# Draw tangent at a point on circle

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Hello, can anyone please tell me the best and easiest way to draw a tangent at a point on a circle, at right angles to the diameter at that point? the point can be anywhere on the circle. I  am using AutoCAD 2018

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Actually, I  meant to say , the most accurate way, so the angle is 90.0 degrees to the diameter

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How is the point marked on the circle?

The easiest way to draw a tangent is to have the Polar Tracking on and use Object Snaps. Hover your cursor near to your point on the circle, then draw a line from the centre of the circle to your point on the circle, and then using the Polar Tracking, you can now draw the tangent at 90°.

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Draw your line from the point on the circle to te centre, then select the line and then move the line picking the end which is at the centre point and placing it at the opposite end. And scale it by 2.

Or draw the line by selecting the point and at the opposite side of the circle use the perpendicular osnap (your line will always be through the centre of the circle that way), then again move the line using the end points.

Edited by steven-g

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Same way we did it back in the day with paper, pencil, and a triangle.

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Another

osmode 517

Line

pick point on circle "near" etc

pick point "CEN"

Enter

RO L enter end 90

You could make it a pretty simple defun joining all steps.

Edited by BIGAL

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Have ortho on.  Draw a vertical line through a point on the edge of your circle.  Turn ortho off.  Rotate the line around the circle center to the required angle, if any.  Extend the line to the required length.

More than one way to mash taters.

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Upgrade to Civil and use LineTangent (_AeccLineTangent). Just pick curve, starting point and distance.

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You can do this without drawing any extra objects.  Rotate the UCS with the 3 point option, osnap to center, to your point on the circle, and in a general direction to show Y.  Set Ortho or Polar on, start the line command and use Quad Osnap to pick your starting point, or use Intersection, etc.  I have quick keys set to U3 to get the UCS command set to 3 point option, and UW to go back to UCS World.

Edit: snap to the point on the circle first, then center, then another direction for Y.

Edited by rkent
clarification

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I  found that XLINE was the easiest solution. XLINE / ANGle/REFerence/ Select the diameter at the point on the perimeter of the circle, enter 90 degrees

Edited by JoeS09

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5 hours ago, JoeS09 said:

I  found that XLINE was the easiest solution. XLINE / ANGle/REFerence/ Select the diameter at the point on the perimeter of the circle, enter 90 degrees......

That does not work for my version of AutoCAD. The REFerence needs to be a line object.

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Yes, I selected the diameter of the circle at the point on the circle where I wanted the tangent, and the tangent was effectively drawn in both directions, which is whatI wanted

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58 minutes ago, JoeS09 said:

..... I selected the diameter of the circle at the point on the circle where I wanted the tangent..........

But we did not know that you already had a diameter. A pity that information was not included with your first post as the responses would have been different.

If the diameter is there, then one simple way of drawing the tangent, without actually drawing another line, is to offset the diameter, and use grips to stretch the far end of the line back to the end of the diameter.

Still, if you want an x-line, than perhaps you should have mentioned that in the first place.

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Eldon, go easy, I am new to AutoCAD. My question specifically mentioned the diameter “ to draw a tangent at a point on a circle, at right angles to the diameter at that point?“

The Xline solution was one I accidentally came across playing with the problem

i don’t quite understand  your solution with offsets and grips but will have a go

Edited by JoeS09

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If you have Polar Tracking switched on, you do not need to use the Angle/ Reference to draw the Xline tangent.

Polar Tracking aligns the line for you when you use the Endpoint Object Snap on the diameter line..

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I have drawn a test circle, drawn a diameter at , say, 15 degrees to the horizontal, and switched Polar Tracking (F10) on.

I  have entered Xline and selected the point where the diameter touches the circle and a line appears. I can rotate the line about the selected point

But how do I make sure it is a tangent at right angles to the diameter?

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I think that drawing an Xline with Polar Tracking is tricky until you know what you are looking out for. Drawing an ordinary line would be much easier.

First of all, set up Polar Tracking by right clicking on the POLAR tab at the bottom of the screen and choose Settings. In the Polar Angle measurement, I use Relative to last segment. You can enter any Increment angle, but 45° is enough for me.

Polar Tracking displays temporary alignment paths defined by the polar angles you specify. As you move the cursor, when you get to a specified angle, a small cross appears at the cursor and the alignment path extends beyond the cursor. When you see this alignment path, you can pick the length of your line or enter it at the keyboard. Drawing a Xline is more difficult because the Xline is on top of the alignment path and you can only see the cross at the cursor.

Practice makes perfect, but when you can use it, Polar Tracking is most useful.

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Just thinking pick circle, draw a line tangent from RIGHT quad, then go into rotate pick point on circle.

Edited by BIGAL

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