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framing square and chõ gen
Posted: Mon Jul 25, 2011 9:54 pm
by craigak
In vol.2, p.109, Chris uses the square to layout the miter cut. I am using my new inch base-10 square.
So the run is 10 and this is the value on the long arm. Chõ gen is 9.28 and this is the value on the short arm. The resulting line produces an angle closer to 48˚. Working with TAN produces a chõ gen angle of 42.8736˚. Any see what mistake I am making?
Thanks,
Craig
Re: framing square and chõ gen
Posted: Mon Jul 25, 2011 11:30 pm
by Chris Hall
Yikes! You're not making any mistake Craig. The drawing in the text is absolutely correct when it comes to laying out the chōgen slope - the mark is made along the short arm of the square, which is at the value for chōgen (9.28 in the case of a 10/4 -sloped hopper). The developed drawing on page 110 showing how the chōgen slope triangle can be developed directly from the unit triangle is also correct.
My mistake comes on page 111 where I show the calculation - I've reversed the 'opposite' and 'adjacent'. Since the miter line is made along the short arm of the square, the cut angle is also produced there, which means that the angle in question actually has opposite/adjacent of 10/9.28, which indeed works out to 47.1240...˚.
i feel bad at such a simple goof up, but hey, nobody's perfect and I'm glad to have the chance to correct the error in the text.
Here's the chōgen triangle on the edge of the board:
- CSG Hopper 2 chogen explained correctly.jpg (94.21 KiB) Viewed 6112 times
And here's the framing square with the same measures on the edge of the board:
- CSG Hopper 2 chogen on hopper.jpg (78.13 KiB) Viewed 6112 times
Yep, revision 5 will have to come down the pike soon enough. I'm astonished that one got missed, so good on you Craig for finding it! I hope you find more (sorta
)
Re: framing square and chõ gen
Posted: Tue Jul 26, 2011 11:00 am
by craigak
Chris,
It is gratifying to make some sense of this stuff. I am astonished by your knowledge of this material and the way you present it. It has been a slog for me but I keep at it.
Re: framing square and chõ gen
Posted: Tue Jul 26, 2011 11:24 am
by Chris Hall
Like all of you, I'm learning as I go.
Craig, glad it's making more sense to you now. I know how easy it is to get hung up on and bogged down by a particular detail - you're doing well to forge ahead.
Re: framing square and chõ gen
Posted: Thu Jul 28, 2011 10:18 am
by craigak
Ok, so where would the angle 47.1240˚ be in the 4/10 triangle shown on pg.110?
Craig
Re: framing square and chõ gen
Posted: Thu Jul 28, 2011 5:57 pm
by Chris Hall
Consider that opposite over adjacent was used to solve...
"the angle in question actually has opposite/adjacent of 10/9.28, which indeed works out to 47.1240...˚"
What angle is opposite the length of 10?