Discussion of Polar Pattern and Linear Pattern behaviour

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FreeCAD97990
Posts: 18
Joined: Sat Jul 01, 2017 12:11 pm

Discussion of Polar Pattern and Linear Pattern behaviour

Postby FreeCAD97990 » Sat Jan 26, 2019 1:02 am

I first noticed at least a year ago that Polar Pattern fails when you use it to Pattern a Pocket feature if one or more of the Patterned Pocket features fails to intersect with the Base Feature.

I have found this quite awkward when there are a number of cut-outs on the Base Feature. Either you have to Pocket and Pattern the areas between the cut-outs individually, or else you have to fill in the cut-outs, Polar Pattern the whole lot, and then re-created the cut-outs again. Then repeat as the design develops and the cut-outs change!

I've been looking at the way that Pocket (when used by itself without Polar Pattern) behaves, and comparing that with Polar Pattern. When using Pocket by itself on the Base Feature there are two bad things that can happen. The first is that the Pocket splits the Base Feature and creates multiple Bodies. Pocket issues a Transformation error if that happens. The second is that the Pocket fails to intersect with the Base Feature. If that happens, Pocket does not change the Base Feature and does not issue an error. I think that both of these cases are appropriately handled and work fine.

If you use Polar Pattern on a Pocket feature, then again bad things can happen. The first is that one or more of the Pattern of Pockets splits the Base Feature and creates multiple Bodies. If closely spaced, the Pattern of Pockets can also overlap one another and make up a 'chain of holes' that stretches across the Base Feature and again creates multiple Bodies. Polar Pattern issues a Transformation error if either of these happen. I think that both of these cases are appropriately handled and work fine.

The other thing that can happen is that one or more of the Pattern of Pockets fails to intersect with the Base Feature. Well, Polar Pattern is very helpful here, because it updates the view to show what the new shape will be with the Pattern of Pockets removed. And any that do not intersect with the Base Feature are highlighted in red. So the user can easily see what is happening and what the result of the operation will be. I think that Polar Pattern is better than Pocket here, because Pocket does not highlight in red.

Unfortunately, if any are in red, Polar Pattern also issues a Transformation error. I am wondering why that is. Clearly, the Pockets that have failed to intersect with the Base Feature cannot give rise to multiple Bodies. And in particular, I am wondering whether Polar Pattern fails here because the same criterion for failure that is used for 'Polar Pattern with Pad' has been inappropriately applied to 'Polar Pattern with Pocket'. (Clearly 'Polar Pattern with Pad' must fail if any Pads fail to intersect with the Base Feature because it creates multiple Bodies.)

Any ideas?

The same seems to apply to Linear Pattern...................

Congratulations if you have read this far, and sorry if this is all garbage!
chrisb
Posts: 14083
Joined: Tue Mar 17, 2015 9:14 am

Re: Discussion of Polar Pattern and Linear Pattern behaviour

Postby chrisb » Sat Jan 26, 2019 1:25 am

Perhaps it is sufficient to issue a warning if some features don't intersect, especially for intermediate hole hitting ones. Cutting the body in more than one piece is currently disallowed but there was already talk here that this restriction might be dropped.
FreeCAD97990
Posts: 18
Joined: Sat Jul 01, 2017 12:11 pm

Re: Discussion of Polar Pattern and Linear Pattern behaviour

Postby FreeCAD97990 » Sat Jan 26, 2019 1:58 am

Hi chrisb,

Thanks for your reply.

I just had a look back at my first ever forum post (July 1st 2017) which was about this same issue, and I made the suggestion there that a warning would be sufficient.

The point I was trying to make when I spoke about Pocket (used without Polar Pattern) is that Pocket does not even make the user aware that the Pocket feature has not intersected the Base Part. Whereas Polar Pattern does so in red...... and as you say could issue a warning too.

I'm not a coder...not even close...but I'm assuming that there is no technical reason that the Transform must fail (like for example that Freecad would need to keep a record of which intersected and which didn't and that would mean lots of extra coding which wouldn't be worth it). If it comes down to a straight choice of saying either:

'Transformation Failed (because we think the user might be confused into thinking that all had intersected)'

OR

'Yes here is the Transformation (and we trust that the user has looked at and understood the red warnings on the screen)'

I think the second is definately the one to go for....


Lastly as a humble user....a body should mean one piece.......