Centerlines within Circles: How do professionals make them? How should I teach?

[p_burgener751498]

How do professional Vanilla AutoCAD users make the "cross hairs" of centerlines within circles? Which way should I teach my students?

Background: Looking thru old threads, AutoCAD users have several ways they make the "sniper scope" cross-hairs for circles, in vanilla AutoCAD. I've always taught my students to use the proper layer (that has the proper linetype and color ced), scale them by 1.3 to make the extensions out the quadrants, and globally adjust LTSCALE. This works until the largest circle diameter is some 6.9 (as I recall) times the diameter of the smallest circle. After that I suggest tweaking the "Linetype scale" multiplier factor within Properties for the largest circles.

With the newer "Centermark" command, I feel you have to adjust 3 or 4 system variables first, then make the cross hairs, then tweak several numbers in the Properties dialog box.

I notice one person suggested using Points for the cross hairs. Another suggested using a block called "centerlines" scaled to suit. I've even mentioned to students they could draw diameters with continous line, scale them by 1.3 from the center of the circle, draw two small concentric circles and trim away the gaps, as a last-chance option, when you hear that the client just arrived.

I've even mentioned in class that you can make more and more Centerline linetypes like CenterX4, CenterX8, etc. That way deviates from Vamilla AutoCAD, though.

So which way should I teach my students?

[david-k]

Why not set your dimension style to draw the centerlines?
Or have you tried that?
Dimstyle.PNG

[tedg]

I haven't really played with the "centermark" command, what I've done in the past is draw 2 center lines across the circle extending it equally outside the circle. (lines on a center line layer).
HOWEVER,
after reading your post and david-k's suggestion, that is the way to go in my opinion, set up your centermark variables
You should look into the system variables (sysvars) for the setting for this, type "sysvdlg" and you will get a dialog for all your variables, and then search "center*" and you'll get the all the "centermark" variables you can control. (see screen shot)
You can preset which layer they go on (if you wanted, but I would use dimension layer), set the linetypes, gaps, extensions, etc.

I suggest setting up the way you want, and not mess with ltscales etc, it should work the way you want it no matter the circle size, set this in a drawing TEMPLATE (.dwt) for your students to use.
Just for giggles I set the "centerexe" to 3/8" instead of the default .12" to extend past the edge of the circle, which is a nice look.

[p_burgener751498]

Thanks. Both are good ideas but neither increases the centerline extension for larger circles. I'd like the extension to be a percentage of the circle diameter, not a specific distance. -paul

[tedg]

Thanks. Both are good ideas but neither increases the centerline extension for larger circles. I'd like the extension to be a percentage of the circle diameter, not a specific distance. -paul

Well that's not something that's built-in in AutoCAD that I'm aware of, but it could be done with lisp.
The quickest way I can think of is to create a block of the cross hairs that is 1x1 unit with the insertion point at the intersection,
Then when running it, the user types in the circle diameter (or pick quadrants) and then pick the center of the circle, and it places the block at 1.15% (or whatever scale you decide, would be built in the code).

But remember, if you're "teaching" people to use the the software, this isn't an OOTB feature and would not be out in the world at another workplace if they got a job doing CAD.

(update)
Just for giggles, I took a stab a the lisp routine and block I mentioned above, it works pretty much as I described.
If you were to use this, you would need to place and path the block dwg somewhere (or insert the dwg as a block into your dwg template, so it's available each session).
You would need to edit the layer name you use (I used "dimcen").
This scales the block x1.3 of the circle diameter you provide.

hope this helps, was fun to do.

(defun c:cm (/ osm cmde la lr1 scla sclb diam cntr)
(setq osm (getvar "osmode"))
(setq cmde (getvar "cmdecho"))
(setq la (getvar "clayer"))
(setvar "cmdecho" 1)
(setvar 'osmode 16)
(setq diam (getdist "circle diameter? "))(terpri)
(setvar 'osmode 4)
(setq cntr (getpoint "Select Center of Circle" ))(terpri)
(setq scla 1.3)
(setq sclb (* diam scla))
(setq lr1 (tblsearch "layer" "dimcen"))
	(if (= lr1 nil)
	(command "layer" "make" "dimcen" "color" "1" "" "" ""))
(command "layer" "set" "dimcen" "")
(command "-insert" "_centermrk" cntr sclb "")
(setvar "cmdecho" cmde)
(setvar "osmode" osm)
(setvar "clayer" la)
(princ)
)
(princ)

[cadtag]

Thanks. Both are good ideas but neither increases the centerline extension for larger circles. I'd like the extension to be a percentage of the circle diameter, not a specific distance. -paul

If you are teaching students how to (a) use the software and (b) how to actually draft a set of drawings, then personal likes/dislikes of the instructor should be a very distant third ( or forty third) place. Every architect, civil engineer, mechanical engineer, manufacturer, etc. will have their own personal idiosyncratic tweaks that a new employee will have to work with. Grading them on what the percentage of centerline extending past the circle diameter is going to do them a dis-service. Better to teach and grade on what the software does OOTB, and after that is clearly understood, introduce personal prefereces, but _only_ as personal preferences.

[tedg]

If you are teaching students how to (a) use the software and (b) how to actually draft a set of drawings, then personal likes/dislikes of the instructor should be a very distant third ( or forty third) place. Every architect, civil engineer, mechanical engineer, manufacturer, etc. will have their own personal idiosyncratic tweaks that a new employee will have to work with. Grading them on what the percentage of centerline extending past the circle diameter is going to do them a dis-service. Better to teach and grade on what the software does OOTB, and after that is clearly understood, introduce personal prefereces, but _only_ as personal preferences.

Agreed.
If you're teaching students to use the software and create drawings to hopefully get a job, you should stick to what AutoCAD gives you.
Because as cadtag mentions, every place will be different on how they want to present drawings, and maybe not want personal tweaks such as this, unless it's their company standard.

With that said, you can use the centermark settings built into AutoCAD as I suggested before, to show them how to do it which would help them in the future.