Designing an injection machine for keyboard science

User avatar
PlacaFromHell

07 Jul 2020, 04:32

Hello guys. As some of you know I'm working in a very complex keyboard project, where I'm forced to work with custom parts. For a finished product 3D printing or CNC is not even an option, so I'm trying to make my way into injection moulding, but as you may know, that's EXPENSIVE AS FUCK. So far I decided that I may do my own injection machine to start making some prototypes, here's what I designed, hopefully someone will find the concept useful:

Image

Let me explain how this thing works. First at all, the heating element is composed of four 110V electric oven candles, controlled by an Arduino via a relay. A PT100 or so sensor is connected to provide actual feedback of the temperature and mantain it at the desired level. Like so:

Image

A tiny keypad will be added to select the temperature for any desired plastic.

The candles are fitted inside the darker bottom piece, where the plastic beads actually go. Up we have a mobile part which looks very similar, there's were we make the pressure by pulling down the lever, returned by one or maybe two springs trapped in the central frame.

Let's take a look of the first mold, I took different perspectives so you can appreciate the shapes better:

Image

Aaaaand that's my first keycap :) What do you think, will this work?

User avatar
SneakyRobb
THINK

07 Jul 2020, 18:08

Hi,

Rambling thoughts.

For the press. Maybe there is some off the shelf cylinder part like, car brakes, general purpose hydraulic cylinder or something that is metal with good tolerances for the pressing part.

Not sure if it sold and obviously expensive but I remember this device.
https://www.techkits.com/products/model-150a/

Seems similar with the handle, so your basic design to me looks plausible.

Have you considered resin casting or even a 3d resin printer? The prints Ive received which were made on a $400 CAD machine had very smooth surfaces and a high level of detail. If you are making just 1 keyboard it may make sense to do that. Especially if you need to CNC molds.

What kind of plastic are you thinking of using for the injection molding? For the heating element I wonder if something like a 3d printer hot end would work. They have both a heating element and a thermistor to monitor the melting.

I think figuring this out would be cool and worthwhile.

User avatar
DiodeHead

08 Jul 2020, 08:50

I hope it helps or at least inspires.

User avatar
PlacaFromHell

08 Jul 2020, 09:02

My post just duplicated.
Last edited by PlacaFromHell on 08 Jul 2020, 09:04, edited 1 time in total.

User avatar
PlacaFromHell

08 Jul 2020, 09:02

SneakyRobb wrote:
07 Jul 2020, 18:08
Hi,

Rambling thoughts.

For the press. Maybe there is some off the shelf cylinder part like, car brakes, general purpose hydraulic cylinder or something that is metal with good tolerances for the pressing part.

Not sure if it sold and obviously expensive but I remember this device.
https://www.techkits.com/products/model-150a/

Seems similar with the handle, so your basic design to me looks plausible.

Have you considered resin casting or even a 3d resin printer? The prints Ive received which were made on a $400 CAD machine had very smooth surfaces and a high level of detail. If you are making just 1 keyboard it may make sense to do that. Especially if you need to CNC molds.

What kind of plastic are you thinking of using for the injection molding? For the heating element I wonder if something like a 3d printer hot end would work. They have both a heating element and a thermistor to monitor the melting.

I think figuring this out would be cool and worthwhile.
Hi :D

I'm hoping to do so. A giant bench shear lever will do the job. If I can also find a bench drill base it would be ideal. I will try to avoid solid pieces with a hell of metal inside. For example, if I ever need to make the base myself, I would fill an empty tube with concrete. For the piston I may only get a cut of the tip and then put a piece of pipe too.

That machine is quite similar, so I have more confidence on my design.

Yes, I have considered other methods like resin casting or resin printing. For resin casting I'm in a dead point only by not having a vacuum chamber to deal with the bubbles. For the resin printing, I may do a run of, let's say, 2-3 switches to test the design before anything. The idea is make a product that can be run in a GB some day, so I want the best end result possible.

I want to use POM for the switches and PBT for the keycaps. They both melt between 210-250ºC if I remember well. Your idea is not crazy, but the oven candles are super cheap.

If you don't mind I would need to make you some questions later :D Thanks for the advices.

User avatar
PlacaFromHell

08 Jul 2020, 09:26

DiodeHead wrote:
08 Jul 2020, 08:50
I hope it helps or at least inspires.
That's so nice, but looks so expensive too. I would have to sell a kidney to pay a Nema 34 :D

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