# How to draw an S bend

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• 18th Sep 2017 03:52 am
PJ01
How to draw an S bend
Hello, I am a raw newby, and my class starts next week. Can't wait.

Can anyone please advise the best way to draw an S curve AoB in the attached drawing? How do you determine the radius of the arcs AO and BO?

At point B, the curve needs to be a bit more horizontal initially, like at point A. My mistake with the sketch
• 18th Sep 2017 08:31 am
SEANT
The vertical requirement, 't', is specified; is there a similar horizontal requirement?
• 18th Sep 2017 08:52 am
guran
Start an arc att "A" with END at "O" and DIRECTION parallel to the horizontal lines, and then do the same from "B". You can also use the kommand BLEND.
• 18th Sep 2017 09:29 am
SEANT
Ah, yes. Arc - Start, End, Direction is the way to go.
• 18th Sep 2017 09:51 am
BIGAL
This is a double reverse curve and the formula that applies is relevantly simple you have 3 variables r1 r2 and offset for parallel lines. You can do set r1 what is r2? r1=r2 etc My cheat sheet is at work. I have it on my wish list to do one day but was looking at the more complicated non parallel lines solution. Just need a starting pt, there is also what is the rad for a offset given a length the double must fit between.

If you look at the diagram you can see the diagonal line intersects the circles.
• 18th Sep 2017 10:23 am
PJ01
Thanks kindly, for all these suggestions. Tried the Arc: Start, End, Direction command and it worked perfectly
• 18th Sep 2017 12:07 pm
eldon
I would do it another way with some temporary lines. First of all,draw a line between A and B. (If you have the osnap Mid between 2 points then this line is unnecessary.)

Then draw a line from X to A (X is a point somewhere along the line - use Osnap Nearest). Then start the command Arc, and when the start point is needed, give a null response (i.e. just press Enter or right click). The arc will start drawing from the end of the last line drawn, tangential to that line, i.e. will start drawing from A, tangential to the line A. Draw the arc to the mid point of the line A-B at O (or use the osnap mid between 2 points). Then repeat the arc command by pressing Enter or right click, and again give a null response to specifying the start point. The arc will draw tangentially from the last arc, and finishes at B.

Erase temporary lines and job is done.
• 18th Sep 2017 03:20 pm
rkent
Use the BLEND command, Tangent for the Continuity option. (This is in plain AutoCAD)
• 18th Sep 2017 03:44 pm
eldon
Quote:

Originally Posted by rkent
Use the BLEND command, Tangent for the Continuity option. (This is in plain AutoCAD)

Doesn't BLEND create a spline? Whereas the OP appeared to want two arcs.
• 18th Sep 2017 05:19 pm
steven-g
I would just find the centre of the arc, which is the intersection of two perpendicular lines, one perpendicular from point A the other perpendicular from the centre of line Ao

Attachment 62204
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