is what the little ball peen hammers are for.

15. Stainless
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An arbor press will do it.

I heard about a guy who sanded down the gauge pin to fit. Boss told him to make sure the gauge pin fit each part!

16. Aluminum
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Originally Posted by Buttpoop
You can't guarantee they are lined up perfectly to gauge the diameter.
I guess a little geometric explanation would prove how two round pins wouldn't line up in a round bore that they properly add to equal the bore diameter.

Sent from my SM-G960U using Tapatalk

17. Aluminum
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In fact two pins only show the maximum diameter of a bore. I guess using 3 equal dia. pins could show if the bore is round to a set tolerance .

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18. Pin 3 makes the other two stand up straight.

If the hole isn't actually round, then all bets are off.

19. Aluminum
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It the two pins add up to fit the diameter they can only fit standing up straight and show the maximum diameter . Try in a variety of rotations "clocking" to fit.

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20. Aluminum
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After determining the max diameter, use two pins that are same diameter that fit the maximum hole size ,then use a third smaller pin to check the size 90 degrees to the maximum to determine if the hole is actually round.

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