# It's not my fault! (Geometric Right Angle Guage)

 Project by Tootles posted 04-19-2012 08:16 AM 2121 views 7 times favorited 13 comments

It’s not my fault ;-). Dusty 56 started it. Then Jaykaypur did it. And finally JR45 did it too. I just couldn’t help myself … (sob)

Really though, I have had a bit to say on Dusty56’s and JR45’s posts about this guage being based on a theorem of circle geometry (an angle inscribed in a semi-circle is always a right angle), not on the Pythagorus sum of squares theorem. Sure Pythagorus is valid, but he came well after the geometry, especially if a guage such as this was used by the Egyptians to build the pyramids some 2000 odd years earlier.

I also posted in JR’s project 5 steps (see below) to make this guage so I figured that I should put my money where my mouth is and test the process. And while I’m not going to deny that JR’s laser guided block plane might have made the job a whole lot easier, I just don’t have one of those so I had to rely on my dusty rusty old No. 4 – like the ancient Egyptians would have had to since lasers hadn’t been invented back then. (!)

The five steps that I followed to make the guage were:

1. First make the short arm, complete with pointy end and hole for the pivot bolt.
2. Cut the long arm more than double the length of the short arm and drill the pivot hole in the centre of the arm – some error can still be tolerated at this point.
3. Align the short arm along the long arm in one direction, then use the short arm to mark the shape of the long arm.
4. Align the short arm along the long arm in the opposite direction, then use the short arm to mark the shape of the long arm.
5. Shape both ends of the long arm using the short arm to check that the ends of the long arm are accurate.
6. Apply finish, in this case wax because it is quick, easy and I still love the feel of it.

Okay, I lied – there is a sixth step. After all I am posting this as a project which requires it to be completed, not just half-done. I did take photos, so if the instructions are not clear enough, and if enough people ask nicely, I could do a blog.

So now the ultimate question, what am I going to do with it? And well you might ask!

Actually, the most useful thing I can think of to do with it is take to to school if and when I ever teach the geometry of circles as a demonstration of the practical application of maths (you weren’t expecting me to say that now, were you?). The next most useful thing would be to use it in my woodwork class to check the squareness of some sliding lid boxes that my students will be making this term. I could use it to dazzle my students with my brilliance – in my dreams! But more realistically, it could be useful when I assess their work because it is a quick check using a guage that actually fits into the boxes

Whatever I do with it, it was a fun way to spend a little time in my workshop this afternoon. And isn’t that just what it’s all about?

Oh, materials are a strip of oak that I had in my scrap bucket and a bolt, washer and wing nut that I had on my shelves. So while I suppose the bolt and wingnut cost me something sometime, the effective cost for today is \$0.00.

At 10” long, I’m guessing the woodpeckers one would be about \$25. So special one-time offer, \$12.50 anyone?

-- I may have lost my marbles, but I still have my love of woodworking