Shape Large Panels with your Router

do the math and you get what you need instead of what you hope is correct. nice looking jig there.

-- It is all in your perspective.

Nice looking jig.

-- CJIII Future cabinetmaker

All the math makes my head hurt. Cool jig none the less…..lol

-- Dan ~ Texarkana, Tx.

Math = Perfection
Trial & Error = More Sawdust + Profanities.
Therefore, logically, Trial & Error > Math

:D

also cool jig :)

-- - Jei, Rockford IL - When in doubt, spray it with WD-40 and wrap it with duct tape. The details will attend to themselves.

Josh, I did something similar when making some curved backs for a chair. I’d like to make a suggestion, though. Instead of mounting the router base to the aluminum, I would let it move side to side, and then bolt two pieces of mdf (or some other square stock) to the angle aluminum on the outside of the wood frame. This will insure that the aluminum runs perpendicular at all times to the jig instead of getting skewed.

-- --Bob http://www.areddy.net/wood

You lost me at D= but I get the idea. Nice bench underneith.

-- DocK, WV

iterative calculations can be fun, but http://mathworld.wolfram.com/CircularSegment.html shows how to get at the same answer without it… you do need to be able to take inverse trig functions though. also, i calculated exactly double your angle: 11.45º. so i think your angle is 1/2 of what it should be if you were tracing an arc with a trammel… so how did that work out? anyway, i have to admit that i wouldnt have bothered with the math and wouldve done it with the cursing and sawdust!

At work we make a lot of curved window casings. We use a very simple formula to find the radius, that only uses your 15” and .375”, and no trig. Don’t know off hand what it is, but I’ll check tomorrow and post it.

Usually, I’ll just draw it in a CAD program in 5 seconds and it’ll tell you the radius. :-)

Just googled and found it.

http://mathforum.org/library/drmath/view/55037.html

-- Gerry, http://home.comcast.net/~cncwoodworker/CNC_Woodworker.html

Excellent jig. Well thought out and executed with good workmanship.

-- Donnie-- listen to the wood.

Bob – the MDF pieces to keep the jig from getting skewed is unnecessary, if the aluminum frame gets skewed at all it lifts the router bit, so you can never cut too deep by skewing. It seems to me it would just get in the way

AaronK – I did calculate the half angle, if you look at the second equation – W = 2sin(theta)R – I multiply the horizontal by two.

CAD programs are already nice, but if you just have some determination, paper, and a calculator you can do it the fun way.

-- Josh Lawson - Ankeny, Iowa

Hi Josh. Interesting approach to solving the problem of describing an arc that meets the conditions of being 3/8” deep and intersecting the ends of your board at the top. I would have driven a nail in the edge of the board at 3/8” and half way between each end. Then taken a flexible straight edge and hooked it below the nail and bent the two ends up until it intersected each end of the board. Draw the arc. No math, no headache, no trial and error. Now, tell me why it wouldn’t have worked because I doubt I’m smarter than you.

Best,

-- Jim

sometimes you just want exact. i can understand his approach :-)

Outputter – You described the same method I use for the majority of my arcs, it’s only when I want a very precise arc that I bother with all the math. (Don’t forget I am a bit of nerd, so some part of me enjoys whipping out my giant calculator I paid all that money for in college). I’ve also had some mixed results using the flexible straight edge method, I have trouble getting the arc to be truly a simple curve instead of a complex curve (non constant radius) I seem to get more of a parabola than an arc.

-- Josh Lawson - Ankeny, Iowa

you did it dude! goodJob! this is one jig that cant bring my self around to building, but alwaya can use it.

Nicely done.

-- Rick, Pa. Courage is what it takes to stand up and speak; courage is also what it takes to sit down and listen.