Concentricity in Assemblies

[Anonymous]

How do we join concetric surfaces in Fusion 360 assemblies?

The scenario is very simple ...and yet frustratingly difficult to assemble in Fusion.

Imagine you want to joint a pipe to another without a lug or larger diameter tube to fit 90 degree cut ends into. The best way for us, using PVC glue is to cut the end of one tube with a circular arc that matches and mates perfectly to the OD of another tube.

Further, we can get angles and compound angles for our truss members, simply by angling the hole that cuts across the end of a tube.

In the lab (high school engineering class), we use a 7/8" hole saw on a drill press to cut across the cheap and easily accessible 1/2 PVC, which is actually 7/8" OD.

The concept is simple but even with construction geometry, points on planes etc.. we can not seem to get the cut round surface to mate to the OD outer surface of another tube it butts up against.

I will attempt to show the scenario as far as we have it in a screen shot.

Any ideas or advice would be greatly appreciated. I could see this being a situation that places special demands on the tube creation at the very beginning. In other words I could envision this requiring us to make tubes from 2d concentric circle extrusions instead of using the cylinder+hole quick method we usually attempt.
 
You can see in this picture I was able to nudge the one on the left into position manually after repeated trial and error attempts.....that is what it is supposed to look like....but the cut tube on the right is 90 degrees out of rotation and just all kinds of wonky, no matter how I try to rotate the joint origins. I'm not asking for SW simplicity, but I am asking for a way to get the surface of the cut peice concentric to the OD of the cross peice.....and constrain it there. Ultimately I want each team member to contribute at least one part  and then have them collaborate on building their bridges from those elements ....like virtual  PVC K-Nex or Legos....modular....
" Hey Greg, grab another 45 degree 8" and a pair of 6" vertical 90 degree pipes etc.... "

-Tech4Teachers

[innovatenate]

I think the trick here is to look closely at the Joint Origins while creating an Assembly Joint.

With the Joint command active, whenever you hover over geometry (e.g. a face), several joint origins will show up in the workspace. If you hold down the CTRL (windows) or Command (Mac) key at this point, ti will "lock" this geoemtry as your selection. With the geometry selection "locked," you can move the cursor around to select different Joint Origins to use in the Assembly Joint command.

Check out the below screencast and let me know if it helps explain how you may use these to your advantage in this particular scenario when aligning the pipes.

Please let me know if you have any questions.

[Anonymous]

Wow thanks for the awesome and fast video response, unfortunately I had zero success reproducing your results.

No matter what I press, I can't seem to get the same joint options that you get on my iMac using command or using control (or option for that matter).

The joint that you are presented with is oriented 90 degrees (perpendicular) to the central axis of the cut pipe and so it attaches perfectly to the central axis of the other un-cut pipe (which is perpendicular to it).

I never get that option.

My joints on the cut pipe joints are either in a planar center with the angled edges (see 1st picture) , 

or at the same center point you used, except axially in-line with the center axis of the pipe.

See Picture 2

 

The only joint I can get that is oriented correctly is at one of the cut tips (see 3rd picture), If I use that one, I get weird results that swing wildly like my fist posting.

See how this is the correct perpendicular orientation to this tube's central axis....but I can only get this option on the tip not at the center.

Here is what you had...see how it is in the center but perendicular to the pipe's long axis. (1 minute and 42 seconds in)

Is it possible the mac and PC versions are different?

How did you build your pipe?

I made mine using the create cylinder then create hole workflow, finally I copied and pasted the pipe and repositioned it roughly where it wanted it, and made the cross cut with a tangential plane to the outer surface and a sketch on it that I pushed/pulled through the end of the pipe to get the semi-circular cut.

I tried another hole, perpendicular to the pipe end, but it would never snap to the center of the pipe, and always left remnants of uncut pipe that were unwanted.

Did you build yours entirely from sketches instead of cylinder and hole?

Thanks so much for trying, I have a long drive ahead of me so I'll head out and check for fresh ideas tomorrow, in other words, it's Friday night and it's time for dinner, we can pick this back up tomorrow or after the weekend. No rush getting back to me.

Best Regards

-Tech4teachers

[innovatenate · Accepted solution]

I suspect the trick is to zoom in close enough to get the face of the cut-out in that pipe. The wall-thickness for my pipes looks to be much higher compared to yours. I suspect it may be hard to select that face unless you are  really zoomed in. You may be selecting some other geometry (e.g. an edge) for the geometry selection, which would explain the mis-aligned Joint Origin.

One trick you may use to linger on the left click when selecting the geometry. This will bring up a selection filter that will allow you to select the geometry from a drop down menu.

There should be no difference between the Mac and Windows versions (other than the keyboard shortcuts are different). 

I've made another quick screencast to show how I created those pipes. 

Hope you had a nice drive and this suggestion finds you. Please let me know if you have any questions.

Thanks,

[Anonymous]

Hooray!

That did the trick, thanks Innovatenate, no construction geometry necessary.

It really does come down to the wall thickness and the zoom level, I had zoomed in ....but I REALLY needed to zoom in a lot further to get the joints to show separately and stop competing for the same pixels on my screen. Apparently when that happens the axial joint always wins out.

Changing the wall thickness, temporarily, also did the trick as an alternate path to success.

So, really, two excellent solutions came out of your work on this, thank you thank you thank you.

To sum up, especially for my students who are checking this posting:

If you don't see the perpendicular joint icon appear it is because you either need to zoom in much much further,

OR

You need to temporarily roll back to the hole (or shell, or sketch and push/pull, or extrude....isn't it great to have choice for your workflow), change the diameter to something with a much thicker wall and after the assembly is made change it back.

4 ways to build concetric pipe cylinder holes, and two ways to make your joint snaps visible.

I will mark this request as resolved and hope that many more people benefit from these great tips and advice (and videos) from Innovatenate.

Thanks again,

Tech4Teachers