Gauge pins....where have you been!

[Dan Dubeau]

You can measure hole sizes larger than the largest pin in your set by using three pins. This depends on the mathematical fact that three mutually tangent circles of differing diameters can be circumscribed by a single tangent circle ( the so-called outer Soddy circle).

The trick is deciding which three pins to use to provide a given measurement. I've written a program to do this and it's on my page. Look for the PLUG.ZIP archive.

My Metrology Prof in college really focused on alternative gauging methods like that. Also using balls to measure the depth of holes, and other odd ball situations we'd probably never encounter in the outside world, but it was more an exercise in creative thinking, than practical application. It has come in handy a few times when I was working in inspection though.

Wish I had your program back then to save me the math lol.

[mklotz]

... using balls to measure the depth of holes,

The FTAPER.ZIP archive on my page contains a program to determine a female taper angle using two spheres of differing diameter.

Some knowledge of analytical geometry can be a real asset in the machine shop.

[mklotz]

With your program to pick pin sizes that is an outstanding adder for a great tool set!!!!!!

Here's an example output from PLUG. It shows the pin triplets that can be used to measure a 1.25" hole with a pin set that has as its largest a 1" pin. The asterisks indicate the best solution found up to that point, so the last asterisk in the list indicates the most accurate approximation to the input hole size.



Hole size = 1.250000 in

0.5298, 0.5788, 0.6248 => 1.2499924 (error = -0.0000076) *
0.5308, 0.5918, 0.6118 => 1.2499911 (error = -0.0000089)
0.5318, 0.5728, 0.6288 => 1.2499970 (error = -0.0000030) *
0.5318, 0.5858, 0.6168 => 1.2500031 (error = +0.0000031)
0.5328, 0.5818, 0.6198 => 1.2499971 (error = -0.0000029) *
0.5348, 0.5928, 0.6078 => 1.2499922 (error = -0.0000078)
0.5358, 0.5728, 0.6258 => 1.2500016 (error = +0.0000016) *
0.5398, 0.5738, 0.6218 => 1.2499927 (error = -0.0000073)
0.5398, 0.5898, 0.6068 => 1.2499916 (error = -0.0000084)
0.5408, 0.5628, 0.6308 => 1.2500005 (error = +0.0000005) *
0.5408, 0.5848, 0.6108 => 1.2499937 (error = -0.0000063)
0.5438, 0.5658, 0.6258 => 1.2499921 (error = -0.0000079)
0.5448, 0.5908, 0.6018 => 1.2500009 (error = +0.0000009)
0.5468, 0.5818, 0.6088 => 1.2499992 (error = -0.0000008)
0.5478, 0.5598, 0.6278 => 1.2499922 (error = -0.0000078)
0.5478, 0.5788, 0.6108 => 1.2500049 (error = +0.0000049)
0.5518, 0.5618, 0.6228 => 1.2500007 (error = +0.0000007)
0.5518, 0.5858, 0.6008 => 1.2500044 (error = +0.0000044)
0.5528, 0.5688, 0.6158 => 1.2500092 (error = +0.0000092)
0.5578, 0.5718, 0.6088 => 1.2499917 (error = -0.0000083)
0.5598, 0.5688, 0.6098 => 1.2500002 (error = +0.0000002) *
0.5598, 0.5858, 0.5938 => 1.2500049 (error = +0.0000049)
0.5598, 0.5868, 0.5928 => 1.2499923 (error = -0.0000077)
0.5618, 0.5798, 0.5978 => 1.2499927 (error = -0.0000073)
0.5638, 0.5758, 0.5998 => 1.2499961 (error = -0.0000039)
0.5658, 0.5728, 0.6008 => 1.2499976 (error = -0.0000024)

[old mart]

I would like a set, but even a box of drill blanks is expensive.

[RSG]

Anything over 1", tri-mikes are the way to go.
Over 2", indicating bore gauges are great.
(Tri-mikes over 2" are mega expensive).


-Doozer

Ya, for my bearing journals on my reels I use a Mitutoyo .5-.625" Holtest mic! Almost a grand for the one instrument but worth it....

[JRouche]

I've wanted some for a while but put it off until a month ago! I bought three sets .011" - .06", .061" - .25", and .251" - .5"

I can't believe how much I've used them already. What a handy little instrument. Of course I'd love to have gotten the Mit or Starrett brand but for my needs these are fine.

