Assembly elements askew!

jeff_mcaffer

Somehow while creating an assembly something got skewed by 0.194deg. As a result, everything is just that little bit off. In particular, the "workbench" is fastened to the legs via "Fastened 12" but rather than being square, it's rotated 0.194deg. As best I can tell, the legs are all square to one another. 

I'm not sure how to find the root cause or fix the problem. 

There does not seem to be a reference plane or some such that I can measure each part against to see which one is out. Everything in the assembly should be at right angles. The only thing I can think of is when I inserted various parts I had to rotate them to get the right orientation. That rotation seemed error-prone (or I simply don't know how to it other than grabbing the angle handle and dragging it around). Where I did have problems, they seemed obvious, and I was able to revert/fix. Given this angle is so small, it's possible I had that issue and didn't notice. Either way I'd love some pointers on how to diagnose/fix.

Similarly, suggestions on how to avoid the root cause (whatever it turns out to be) would be great.

Thanks
Jeff

jeff_mcaffer

OK, I did some more digging and found out that the "workbench" part got skewed somehow (presumable prior to being fastened). Rather than fiddling with unfastening rotating and re-fastening, I deleted it, inserted a new one and fastened. Note that that part does NOT need to be rotated at all after insertion.

So that leaves me with the question: How do parts "randomly" get rotated in an assembly? I've no doubt that I did it but don't know how I could have done it accidentally. The workflow is to select the part, grab the angle handle, move it some, move off the handle and click to confirm. Seems hard to do accidentally. Is there another way that the part could have been rotated? Random keystrokes?

glen_dewsbury

@jeff_mcaffer
Not random.
Check your angle sketch. One of the leg lines is not square with the sketch.

glen_dewsbury

Ps. Have you looked at the frame tool to make your angle frame?

S1mon

Assemblies leave everything floating by default. You need to fix or mate at least one part to the origin, and then use functional mates or one big group mate to tie everything else down. It is one of the weirder parts of Onshape to get used to, but after a while it all makes sense.

jeff_mcaffer

@glen_dewsbury you're the master! How did you find that leg that was not vertical?

That may well have been the cause of the problem. I don't remember how I mated the workbench. Perhaps when I deleted and re-added I mated it differently and avoided the problem. For sure it was the cause of the next problem I have been scratching my head over all morning. That slight off-angle, when combined with a mated part, left one end of two "parallel" parts .05" higher than the other. I was searching all over my mates for anything that could be amiss. It would have been many hours before I looked at the shape of my angle iron part. Thanks!

As for the frame tool, I had not looked at that. Will investigate. There are some quirks of the layout I'm doing so we'll see how it goes.

@S1mon Got it. Thanks. I also have taken to inserting a simple cube part and then using its faces as my reference planes to tell if a part in the assembly is "true". It would be nice to have something like the standard sketch planes show up in assemblies.

S1mon

I often add a mate connector at the origin to help keep my head wrapped around where everything is. Rather than mating parts to the origin, I mate to that MC.

glen_dewsbury

@jeff_mcaffer
I tried mating the parts my self and realized at least one part was out of square since the result came back the same. Wasn't hard to track after that. The table top was fine which left the angle. Just had to turn on constraints. Of course it's never happened to me before.