small wooden ramp, inches per foot to degrees, convert? do I have this right?

[bill yohler]

building a small ramp, 1/2" plywood topped. pretty simple one. four feet long, four inches rise over four feet (I'll 'knife point rip' the shallow end/bottom of the plywood where it meets the floor). the big question is: what angle, in degrees or, better yet, 'degrees and parts of a degree' is a taper of one inch per foot?

add'l info/clarification: finished dimensions, _side_ of ramp: right triangle, four inches tall by four feet long at base (where it sits on garage floor its entire length)

I'll need this same info (angle in degrees) to set the rip angle at the top of the 2 x 4 ripped 'underneath crossbars' I make for it....at intermediate positions. (ps-I couldn't find any formulas or calaculators or 'tips' in google for figuring this out...)

I'm gonna guess: if it's 6 in 12 pitch, it's 45 degrees, right? so if it's 3 in 12, it must be half that, or 22.5 degrees, right? assuming I got 3 in 12 right, then 1 in 12 pitch must be a third of that, or 7

1/2 degrees, do I have that right?

thanks much :-)

[Doug Miller]

[snip]

Nope, actually 6-in-12 is about 26.5 degrees; 45 degrees is 12-in-12.

No, sorry, that's not right, and it's not that simple. A little bit of trigonometry is needed here; the angle is the inverse tangent of the ratio of the vertical distance to the horizontal distance (rise divided by run).

If you're using a Windows computer, you can use the Windows' built-in Calculator program (click Start | Programs | Accessories | Calculator) to figure out the angles.

1. Click View on the menu bar, then select Scientific.
2. Make sure that "Dec" and "Degrees" are selected.
3. Enter the inches, click the "divided by" ( / ) key, enter the feet, click the equals sign.
4. Checkmark the "Inv" box at the left side of the window, and click the button labelled "tan". This gives you the angle in degrees.

You should get 4.76 degrees.

-- Doug Miller (alphageek at milmac dot com)

How come we choose from just two people to run for president and 50 for Miss America?

[Andy Dingley]

Near enough. It's actually 5°, because you're describing an angular ratio, where we really want a linear ratio:

tan(angle) = 1/12

Strictly it depends on whether "1 in 12" is a rise of 1 in a horizontal distance of 12, or a slant distance of 12. But the difference at this shallow angle is only 4.76 or 4.78 degrees.

-- Smert' spamionam

[charlie b]

For one inch rise per foot, the tangent value is 1/12 = 0.0833 The angle whose tanget is 0.0833 (ArcTanget(0.08333) is 0.0831 RADIANS There are 2 Pi RADIANS in a circle which is 360 degrees, so there are 57.3 degrees per radian (ok so it's 57.295779513 but 57.3 is close enough) 0.0831 Radians X 57.3 degrees/Radian = 4.76 degrees. 5 degrees would probably be close enough.

Nope. For 45 degrees, the rise must equal the run or 12 inch fise for a 12 inch run. But a 6:12 is not 22 1/2 degrees. half of the 12:12's 45 degrees, but is 26.565 degrees and a 3:12 is 14.0362 degrees not one quarter of 12:12's 45 degrees or 11.25 degrees. Tangent to degrees isn't a linear relationship.

you're welcome / \ < o o >

V /-\ \___/

[JAW]

You have a 1" rise per foot, that mean you have a 1:12 slope. Use any scale (let's use pez containers), so you have 12 pez containers along the 2/4 and 1 pez container perpenduicular to that. Strike a line from the end of the board to the top of the perpendicular pez container.

(or use the scale provided here) |-----|-----|-----|-----|-----|-----|-----|-----|-----|-----|-----|-----|

|-----| = 1 pez.

The lesson hare is that you do not need the angle, or you do not need to use math.

bill yohler wrote:

[bill yohler]

thanks much to ALL you guys: doug andy AND charlie :-)

I'm _sure_ glad I posted that inquiry now :-) - turns out my 'guesstimates' on how to convert the two were what I'd call 'way foggy'. I especially appreciate the 'windows calculator' method reply (which I had no idea was even 'lurking within' windows :-)

gonna go with that 4.76 degrees/wow, cool, and thanks AGAIN :-)

[Doug Miller]

You're welcome, glad to help -- and thank YOU for the followup. Too many guys pop in with a question, get the answer, and are never heard from again.

-- Doug Miller (alphageek at milmac dot com)

How come we choose from just two people to run for president and 50 for Miss America?

[Reyd Dorakeen]

A^2+b^2=C^2 A=bottom, or 12

12^2+1^2=c^2 B= side, or 1 12^2+1^2=145^2 C= slopeing part C=12.04159 12/12.04159=(cos a) cos a= 0.99654 cos^-1 0.99654=4.76 A=4.76 CHECK: tan a=1/12 _ tan a= 0.083 tan-1 0.08333= a a = 4.76 somebody correct me if I'm wrong but I think its 4.76 degrees at the bottom (where it starts to rise) and 85.236 at the top(between the right angle of the end and the top of the rise) No guarantees, but I had to find some actual use for the last week of math hell:-/

in article xydMb.136658$ [e-mail], JAW at [e-mail] wrote on 1/11/04 7:00 AM:

[charlie b]

Yup, and it's nice to get confirmation your calcs were right.

charlie b