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 Post subject: Casting and cores
PostPosted: Wed May 27, 2009 8:32 pm 
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Location: A Coruña - Spain
Hello, I have a doubt about the casting puzzle.

What used to build the core, when it is not common core (3x3 or other)?

Sorry if you already have tried it, but it is quite difficult for me to review the entire forum because of my bad English.

Thanks.

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 Post subject: Re: Casting and cores
PostPosted: Wed May 27, 2009 8:34 pm 
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From what I've read, people usually just get the core printed.

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 Post subject: Re: Casting and cores
PostPosted: Wed May 27, 2009 8:42 pm 
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Most often, like VDude said, people usually get the core printed. However, it appears Drewseph has figured out a way to cast cores, look at the 2nd picture (the one with the molds):

http://twistypuzzles.com/forum/viewtopic.php?f=15&t=12499

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 Post subject: Re: Casting and cores
PostPosted: Wed May 27, 2009 10:06 pm 
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Casting cores is good when you need a specially designed one. The teraminx, pentagonal prisms, things of that nature. When i'm doing a basic 6 armed puzzle though, like an octahedron, i simply buy a 3x3 DIY core from puzzleproz.

Printing a 3x3 core costs around $10, it simply is not worth it to use them.

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 Post subject: Re: Casting and cores
PostPosted: Wed May 27, 2009 10:11 pm 
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Excuse me if I am incorrect, but cannot a core be casted, then a small hole drilled, smaller then the screw, then you could delicately use the screw to carve the threads?

I know this is done a lot in woodworking, but I am not sure if the plastic could stand it.

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 Post subject: Re: Casting and cores
PostPosted: Wed May 27, 2009 10:57 pm 
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Fractangle wrote:
Most often, like VDude said, people usually get the core printed. However, it appears Drewseph has figured out a way to cast cores, look at the 2nd picture (the one with the molds):

http://twistypuzzles.com/forum/viewtopic.php?f=15&t=12499


I just realized that Drew made a core that you cast in two parts and then interlock them. This seems like a good way to avoid too many screws in the mold.


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 Post subject: Re: Casting and cores
PostPosted: Wed May 27, 2009 11:39 pm 
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Scott Bedard wrote:
Printing a 3x3 core costs around $10, it simply is not worth it to use them.

I am SO glad I'm still at a university. The Engineering School here at CU Boulder has an FDM machine that costs only $9 per cubic inch. For me, a core typically costs around $2. I am so glad I got into this hobby so early in college. I am taking advantage of the insanely low price while I can!

In the process of making the puzzle that I will be posting within the next few days, I went through three printed cores before I found a way to keep the layers of the printed plastic from splitting when I put the screws in. I don't have my camera on me, now, so I'll try to describe the tool I used, and I'll post pictures later. It is a small metal ring with an adjustable inner fitting. The ring is split in half, (into two half circles). There are two screws that you use to connect the two halves together. I put the ring around one arm of the core and tightened it around the plastic. Then I screwed in the screw, waited about 30 seconds to be sure the threads fully sank into the plastic, and then removed the metal ring.

If that wasn't clear, I'll post some pictures of it when I have my camera.

Good luck, Chino. You are a great hand-made-puzzle maker, and I'm sure that your CAD endeavors will be successful eventually.

-π (Eitan)

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 Post subject: Re: Casting and cores
PostPosted: Thu May 28, 2009 7:42 am 
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Fractangle wrote:
Most often, like VDude said, people usually get the core printed. However, it appears Drewseph has figured out a way to cast cores, look at the 2nd picture (the one with the molds):

http://twistypuzzles.com/forum/viewtopic.php?f=15&t=12499


I've seen pictures of Drewseph, I understand that the core was made in spherical form to avoid cracks, this would be the main problem of a casting core type 3x3. Thanks for the link.

pirsquared wrote:
Scott Bedard wrote:
Good luck, Chino. You are a great hand-made-puzzle maker, and I'm sure that your CAD endeavors will be successful eventually


Thanks, CAD is no problem, I'm just experimenting with the casting, I hope to show that any other puzzle soon.

Greetings

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 Post subject: Re: Casting and cores
PostPosted: Thu May 28, 2009 8:16 am 
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I have found a rather rough method of casting cores which surprisingly works quite well. I found that placing a spider in a cup (securing it from an arm), pouring remeltable PVC over and then cutting the mold like so that it could be removed actually works. The parts require quite some cleanup (drilling) but it does work. The molds last like 5 castings but that is OK since the material is reusable.

