Diagonal Line Rotation

[Anonymous]

Hey all, I'm banging my head against the wall over here after a long day of drafting. I have a 19' diagonal line that I am trying to make in a section view. For this project, it doesn't matter what the angle is as long as the line starts at (for example) 2' high and ends at a specific height and is a fixed length of 19'. This is a ramp with a stud wall configuration and a 3/4" plywood deck that tapers down to the plywood hitting ground level. The surface of the ramp needs to be 19' regardless of the angle and total flat surface covered. I'm having a lot of trouble getting this drawn where the top surface of the plywood can start at 2' and then angle down and have the bottom surface of the plywood touch the ground. Is there a rotation command that would help with this? I've tried drafting a lot of construction lines to figure this out but I'm at the point where I'm hitting a wall. Any help would be greatly appreciated.

[Anonymous]

I've played around with dimensional constraints and gotten really close, but I'm not having luck getting it exactly right.

[pendean]

Posting the DWG and pointing to areas of concern would probably go a long way to helping you out.

[Anonymous]

File is attached! Sorry, I should have done that in the beginning. I've removed most of the other drafting from the file to try to make it cleaner. I included some leader labels to try to orientate to what items are. Thanks

[Anonymous]

I think I might have just gotten it! I'm not exactly sure why it worked though. I drew two diagonal lines, one each, corner to corner, and then I used the rotate command with a base point on the top right endpoint. I then tried using "r" to move to an absolute angle using the top right point and the intersection of the diagonal lines as the two reference points.. that allowed me to make it happen. I'm not sure I completely understand why though. (That could be because my brain is fried at the moment) I have attached a file with the finished product.

[Anonymous]

Well, I got too excited too quickly... still not right. 😞 Any help would be greatly appreciated. Thanks

[sthompson1021]

Whats not right? Unless you miter the edges of the plywood it won't be perfectly flat.

[Anonymous]

so basically you want a right triangle with a height of 2' and a hypotenuse of 19', right??

that leaves a base of 18'-10 47/64"(+/- )

(BTW, if this is a wheelchair ramp the ADA requires a 1:12 slope; 24" high is 24'-0" long)

[Anonymous]

If you zoom in on the file labeled "success" the bottom of the plywood crosses in to the floor by a tiny bit. It is close, but still not correct. I'm curious about learning how to do this the right way. I'm not planning to miter the plywood as a finished flat front and back edge are not necessary for this project and the material needs to be re-used.

[Anonymous]

Hi Randal! Yes and no. The overall shape is roughly a right triangle, the problem is that the plywood is not going to taper completely flat to the floor. So there is a 3/4" inch height on the corner that would normally be flat which is kind of what is throwing the wrench into this for me.

[Anonymous]

so the length you're looking for is the diagonal of the 19' x 3/4" plywood, not 19'

which would (mathematically) be 19'-0.001233"

So the right angle would be .... close enough to the same you can't cut it that close with a circular saw.

thickness exaggerated, the dashed line is the diagonal of 19'-0.001233"

[Anonymous]

Oh yes, I totally understand. Can't get that close of a cut with with 56" sawstop either. 😉 Honestly, the way this drawing is now would be good enough for me to build this, but I'm always trying to get better at drafting and would be really interested in learning the correct technique to get this drafted.

[Anonymous]

see the screenshot I added to my previous post

[Anonymous]

I actually just saw that! Thanks. That looks right, I guess I'm just missing the knowledge piece of how to get that orientated so that is hits both the 2' point and then the bottom right corner hits the ground.

[Anonymous · Accepted solution]

I guess you want to know how I drew it.  

Draw the 19' plywood rectangle,

draw the line 2' lower,

draw a circle from the top left corner of the plywood through the lower right corner of the plywood, ( that's a radius of the diagonal)

rotate the rectangle from the center of the circle RELATIVE to the angle along that diagonal to the intersection of the circle and the line 2' lower.

[Anonymous]

Randall, you're the bomb. Thanks. I'm going to re-draw this a few times so I can make sure I understand the drafting technique behind this. I haven't had much experience with relative rotation so thank you for walking me through it. (I understand it in concept but was confused about the input order. I also had tried using circles, but I wasn't using the diagonal as the radius) Thank you very much for your help on this.

[Anonymous]

you are quite welcome.

Both rotate Relative (actually its reference not relative, but relative makes more sense to me in my head) and scale Relative(Reference) allow you to "show" AutoCAD the starting angle (or length) by selecting points, then selecting (or keying in) the desired angle (or length).

A line at some unknown (and un-cared about) angle.

Command: R
ROTATE
Current positive angle in UCS: ANGDIR=counterclockwise ANGBASE=0.000000

Select objects:  <pick line> 1 found

Select objects: <enter>

Specify base point: _endp of <pick the point about wish you want to rotate>
Specify rotation angle or [Copy/Reference] <0.000000>: R <enter R for relative/reference>

Specify the reference angle <0.000000>: endp <pick the point about wish you want to rotate>
of Specify second point: _endp of <pick the other endpoint or midpoint or nearest on the same line>
Specify the new angle or [Points] <0.000000>: <Ortho on> 45 <key-in 45 for a 45deg line or pick a new point through which you desire the line to pass>

So the center of rotation is the top right end of the plywood, the "reference" points are that same point and the LOWER left end (that "shows" AutoCAD the "current" angle) and the new point you want that angle to pass through is the intersection of the lower line and the circle.

[Anonymous]

Thank you! That makes complete sense. I was just able to get this drawn a few times in a row. Thanks for helping me wrap my head around this. 🙂 I've done a couple of raked decks over the last few years but usually where the length covered on the ground was the stipulated dimension. Thanks again!

[Anonymous]

You're welcome, glad to help.