Engine Stamp Pad Characters

[Michael H.]

Recently, there has been a great deal of discussion about engine block stamp pad numbers/characters and part of the latest discussion had to do with the size of the characters. These small figures are difficult to measure accurately and it would be easy to miss the actual size by 1/32" or more. One of the contributing factors would be the depth of the characters. The deeper the character, the greater the dimension from top to bottom. I'll explain later.

There's an easy way to get a much more accurate dimension for each character. Here's an example. If you tried to measure the thickness of a piece of paper with a ruler, it would be impossible to do. If, however, you measured the thickness of 1000 pieces of paper, then divided the total by 1000, that would automatically divide any error by 1000 and you would come up with a nearly accurate dimension for each piece. We can do this with engine stamp numbers too. We'll come back to this in a minute but first an explanation of how the characters are spaced in their fixture.

Each individual character in an engine stamp tool is on a steel slug that fits into the holder. Each slug is exactly as wide as the character is tall. So, if we're using 1/4" tall characters, the slug in the holder would also be exactly 1/4" wide. So, the C/L of one character to the C/L of the next character in the holder would be exactly 1/4", right? Now, lets suppose we're using characters that were one inch tall. (easier math) The entire package of slugs would be seven inches from end to end. If we knew the exact width of each character, and we do, we would be able to calculate the entire length of the package of characters in a row. (not the same as the dim for the slugs)

We know that each of our character is exactly half as wide as it is tall so a one inch tall character would be 1/2" wide. If we add the total width of the five center characters to the dimension to the edge of the end characters, we will have an accurate total for the length of the numbers stamped into the block. (hopefully, the pic in the next post will clarify some of this)

This would be the same exact thing as our paper measurement above. Instead of trying to accurately measure just one character, we are measuring a group, and from that dimension, we can come up with a total height for each character. (see, I told you the paper was important)

Also, of importance, is the fact that most restamps that are not done with a proper stamp holder are almost always incorrect as far as length of the entire package. Once you determine the proper character size and calculate this total length, a tool can be made to quickly measure this package length. I'll post a scan of the ones I used at the Bloomington Event in the early 80's.

The first thing needed is the length of the number packages from a known original block. Or, it can be done backwards, using the accepted character sizes from the judging sheets or JG. Using the method I posted, you should then be able to calculate the correct dimensions for the characters. I know the numbers and sizes for calculations are correct as GM bought ALL of their stamp tools from the same source. Hope this makes sense to all. I feel a little like Bullwinkle trying to explain to Rocky why the earth revolves. I'm not good at explaining things properly. The scans should help. Please post your results.

Hanson

[Michael H.]

Re: Engine Stamp Pad Characters

Just an example using round number dimensions for ease of calculations. Once a correct size is chosen, this drawing will help establish the total length for your chosen character dim.

[Harmon C.]

Re: Engine Stamp Pad Characters

Michael

I will try my luck with the new math and say if the last box had an (0) in it the total would be 6 1/2inches. If someone bought number sets today would they be the same size when put in a home made holder?

[Ken K.]

Re: Engine Stamp Pad Characters

Thanks Michael for shedding some light on this subject. The question that everyone wants to know is, What the "Correct" size of the fonts? What our your "key" measurements on making sure the stampings are original? The diagram below is my understanding on what you are telling us. There are two different size examples shown. I'm not sure if any of them are correct. Members may want to put on their shoes and go out to the garage a get a "Good" measurement to verify what is being said. "Testing the Formula."

[Duke W.]

Re: Engine Stamp Pad Characters

That was a very good explanation. Even I understood it.

Duke

[Steven C.]

Re: Engine Stamp Pad Characters

Ken, I agree members would like to know the dimensions, however, a more fundamental question may be this – Is the internet the best mechanism for communicating this type of information given the fraud and misrepresenation that exists in the hobby today? It is a very slippery slope.

JMHO

[Michael H.]

So... What Size Are The Characters?

In posts above, Lyle has the math right on the money and Ron came very close to the actual correct decimal sizes of each of the 7 digit character groups. As shown in Ron's post, the 1/4" character groups would produce a total package length on the engine pad of 1 5/8". (1.625) This, obviously, is WAY too long, so we know, without question, that 1/4" is not the original size. The actual length of the engine plant character package is very near 1 1/4" and when you use a 3/16" character in the formula, the package length comes out to exactly 1.21875, or very close to 1 1/4".

But if the engine plant stamp was 3/16", what was the VIN stamp? More math will show that these characters were even smaller than the previously accepted 3/16". If you measure an original, you find that the length of the package is just over one inch. If we use a 5/32" character in our formula, the total calculated length for the group is 1.015625, just a hair over one inch.

So.. the correct length for the large engine assy plant numbers package is 1.21875, or roughly 1 1/4".

The correct length for the small VIN characters would be 1.015625, or roughly 1 1/32".

A very simple formula for determining the total length of a character package is, multiply the individual character height by 6.5. This will eliminate all the math and give you these same results.

"But my characters are actually almost 1/4" high. How can this be possible"?

The character center lines and height figures are those found at the center of the peaked portion of the character on the stamp. This dimension would be the exact size of the stamped impression it were not for the tapered, or pyramd shape of the character on the stamp. If you hammered the tool just hard enough to leave a thin line but not hard enough to actually displace metal on the block, the stamped character would measure exactly as advertised. If you hit it hard with a nine pound hammer and bury the characters deep into the surface, they become wider and taller, which accounts for the increase in dimension. Most original stamps will be medium depth and increase the package length and character height by about .020-.050". That's why most original engine stamps appear to be 3/16" and 1/4". Original stamps must be measured from the center of the leg of a character, not the top/bottom edge of the depression.

The tool that holds the individual characters is machined to fairly close tolerances. The typical side to side clearance in the character package could be anywhere from .010 to as much as .030, which means that there is another possible reason why the length of a stamped set of numbers doesn't come out exactly on the numbers.

I'll post a pic of the easy to make tools that I used decades ago when judging. They're actually small enough fit in your wallet.

Thanks to Bill Liddle for getting me interested in metal character stamps in the 70's.

[Verne Frantz]

Re: Engine Stamp Pad Characters

Michael,
You stated, " Each slug is exactly as wide

as the character is tall. So, if we're using 1/4" tall characters, the slug in the holder would also be exactly 1/4" wide"

Are you really sure about that? Because, if not, it sure would throw off all the math. Aren't the characters on the die tapered like a chisel point? That alone would make the size of the stamped character smaller than the slug's outside dimensions. Am I missing something?

[Michael H.]

Re: Engine Stamp Pad Characters

Yes Verne, that's exactly how all the "steel Type" is made. The height of the character always equals the width of the slug. The entire character is well inboard of the edges of the slug.

The characters do have a chisel point, as you mention, but the initial measurement is taken from the peak of that chisel point. That's why the measurement of an actual stamped character has to be made from the center of the trough instead of the edge. The deeper the impression in the block, the wider/taller the character, which would give the incorrect larger measurement.

Terrible hand drawing coming in a few minutes

[Michael H.]

Terrible Drawing of Individual Type

The height of any character is always exactly the same as the width of the steel type slug. The dimension is taken from the PEAK, or chisel point, of the raised character, not the edge. The characters are roughly .040" tall on the slug and the pyramid is somewhere near a 90 deg included angle. That's why the stamped impression in the block keeps getting taller as the stamp is buried deeper and deeper into the stamp pad. If you measure a character on a slug, a capitol I for example, the peak to peak dimension will be the exact dim that the slug is advertised to be. If, however, you were able to measure from the base of the top pyramid to the base of the bottom pyramid, the dim would increase substantually.