Trefoil Knot Mold

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Toby
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Re: Trefoil Knot Mold

Post by Toby » Sat Jun 07, 2014 7:45 am

Edit 7/19/14: See first post.
Last edited by Toby on Sun Jul 20, 2014 2:51 am, edited 1 time in total.

Toby
Posts: 330
Joined: Wed Apr 09, 2014 9:44 pm

Re: Trefoil Knot Mold

Post by Toby » Sun Jun 08, 2014 6:39 am

Edit 7/19/14: See first post.
Last edited by Toby on Sun Jul 20, 2014 2:50 am, edited 1 time in total.

jsc
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Re: Trefoil Knot Mold

Post by jsc » Sun Jun 08, 2014 5:20 pm

Toby, this won't work for knots in general, but for this one, wouldn't it work to place a split plane through the short axis, ignoring the twist? Then you would have a two part mold instead of a high-n part one.

Toby
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Re: Trefoil Knot Mold

Post by Toby » Sun Jun 08, 2014 6:50 pm

I'm not sure. With a silicone mold I think it would work because of the flexibility. But without any flex in the PLA it might not be possible to get the cast out of the mold.

Also printing those parts to get a smooth inner surface might be difficult. At least I can't visualize it. Everything's curved in every direction so there's no well-defined "top" surface that can be made smooth at the end. But if you'd like to try let me know and I'll upload a version of the mold (and/or the original model) as a single object you can slice in half.

Mostly though I'm just aiming for methods that will work with complex casts like the trefoil knot, where some sort of multi-part mold is necessary. With the experience I got last night I'm motivated to try casting the trefoil knot now, without having to reprint the mold I already have.

Toby
Posts: 330
Joined: Wed Apr 09, 2014 9:44 pm

Re: Trefoil Knot Mold

Post by Toby » Tue Jun 10, 2014 10:21 am

Edit 7/19/14: See first post.
Last edited by Toby on Sun Jul 20, 2014 2:49 am, edited 1 time in total.

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jimc
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Re: Trefoil Knot Mold

Post by jimc » Tue Jun 10, 2014 12:26 pm

only put it in sand halfway and drill a hole in the top of the lower loop. when you see the plaster come out the hole then close the hole off and continue the pour until its full to the top of the upper loop.

Toby
Posts: 330
Joined: Wed Apr 09, 2014 9:44 pm

Re: Trefoil Knot Mold

Post by Toby » Sat Jun 28, 2014 7:05 pm

Edit 7/19/14: See first post.
Last edited by Toby on Sun Jul 20, 2014 2:48 am, edited 1 time in total.

mbonadio
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Re: Trefoil Knot Mold

Post by mbonadio » Mon Jun 30, 2014 10:59 pm

This looks amazing and is something I've wanted to try...can you elaborate on your techniques..what software did you use to create the mortice and tenon on the original drawing and how did you break it all up into the smaller chunks? Also, what plaster are you using to make the model?

Thanks
Michael

Toby
Posts: 330
Joined: Wed Apr 09, 2014 9:44 pm

Re: Trefoil Knot Mold

Post by Toby » Tue Jul 01, 2014 2:11 am

Edit 7/19/14: See first post.
Last edited by Toby on Sun Jul 20, 2014 2:47 am, edited 1 time in total.

mbonadio
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Joined: Tue Jun 24, 2014 7:14 pm

Re: Trefoil Knot Mold

Post by mbonadio » Wed Jul 02, 2014 11:36 pm

Toby wrote:Michael, The software I used is homegrown (which I modestly call "TobyCad"). Almost certainly this can be done in Openscad if you can write that sort of code.

The technique is to first create the 3D path for the trefoil knot, for which there are formulas you can find online (or I can give them if you want this specifically). TobyCad allows for Javascript plugins, so getting the trefoil path into the software was easy.

Once you have the path then you need to extrude cross sections along it. Here's a picture of the two cross sections I used:
trefoil_cs.JPG
To break it up into pieces you need to extrude along sub-sections of the path, while using transformations at each point as if it were the whole path. In this case the path had 400 points and I broke it into 20 sections of 20 points. So all told there were 40 printed parts, 20 for the top cross section and 20 for the bottom one.

The plaster I used is called "Permastone", which is a brand by Activa you can find on Amazon or in Hobby Lobby. It's very strong stuff- more like cement than what you might normally think of as plaster.

Hi Toby,

Are you planning on open sourcing TobyCad :-) I would love to check it out and see how it works...what do you intend to do with it?

Cheers
Michael

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