Welcome! Log In Create A New Profile

Advanced

Predictability of scale....

Posted by Replace 
Predictability of scale....
December 23, 2016 10:18PM
I am fond of Scale.
But there is a question on the usage:

When I want to make a hollow object, with predefined wall thickness,
I design the object and Difference it with a scaled smaller copy, that is translated in Z, to a defined altitude that reflects the wall thickness on the build plate.

However, the thickness of other walls: left, right, front, rear and top , (or with more complex objects all other outside surfaces) is depending on the scale parameters.

Can I calculate the thickness as a function of both the original size and the desired thickness, to get the scale parameter ?



Thomas


www.3daybreaker.blogspot.com

Orca V4.4 rebuild to Ramps with Mk8 and E3D, as well as a Rostock Delta Mini and an OLO in backorder :-)
Re: Predictability of scale....
December 24, 2016 06:58AM
Your proposed approach using a difference with a scaling version of the full object to get a predefined wall thickness will not work in general. It will only work for very specific simple shapes (such as cubes and spheres), since it will result in a variable wall thickness that is essentially proportional to the distance from the origin.

What you would need to do this computing the Minkowski difference of you object and a sphere with a radius equal to the wanted wall thickness and subtract the result from the original object. But, unfortunately, OpenScad only implements the Minkowski sum, not the difference... sad smiley

The only "easy solution" I could see, is to let the slicer do the work by printing the full object with a 0% filling and the number of shells and top/bottom layers that correspond to the desired wall thickness.
Re: Predictability of scale....
December 25, 2016 04:01AM
I was not aware of a possible minkowsky difference . Enyhow it is not there confused smiley

Your solution gives me a hard time programming internal ribs and supports in the hollow shape, as far as I can think-up now.

But I will keep it in mind designing. Thanks


www.3daybreaker.blogspot.com

Orca V4.4 rebuild to Ramps with Mk8 and E3D, as well as a Rostock Delta Mini and an OLO in backorder :-)
Re: Predictability of scale....
January 26, 2017 06:54AM
Just a note regarding the Minkowski difference: In this other thread I proposed a simple implementation of the Minkowski difference using the Minkowski sum on the "negative" (i.e. a cavity) of the original object...
Sorry, only registered users may post in this forum.

Click here to login