Scale complex shape for print and assemble

Wondering if anybody has any tips or software solutions to easily "scale" a complex shape with multiple insets to allow for assembly clearances after printing. I've attached a picture with the simplest example. The item attached is designed as a 3 piece model. The yellow is all one piece and includes a flat area to which the black lays on top of, and the black is 2 separate pieces (insert of O, and surround of O).

Attachment 8520

The issue at hand is, I can easily scale the inside of the O to say .99 and have it assemble, but if I scale the black area outside of the O to 1.01, then it becomes too large for the overall dimension. If I scale the O itself to .99 so that it can fit inside of the black area as designed, then the interior "hole" of the O is also scaled down which requires further scaling of the interior.

What I REALLY need to be able to do, is shrink just the outer diameter of objects. If you have any thoughts, they'd be appreciated. Here is the much more complex design that this O is a part of. The yellow again is all one piece (1mm thicker than the rest of the pieces to provide a platform), the red line is a stand alone piece, and the black is 6 pieces (top of X, bottom of X, center of O, center of A, center of A, the rest).

Attachment 8521

Again, any ideas are greatly appreciated. If I've chosen poorly for the thread location, my appologies.

This is not a new thing to 3D printing, it has been a problem for ever in engineering. It is all covered under the general area of "limits and fits" and is always catered for on the drawing board before you get anywhere near making the things.

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Originally Posted by Mjolinor

This is not a new thing to 3D printing, it has been a problem for ever in engineering. It is all covered under the general area of "limits and fits" and is always catered for on the drawing board before you get anywhere near making the things.

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Right... So, any tips or ideas on the easiest/best way to deal with this problem on the drawing board that is commonly used 3D design software frequented by 3D printing hobbyists?

Well unfortunately there are no standard tables of limits and fits for polymers so it is still a suck it and see pastime. I suspect it will always be that way generally because of the millions of different plastics with subtle, unknown changes in the chemical make up that affect shrinkage and other properties.

Depending on your slicer a hole will be one extruded thickness small and whatever the plastic it will have a known average shrinkage rate, after that it really is suck it and see. If you are using ABS then Acetone will allow the holes to fill after it has been assembled.

this is actualy really really easy.

Load the models into your slicing software and group them together.
Then just scale everything at the same time. It resizes as a single model, so everything stays in proportion.
You can ungroup after and resave the individual files as .stl

Or am I missing something ?

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Originally Posted by curious aardvark

Or am I missing something ?

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Yup..................

Jackso is asking how to scale the features seperately, so that they can scale the inside of the 0 down and the outside up. If it were a 2D CAD file that is being extruded, you can use the Offset feature on each line to move it inward or outward as needed before re-extruding the model in the software. If it's saved as a STEP or other feature-based format, you might be able to go in and re-scale features independently, depending on what modeling package you have.

Unfortunately, it's most likely an stl file, which is interpreted as a single piece without defining ends or beginnings of discrete features, in which case, your best bet is to trace over it to make a new object.

Quote:

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Originally Posted by Mjolinor

Well unfortunately there are no standard tables of limits and fits for polymers so it is still a suck it and see pastime. I suspect it will always be that way generally because of the millions of different plastics with subtle, unknown changes in the chemical make up that affect shrinkage and other properties.

Depending on your slicer a hole will be one extruded thickness small and whatever the plastic it will have a known average shrinkage rate, after that it really is suck it and see. If you are using ABS then Acetone will allow the holes to fill after it has been assembled.

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I understand the limits of various plastics, and I'm not looking for a "default value", I already know that I need about 0.3mm of clearance to get PLA printed by my printer to assemble. My question is how I might adjust the files to achieve that 0.3mm of clearance on both an inner and an outer dimension, when in this case the inner dimension needs expanding 0.3mm and the outer dimension needs shrinking 0.3mm.

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Originally Posted by Feign

Jackso is asking how to scale the features seperately, so that they can scale the inside of the 0 down and the outside up. If it were a 2D CAD file that is being extruded, you can use the Offset feature on each line to move it inward or outward as needed before re-extruding the model in the software. If it's saved as a STEP or other feature-based format, you might be able to go in and re-scale features independently, depending on what modeling package you have.

Unfortunately, it's most likely an stl file, which is interpreted as a single piece without defining ends or beginnings of discrete features, in which case, your best bet is to trace over it to make a new object.

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Exactly! I've been using 123D Design, and have become pretty decent at using it. The base image for this project is a svg imported into 123D design. I tried using the offset tool prior to extrusion of the shapes, but for some reason, the offset tool won't work on the complex shapes like the "rocky font" text. I was hoping someone might know of a trick in mesh maker, or make, or any other tool that might get it to work.

This is Casting Design 101. You should be happy you don't have to deal with draft.