[Zabco]

Wanted to reply to your post on the 28th Don but I was at the Lafayette RC truck show this weekend and only had access to open public wifi and I don't like submitting passwords over those.

Alibre's assemblies can be a huge PITA. Most times they fall right in place and other times they just aaaarrrrrggghh. A few things I've learned about them over the years.

You can only have 3 constraints between any two objects or assembly.

Sometimes just changing the order you create the constraints will make a difference.

Under each part listed on the work history on the left side of the screen will be a list of each constraint you created for that part as well as a list of all the constraints created for the assembly as a whole. If a constraint has failed for some reason it will be shown in red. I usually just delete these as they can cause confusion when trying to figure out how things went together.

Get one part in place, usually 0,0,0 and anchor it. If you don't you run into the possibility of parts suddenly flip, flopping around and you can't figure out how the heck that happened. And usually the only way to correct it is to delete parts and start over.

It's often easier with complex systems to make parts into sub-assemblies and then assemble the sub-assemblies in a final assembly. But there is a catch to this method. In your last post as an example, you explained how you had the steering knuckles and tie rods able to move back and forth. If you were to make that drawing a sub-assembly and then add it to an assembly of say, the entire frame, those knuckles and tie rod will no longer be able to move. They will be frozen in whatever position they were in when you last saved the file. Only parts added in the current assembly will be able to move.

I don't know to how many decimal places Alibre takes their precision but it must be quite a few. If you try to constrain two parts and the difference in distance or angle is off by the slightest amount they will not go together. For example if I want to assemble a cross beam to a frame and they both have a square 4-hole layout that bolts would be put through to bolt the parts together I would probably assemble them in Alibre by first mating the two flat faces together, then make a coincident constraint between two of the holes in the frame and the bear. But the parts would still be free to move about each other around that bolt hole. To fully fix the beam in place I need to add a third coincident constraint between another pair of bolt holes. Three point of constraint and the two parts can't move in relationship to each other. But when I designed the beam I got the distance between the two pairs of holes .0001mm shorter than the same pair of holes in the frame. Such a tiny amount of length that you couldn't see it in the real world and a bolt would still easily fit, Alibre won't accept it. Round-off errors if you do your math outside of Alibre can cause a real problem. I don't know of any setting that you can change to allow a certain amount of 'play' between parts. The same is true when trying to mate parts with angled surfaces that are already constrained to other parts.

The nice thing about the assembly window is that you can create new parts or edit existing parts within the assembly. In my example above where I can't make the third constraint because of the slight difference in distance I could edit the beam by deleting the holes in the beam, place new holes on the face of the beam and make them individually coincident with the holes in the frame and then do an extrude cut on the beam. Perfect match, constraint made and when I save the assembly file the part file for the beam will be updated.

If all else fails, make a plane and use it to constrain a part. Planes have to be created relative to another plane, face or line of an object. So Alibre knows exactly where the plane is located. You can then do a direct of offset constraint between the plane and the part or sub-assembly you are having problems with.