[求助]：新手求教如何画螺纹以及两个半径不同的圆的切线？

new1412

螺纹就是那种田螺的纹路。。。
还有两个圆的圆心在不同的水平线上，且半径不同，不知道怎么画它们的切线，好像有方法我忘了，请指教下

有人知道吗？在线等

hojing7

两个圆的圆心在不同的水平线上，且半径不同，怎么画它们的切线
http://www.xdcad.net/forum/showthread.php?s=&threadid=555530

congjige

1.你说的是渐开线，一下说不清。找一下柔柔长老近期有个帖子，你看看。
2.这个问题近期出了三个帖子，再给你说一下，(1)画好两个圆，(2)右击工具条、(3)点对象扑捉、(4)L回车，（5）点对象扑捉的第十项后，到第一个圆找切点点击。在点对象扑捉的第十项
到第二个圆找切点点击。CAD会自动生成切线。

new1412

感谢2楼和3楼，我收藏了，明天试一下，我刚来这论坛的，呵呵

yxfefeng

x=r(cos(theta)+theta*sin(theta))

y=r(sin(theta)-theta*cos(theta))

r - 基圆半径

theta - 成形角，弧度值

在不同theta时算出x和y即可。


autolisp 写的程序
;*************************************************************************************
;This program is to draw a involute in AutoCAD, anyone can use it freely without permission.
;Take the risk youself, suggest you to open a new drawing and run this program first, then
;copy it to your drawing.
;Chen Xiangsong
;
;Distance Offset: means when you draw a curve rather than a standard involute.
;   it starts to draw the curve not from the base circle.
;   it is curtate or prolate involute. it is useful as you draw gear root.
;   standard involute, enter 0
;
;Radius of Base Circle: You have to know the meaning, or the program is useless to you
;
;Angle to go:  means the length of involute you want. in degrees. it is not pressure
;   angle, it is the pressure angle add involute Phi.
;
;Accurancy:  the density of points you want on the curve, the smaller the more accurate.
;   but will slow down your pc's speed. I normally enter 0.01
;
;Center of Curve: PLEASE PICK A POINT ON THE SCREEN RANDOMLY, IT IS VERY IMPORTANT.
;   DON'T PICK A SPECIAL POINT. That's the disadvantage of my program.



(defun c:involute ()
(command "_undo" "be")
(setq os (getvar "osmode"))
(setvar "osmode" 0)
(setq q 0)
(setq f 0)
(setq h (getreal "\nDistance Offset:"))
(setq r (getreal "\nRadius of Base Circle:"))
(setq t (getreal "\nAngle to go:"))
(setq n (getreal "\nAccurancy:"))
(setq cent (getpoint "\nCenter of Curve:"))

(if (= h 0)  (command "pline"  (list (+ 0       (car cent)) (cadr cent))
     (list (+ (/ r 2) (car cent)) (cadr cent)) ""
  )
  (command "pline" (setq trimpoint (list (+ h r (car cent)) ((if (> h 0) - +) (cadr cent) (/ r 1))))
     (list (+ h r (car cent)) ((if (> h 0) - +) (cadr cent) (/ r 2))) ""
  )
)

(while (< f (* t (/ pi 180)))
(setq a (atan (* r f) (+ r h)))
(setq ri (/ (+ r h) (cos a)))
(setq q (- f a))
(setq pt0 (polar cent q ri))
(command "pline" "" pt0 "")
(setq f (+ f n))
)
(command "pedit" (entlast) "j" "all" "" "f" "")
(command "circle" cent r)
(setq bs (entlast))
(command "line" cent (list (+ 1 r h (car cent)) (cadr cent)) "")
(setq lt (entlast))
(if (= h 0) (command "trim" bs "" cent "")
  (command "trim" lt "" trimpoint "")
)
(command "erase" lt "")

(setvar "osmode" os)
(command "_undo" "e")
(princ)
)

wangyining

谢谢3号楼主,我也学会了.最好再画切线时只在对象捕捉中只打开切点这一个栏目.

JUZE

好象出来的不是切线 哦，，，是圆的两个顶端点。。。。