# How to create different weight of similar model

I have created the model with the specification given below.

How can i have different size as per the specification (5, 10, 15, 20, 25kg)

Any extension or how it works. Thanks

disk weight.skp (979.6 KB)

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2016 pro

OK, so that’s a complex shape. SU can tell you what the cubic capacity of the shape is. That will give you a proportion related to its weight. You can then work out what cubic capacity would be needed for other weights. Then it gets harder! If you simply wanted to scale, it would be a doddle. But you probably want to keep certain dimensions constant. That makes the equation more complicated. What you are trying to do is to work out what the diameter would be for a given weight, leaving all other things equal.

Good luck!

As @simoncbevans points out, this is not a simple problem even without SketchUp! There are a lot of dimensions that must stay fixed while changing the weight. Even the diameter of the handles and the width of the associated flanges stay at 35mm while the overall circumference changes. So scaling is highly non-uniform.

You can do yourself a favor by changing the model units to mm instead of Architectural feet and inches. That way you can enter, tape-measure and display dimensions without having to do conversions!

It might be easiest to break the overall plate into four sections: the central hub, the basic web, and the two distinct portions of the rim. The hub must stay the same size for all weights (right?). The web must scale up to meet the inside of the rim without enlarging its center where it meets the hub and while staying the same thickness. The two parts of the rim (handles and square sections) can be redrawn using follow-me of their fixed cross-sections around arcs that have been scaled up or redrawn to a new radius. It will be ok to over-extend the handles so that they run a bit inside the square parts of the rim. That’s easier than trying to make them end exactly at the face of the square parts and will get cleaned up in the next step.

Once all that is done, you can use outer shell to merge the parts into a single solid for which SketchUp can calculate the (approximate) volume. Outer shell requires that all the parts be SketchUp solids, so you will have to model cleanly to assure that this is true. Use Solid Inspector 2 to find and correct flaws.

With all that said, unless you have separately done the math to know the right sizes for each weight (or can get them from some standard specification) you will have to try a size and see whether it hits the target weight. Look at Entity Info to get the volume of the solid and multiply it by the density of cast iron to get the weight. If it is not correct, repeat the whole process for an adjusted size. Because of the complicated relationship between fixed dimensions and variables, this will be a tedious trial and error process! Bear in mind that a) because curves in SketchUp are represented as series of straight edges and flat polygonal faces, the calculated volume will always be a bit less than the theoretical one for real curves, and b) casting isn’t all that precise either: real weights are made a bit oversize and ground down to the target.