Need Help to Measure a Thin Gap

We used solid soft solder to measure kisser blocks on the conversion presses for aluminum beverage can ends. You could tell a variance of a tenth. It was critical because the score ( the place that opens ) has a tolerance of +- two tenths. It would only work if it was measuring a gap that moved. Low temperature alloys such as cero cast works well to measure things that can’t be accessed with measuring tools. Gun smiths use it to cast chambers so critical measurements can be taken.
 
Nutfarmer said:
We used solid soft solder to measure kisser blocks on the conversion presses for aluminum beverage can ends. You could tell a variance of a tenth. It was critical because the score ( the place that opens ) has a tolerance of +- two tenths. It would only work if it was measuring a gap that moved. Low temperature alloys such as cero cast works well to measure things that can’t be accessed with measuring tools. Gun smiths use it to cast chambers so critical measurements can be taken.
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I have used Cerrosafe many times to determine unmarked chambers in rifles. Excellent product!
 
Nutfarmer said:
We used solid soft solder to measure kisser blocks on the conversion presses for aluminum beverage can ends. You could tell a variance of a tenth. It was critical because the score ( the place that opens ) has a tolerance of +- two tenths. It would only work if it was measuring a gap that moved. Low temperature alloys such as cero cast works well to measure things that can’t be accessed with measuring tools. Gun smiths use it to cast chambers so critical measurements can be taken.
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To clarify, do you mean that Cero Cast is softer than solder (so easier to compress) or do you mean that you melted it and flowed into the area to the area to be measured?
 
Lots of reasonable ideas have been offered. It looks like I'm going to have to do some experimentation to see what will work, particularly for the low force case. I can use some fine wire (.005"?) to maintain a gap between 2 solid 1-2-3 blocks and see if 10 pounds will squish a small length of solder, etc, etc.

Keep them coming. Muck appreciated. Thanks to all.
 
extropic said:
To clarify, do you mean that Cero Cast is softer than solder (so easier to compress) or do you mean that you melted it and flowed into the area to the area to be measured?
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Yes, I melt either with my wood stove in the winter or a torch in the summer in a casting ladle and pour it into the chambers after blocking the bore with a patch.
 
Cerrosafe is a low melting point alloy that will melt in hot water and maintain it dimensional properties when solidified. It can be reused. The tool and die techs would use it to cast tooling to check dimensions that would be hard to measure any other way. It is melted and poured into the area to be measured. The casting then can be removed and easily measured. See Harry Kurtz post.
 
extropic said:
I want to measure the change in gap between two planar surface resulting from a change to the force pushing the surfaces together. I need practical suggestions. No LASER scanners. Just conventional measuring tools.

These are steel surfaces with fine surface texture (probably 8 or better). The parts can not be modified for this test. The surfaces are vertical. The surfaces are circular. For each measurement, I want to measure the gaps at 3 places, equally spaced around a diameter. The magnitude of the gap is .001" to .005". I want to measure the gap to .0001" resolution.

Simple explanation: Imagine, with the surfaces separated, I stick a small bead of Silly Putty, at 3 places, equally spaced around a diameter on one surface. Then I bring the second surface to bear and apply the lesser force. The beads of Silly Putty will be compressed to the thickness of the gap.

The problem is, how do I measure the thickness of the compressed Silly Putty without altering it's thickness. I don't think Silly Putty is an appropriate material.

I thought of using 3 drops of a quick curing epoxy. Spray the steel surfaces first with a light oil to prevent the epoxy from adhering. Sounds reasonable to me. I'm thinking the flattened cured epoxy beads would be tough enough to survive their thickness being measured with a micrometer.

After measuring the gap at the lesser force, I would reset and perform the process again at the greater force.

My questions to the group are: Do you think the epoxy will be OK? What material would you recommend to replace the epoxy? Is there a much better way to measure the gaps?

Thanks for reading.
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Plastigauge get it at an automotive store
 
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