Molding Mendel Parts

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Making Mendel Plastic parts from Molds

Release status: Working

Polymorph frame.jpg
Molding Mendel parts
CAD Models
External Link

This page has some instructions on how you can get the Mendel parts by casting them, if you cannot get printewd ones.

Using Shapeways printed mold and casting the parts from polymorph

Here are instructions to make the parts from polymorph plastic (melts at 60 degrees). So far I have made a couple of Mendel vertex corner pieces, but more will follow. I will make the molds for other feasible parts as well. However, I assume there are some pieces you cannot mold and you just have to get them some other way.

You can get the mold from Shapeways. In addition you need some polymorph and a some vaseline (petroleum jelly) as a Release Agent.

The price for the corner pieces will be:

  • Mold 21 $ (+ VAT)
  • ~250 g of polymorph, you can get 1 kg of Polymorph somewhere around 20$

First, if you can have the printed versions, get them. If you have a cnc mill, mill them. If you don't, this is one way to get them. When you have the finished mendel, you can replace them with printed versions, if you like :-)

Here are short instructions:

  • get the mold and polymorph
  • grease mold with vaseline. Actually I changed my car's bearing a short time ago, so I had some axel bearing grease. I suppose it is mostly vaseline. Use as thin level as possible, but carefully put it everywere inside the mold. Usually corners tend to get too much of it.
  • Fill the mold with polymorph granulates
  • Put some water on the bottom of a pot. I filled somewhere 1,5 - 2 cm.
  • Carefully heat the water up to ~75 degrees (Celsius). Put the mold in the water
  • Wait about 10-15 mins until the polymorph has melted. It does not actually get very liquid, but it is more like jelly. Turn on the cooking plate as necessary to keep the heat up, but be carefully not to heat too much. Shapeways Strong & Flexible material is specified to last 80 degrees C. Use accurate temperature meter, if possible.
  • When the granulates has melted and are clear, add some more. Heat more, and add the granulates as necessary until the mold is filled with clear polymorph. You need to add them a few times.
  • Take the mold out, make the surface even with spoon or with your fingers. Be carefully! Plastic is quite hot at the beginning. However, the surface of the plastic cools down quite quicly and it seems not to be good thermal conductor, so it won't burn after a while. (please don't sue me if you burn youself!!)
  • Put a couple of screws on the polymorph near the 8mm holes.
  • Cool the mold down. I put it on the freezer. Be patient and let it cool down until it is all white, about 10-15 mins.
  • Use tongs to get the piece out of the mold. This is why you need to push the screws on the piece ;-). It does not get out very easily, but using decent force, you can do it. After you get the piece out, you can remove the screw. The piece tends to jam near the holes, so the screws should be also nearby.

Repeat this 12 times. You can get approx 2 pieces (half of the vertex) in a hour, so you need about 6 hours to get the frame ready.

Some thoughts: I think the mold walls could be somehow thinner, so it might be easier to remove the piece. The Shapeways material is quite flexible, but 2mm walls in the current mold does not blend too much. Thinning the walls would make it also cheaper :-). Ill remember this when making the next molds.

I will continue making the molds for the other parts as well. However, I will focus on those that cannot be cnc milled easily.

I think the mold could also be used with some resin. Polymorph is just quite easy and forgiving material to play with.

Here are some images: The actual mold:

  • Frame vertex mold

Molded piece:

  • Molded half of the frame vertex

Vertex made from 2 molded pieces:

  • Vertex made of polymorph

The hole.

  • Polymorph vertex2.jpg

Mendel frame finished.

  • Mendel frame made from polymorph vertexes