Should be a simple parametric design but I can't figure out how to drive the dimension, help anyone?

[dan.ballarin]

I was going to design and 3d print a set of Painter's Pyramids (they lift the board off the table to spray paint).  It's a simple design and I COULD just be done with it, however I want more parametric designs exercise. So I made 2 triangles and Loft to make the pyramids, only using constraints. The sketched lines are all black, but I can drag one line to make it bigger and smaller (right line on sketch 1). I added a 3mm fillet on all 3 lateral sides which shortens the overall finished pyramid height. Then use intersect to project the top of the new shortened pyramid.

My issue I can't seem to figure out is how to drive the finished height of the pyramid AFTER the Fillet. At first I wanted to be able to plug in a "user parameter" for both the fillet AND finished height, however I can't seem to figure out how to just drive the finished height with a fixed fillet.  It states that it would create an over-constrained dimension even though the only.

I am having a hard time wrapping my head around how I can drag the 1 line of the sketch to make the pyramid bigger or smaller, however I can't dimension the final height. Any help and resources toward more parametric design understanding is also appreciated.

See attached file. Thanks for any help and happy new year!

[dan.ballarin]

To finish my typo: "It states that it would create an over-constrained dimension even though the only...dimension I added was the fillet."

[etfrench]

@jeff_strater Even though the first sketch shows it's fully constrained, it isn't, as one of the triangle legs can be moved.

@dan.ballarin The fix for making the height parametric is to add a dimension to the height of the triangle:

[etfrench]

@dan.ballarin Oops, it's not quite that simple😀

[etfrench]

Instead of creating a plane parallel to XZ, create one parallel to YZ. Use the height dimension from Sketch1 as the distance. Project the center point of the triangle in Sketch1 to a sketch on that plane. Loft from Sketch1 to the point.

[mango.freund]

i do it with a centerline and parametric. greeting mango

[hamid.sh.]

Because you want drive the finished height of the pyramid AFTER the Fillet you can follow this:

Firstly, fillet with radius R at top of the pyramid is a sphere with radius R, tangent to every face, as you can see from the picture below (I added an sphere to your design to show this):

Now to be able to drive the height AFTER the fillet, you need to know what should be the apex, to use it for loft. Make a sketch on the point passing through the midpoint of of the base triangle sides, then draw this sketch:

In this sketch; 1. circle's radius is equal to your fillet  2. circle's center must be right above base triangle's center 3. top-most point of the circle will be your final height after the fillet, so fix it at your height 4. a line must be drawn, tangent to the circle and its end must be right above the triangle's center point. Now use this point for your loft.

Note: This method only works when your base is an equilateral polygon.

[jeff_strater]

thanks, @etfrench - created bug FUS-96330 for the false fully-constrained logic.

[dan.ballarin]

@hamid.sh.  Thank you, this is what I was trying to do... Driving the dimension AFTER the Fillet. I don't think I would have ever figured this out, but it makes sense.

@etfrenchand @mango.freund ,  am I missing something on your attached files? The millimeters entered in the parameters box seems to reflect the dimensions before the fillet.

[hamid.sh. · Accepted solution]

@dan.ballarin not sure if you're still looking for this, but in the light of new "Tangent Relationship" feature it is possible to do it with yet another method. Just change "height" parameter and you'll have top of filleted pyramid exactly at that height:

 

Also, contrary to your title, it's not a simple parametric design with current features. The both method I showed you work, but none is very simple.

[dan.ballarin]

WOW, I have so much to learn. I can barely understand your methodology but it works flawlessly! I need to really sit down and study how you did it. I am impressed with your skills.

[hamid.sh.]

Thanks but I don't have any special skill! You only need to know fillet of 3 edges is a sphere tangent to the 3 faces. Once I know that I jointed 3 sides and let the sphere stay tangent with them. Intersection of these 3 sides is your apex.