spline vs polyline

[Anonymous]

I was watching a tutorial about how to make a gear. they joined two curves by blend curve. then they wanted to copy this with polar array, but said the newly created line by blend curve is a spline, and first we must convert it to polyline. why is that?

[neaton]

Splines can be arrayed and extruded so I can't think of a reason to change them unless there is something done later in the video that requires it to be a polyline.

Could you post the video link so we could see why it might say to change to a polyline?

Nancy

[Anonymous]

Ok.. here it is:

https://thesourcecad.com/autocad-tutorials/

On that page, go to 2D tutorials, Part 8, #5 - 2D Spur Gear

[j.palmeL29YX]

I don't know (beside others) why the author used the blend command to fill the gaps. (The blend command always creates a spline). I'd draw an arc (center at the centerpoint of the big circle, startpoint and endpoint at the ends of the small arcs). So you don't have the problematic mix of arcs and splines.

cadder

[neaton]

Great solution @j.palmeL29YX.

When you convert a spline to a polyline it is creating X+1 number of line segments so precision 10 creates 11 line segments (10 internal line nodes). The arc solution is the correct one for a machined part.

Nancy

[leeminardi]

There is no apparent reason why the spline is converted to a polyline.  As others have pointed out an arc would have been a better solution.  Perhaps the author wanted to show a few new functions (blend and convert to polyline).  The pedit command can be used to join arcs and lines together to form one object (a polyline).  pedit will not accept splines so perhaps this was on the mind of the author. I also considered that perhaps the author had some need not to have a spline in the gear tooth profile in anticipation for some later tutorial but I could find no evidence of that.  The main purpose of the tutorial was to show the use of polar array.  This was done very well.  I would have liked to see a real gear tooth profile (an involute curve) used instead but that is beyond the goal of the lesson.