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 Post subject: Re: Casting and cores
PostPosted: Fri May 29, 2009 10:46 am 
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My rule of thumb with casting cores is that if it's a "spider" type core, it's nearly impossible to cast. If it's a ball, or a polygonal shaped core, it can be cast, however in my experience, it doesn't work very well. You have to be able to drill your holes perfectly straight or your puzzle won't turn properly. If you're making a puzzle you want to be a high quality puzzle, just get them printed. Some of them are rather expensive ($68 for the petaminx, for instance), and others aren't too bad- ~15-25 each. When you're planning on making a puzzle that will sell for a few hundred dollars, it's worth using top quality stuff, and not cutting corners.

As Scott said, if it's something simple, like a domino or the core is symmetrical and there is one hole perpendicular to the center, then a drill press will work and it's not that bad. As for 3x3 cores, they cost like 50 cents a piece. I would typically buy 50 of them at a shot, along with the centers and spring/screw/washer kits to go with them.


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 Post subject: Re: Casting and cores
PostPosted: Fri May 29, 2009 3:02 pm 
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Casting a skewb core, a 3x3 core and any spherical core is easy. never go for a do a polygonal shaped one, always go for a pherical half with holes built into the STL for where the screws go. you then place long metal bars into the holes and build a wall around the part and pour the mold in. the bars will make a hole thats perfectly aligned to the core, so no drilling is needed, just insert bars, pour resin, remove bars remove part.


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 Post subject: Re: Casting and cores
PostPosted: Fri May 29, 2009 6:33 pm 
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Drew-
how did you do that? I was always curious about that photo. How did you make those screws align so perfectly? Did you drill holes into your lego mold? I figured you put screws into the master and molded around that, but I can't figure out how you made the mold around it.


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 Post subject: Re: Casting and cores
PostPosted: Fri May 29, 2009 7:06 pm 
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flambore wrote:
Drew-
how did you do that? I was always curious about that photo. How did you make those screws align so perfectly? Did you drill holes into your lego mold? I figured you put screws into the master and molded around that, but I can't figure out how you made the mold around it.


I can't speak for Drew, but I'm pretty sure that the bars were short enough that they didn't touch the legos.
Then all ya gotta do is pull the bars through the inside of the shell if you simply want them out
OR
Take an exacto and cut a hole to let the bar slide out. See the big hole in the front of the large half?


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 Post subject: Re: Casting and cores
PostPosted: Fri May 29, 2009 11:13 pm 
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the bars were cut into 5 inch length, I then built up a lego wall the was large enough to allow for about 3/4 in space from the core to the lego wall and I then inserted the bars into the core.

I used wire clippers to cut the bars to the length needed so that each of them were different size and were snug against the wall.

I then placed a small ball of clay around the wire and the wall so that after poured molds cured there would be an indentation in the mold and a visible wire tip.

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 Post subject: Re: Casting and cores
PostPosted: Fri May 29, 2009 11:20 pm 
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Its so funny but I've thought about that pic ever since I saw it and never understood it until now. Now that I know, I'm not any less impressed, but I thoroughly enjoyed the mystery.

EDIT - So with enough care and planning, you could do the same thing for essentially any armed spider? (insert drizzle joke about spider with gun)


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 Post subject: Re: Casting and cores
PostPosted: Fri May 29, 2009 11:51 pm 
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the limit is 6 arms, after that the arms create so much overhang on the mold that you'd rip it apart just to remove the core. so over 6 arms you must go with a sphere half shell like I do

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 Post subject: Re: Casting and cores
PostPosted: Sat May 30, 2009 12:17 am 
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I should have been more specific (thanks glenlevit), I was saying the sphere makes casting a core possible. I may have to give this a shot with this 8 armed spider I'm having to print each time.


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 Post subject: Re: Casting and cores
PostPosted: Sat May 30, 2009 1:27 am 
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12 armed cores for helicopter / bevel cubes can be cast! YAY!

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 Post subject: Re: Casting and cores
PostPosted: Sat May 30, 2009 2:19 am 
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Here is a core I cast:

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It's not very pretty but it does the job just fine (it is the only part in my helicopter cube that is cast, actually).

I simply glued it down from one arm, poured the rubber over, cut the mold open, removed the piece and cast the resin into it. It took a bit of finishing (filing flat the open face, drilling out the holes with a drill press). Obviously the mold doesn't last long but again I'm using remeltable stuff. Don't use remeltable rubber for making any kind of other puzzle mold and especially don't use it with FDM parts.

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