Instructables

Make plastic parts from scratch

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Picture of Make plastic parts from scratch
Fro another project I need custom shaped plastic parts. Since my 3D printer is only in the design stage right now (I just finished software prototyping) I decided to try my hand at casting. This is my first attempt

The piece is sculpted with Plasticine and cast from fiberglass resin. These are not the best mateials to use but they are cheap and get the job done.

I was inspired by  Sylvia's Super Awesome Show, she made it look easy.
http://www.youtube.com/watch?feature=player_detailpage&v=1uNopuOBWoA
 
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Step 1: What you need

Picture of What you need
The main ingridient here is fiber glass resin, you should find it in hardware shops. the shop near me also had casting resin, wich is better for making big casts, but it was twice the price. Fiberglass resin will work but when it cures it gets hotter than casting resin, in a large cast it can get so hot that it cracks or burns.

Plasticine (oil clay)is used for making the master shape. Real Plasticine is meant to melt hen it gets to about 100C which would make it easy to get out of the mold. Unfortunately mine was a knock off that just caught fire.

Plaster of Paris is for making the mold. you pour it around the Plasticine sculpture.

Not pictured is Lego, for making a box, and plastic wrap or aluminium foil for lining the box.


Step 2: Make the piece

Picture of Make the piece
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Since this was only a test I didnt have a plan for what i was going to make but i sugest to have a diagram to refer to.

I rolled the clay flat an trimed the excess. Then I made a right angle shape.  In the join i added a small sausage to make sure there was proper contact between the pieces. I did not want a mold with gaps.

I cut out a small cylinder and attached it to the top. This created an overhang in the mold that gave me trouble later.

Since i was trying to create a right angle I molded it onto the corner of the kitchen counter.

Cutting the clay is much easier if your tools are lightly oiled.
MaskMarvl1 year ago
I've done some casting before as well... you might want to try creating your sample with candle wax. That way you could just heat up your mold (once it's completely solid and dry) and the wax will melt out. :)
Did you think about pouring the plaster of paris in 2 stages? You could pour half, let it set, apply some sort of barrier then pour the other half. It would save having to cut the mould as it should just pull apart. (I have absolutely no experience in this so could be talking rubbish - it's just the first thing that occurred to me!)
Yep, that's what I meant to finish typing about the silly putty comment below. You fill the bottom half of your box with silly putty, coat with talc or a very thin layer of vaseline, and press your part into the putty. It also helps to press in a couple of dowels or pins to make alignment pins for your mold. Then you pour the plaster, let it completely set, and remove the half. Flip it over, put it back in the box, and recoat with your lubricant and pour the other half. Works like a charm, especially for pieces that have an obvious and easy two-part seam.
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That would be a much better way of doing it.When i was pouring the plaster i was excited so i just rushed through and didnt think very far ahead.
There are a lot of great tips on making molds of all kinds on YouTube. Look for username "SmoothOnInc" for some nicely detailed ones. Being a company, most of their videos are pushing their own products, but a lot of it should extend to competing brands or DIY solutions.
anode5052 years ago
LOVE the Lego mold idea! kudos!

There is also Shapelock (also goes by another name) Put in 150F water and its mold-able and reusable.
Devillocks2 years ago
Very nice for a first casting attempt, reminds me of my first stabs at it years ago. I've made tons of miniature and action figure pieces this way since then. If I may,
a few tips :)

To avoid having the piece sitting on the floor of your box, add a straightened paper clip or wire protruding from the top of the model, in this case it would stick out from the cylinder you added. Then place a wooden dowel across the top of the box and wrap the wire around it to suspend the part in the middle of the mold. This also creates a channel to pour into and makes is easier to lift and remove.

For your box, Legos are definitely a good way to go, to avoid the little pockets at the bottom, you can get the flat cap pieces and cover the bottom with them for a smoother base. Another tip the guy I learned from showed me is to fill half of your box with Silly Putty, keeping it as level as possible, and then lightly dusting it with as fine a talc powder as you can get to keep it from sticking together.

To avoid bubbles in the resin, mix thoroughly, pour slowly and evenly, and when you are finished, take an object and tap lightly against the sides of the mold a few times, this helps break up the air bubbles before the piece sets.

Anyway, this looks great, and I look forward to a Part II soon!
Orangutanlibrarian (author)  Devillocks2 years ago
Thanks for the feed back. As I did this I realised i was making noob mistakes that i could skip on the next attempt. The bubbles were worrying me though, thanks again.
Great project!

What was the total cost of materials? Just wondering if this is a better option then a low temp thermal plastic like ShapeLock. In about 5 minutes time i could have a chunk heated and shaped and ready for use about 10 minutes later.

This reminded me. I need to make some shelf supports of my own.
nice stimulating project . What about silicon for the mold, interesting material, inexpensive and hot temperatures resistant
Orangutanlibrarian (author)  aristide2022 years ago
I did think about it but I haven't seen it in shops and plaster is cheap and heat resistant too.
Total materials cost was about R70, which works out at around $6 US but i have no idea how much it would cost in other countries. I still have enough material to make many more molds, so it is realy cheap.

I looked at shapelock and home-made bio-plastics but this still was cheaper than shapelock and, i suspect, stronger than both.

Thanks for you interest
djimdy2 years ago
It was more likely the hardener, which is a pretty strong solvent. Resin should just be resin, a bunch of short-chain polymers, just kinda standing there.
teddibear12 years ago
Have you ever considered making your own plastic? Dissolving styrofoam packing with acetone converts the styrofoam to a hard styrene plastic. The liquid hardens within minutes, and it don't get much cheaper than that.
Senseless2 years ago
"Unfortunately mine was a knock off that just caught fire..."

LOL Love that line! Been there!

Nice instructable, I've worked with fiberglass half my life when I had my autobody shop, and cast some blocks and ground them out with an air dremel before but never realized or thought of looking for something to make molds from.
gtoal2 years ago
Look for a material called PCL (Polycaprolactone). Also cheap, and would have been ideal for this project.
rendermatt2 years ago
Cool
WoundedEgo2 years ago
Nice idea. When I saw the title and the picture, I thought you might suggest just heating and bending plastic, which might also serve in some situations.
mxsailor2 years ago
Good post! That's how we learn to do stuff! You just do it and you learn from your mistakes. A lot of people wouldn't try because "they don't know how." You're going to be a great do-it-yourselfer because you just do it.
askjerry2 years ago
Take a look here: http://alumilite.com/

Alumilite is a 2-part plastic that is very easy to work with. It also holds high detail, can be machined, and can be colored. (Even metallic.)

No... I don't work for them... but I use the stuff all the time.