home made injection mold

Well....
This project was the start of my huge interest in the world of CNC, and mechatronics in general. Even though the project
itself didn't involve controls of any kind, it gave me the confidence and desire to reach for more and more sophisticate home
projects.
While working for a major appliance manufacturer, I was a design engineer on a team for a new refrigerator. I was
surprised and appalled at the prices of aluminum prototype tooling (injection molds). For instance, a mold for a knob or some
other simple shape was in the range of 6k to 10k bucks! Remember, these are aluminum tools for prototype parts. They don't
have to have fancy ejector setups, no cooling lines, and most of all, no strict constraints on surface finish, parting lines, or
flash.
So during a lunch time discussion with some fellow co-workers, someone whipped out one of their parts that cost 12K to
prototype. I said, "holy crap, I could build that at home!" Well, since I was in a group largely composed of magna cum laude
"engineers" they all burst out laughing and the general consensus was, "yea right". (everyone's finger making little circles
around their ears)
As I am sure everyone on this list will understand, my personal ability to make "things" is a source of great pride and
therefore could never let this assault on my personal dignity go unchallenged.
So I built the mold, then I built a little "machine", cut up some old milk jugs and shot the part. Most of you will be
disappointed with the relative lack of sophistication of the injection molding machine. I got the most satisfaction from the
mold itself.
The mold was machined by hand, manually, with an aluminum base and brass dropouts. The molding machine was made from a block
of steel, an oven thermometer, an arbor press, and 2, 400 Watt cartridge heaters. So that I don't delude you into thinking that
I thought all this stuff up myself, the majority of my ideas came from a book called (strangely enough) "how to build an
injection molding machine", by a guy named Gingery. Some of you may know the source, Lindsay Books www.lindsaybks.com They
publish old and out of print "how to" books that are like buried treasure for tinkerers.
Since I was pressed for time, I skipped the use of any type of thermostatic controls on the heater block. I simply switched
on the heaters and when the block got to about 350F I switched them off. (this took a little practice to control burning). The
milk jug material was clear polystyrene that shot well around 350-400F. I won't mention that all my parts ended up smelling
like burnt plastic, but the damn thing worked, and I sure showed those guys (they couldn't have cared less). But I did
accomplish what I said I would do, and I feel like I proved my point. I quit the big giant corporate world right around the
time that finished the mold. I have since gone to work for a 3 man group without all the B.S. and no stress (for less money of
course)
Anyway, the total cost of the project was about 20 bucks for two cartridge heaters and a thermometer. Of course I already
had all the aluminum and such lying around. Time wise I build the mold in one weekend and the molding machine the following
week after work. Not a bad amount of work for 12 grand!
I will take pictures and go through the do's and don'ts and "what I would do different" for those of you who care. Anyone
who want's more detail let me know.
Sorry about the length.


Matt Shaver wrote:

> From: "Matt Shaver" <mshaver@...>
>
> > From: Joe Vicars <jvicars@...>
> >
> > I built a home made injection molding machine and mold one time on a
> bet. It's an interesting story if anyone cares.....
>
> We care, WE CARE! How did you do the heating and temperature control? What
> did it look like?
>
> Matt
>
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