topic Help with basic polyline drawing in AutoCAD Forum

Help with basic polyline drawing

watsongrace2022 — Tue, 17 Oct 2023 20:30:16 GMT

So I am very incompetent at AutoCAD no matter how many tutorials, videos, and instructional things I read and try. I am doing a tutorial course right now and of course I am stumped at the first exercise. I can follow what the guy is doing in the video but I don't understand what it means.

So I am trying to recreate the outer border in this image in the yellow with the dimensions listed:

https://imgur.com/a/GiPfc6v

What I am meant to do is draw a polyline with Line at 250 then type A and then type 45 tab 45 and this makes this little arc piece. What do the 45 and 45 mean? Am I doing radius, direction, center, angle? I don't know what this even means? Then I understand to change it back to Line and 250 and then A for Arc again but this time he types 45 tab 135? Why is this?

Can someone walk me through this?

Re: Help with basic polyline drawing

Patchy — Tue, 17 Oct 2023 20:47:49 GMT

How can anyone draw this without information of the radius?

If they were given, draw a square then fillet with radius for the 4 corners and done.

Re: Help with basic polyline drawing

watsongrace2022 — Tue, 17 Oct 2023 20:53:09 GMT

Yeah I am not entirely sure. This is on the Autodesk course the first practice exercise, too.

All they said in the solution was to use Polyline - Arc - 45 tab 45 for the first arc and Polyline - Arc - 45 tab 135 for the second arc. No specification if these pertained to the radius or what. I was assuming the length? But only an angle was given.

Thanks.

Re: Help with basic polyline drawing

CodeDing — Tue, 17 Oct 2023 21:00:21 GMT

@watsongrace2022 ,

No worries! Just takes some getting used to.

Hopefully this helps.. We just need to understand what we're looking at on the screen. Here I have started my polyline. I made my first 250 unit segment and have just started an arc. (my polyline is magenta, and my cursor is orange) You can see that I have 2 numbers showing on my screen here and one of them is by default already waiting for input. We can also see that there are some gray dashed lines (some helpful dimension lines) and these represent what the numbers will affect. I have added a red bracket and labeled it "C" since we can tell by the gray dimension lines that this input appears to be the CHORD of the arc.. So therefore, when you input your first value of 45, this represents the CHORD length of the arc:

Now, when I hit the Tab button, we can see that the 45 we input as our chord is locked, and we have moved to the next input box. This appears to be an angle of some kind. In my image below I have added a red identifier and labeled it as "A".

...but that's weird, the bottom part of the angle seems to arbitrarily going flatly from left to right in that picture. Wonder why that is? Well, let's head down to our next corner and see what happens when I input my values over there:

...hmmmm, even at this corner it still maintains a left to right orientation, and now instead of 45 degrees upward, I am opening 45 degrees downward. So when I enter 45->Tab->45, then this still checks out ok. Let's check the next corner:

Well look here now! When I do my 45 unit chord, then tab to my angle, it is now shaping up to be about 135 degrees! So it is always opening from the right (or Eastern) side of my model space. And this is why Sometimes you need 45 degrees, and sometimes 135 degrees.

But why does it always open from the Easterly direction? Well, you will have to run your UNITS command, then open the default "Direction":

...which shows us the default Base Angle of East. (so that's where your 45's and 135's come from):

Hope that helps!

Best,

~DD

Re: Help with basic polyline drawing

ВeekeeCZ — Wed, 18 Oct 2023 08:29:05 GMT

It's silly dimensioning.

45 is the radius of corner fillets.

I would draw a square of a = 340 (= 250+45+45), with rounded corners. It could be done by a single command...

RECTANG

Fillet

pick a lower left corner

Dimensions

340

pick an upper right corner

Or just draw a full RECTANG 340x340, then use FILLET command with options: Radius 45 Polyline and pick the square.

Re: Help with basic polyline drawing

CodeDing — Wed, 18 Oct 2023 09:29:16 GMT

@ВeekeeCZ ,

When I drew the polyline with a chord of 45, I don't believe the radius was 45. It was some value in the 30s. So I don't think that method would work in this case.

Best,

~DD

Re: Help with basic polyline drawing

ВeekeeCZ — Wed, 18 Oct 2023 09:41:56 GMT

Ohh, you're right. It appears that it really is a chord. Too quick assumption. I didn't believe that the tutorial would be so complicated.

It would be helpful to see the actual video though.

Re: Help with basic polyline drawing

Valentin_CAD — Wed, 18 Oct 2023 10:11:04 GMT

@watsongrace2022 ,

@watsongrace2022 wrote:

What I am meant to do is draw a polyline with Line at 250 then type A and then type 45 tab 45 and this makes this little arc piece. What do the 45 and 45 mean? Am I doing radius, direction, center, angle? I don't know what this even means? Then I understand to change it back to Line and 250 and then A for Arc again but this time he types 45 tab 135? Why is this?

Turn Ortho Off after drawing a polyline at 250, then type A or select "Arc" from the command line.

Make sure your Dynamic Input in the Status Bar is ON, then type 45 for the Chord Distance and 45 for the Angle.

The 135 is adding to the previous angles - see example:

Re: Help with basic polyline drawing

watsongrace2022 — Thu, 19 Oct 2023 20:22:37 GMT

I really appreciate the thorough explanation! This makes total sense.

I have one last question...with the given information, would it be possible to determine without the solution that the chord is 45 with the only given information being the 90 degree angle?

Thanks!

Re: Help with basic polyline drawing

CodeDing — Thu, 19 Oct 2023 21:12:55 GMT

@watsongrace2022 wrote:
I have one last question...with the given information, would it be possible to determine without the solution that the chord is 45 with the only given information being the 90 degree angle?

No, it would not be possible to determine the chord length based on the picture you provided.

The chord length is inconsequential in this exercise. Any chord length can be input and you would achieve the same shape having 4 - 250 unit sides & 4 - 90 degree rounded angles.

Happy to help!

~DD

Re: Help with basic polyline drawing

Washingtonn — Thu, 19 Oct 2023 21:26:41 GMT

Without the chord information, but given sufficient time, you could stumble upon THE solution but you wouldn't have any way to know it was THE solution. There are an infinite number of solutions (different radius values) that would encompass the detail shown inside the outer border shown. The chord value provides the information needed to find the radius of the 90 degree angle.