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3 sided precision straight edge

P

PeterT

Ultra Member
Premium Member
I see these listed on Ebay (along with other cool stuff from the era). What was the typical use of this triangular profile in machining setups? I doubt for dovetails / scraping because the surfaces have quite a bit of relief & the corners are quite sharp.

1746113449581.png
 
More rigidity than a flat ruler? The indents would facilitate clamping without compromising the top edge?

Does it have scales on it like the wooden and plastic versions do?
 
I doubt anything made to that level of accuracy would be used for scribing or layout. The other end has a hole for a handle like you see on similar metrology gage instruments like for scraping. But this only has a handle on only 1 side vs both, maybe only because this gage is shorter & lighter? These appear in tooling / metrology catalogs & generally for big bucks. But typically they look like link example. But it only has a relief on 1 surface, the other 2 are left planar presumably for blue transfer for scraping. All 3 relieved surfaces (and therefore much smaller measurement surfaces) seems to be a Russian thing? Maybe its more intended for use with gage blocks / pins / feeler gages?

www.jashmetrology.com

Straight Edge Tool | Cast Iron Straight Edge - JASH Metrology

These are used for truing, spotting and reconditioning of dovetailed guide ways of machine tools, slides, and similar workpieces.
www.jashmetrology.com www.jashmetrology.com

1746197892320.png
 
The handle suggest the optical bench idea is incorrect. I've always thought "straight edge" that we use to describe the recondition tool is a bit of a misnomer in that they reference flats not edges .... I guess those really are straight edges :) Can't see them being of value to scraping, but maybe there's some way to use it that escapes me. The one by Jash otoh is used like any other reference flat, blue it, touch it off, etc
 
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YYCHM said:

Triangular Engineering Scale Ruler​

Click to expand...

That was what I initially thought too Craig. Those triangular rules are available for many disciplines not just engineering though. I think I might have 6 or 7 different ones. They are particularly useful for making scaled drawings.
 
SWMBO went to a Catholic private school when she was a kid. I suspect if a nun smacked your knuckles with that ruler you’d never step out of line again.
 
Susquatch said:
That was what I initially thought too Craig. Those triangular rules are available for many disciplines not just engineering though. I think I might have 6 or 7 different ones. They are particularly useful for making scaled drawings.
Click to expand...
I Have both Engineer & Architect triangular scales, in several sizes (6", 12" & 18" standard – like what Craig posted and cute little 6" babies), materials (various plastics and Aluminum) and qualities (engine-divided and molded). Even have a metric version. Also have a collection of bevel-edge scales. All left over from the days before desktop computers when we used slide rules (or trig & log tables).
 
The picture shows what could be adhesive residue. And the dados on each side are not completely centered. With a handle on one end only?

I have never seen anything like it, but it is interesting
 
I'm sure the brown stuff is typical anti-rust coating they smear on before wrapping in the 'butcher' paper.
The slots do look a bit asymmetrical, or at least the upper crown looks that way. Not sure if that's the camera angle. I personally don't think the slots have any relevance to the important outer surfaces (just a guess). But one would think they would equalize them so it looks like you knew what you were doing on a precision stick. I was also wondering if the relief was meant to slide in some other instrument but when you zoom in, its not a ground surface. It just looks milled away/
 

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Well, it was made in the USSR, so off center and out of whack dimensions maybe aren't too surprising. But it is a very odd and interesting piece. Do you know any of the dimensions?
 
Would that give you more surface area to check with feeler gauges, versus a regular straight edge? I'm only guessing

If the bottom two points were machined to be parallel to the top point, it would give three spots to reference from
 
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