Help On Drawing Technique

Hello everone, can anyone please tell me how to draw a smooth concave curve from point A to point B of the following picture?

Regards

Huygen

Is it my system or is the image missing in the above post?

Where are my glasses? Who turned off the lights!

I had better get in quick whilst ReMark has lost his glasses

There are probably many ways, but this way works for me.

Use the property that AutoCAD draws a tangential arc, immediately after drawing a line.

In this case, I would erase your upper line, and with Polar tracking turned on, or Ortho, start from the right hand end of the lower line.

Draw up one unit, then left 7 units, then finish with the line command. Then start the Arc command, and when it asks for a start point, just press Enter (i.e. a null response). Now the Arc starts up tangentially to the line that has just been drawn. Then for the end point of the Arc, click on the left hand end of the lower line. Then erase the line of one unit.

It takes longer to describe it than to draw it.

Eldon,

You make a nice point. I just tried your short excercise. Of course, being a , I tried it the harder way as well. By this I mean draw the top line, draw the bottom line, then come back and start the arc from the top line again. If done that way, it takes 3 or 4 steps sub-steps w/in the arc command. Done your way, I just hit 'a' for arc, 'enter', then mouse to the other osnap point and hit 'enter' again. And it's drawn w/o having to read and interpret the command line.

My trouble will be that I will take a while for me to learn this new trick . . .like to not hit 'esc' after finishing a line command.

The neat part of this tip, is that hitting enter to chose the "null response" as you call it, works in the other direction as well. If you happen to be drawing an arc, you can then use this method to get a line tangent to that arc.

I was formally trained in SolidEdge, and it worked in a similar fashion to this, but I never thought to try it in AutoCAD.

Good tip!

It also depends what you are after. While I was trying to figure it out Eldon posted his method, using that, I think gives the minimum radius of 5 for your circle. However, all radii greater than that also work, with smaller and smaller amounts of concavity.

How do you solve this problem geometrically? Clearly it is a chord and there are multiple solutions, but the limit should be solvable - probably with a compass, I just can't remember/figure it out.

Where's Lee with his fancy Math degree?

Glen

It's cat skinning time...

Be sure Polar is on

Pline >> snap to end of (p)line you want to start from

A for arc

D for direction - use the polar snap to select direction of (p)line

pick point 2

How do you solve this problem geometrically?

I did assume from the initial post, that as a smooth curve was required, it should be tangential.

Then in words, the centre of the arc is at the intersection of the chord perpendicular bisector and the perpendicular from the tangent.

Or in a picture

I want to skin the cat...

Command: a ARC Specify start point of arc or [Center]: _endp of
Specify second point of arc or [Center/End]: e
Specify end point of arc: _endp of
Specify center point of arc or [Angle/Direction/Radius]: d Specify tangent 
direction for the start point of arc:

The neat part of this tip, is that hitting enter to chose the "null response" as you call it, works in the other direction as well. If you happen to be drawing an arc, you can then use this method to get a line tangent to that arc.

Now you try that whilst drawing a Polyline, and after drawing an arc, you try and change to a line, the line is NOT automatically a tangent.

Let's not forget that this has been done for years without Cad.

By the way... How do I load an image into my reply like you smart computer guys did above???

arc.pdf

I find it funny that no one has posted the other curve. The OP requested a "concave curve" I guess it depends on your point of view. And yes I know that the same methods can be used, or the curve can be mirrored. I see the side of a chisel, with the curve in question being the hollow grind created by a grinding wheel.

Where is the OP? Come on, let us know if you got it drawn, and which curve you wanted.

Glen

I find it funny that no one has posted the other curve. The OP requested a "concave curve" I guess it depends on your point of view. And yes I know that the same methods can be used, or the curve can be mirrored. I see the side of a chisel, with the curve in question being the hollow grind created by a grinding wheel.

 

Where is the OP? Come on, let us know if you got it drawn, and which curve you wanted.

 

Glen

The curve is tangent to the first curve's picked endpoint.

How do I load an image into my reply like you smart computer guys did above???

How to add images to your posts

Looky here... Geometry works for the concave side too!!!

Thanks Cad64, Your help is appreciated!

arc1.pdf

Now you try that whilst drawing a Polyline, and after drawing an arc, you try and change to a line, the line is NOT automatically a tangent.

Yes, I have come across that. When going back and forth between lines and arcs in a polyline, you have to pay close attention to the command line or you inevitably get something you didn't want. Often, it takes me two or more tries to get what I intended . There's something about that process that is not intuitive to me like some other multi-step processes I do in AutoCAD or other programs. Just can't get the eye, hand, and brain all working together on the same page.