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Hi,
I'm having a problem with Tangent Planes on a cone.
I'm new to Fusion, so it's quite possible I just don't know what I'm doing. I don't understand what the Reference Plane option does (I've played with it a bit, and haven't figured out what it's doing, and the docs here are not expansive on that detail: https://help.autodesk.com/view/fusion360/ENU/?guid=SLD-CONSTRUCT-TANGENT-PLANE).
In my actual project (as opposed to the test case project I've created), I'm working on something that resembles a colander (images on Google). A flat bottom bowl that is perforated with a zillion holes. The part that causes trouble is putting holes in the more vertical part of the bowl (I guess it's a conic frustum, with the narrow end 'down'). To put the holes there:
1. I'm attaching a tangent plane to a cone.
2. I create a sketch on that plane, and draw a rect/circle a few mm up from the origin of that plane (landing the hole-to-be in the wall).
3. I then extrude that rect/circle to make a hole.
4. I then use Rectangular Pattern and Circular Pattern to copy that hole up the side to the top of the wall, and then copy it about the Z axis about 90 times (every 4º) to cover most of the surface.
I could be done at this point, but I want alternating holes to make it more 'diamond shaped' than grid shaped.
5. I create a second Tangent Plane in the same quadrant of the cone (I notice you can do it in each of four locations, 90º apart from one another), and use the angle to shift it by 2º (half of the 4º spacing I achieved by putting 90 around the circular pattern)
6. I create a sketch on that second Tangent Plane (TP), similar to the first, except that I make the hole a bit higher than the hole I made on TP1's sketch. Now, this hole is a bit above and to the right of the first one.
You can stop there. I went ahead and rect/circle patterned before I eventually noticed the problem, but if you know the problem is coming, and you look for it, you can see it at this point.
The hole created on TP2 is too far to the left. It *should* be perfectly between (but above) the first hole in TP1 and it's sibling to it's right, but it's not. Also, if you *do* perform the rect pattern step, you'll notice that line of holes is *not quite* parallel to the first rect pattern done on TP1.
So, I've done a lot of messing with this problem, and created a test case for sharing (I'll try to attach it here), but I want to pause in case this is enough for someone to tell me that I'm doing it wrong, and I should do "xyz" instead.
I will mention though that it appears that when I rotate the TP, Fusion rotates it as if it were on a cylinder that was coincident with the line where the initially created TP touches the cone. That is, pretend there's a cylinder there, instead of a cone. If you do that, the rotation makes sense. I feel like this is a bug, but again, I'm probably just doing something wrong.
I found this post, and feel this may be somehow related.
So. Test case.
I've spend a lot of time on this (an embarrassing amount - over 12 hours, probably). I've built a simplified test case that demonstrates this with the cone, the two TPs, a greatly reduced number of holes, and 90º steps instead of 4º. Why 90º? Because then I can create a third TP in the next quadrant, and sketch a hole on it that *should* correspond to the hole on TP2. and then you can see the wonky mismatch and angle deviation.
But again - I'm probably just doing it wrong. Shoulda asked for help sooner. 🙂
Here's a screenshot of my test case.
TP1 is the first Tangent Plane, created in "quadrant 1" (arbitrary label).
TP2 is the TP created in the same quadrant, but rotated 90º.
TP3 is my extra (for test case only) TP created in the next quadrant over, and not rotated. What i see there is what I expect TP2 to look like. Of course, this only works out this way because my test case uses 90º instead of the actual 4º I want to use in the real project. The 90º is because it greatly exagerates the effect, making it super-obvious, and it also aligns with the next location I can create a TP at, which will look correct.
Here's one more screenshot where I've rotated to look straight at the right face. You can see how the construction lines on TP1 & 2 are parallel, as if the rotation was around a cylinder, not a cone. Odd that the angle between those construction lines and the imaginary line connecting the two origins is not 90º.
I feel like something is wonky here.
I hope this makes sense - it took a long time to figure out, and I'm afraid that it's too complicated to explain without a video. (But also that a video will take another embarrassing amount of time!)
Thanks,
Jason
Can anyone tell me what I'm doing wrong?
Umm,
We have a problem creating a diamond pattern with the current info. 2.5mm squares and 4 degree offset, are not compatible. the 4-degree turn is too tight in my opinion. What was your intended vertical spacing?
Demo - mock up to show what is a likely result without changes.
As to bug? in Tangent planes, cannot speak to that as I have always found ways to avoid them.
Might help...
Tangent plane on a face at a point, is difficult to create with stability.
Plane on Angle, on the Revolve profile line is so easy, no need to consider alternates.