Anyone else use them?

Nice box, all I have are the standard plastic blow mold boxes, they suck for the heavy sets.

I have pins from .001"-1.000". The larger sets .500" and up are too heavy for the plastic boxes, and they are labeled (the pin position in the box).

I got them probably 15 years ago so they were still affordable. I got them in "Neg" not even knowing why or how to use them. It just seemed odd that there were Pos type also, why would you want a pin that was too large? I'm sure there is a use, I just don't see it.

As for the "-" vs "+" how are they larger or smaller? Is it say for the pin shown (.739") which is Neg, .7385"? And a Pos pin .7395"?

I haven't used the large ones yet, cant think of a use. Some day maybe. JR

[rickyb]

Pins are exceptionally nice for measuring most aspects of rifle bores.

[alanganes]

I have the sets from 0.061 through 0.5" that were something of an impulse buy from a guy on CL. I have used them quite a bit more often than I might have guessed that I would, they are just so handy. The Soddy circle technique that Marv K mentioned has been extremely handy on a few occasions, I first learned of that from him (Thank you Marv!!). Very handy when I have needed to measure holes larger than my 0.5" pin to better than dial caliper precision. I don't need that ability often enough to have fancy instruments like tri-mikes or similar, but it gives me a good way to make accurately sized bores for those times I need to. Most of what I do in not all that fussy, but when you need to it is nice to have a way.

[QSIMDO]

Just got .501 to .625 earlier this week!
Then realized I don't even use all the drill bits in a set, what the hell will I do with all these pins?
Should have bought individuals.

[Paul Alciatore]

If you have a set by thousandths, why is one by drill bit sizes needed? Are they really accurate to the fourth and possibly fifth decimal place so you can measure, say, a 9/32" hole accounting for that extra 0.00025"? That's getting down to millionths of an inch territory.

Or did you just buy the drill bit sizes first?

Yep, for the smaller holes, it is hard to find a better method of hole measuring. I have two sets, one by thou, and one that is in drill sizes. Super handy, even for gauging metric, as you can, at the least, bracket the size to within .025mm, which is usually good enough.

[Paul Alciatore]

Great idea!

You can measure hole sizes larger than the largest pin in your set by using three pins. This depends on the mathematical fact that three mutually tangent circles of differing diameters can be circumscribed by a single tangent circle ( the so-called outer Soddy circle).

The trick is deciding which three pins to use to provide a given measurement. I've written a program to do this and it's on my page. Look for the PLUG.ZIP archive.

[RB211]

Not totally related but...
I have a bunch of ID ring gauges,
used for setting bore gauges and air gauges.
They are great to use as circular parallels on
the rotary table. Sometimes straight vise parallels
are really combersome on the rotary table, and
rings for use as parallel spacers are really handy.



Oh, and I guess you can use them as actual ring gauges.
It is nice to test the ID jaws on your digital caliper to see
how close they are. It lets you know how precise of a measurement
that you can use your calipers for. I have a 20 year old (gosh!) Mititoyo
6" caliper, that I trust like a micrometer. Well almost. But when you prove
it out with gauge blocks or ring gauges, especially right at the size you are
measuring for a particular job, you can have more confidence that it is correct.

-Doozer

PS-
And yes I have a rotary table large enough to use a brake rotor as a curcular parallel.
I have used cast iron pulleys too.

I've used outer race bearings for the same thing for the fraction of the cost, how I calibrated my 3D probe for the CNC.

[luthor]

I've used outer race bearings for the same thing for the fraction of the cost, how I calibrated my 3D probe for the CNC.

Do you mean that you used inner races from bearings as a form of ring gauge?

[tomato coupe]

You can measure hole sizes larger than the largest pin in your set by using three pins. This depends on the mathematical fact that three mutually tangent circles of differing diameters can be circumscribed by a single tangent circle ( the so-called outer Soddy circle).

The trick is deciding which three pins to use to provide a given measurement. I've written a program to do this and it's on my page. Look for the PLUG.ZIP archive.

Given that this is a "home shop" forum, you could use two pins and just add the numbers together for most applications.

[luthor]

Given that this is a "home shop" forum, you could use two pins and just add the numbers together for most applications.

Id like to see you get an accurate measurement using that method.