Author Topic: Filleting an arc to a line makes the arc disappear  (Read 226 times)

adriank

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Filleting an arc to a line makes the arc disappear
« on: March 13, 2018, 02:11:01 AM »
I have just been programming a screen for CNC routing. The router tool is 3mm dia so I need to fillet all the internal corners & I kept finding my arcs were (seemingly randomly) disappearing.

In the end I worked out that the arcs were only disappearing if the end point at the fillet end was pretty much in the right position for where it would end up after the fillet. If I extended or shortened the line significantly it would fillet ok.
If I extend the arc just a little (less than if it were trimmed to the line I'm filleting to) then the fillet works on the wrong segment of the arc leaving a short arc on the wrong side of the fillet.
If the arc is a little shorter than where it'll end up after the fillet then the arc disappears completely.

I worked out this only happens on very high radius arcs. That is, high radius compared to the fillet radius.
In the example attached I'm trying to do a 1 metre fillet on a line and an arc that has approximately a 175m radius.
If the radius is less than 175m (green line) the arc trims correctly no matter what length needs trimming. If it is greater than 175m (red line) it has the problem.

Anyone else see this happening?

Adrian

bdeck

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Re: Filleting an arc to a line makes the arc disappear
« Reply #1 on: March 13, 2018, 07:25:19 PM »
Hello Adriank,

I can verify that the problem occurs on your sample drawing.

Trimming the red arc to the black line prior to filleting it seems to help in this instance.

I've seen many cases where the wrong end of a line or arc trims off. This is an old bug.

One solution is to construct the fillet, using parallel by distance to first create intersecting centerlines, and then centering a 1m arc on the intersection.

Perhaps your research will lead to a simpler solution.
Your research seems to lead to a simpler solution.

Regards,
bd
« Last Edit: March 14, 2018, 02:13:11 PM by bdeck »

Bob P

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Re: Filleting an arc to a line makes the arc disappear
« Reply #2 on: March 14, 2018, 04:34:27 AM »
I got the fillet function to work by trimming both lines back a bit.

adriank

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Re: Filleting an arc to a line makes the arc disappear
« Reply #3 on: March 14, 2018, 08:51:05 AM »
Thanks for taking a look at this guys.
As I mentioned in my original post:

In the end I worked out that the arcs were only disappearing if the end point at the fillet end was pretty much in the right position for where it would end up after the fillet. If I extended or shortened the line significantly it would fillet ok.

That is the work around - make the lines significantly shorter - and then they trim ok.
I was working on a grid to be CNC routed - parallel straight lines in one direction, parallel arcs crossing the lines at approx 90deg. (a mocked up example attached)
Unfortunately the 'trim double lines' function does not work on arcs, only vectors, and individually trimming out every crossing line was proving tedious (top left of example) so I used the section trim tool to roughly chop all four lines at once (centre examples) then filleted the 4 corners (right of example).
I found some arcs were disappearing, some were trimming wrong side but most worked fine - that's why I went in search of the cause. Turns out I was trying to estimate as close as possible where the lines would be after the fillet command and I just got too good at that! Once I got sloppy and hacked out big chunks everything was good.

It's still a bug though!
Adrian