What Did You Buy Today?

[Winegrower]

Keep in mind that there are 1,667,304 possible combinations of three pins in a .251" - .500" pin set.

Well Winegrower, you will be busy and it will require more than a rainy day

It was sunny today, and yes, I can keep track of a million things, but not 1,667,304 things. So just looking at any three adjacent pins, 0.001 apart, the result is fascinating to me. Descartes was an incredible machinist, it would seem. Here's what I conclude, which is nothing more than what RJ, Doug and Larry$ have suggested. But I had to do the math.

1) from a 0.061 to 0.250 set of gauge pins, you can extend the measurement using three adjacent sized pins up to over 0.5 inches. By lowering the smallest pin one step, or increasing the largest pin one step, you can generate roughly half thousands over the extended range. I assert without proof that handling three similar sized pins is pretty easy.

2) by adding a larger base pin, you can do the following:

Adding a 0.375 pin extends to over 5/8" capability
Adding a 0.500 pin extends to over 3/4" capability
Adding a 0.750 pin extends to over 1" capability

In each range you can micro step to below 0.001"

The tolerances of the pins tends to average out, to the level I was interested in pursuing.

So for $50 bucks or so for a small set up to 1/4", and three more pins, you get a 1" set that can check to 0.001".

And this leaves out most of RJ's combinations.

 

[RJSakowski]

Oh man, you have to love the internet. Found it: http://www.ambrsoft.com/TrigoCalc/Circles3/Tangency/Tangent.htm

I guess Descartes figured this out for himself a long long time ago.

OK, I plugged the formula in your link into an Excel spreadsheet and it spits out the diameter of a circle circumscribing three tangent circles.

 

[RJSakowski]

And here it is.

 

[woodchucker]

wouldn't it be more necessary to figure out what size pins fit a circle to check the circle? Rather than here are 3 pins, what circle can I make.

 

[Winegrower]

Yes, because I only consider three adjacent sized pins, there are not that many possibilities and it’s easy to get a list of sizes of the superscribed hole, just scan along to what you want, and there are the three pins to use.

I could clean up my spreadsheet and attach…if any interest. It includes the extension pins as well.

 

[woodchucker]

Yes, because I only consider three adjacent sized pins, there are not that many possibilities and it’s easy to get a list of sizes of the superscribed hole, just scan along to what you want, and there are the three pins to use.

I could clean up my spreadsheet and attach…if any interest. It includes the extension pins as well.

sure, better than relying on the internet if you are w/out a connection at the moment.

 

[Winegrower]

Ok I will get to posting my spreadsheet soon.

 

[RJSakowski]

wouldn't it be more necessary to figure out what size pins fit a circle to check the circle? Rather than here are 3 pins, what circle can I make.

It depends on your goal. I would select two likely pins to start and then the third to get the proper fit in the measured bore. There are a lot of possible combinations of three pins that will fit any given bore. From what I was able to observe, selecting the sum of the diameters of the first two pins to be close to the diameter of the bore give the greatest resolution for the bore diameter and having three pins of equal diameter gives the poorest resolution, although still better than that of the individual pins.

 

[Winegrower]

Here's an Excel sheet that may be interesting. I will find out when my pin gauge set arrives, but it looks like with the dowel pins I have now, .375. .500. .625 and .750 I can measure accurately up to over an inch. The math makes sense, anyway.

You can use this in two ways, where you know the three pin sizes, and where you know the size of the hole you want to measure.

Measurements are in inches, but the spreadsheet doesn't care if you use metric, answer will be metric also.

 

[f350ca]

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Greg