Mystery Square, a Century old ?

[754]

Here is a square an old boy gave me at his shop - closing auction, hanging on the wall, I said that is not from the lathe below it. He said grab it , it's yours.
Can't find a maker's name, I think the ruler slot is 1 inch or under. It measures 5 3/4 x 13/16 ...4 1/8 high and 4 1/4 across the V.
Now does anybody know how they get that slot in there, 90 thou or under by 7/8 or maybe a titch wider..
I did figure out how they did the slot but it took me a while.

[nickel-city-fab]

As a guess, I would say they probably drilled a starting hole, then finished the slot with an abrasive wire saw, similar to stone cutting.

[Blazemaster83]

That is cool, too bad there isn't a maker on it

[Paul Alciatore]

A core in the casting for starters and then some kind of abrasive or saw blade to widen and straighten it. Finally a broach style cutter to bring it to a finished size. Perhaps even a bit of lapping if it is a really high quality one.

[Noitoen]

it looks like any ruler that fits the slot will work. The bolt will push the ruler to the side of the slot centering it unlike the modern ones that use the groove.

[old mart]

With a ruler sticking up in the centre of the 90 degree angles, it would work for 45 degrees, or a centre finder for bar stock, and if it projected the other way, a 90 degree square. I haven't figured how the slot was made, by the way.

[754]

I wil, reveal the slot making detail this evening. I wish i had the original binding screw for the ruler. I think at one time I found something close to this online and it was late 1800, s. Not sure if it was for wood metal or both .
anyone ever see one before. .?

[old mart]

If you turned off the exposed thread on the bolt, and modified the end with a hacksaw and file it could resemble a thumbscrew.

[BCRider]

Ya, I'm pretty sure the bolt isn't OEM 😄 Easy enough to make a replacement once you find something from the same period as an example.

I'm guessing that Paul's mention of a flat core to start is the way. Than a long tapered broach? And finally a hint of lapping as needed to get the rule trued up and dead on center.

[lynnl]

I wil, reveal the slot making detail this evening. ...

So..., that sounds like you know how it was done, i.e. you were just conducting a quiz of the group?
What time this evening will you reveal the secret? After all, inquiring minds want to know.

I first liked Paul A.'s suggestion of a core in the casting. But then after rereading the description (a slot .090 thick), ... that would be a mighty delicate core!

[754]

Ok time to reveal ... it was made in 2 halves, the slot cut in one side, then the 2 halves riveted together, then I assume finish ground..
Now before everyone jumps on me for tricking someone, I actually had in in my hands and looked at it several times trying to figure it out over a period of time, it's just not that easy to see where they did it.
AND I think a few guessed it was partially cored, as in on one side of where the ruler sits the middle does not contact..
at any rate, it is hard to see or photograph.

[JRouche]

That was fun to watch though. Dont stop. JR

[old mart]

Looking at the photograph, I would never have guessed that it was two halves, I expect there are a couple of alignment dowels in there somewhere.

[754]

Even holding it in my hands, looking all over for a name, I the first few times could not see the joined details. There are rivets but they are hard to see they just look like the casting. I will try to photo that part but it may not show up. I honestly was very surprised it was made of 2 pieces.
has anyone seen one before ?