sad but true… I hope it gets supported in future.
There some advances, but for v6.99, I think.
Roberto’s MR will get in for 6.0 I think, but it does not allow dragging a track with arcs, just dragging a single arc in a track to resize it (still useful, but not the same as requested in 6544)
Man… I love KiCAD … Have I mentioned that lately? … nah, I don’t think I have… I’ve been too busy ranting (whining? :‒) ) about oooh, I don’t like this, ooooh, I don’t like that (net classes, etc. in my most recent post/thread)! :‒)
I am sooo looking forward to V6, and I want to applaud the effort of developers and all the great features KiCAD already has and the ones I’ve seen that you’re planning to add in V6… You have no idea how much I wish I could find time available to work towards joining the team of developers!! Oh well… maybe one day…
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Yes, the title of the MR is confusing. It should be called “interactive resizing of arc tracks” instead. It just gets triggered when you do the ‘drag’ operation (both 45 degree and free angle).
I am still fixing a problem with the MR as is (if you move the mouse to the wrong place it creates an invalid arc). Hopefully will have it ready for merging soon.
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‘This RF superstition was debunked years ago’ That’s a very sweeping and erroneous statement in my opinion. The problem of discontinuities and reflections caused by sharp corners is very real one. The cited paper has clearly been written by an ‘EMC expert’ not a professional rf/microwave engineer. Any antenna engineer will tell you that the absolute accuracy of measurements taken in an anechoic chamber is around +/- 1.5dB. All measurements are < 1GHz, yet the TDR plots clearly show a measureable effect. What this paper misses in spectacular fashion is the cumulative effect of cascaded mismatches, so it is important to minimize them. The effect is at its worse when reflections add in phase. There is no full two port s-parameter measurement given in the frequency domain and not a single reference to any field theory. The geometry of the test pieces is not defined - so it is impossible to verify these results. In short this paper is not particularly scientifically rigourous and should be treated with caution.
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Rounded corners also help with high currency applications: https://blog.samtec.com/wp-content/uploads/2020/06/05_14_2020_geek_speek_perils_RA_turns.pdf
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I hadn’t thought about the mechanical aspects - but clearly a 90 degree corner can act to concentrate stresses. A fact sadly demonstrated by the DeHavilland comet, whose square windows had disasterous consequences!
It is not just flexis where sharp corers must be avoided. I have seen regular PCB tracks break where a track joins the pad of a connector that has flexing stresses. Bolted on terminals are prone to this
One of the things that teardrops solve. (The other is a bigger tolerance for drill location (translates to smaller possible via’s).
A bit weird that this issue for teardrops is still open after 12 years (2008-01-27).
On the plus side, It’s got a milestone for KiCad V7 and several scripts for teardrops already exist. I’m guessing that one of the reasons it took so long was the absence of arcs in tracks, which is now coming in V5.99. 
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The preferred ways to implement teardrops depends on arcs (in tracks and/or polygons, depending on if we implement teardrops as a collection of tracks or as a single polygon) and also groups: if we implement teardrops as tracks instead of a polygon, we want to group those tracks together so that they can be easily deleted and re-generated.
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