topic Re: Parametric diameter not respected? in Fusion Design, Validate & Document Forum

Parametric diameter not respected?

GregHeumann — Thu, 17 Sep 2020 01:38:51 GMT

To create this piston, I drew a circle of parameter "PistonDiameter". I extruded in both directions.

To draw the connecting rod slot I tried twice. I created sketch 2 on the bottom of the piston.

1st I created tangent planes and a mid plane - then a "center line" down the mid plane) and drew a 2 point rectangle symmetrical around that (that's what is in the screen shot below.) Rectangle length was ="PistonDiameter". Sharp eyes will see the right side "tangent plane" is NOT in fact tangent, but more importantly both ends of the rect don't end up tangent to the circle.

Trying again, much simpler - projected sketch 1's center point, drew a centered rect on that, and set the length to "PistonDiameter".

EITHER WAY the rect isn't the same as PistonDiameter. I triple checked this. Can't understand why.

Re: Parametric diameter not respected?

davebYYPCU — Thu, 17 Sep 2020 02:33:36 GMT

Piston Diameter is not equal to Inner Cylinder Diameter.

You have forgotten your design intent.

Projected circle = Inner Cylinder Diameter.

Piston extruded from wrong sketch.

Might help....

Re: Parametric diameter not respected?

wmhazzard — Thu, 17 Sep 2020 02:29:09 GMT

You must have had the sketch for the cylinder visible when you extruded the piston as and the extrude picked up the cylinder sketch and made the piston .8" in diameter.

Re: Parametric diameter not respected?

GregHeumann — Thu, 17 Sep 2020 05:30:22 GMT

PistonDiameter is supposed to be less than cylinder diameter. There must be some clearance. That clearance is also a parameter. If you look at PistonDiameter you'll see it is a function of cylinder inside diameter minus that clearance. That is not the problem. The circle from which the piston is extruded AND the rectangle to cut out the clearance for the connecting rod are both defined by PistonDiameter, not cylinder diameter.

Re: Parametric diameter not respected?

davebYYPCU — Thu, 17 Sep 2020 05:31:50 GMT

Wrong, your piston is .8 diameter.

Re: Parametric diameter not respected?

GregHeumann — Thu, 17 Sep 2020 05:36:26 GMT

I went and used inspect to measure the piston diameter and it is indeed .800, which is cylinder diameter - and it should be .795 which is piston diameter. So that seems like a good explanation. I don't know HOW that happened because I selected the circle in the piston sketch to do the extrude, and its diameter is .795. Have to leave it a mystery!

Re: Parametric diameter not respected?

davebYYPCU — Thu, 17 Sep 2020 05:41:07 GMT

Simple mistake, two sketches live at the time of selection. You selected the inner circle of this sketch. Hide that sketch to avoid the problem. Edit the Extrude and select the correct sketch.

Might help....

Re: Parametric diameter not respected?

GregHeumann — Thu, 17 Sep 2020 06:01:23 GMT

That must be what happened. I started over on the piston and got it right. I could have sworn I had the piston sketch active when I selected it for the extrude but....... I will be more careful next time! Thanks!