The problem is that the Tangent Plane, when rotated about the cone, does not maintain its orientation on the cone
Construction planes are not geometry, so have very limited use when trying to duplicate them. (Can be done but too complicated when simple alternates exist)
Your file has no rotated planes - these 2 are aligned.
Sketching on body faces is more stable and duplicating in patterns bodies or faces is very simple.
Back to the design,
Start with two cutter bodies that are lower cutters for row 1 and row 2, in correct spacing orientation, pattern them up the wall, and follow with circular pattern. (Max fit is 6 degrees)
Might help...
Thanks for the suggestion - I haven't tried it yet, but will. I didn't know I could create a Plane at Angle on a circle (I think that's a paraphrase of "Plane on Angle, on the Revolve profile" - if not, then I didn't quite understand what you meant). That would be more simple that what I DID try an hour or so ago.
What I tried was laying out some construction lines on the top surface of the bottom plate that gave me some lines I could use as the basis of a pair of "Planes at Angles". Actually, I guess it may be what you were describing above, but I added a couple of lines that were tangent to the circle. Perhaps they were implied/assumed.
That appeared to ultimately yield perfect results on the bottom row, but I did notice things "got weird" if I adjusted the angle (circled in image) after creating the planes.
By "got weird", I mean I started seeing evidence of the plane ... rotating. Not rotating about the line it was defined on, but rotating on its own Normal (local Z, I suppose). However, I got what appeared perfect after I created it in the correct spot, and didn't mess with it:
I haven't put the second hole through the pattern process yet, and it's at the same height as the first row to make the alignment easier to eyeball. I measured with the measurement tool, and saw the spacing was only off by .001 mm. I'm hoping that's just some odd rounding error. I'd have expected it to be correct to a finer degree.
Finally, the reason I say "appeared" to yield perfect results is because I didn't complete the tiling. You did, and on the bottom row it looks good..., but I don't know if you noticed, but at the top row in your image, you can see the holes have biased to the right (or perhaps left). Suggesting the second column of holes was drawn on a plane slightly rotated:
Ok, after writing the above, I spent a few more minutes revising, and was able to put this together, based on the layout line approach:
Took a few measurements, and it seems correct.
Just for grins, I've changed the angle in the layout to 15º (performing no other adjustments) and got this:
Now, obviously, the placement of the holes is wrong; ignore that. Focus on the change in spacing from bottom to top. The holes no longer go straight up the side! This is what I was talking about when I mentioned things could still get weird.
I feel like that's a violation of the parametric nature of the product. I should be able to go back and edit that angle (did I type 5º? that isn't right; make it 6º), and it should 'play through'. But it doesn't. Not perfectly. It has side effects that are different from creating it that way in the first place. But perhaps I'm not understanding something. I will cheerfully acknowledge I'm new to this product, and that it's view of a plane is actually more complex than "just a plane" - it includes a local origin, and a local definition of the orientation of the X, Y and Z axis. So far, I haven't figured a way to affect how those are defined, and I'm assuming that it's "just set" at creation time to something that seems sensible, based on the info used to create it. Again, a blind spot in my understanding.
At any rate, I feel like I have a workable solution here, and perhaps I can just "get on with it." (Though I love to pick and tease at something that doesn't look quite right...)
Thanks for your help in learning a few more ways to look at a design challenge such as this!
@jsibre wrote:
Hi, the part that I think is a bug is that if I change the other angle (5º, 15º, the angle that has been used to move the plane a few degrees around the cone), it does not create the same end result as it would have if I created the plane AFTER that angle had been set.
This bug can be reproduced for Tangent Plane, Plane at Angle, and Plane Tangent to Face at Point. It may be present in other features; those are the only three I've used while on this little adventure.
I can send you samples 'proving' that, but I'd rather not. It'll take more time. The conversation above demonstrates it on Tangent Plane and Plane at Angle. I saw it on Plane Tangent to Face at Point as well, but I don't think I provided any screenshots of that.
I would like to see one of those samples. I looked at your design a bit, but I don't really understand what the problem is in that design. If you can demonstrate, on a simple design (preferably just a cone and a tangent plane) a case where the behavior does not seem right to you, please do share it. Yes, it will take more time, but if there is a bug there, I'd like to see it get fixed, and that time will be appreciated.
Are you using a reference plane in creating your tangent plane? If not, Fusion will use the pick point on the cone (which is not a stable entity, and almost impossible to re-create) as the point of reference. You will get a much more predictable result using a reference plane.
Jeff Strater
Engineering Director
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