Snapping to Perpendicular in AutoCad

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Savvy drafters know half a dozen ways to get square. June 28, 2005

We switched cad programs about 6 months ago to ACAD and have been unable to replicate the process of creating a particular perpendicular line with ACAD. I am starting with an existing line of some angle. I want to draw a line starting on (nearest, end pt, mid pt snaps) the existing line and perpendicular to the existing line. The only way I've been able to do this is to offset a line parallel to the existing line and then draw perp to the offset line. This is too much effort to accomplish what should be a very simple thing. What am I missing?

Forum Responses
(CAD Forum)
From contributor J:
The way I do this is to select the line command, and when it asks for the first point, I choose my coordinates or snap (endpoint, etc.), then type in the following:
Welcome to AutoCAD. Let the games begin.

From contributor V:
I think the above solution works only if you will temporarily assign the UCS to the OBJECT (the line from). Use UCS> NEW> OBJECT then BACK to UCS World
or you can use SNAPANG and ortho (F8).

You can draw the perpendicular line from line if you use this sequence of commands: LINE, PERP (select line), click somewhere on the side where you want the line to be drawn. You will have to move the drawn line to the point you want it to be from. Other possibility is with lisp. Try GOOGLE to search for one.

From the original questioner:
When I try your procedure, I get a line drawn at 90 degrees vertical, not perp to my original line.

From the original questioner:
Contributor V, I tried your method and it does work, although it seems a rather convoluted way to achieve what should be a simple task. I am unfamiliar with the lisps you referred to, so at this time, it would appear that I'm stuck with your suggestion unless someone comes along with another and/or I get the time to learn about lisps.

From contributor J:
Do you know what angle your original line is at? If so, add or subtract 90 and adjust the angle in the formula.

From contributor P:
Simplest thing to do is to turn osnap on, and choose "snap to perpendicular." That should work.

From contributor R:
Hit F8 button on keyboard.

From the original questioner:
Yes, I can use list to find the angle of the original line, I was just hoping for something more straightforward. Using my old program, the snap to perp would work with either the start or end points. The snap to perpendicular in ACAD only works with the ending point, not the starting point.

F8 only turns ortho on and off and has no impact on drawing perp to another line, unless the original line is drawn either horizontal or vertical. Thank you for the suggestions and keep them coming.

From contributor P:
"The snap to perpendicular in ACAD only works with the ending point, not the starting point."

This works with any point - starting, end, midpoint or any point in between. Besides "snap to perpendicular", turn on "endpoint", "midpoint", "nearest". In the Draft Setting options, turn on "polar tracking" and "relative to last segment" to visually see the perpendicular angle.

"Snapang" is another strategy. Type the command. Select a point on the line, then select another point on the line to give acad the angle. Now your cursor is parallel to the angled line. Now you can use ortho and osnap to get lines perpendicular to the original line. To change your cursor back, type "snapang" again, type 0(zero) twice to get the cursor back to its original state.

Personally, the other is simpler. But either works.

From contributor M:
Actually, it's very simple. Just turn on your OTRACK by going to Tools/Drafting Settings or just hit F11. Draw the line at any angle, and when you start drawing the second line, snap to end or mid, keep your pointer at that same point for a little bit and move it in the perpendicular direction away from your first line. It should show perpendicular "track," showing length and angle. At this point, you can type the length or snap to the next entity (Perpendicular: Intersection). This worked when my starting point was end or mid but not nearest.

From contributor C:
Contributor M hit the nail on the head! I'd never really used Object Tracking. I'd do what the questioner mentioned and offset a line parallel to the first in order to create a line perpendicular to one at an odd angle. I just tried it and it works great! Just make sure you turn on the perpendicular snap in OSNAP's first. Just goes to show there's always good stuff to be learned here!

From contributor K:
Another way is to use "object ucs". Select the line or object you want to be perpendicular to and then use ortho mode to draw. Your ucs will now be aligned to the new angle and any ortho line will be perpendicular or parallel to the new ucs.

From the original questioner:
I have tried both of your methods and they do indeed accomplish what I am after. Contributor M, yours works well, provided the start point is the end or midpoint, just as you said. Contributor P, your method seems to have nothing to do with the snap to perp setting. It works for me with or without that setting selected. Thank you all for your input and assistance.

From contributor S:
Contributor P, I like your method, but what if the line you are snapping to (to get the angle) is a curve? It isn't working for me. Sounds to me like the offset method is no more of a pain than any other one of these methods, if not the best one mentioned so far, especially for complex curves. The only downside for me is that with offsetting, I have to go back and join the polylines to one entity (so I get 1 routing instead of 4, 5 or more).

From contributor C:
Here's another way. Click on the line tool, then click on the perpendicular snap (or type PER). Now select anywhere on the line that you want the new line to be perpendicular to. This defines a "deferred" start point along an infinite line coincident with the line you have selected. Now select an end point and you will have a line that is perpendicular to the first but not necessarily through an endpoint, midpoint or even on the original line.

From the original questioner:
Contributor C, I like your solution best. Now that I have a handle on that, my next issue is drawing a parallel line without using the offset command. My issue with offset is that I simply want a line parallel to, not necessarily the same length or starting and ending in the same place as the first line. Once again, I have been trained by the previous program to select a line to be parallel to, select a starting point and select an end point. I haven't figured out how to accomplish this with ACAD.

From contributor C:
Here's how to do a parallel line. Click on the line tool and select the start point for the new line. Now click on the parallel snap icon (or type PAR and ENTER), then hover (don't click) for a moment over the line you want to be parallel to. The parallel symbol should light up and when you move the cursor away, there should be a temporary tracking point left behind. Now move near where the end point of the new line should be. The parallel symbol will light up again over the tracking point and AutoCAD will display an alignment path (Parallel: 14.0354).

From the original questioner:
Contributor C, what are the chances of being able to use some sort of combined offset/parallel command? I understand the method you mentioned, but I am looking for the ability to offset a particular distance, select the start pt, and then select the end point. Perhaps I'm looking for something that doesn't exist in ACAD. At present, I have to offset the correct distance, and then trim and/or extend the new line to the desired length. I was just hoping for a faster way.