# Making 'sand mould' imprint

I’m not sure what the terminology is, but what I’m trying to do is to leave the imprint of an object in a solid if it was effectively dropped from above, such that the ‘sand’ doesn’t reform after the object has moved through. The effect would be similar if you took an object (I’ve drawn an angled torus in the attached example) and as it entered a solid from above, you took loads of Boolean differences, as it moved through the solid, so it would leave the entered solid with the voids behind its path. In the attached drawing, I’d like all the space above the torus outline to be empty. Sorry I don’t have the correct words to describe this! I don’t think this is an in-built function (though could well be wrong) and have wondered about writing a script to gradually lower a copy of the torus into the solid, doing Booleans all the way.

Thanks for the help. Hope someone understands what I’m trying to say!
Torus imprint.3dm (217.7 KB)

This is sometimes called 2-1/2D. I believe Drape will accomplish what you are looking for,
although, I’m not sure how you would set an appropriate draft angle as Drape does not give you control over that.

That’s exactly what I am after. Thanks very much for the quick reply!

Ben

If you want something more accurate than Drape, you can first run Silhouette on your object from the “pull” direction (i.e. Top). You will then need to clean up the silhouette curves (perhaps, depends on the complexity of the object) and then split the object with the curves. Then extrude the curves above the top of your sandbox, join them to the split object and then use BooleanDifference. You may need to cut off the top end of the extruded curves and cap to make a solid object before the Boolean operation.

Torus imprint-sample.3dm (3.7 MB)

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Similar to Drape, silhouette does not allow one to specify a draft angle as far as I can tell. Perhaps draft angle is not relevant to Ben’s concern.

Using a B&W image, with gaussian blur, can generate a draft angle, although its not specifcally user definable in degrees.

Given the sand mold is likely non-reusable and would be destroyed after the casting, any draft angle might be irrelevant.

with Draftangleanalysis you can create curves at the desired draftangles, then extrude these curves tapered at the same angle.

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Draft angle might not be relevant if the right process is used. Such as this:

The normal process of making sand molds for casting purpose cannot handle vertical surfaces because without draft the sand gets torn up.

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After the part is cast what you say is absolutely correct.
The problem comes when making the mold around the pattern: draft is required to remove the pattern without destroying the mold…

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Thanks for this. I like this technique better because of the accuracy I should be able to get out of it. The technique is not actually for sand-moulding. I use it when CNC’ing a complex part which needs to be done in 2 passes (top and bottom ish) This technique is used to create a bed for the part to sit in when half of it is machined and then I can do the inverted half. So drape is a little course (though it might work if I fiddle with the variables enough). I tried this technique and had a lot of cleaning of the silhouette to do, as you suggested (pretty complex shape). I did this very carefully as there were lots of lines very close. I ended up with 2 closed curves so I think I did it ok. Anyway, the split failed (lack of intersection). I then tried offsetting the silhouette curve in by 0.3mm. That worked but didn’t give the right split of the object. I can’t share the part unfortunately as I have a confidentiality restriction, so not sure what to do but will try to see what I can do with Drape. Thanks for help. Your explanation is very clear and I know what to do at least! Ben

Thank you Drape Command!
Draped over an imported STL mesh!

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spooky stuff

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Doing James Hetfield from Metallica next as someone pointed out the Enter Sandman link

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ahhhh more spooky stuff, enter sandman sounds like it makes even more sand(s)

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So easy to do with Drape!