topic Re: How to array while rotating? in AutoCAD Forum

How to array while rotating?

Anonymous — Thu, 22 Sep 2016 20:05:18 GMT

I want to draw an accurate gear and I found a guide, but one step I don't know how to do. Can anybody help me, please? I have to do an array of an polyline and at the same time rotate it.Hear is the guide, go to paragraph 6.2.5 the second image (the middle of the page): http://lcamtuf.coredump.cx/gcnc/ch6/#6.2

Thanks in advance, Nelson

Re: How to array while rotating?

parkr4st — Thu, 22 Sep 2016 20:43:53 GMT

youtube has several good videos

search youtube for how to draw a spur gear in autocad

one example

https://www.youtube.com/watch?v=WuKkQ1pPRVY

Dave

Re: How to array while rotating?

imadHabash — Fri, 23 Sep 2016 11:58:32 GMT

i made this screencast for your case... i hope it's help.

Re: How to array while rotating?

Anonymous — Fri, 23 Sep 2016 18:46:34 GMT

Thank you for tour replies. But I want to draw an accurate gear and the guide I linked to seemed to me quite good. The step in the picture is when I get stuck.

Re: How to array while rotating?

Kent1Cooper — Fri, 23 Sep 2016 21:21:54 GMT

@Anonymous wrote:

.... I want to draw an accurate gear and the guide I linked to seemed to me quite good. The step in the picture is when I get stuck.

It's not something that can be done with just Array, but I think I've got it, based on their description in the two paragraphs just above that image. One thing I think they could be clearer about is this formula:

360° / c_pitch * n

which I think should make it clear that it's not

360° / ( c_pitch * n)

but rather

( 360° / c_pitch ) * n

[at least that's what I used in the code, after trying the other which gave obviously incorrect results]. See whether this does it for you:

(vl-load-com)
(defun C:Tooth (/ cir notch dist steps circ ctr rot inc)
  (setq
    cir (vlax-ename->vla-object (car (entsel "\nPitch Circle: ")))
    notch (car (entsel "\nInitial Notch Polyline: "))
    dist (getdist "\nStepping distance of infinite gear: "); [their "successive offset"]
    steps (getint "\nNumber of steps in defining tooth: ")
    circ (vla-get-Circumference cir); [their C-subscript-pitch]
    ctr (vlax-get cir 'Center)
    rot (* (/ (* pi 2) circ) dist); rotation per step [their "matching angle around the center"]
    inc 0; initially
  ); setq
  (repeat steps
    (command
      "_.copy" notch "" ctr (polar ctr 0 (* dist (setq inc (1+ inc))))
      "_.rotate" "_last" "" ctr (angtos (* rot inc))
    ); command
  ); repeat
); defun

It assumes the same orientation as in their images. It requires that square-cornered initial 3-edged notch to be a single Polyline. And it does only one side, so you have to Mirror all the results except the initial one about the midpoint of the initial one's horizontal middle segment. Experiment with the size of the stepping, the number of steps you need to take the shape far enough, etc.

Do it with Osnap turned off. If it works, the usual bells and whistles can be added, it could be made to do both sides, possibly to draw something like a Spline along the results, etc.

Re: How to array while rotating?

GrantsPirate — Mon, 03 Oct 2016 19:46:42 GMT

I looked at the link you provided. The next step is to draw a curve on the outline of the objects you have shown, just look at their next example as to what you should end up with. Use the pline command or spline command and set endpoint osnap on and pick on the ends of the lines inside the circle, use intersection osnap for the intersections outside the circle.

Re: How to array while rotating?

Llam.Tech — Mon, 03 Oct 2016 19:33:22 GMT

Hello Nelson,

I guess you are thinking of a POLAR array. 🙂

Re: How to array while rotating?

Anonymous — Mon, 03 Oct 2016 19:53:40 GMT

Oh sorry guys for my late response. I realised that for my purpose the gears hadn't to be perfect, so I searched for an easier method. Eventually, I used this one: https://www.youtube.com/watch?v=UM6o4D4YIcE. Anyways thanks for your replies. I didn't expect so many replies.

Re: How to array while rotating?

Kent1Cooper — Mon, 03 Oct 2016 20:18:03 GMT

@jay.llamoso wrote:

Hello Nelson,

I guess you are thinking of a POLAR array. 🙂

Once the shape of a tooth has been defined, you can use a Polar Array to spread the teeth around the gear, but you can't use it to make the tooth-defining steps in the image in Post 4. A Polar Array makes rotational copies around a common rotation base point, but what's needed is copies shifted over and then each rotated around a base point likewise shifted over, with each successive one shifted farther than the previous one. That's what the guide they linked to is describing, and what the code in Post 5 does. [And if I do say so myself, I think it's pretty cool to watch it do its thing!]