;;; --------------------------------------------------------------------------- ;;; FlexDuct.lsp ;;; code compiled by YZ August 2026 ;;; --------------------------------------------------------------------------- ;;; FLEXIBLE DUCT ;;; ;;; PURPOSE ;;; Draws flexible ductwork along a route you pick - two walls at the duct ;;; width, with the corrugated coil between them that says "flexible" on an ;;; HVAC drawing, and a plain collar at each end where it clamps to rigid. ;;; ;;; Follows a run of straight legs, rounding each corner to a bend radius, so ;;; a drop from a branch to a diffuser takes a couple of picks. ;;; ;;; WHY THE COIL MATTERS ;;; Rigid duct and flexible duct are drawn the same way but for the coil, and ;;; they are costed and installed quite differently. A run drawn without it ;;; reads as rigid, and the difference shows up on site rather than on the ;;; drawing. ;;; ;;; WHAT WAS FIXED ;;; - It drew no coil at all. The name promised flexible duct and what came ;;; out was two parallel lines - which is rigid duct. ;;; - The collar at the end was set by two numbers written straight into the ;;; code, 9 and 7, in drawing units. On a plan at any scale but the one it ;;; was written for, the collar was either invisible or enormous. ;;; - Pi was written out by hand in four places, twice as 3.1415926 and twice ;;; as 3.14159265, and a right angle as 1.57079633. ;;; - Corners were rounded by running the FILLET command against points picked ;;; on the lines just drawn, with the radius set from a comparison of two ;;; distances that got it the wrong way round on a left-hand bend. ;;; - Every variable was global - eighteen of them, including W, Z and L. ;;; - CMDECHO was set to 0 and never restored. ;;; ;;; FLEXDUCT - draw a run of flexible duct ;;; --------------------------------------------------------------------------- (vl-load-com) (setq *Flex:Width* nil) (defun Flex:Layer ( name colour ) (if (not (tblsearch "LAYER" name)) (entmake (list '(0 . "LAYER") '(100 . "AcDbSymbolTableRecord") '(100 . "AcDbLayerTableRecord") (cons 2 name) '(70 . 0) (cons 62 colour) '(6 . "Continuous")))) name ) (defun Flex:Line ( p1 p2 layer ) (entmake (list '(0 . "LINE") (cons 8 layer) (cons 10 p1) (cons 11 p2))) ) ;;; A polyline from (point . bulge) pairs. (defun Flex:Poly ( pairs layer ) (entmake (append (list '(0 . "LWPOLYLINE") '(100 . "AcDbEntity") (cons 8 layer) '(100 . "AcDbPolyline") (cons 90 (length pairs)) '(70 . 0)) (apply 'append (mapcar '(lambda ( pr ) (list (cons 10 (list (car (car pr)) (cadr (car pr)))) (cons 42 (cdr pr)))) pairs)))) ) ;;; The corrugation: a run of half-circle arcs across the duct, stepped along ;;; the centreline. Alternating the bulge sign is what gives the coil its ;;; characteristic lean rather than a row of rings. (defun Flex:Coil ( obj total width spacing layer / d pairs pt tan ang half n side ) (setq d (/ spacing 2.0) pairs nil n 0 half (* width 0.42) side 1.0) (while (< d total) (setq pt (vlax-curve-getPointAtDist obj d) tan (vlax-curve-getFirstDeriv obj (vlax-curve-getParamAtDist obj d)) ang (+ (angle '(0 0 0) tan) (/ pi 2.0))) (Flex:Poly (list (cons (polar pt ang half) (* side 0.55)) (cons (polar pt (+ ang pi) half) 0.0)) layer) (setq side (- side) n (1+ n) d (+ d spacing))) n ) (defun c:FLEXDUCT ( / *error* vars vals pts p width bend lay obj cl total n v spacing collar ent ) (setq vars '("CMDECHO" "BLIPMODE" "OSMODE" "CLAYER") vals (mapcar 'getvar vars)) (defun Flex:Restore ( ) (mapcar 'setvar vars vals) (while (= 8 (logand 8 (getvar 'undoctl))) (command "_.UNDO" "_End")) (vl-catch-all-apply '(lambda ( ) (*pop-error-mode*)) '()) (princ) ) (defun *error* ( msg ) (Flex:Restore) (if (and msg (not (wcmatch (strcase msg t) "*break*,*cancel*,*exit*"))) (princ (strcat "\n** FLEXDUCT error: " msg " **"))) (princ) ) (setvar "CMDECHO" 0) (setvar "BLIPMODE" 0) ;; AutoCAD 2015 and later refuse (command) inside an *error* handler unless ;; the routine says up front that it will use one. (vl-catch-all-apply '(lambda ( ) (*push-error-using-command*)) '()) (command "_.UNDO" "_Begin") (initget 6) (setq width (getdist (strcat "\nDuct width" (if *Flex:Width* (strcat " <" (rtos *Flex:Width* 2 3) ">") "") ": "))) (if (null width) (setq width *Flex:Width*)) (if (null width) (princ "\nNo width given.") (progn (setq *Flex:Width* width) (initget 4) (setq bend (getdist (strcat "\nBend radius at corners <" (rtos width 2 3) ">: "))) (if (null bend) (setq bend width)) (princ "\nPick the route along the duct centreline.") (setq pts nil) (while (setq p (getpoint (if pts (car pts) nil) (strcat "\nPoint " (itoa (1+ (length pts))) (if (> (length pts) 1) " " "") ": "))) (setq pts (cons (list (car p) (cadr p) 0.0) pts))) (setq pts (reverse pts)) (if (< (length pts) 2) (princ "\nTwo points at least are needed.") (progn (setvar "OSMODE" 0) (setq lay (Flex:Layer "Duct-Flexible" 4)) (setvar "CLAYER" lay) ;; The centreline, as a polyline so it can be filleted and ;; then measured along. (Flex:Poly (mapcar '(lambda ( q ) (cons q 0.0)) pts) lay) (setq cl (entlast)) ;; Round every corner in one pass. (if (and (> bend 0.0) (> (length pts) 2)) (progn (setvar "CMDECHO" 0) (command "_.FILLET" "_Radius" bend) (command "_.FILLET" "_Polyline" cl))) (setq obj (vlax-ename->vla-object cl) total (vlax-curve-getDistAtParam obj (vlax-curve-getEndParam obj))) ;; The two walls. (command "_.OFFSET" (/ width 2.0) cl (polar (vlax-curve-getPointAtDist obj (/ total 2.0)) (+ (angle '(0 0 0) (vlax-curve-getFirstDeriv obj (vlax-curve-getParamAtDist obj (/ total 2.0)))) (/ pi 2.0)) (max (/ width 2.0) 1e-6)) "") (command "_.OFFSET" (/ width 2.0) cl (polar (vlax-curve-getPointAtDist obj (/ total 2.0)) (- (angle '(0 0 0) (vlax-curve-getFirstDeriv obj (vlax-curve-getParamAtDist obj (/ total 2.0)))) (/ pi 2.0)) (max (/ width 2.0) 1e-6)) "") ;; Collars at each end, sized from the duct rather than from ;; a number typed into the source. (setq collar (* width 0.14)) (foreach d (list 0.0 total) (setq p (vlax-curve-getPointAtDist obj d) v (+ (angle '(0 0 0) (vlax-curve-getFirstDeriv obj (vlax-curve-getParamAtDist obj d))) (/ pi 2.0))) (Flex:Line (polar p v (+ (/ width 2.0) collar)) (polar p (+ v pi) (+ (/ width 2.0) collar)) lay)) ;; And the coil that makes it flexible. (setq spacing (* width 0.55) n (Flex:Coil obj total width spacing lay)) ;; The centreline has done its job. (initget "Yes No") (if (= "No" (getkword "\nKeep the centreline [Yes/No] : ")) (entdel cl)) (princ (strcat "\nDuct " (rtos total 2 3) " long, " (rtos width 2 3) " wide, " (itoa n) " corrugations.")))))) (Flex:Restore) (princ) ) (princ)