Break command at specify point
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An image or sample drawing would help. [I'm not sure what you mean by "relatives."]
Kent Cooper, AIA 
Hello,
I think you can draw an arc and then draw lines at say 45 degrees and 135 degrees by typing "@" (then length of line) then "<" (then the degrees). Then you can erase the line and you have an arc at specified degrees. See pic for 0 degrees start point.
Dave B.
@Anonymous wrote:
Breaking exactly between 2 points on arcs in degrees. 45 degree, exemple. From 90 to 135. How to? ....
To do that particular one, here is one way that requires the User only to select the Arc:
(defun C:BA90135 (/ arc ctr); = Break Arc from 90 to 135 degrees
(setq
arc (car (entsel "\nSelect Arc to break from 90 to 135 degrees: "))
ctr (cdr (assoc 10 (entget arc)))
); setq
(command "_.break" arc
"_none" (polar ctr (/ pi 2) 1)
"_none" (polar ctr (* pi 0.75) 1)
); command
); defun
But of course you wouldn't always want that combination of directions. If the 45-degree multiples are among your Polar angle settings, you can do this:
(defun C:BAPD (/ orth asnap arc ctr); = Break Arc at Polar Directions
(setq orth (getvar 'orthomode) asnap (getvar 'autosnap)); save Ortho/Polar conditions
(setvar 'autosnap (+ (boole 2 (getvar 'autosnap) 8) 8)); turn on Polar
(setq
arc (car (entsel "\nSelect Arc to break between Polar-angle directions: "))
ctr (cdr (assoc 10 (entget arc)))
); setq
(command "_.break" arc
; User specify directions: pick in Polar mode or type in current angle format:
"_none" (polar ctr (getangle ctr) 1)
"_none" (polar ctr (getangle ctr) 1)
); command
(setvar 'autosnap asnap); reset Polar/Ortho conditions
(setvar 'orthomode orth)
); defun
That could also be made to change the Polar angle choices for you, if you want, for instance to lock it in to only the 45-degree multiples even if your current settings include others.
And BAPD will accept typed-in angles other than those in the Polar angle settings -- it could be made to reject those, if you want.
Neither of those has error handling yet, or a check on whether you actually picked an Arc [they would also work on a Circle, though in some cases BAPD would break out the wrong part of it], etc., but see what you think -- those enhancements can be added easily enough.
Kent Cooper, AIA
@Anonymous wrote:
.... POLAR SNAP solution. ....
Polar [F10] in conjunction with Object-Snap Tracking [F11]. Have CENter among your running Object-Snap modes, and the 45-degree multiples among your Polar angles. Call for the BREAK command, pick the Arc, choose the First option, hover over the Arc with the cursor so that a little cross appears at its CENter, then hover over that cross so that it "lights up" and you can Polar-track from there in the 90-degree direction [you don't need to pick on the Arc, just establish the direction], then for the second Break point, again hover over the Arc to get the CENter mark, hover over that to grab it as a base point for Polar-tracking to the 135-degree direction from there.
Kent Cooper, AIA