How to make a simple mate between 2 rods and a support?

trenton_carr

Hi
I'm trying to mate 2 holes in a support bar to 2 rods but it refuses to mate.
I've made revolute mate to the 1st rod and after that I cannot get any other mate to work to match up the 2nd rod.
Assembly works fine in SW and Creo. The shaft is not connected in any way.
Hole and rod centres are exact.

Any assistance please?

Thanks.

brian_brady

Could this not have been assembled with a single Fasten mate and an angular offset of 45˚?

lni64

If the support bar is supposed to be movable in z I'd use two cylindrical mates. If it is to be fixed in z I'd use one cylindrcal and one rotational mate. Using two rotational mates can easily lead to overdefined mates since both will try to fix z.

bradley_sauln

In addition to @lutz_niggl I want to take a step back to make sure that you understand how our mates work. They are fundamentally different from SW and Creo. For more information on how mates in Onshape work you can look here: https://cad.onshape.com/help/#mate.htm?TocPath=Assemblies|Mates|_____0

trenton_carr

lutz_niggl said:

If the support bar is supposed to be movable in z I'd use two cylindrical mates. If it is to be fixed in z I'd use one cylindrcal and one rotational mate. Using two rotational mates can easily lead to overdefined mates since both will try to fix z.

Support bar is not movable and I've tried all the mates as stated in OP.

I cannot seem to find the reason.

lni64

If you can give me access to your document I can have a look at it. It should be really simple to fix.
If sharing is not an option you can have a look here: https://cad.onshape.com/documents/162727ed93bbb391c1a00286/w/bea92ea5a9b177b871e64254/e/3b3d41d0cd19f0609e611aa7

trenton_carr

Here's the link, thanks for looking.
https://cad.onshape.com/documents/580793fe106cdf112af16d66/w/00444d4baa4cef48f38769aa/e/53eb9c35f72a9d258dad426c

lni64

@trenton_carr unfortunately I have to leave for a couple of hours. If nobody else is helping you meanwhile I'll have a look later. 

michael3424

Is the center distance between the outer holes in the gimbal the same as the distance between the studs (Part 1)?  They look a little off to me.

trenton_carr

@lutz_niggl Thanks

@michael3424 Yes perfectly equal dimensionally. Assembles fine in SW and creo.   

lni64

@trenton_carr:  I can reproduce your problems with mating the support bar to the rods. @michael3424 is correct, the distances of the holes in the motor do not exactly match the distance of the holes in the bar. (Looks like the deviation is smaller than the displayed accuracy)

To check this I redesigned the support bar with the correct distance (sqrt(2)*31mm). This bar can then be mated to the rods without any issue. The red bar is the new one, the gray is the original bar. 





Here the corresponding document: 
https://cad.onshape.com/documents/5807ed1a26b0d21143965d65/w/6a102689003bc09d6c2247e6/e/e0d10fe051caea25d2a7b568

trenton_carr

Thank you very much for helping find the issue.

I've tried to find the root of the problem so had a look at the source file in Creo.


 Accurate to 4 decimal places, I can only assume then that a rounding error happens either during export to parasolid or importing from parasolid.

Either way I cannot spent time remodelling parts that should fit.

Thank you for your help once more.

lni64

Quite interesting, I also belive that this is some rounding effect in either the importer or the exporter. Here a screen shot of a distance measurement in Onshape. It shows a small deviation in y direction which is probably the reason for the issue. I think this is something Onshape should have a look at.

brian_brady

Could this not have been assembled with a single Fasten mate and an angular offset of 45˚?

trenton_carr

brian_brady said:

Could this not have been assembled with a single Fasten mate and an angular offset of 45˚?

Thanks, this does work, but does not explain the underlying problem.