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Assembling with tangent constrains


New member
I am trying to assemble the torsion spring shown in yellow
on the image, to the base part that is shown in red. I want to get the leg of
the spring torest against the split pin shown in grey.

View attachment 635

I thought this would be easy enough using a tangent
constraint, and I added a datum plane to the spring to make things easier. Even so,
I can't get the tangent constraint to position the spring the right way around.


New member
Try constraining with surfaces (for both components) instead of dataum planes - this seems to workpretty wellfor me.


New member
Thanks for the reply. I tried assembling using the two
cylindrical surfaces to start with, but I just get the different, but still
wrong arrangement that is shown below. I need the leg of the spring to be on the other side of the split pin.

It could be that the cylindrical surface of the split pin is
just one surface so I can only select one surface. - ProE splits a complete
cylindrical surface into two, so you can control the tangent by selecting
alternate halves. This hardly follows design intent rules though; surely it
should be the side of the surface that is changed to define the tangent?

View attachment 637


New member
You could place a very small flatonthe spring that you couldconstrain tangent to the pin or hole surface. Make the flat small enough not to be noticed on the drawing or model.


New member
Workarounds.. ??

would it be possible to create a curve that passes through the center of the cross-section of the end of the spring, and create a point offset from the split pin by the diameter of the crosssection and then use a "Pnt on line" place constraint or within mechanism aslot follower connection between them which would allow the spring to slide across the split pin if required?

I dunno, it could be completly wrong..

or perhaps you could create a secondary surface on the top of the spring, and use this as your cylindrical surface instead teh original one?

just clutching at straws, I've never tried either in a case like this... bu I'd be very interested to see the solution!
Edited by: james.lynch


New member
Thank you for the replies.

James., maybe I could get some sort of work around like you
suggest, seems like quite a lot of work though, as the datum point has
to be at the correct contact point, which is dependant on the diameter
and position of the spring. I'll have a go with the mechanism
connection you suggest.

I've just read the follwoing in the ProE help file, but it doesn't
really help. I am trying to mate the surfaces, as you can see
from those higlighted in the image below,

"Use the Tangent
constraint to control the contact of two surfaces at their point of tangency.
Keep in mind that this placement constraint functions like Mate
because it mates surfaces; it does not align them. An example of the use
of this constraint is the contact surface or point between a cam and its

View attachment 638


New member
Did you creat those surfaces or are the the result of Pro splitting one surfaceinto two? I've had problems before with the latter..


New member
On the split pin, there is just one surface, and as I mentioned, I
thought this could be the problem. However, I've tried assembling to a
cylindrical protrusion too, as shown in my previous post, and it still
doesn't work. In this case, ProE splits the surface into two.

I'm currently trying to define it as as cam-follower mechanism, but I'm not getting very far...