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Centerlines on Circles - What's popular?


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I understand drawing Centerlines on circles got easier with the Centermark tool that came out in R2017.  Are people using it? 


By default it looks like the extensions are a bit small, especially on large circles.  Do you simply type Centerexe and raise the value more and more, the bigger the circle is, before placing the Centermark?  Do you grip edit all four extensions?  Do you change all 4 extension distances within "Properties" (wish I could shift-select all 4 at the same time)?    


I'd like to have the extensions be exactly 15 percent of the diamter.  Can I rig the new Centermark to be proprotional to the diameter? 


I also notice there are several breaks in the lines when I use Centermark on large circles.  Do I need to change the linetype to Continuous within Properties, for each and every Centermark I draw?  


Background: For decades I've taught  students to select the right layer (center, center2, or centerX2), draw a line from 3:00 quadrant to 9:00 quardrant, scale it by 1.3, and then mirror is about a 45 degree line (easy with polar tracking set to 45).  If there are too many breaks, I change the layer to one with a "higher" linetype.  If all else fails, and there's no LTSCALE that can satisfy all the various diameters of circles (like if the largest circle diameter is greater than 6.9 times the smallest circle diamter), then I "cheap" and assign an Linetype Scale "modifier" within the properties of the largest or the smallest circles.  


Or am I just getting old and need to get used to the same small extensions and multiple breaks?  

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The problem with some 'built in' functions like that is that they rarely give you exactly what you would like to see.
What might suit an electrical discipline may not suit mecanical or architectural, and vice-versa.


I've always simply set the correct layer/linetype, drawn H&V centrelines between the circle quadrants (have quadrant osnap turned on), and then used the 'lengthen' command to extended the lines (usually by about 10mm each end, depends on what size the circle is, I had a macro on a button to extend any line by 10mm with a single click).


You can use percent as a parameter of lengthen rather than specifying a distance, the problem being that once you have lengthened one end of the line you have to calculate a smaller percentage for lenthening the other end.
You could alternatively 'scale' both centrelines about the center point.
Another problem with using percent or scale is that you may end up with an 'odd' length of line rather than a round number. (eg. 20.3268).


I was working with LT most of the time so couldn't use a lisp.
But if you want to get your students into lisp then it shouldn't be too dificult to automate the whole process with one click of the circle.

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