Experimenting with DEC handles and knobs

[Roland Huisman]

So this weekend was for experimenting with silicone and plastics...
I have a G104 board which I got from Ebay once. It was defective and the
handles were taken off... I bought it for spare parts but I fixed the board instead...

Since I'm busy making the M993 card for my RK05 drive I also need a few handles.
So I removed a blank handle from a W967 wire wrap board to make a PU (poly Urethane) copy of that.

First I made a silicon negative of the handle. The handle needs to be free
in the silicone. So I glued a few pieces of a pencil underneath the handle.
The little bit's of glue will be the filling opening in the negative.

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After mixing the silicone I put it in a vacuum chamber to let all the air out.

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The handle is glued to the bottom of this little tub so it won't float in the silicone.
Now I can pour the silicone in...

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After putting it in vacuum I got all air out of the silicone. One thing I didn't realise before
and that is that there is a lot of air in the wood of the pencil. So the next time I will use
some sort of plastic or a piece of wire... But the result is okay after a while in the vacuum chamber.

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And since I'm missing one switch on my PDP8/m I thought it will be nice to make a silicone negative from those too.

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After a few hours of drying I can take the originals out...

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Time for making the A part of the PU with a little bit of colour.
Making only the A part on colour gives the advantage to mix
a next piece of plastic in the same colour.

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Then mixing the A and B component and fill up the negatives.
While I have way to much I put in the green into the know negative as well.
Just to see how the results would be...

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Hello Digital

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Not to bad I think... But it seems I need a better vacuum pump.
At some knobs very small details disappeared. So I need to optimise the process.

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Well not exactly the right colour. I have to optimise that too.
And I have to determine the right colours for the knobs as well..
And I need to mix the magenta for the M993 as well...

But hey, for a first attempt I think it's nice

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Regards, Roland

[DDS]

A friend owned a small volume machine shop here in the Miami area. One of the things he frequently worked on, either making from scratch or repairing damage, were molds for injection molding of plastic parts like the ones you're trying to re-create. Those molds are made of steel or aluminum and large relative to the volume of plastic being injected. In other words, quite rigid. The plastic is injected, as under pressure, and heated. Also the molds were designed to let air out along the flashing lines.

I've never seen anyone re-create that process in a way that would work in a small volume or home workshop environment. Given that you're using relatively flexible silicon molds and allowing the resin to flow into the mold with an assist from gravity, your results shouldn't be expected to be as good as the injection molded originals. What you've shown in the photos looks as good as anyone else's I've seen on the web. There is a company out there with a mold kit for pouring an AR-15 lower receiver. As you can imagine, the stress on that part would normally be somewhat greater than a circuit card handle and the margin for error therefore somewhat less. They recommend heating the resin before pouring to get better fill-out and IIRC tapping the mold to encourage bubbles to rise and escape through the pour opening.

Experiment a bit and don't let the perfect become the enemy of the good enough.

[Uniballer]

I am impressed. I really like the idea of the silicone molds. Perhaps heating the resin as DDS suggested will help you achieve better results on the small details.

[Roland Huisman]

Thanks for the replies I think he outside of the knobs look really great already.

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But here is my problem. A little pin on the knob is a little hole in the negative.
When there is air in that hole the PU can not reach that place. Here you can see
what happens. That little pin on the left one is disappeared at the right one.
The cause is a little bit enclosed air.

15.jpg

After mixing the A and B component, the PU gives me about 6 minutes to handle. At the
places where the pencils were is my PU buffer. When the air goes out of the negative the PU goes in.

But my vacuum pump is a quite low volume version and it can't really get to zero.
I still have about 300 millibar left... I think, when I get this to zero fast, that I will
have no air enclosed any more.

But I have to put in the PU, get it to vacuum and back to normal pressure again all in
about 6 minutes. Then the PU starts to heat up and is getting hard already.
So I will go hunting for another vacuum pump en let you guys know the results.

Regards, Roland

[DDS]

Thanks for the replies I think he outside of the knobs look really great already.

14.jpg

But here is my problem. A little pin on the knob is a little hole in the negative.
When there is air in that hole the PU can not reach that place. Here you can see
what happens. That little pin on the left one is disappeared at the right one.
The cause is a little bit enclosed air.

15.jpg

After mixing the A and B component, the PU gives me about 6 minutes to handle. At the
places where the pencils were is my PU buffer. When the air goes out of the negative the PU goes in.

But my vacuum pump is a quite low volume version and it can't really get to zero.
I still have about 300 millibar left... I think, when I get this to zero fast, that I will
have no air enclosed any more.

But I have to put in the PU, get it to vacuum and back to normal pressure again all in
about 6 minutes. Then the PU starts to heat up and is getting hard already.
So I will go hunting for another vacuum pump en let you guys know the results.

Regards, Roland

Two possibilities come to mind. You could cast those pins separately, then glue them into a blind hole drilled into the switch handle body. Or you could drill all the way through the body and install a one piece steel pin that protrudes the correct amount on both sides. The pin could even be a nail of the correct diameter with the ends cut off. Now that I think on it, it might be possible to make the pin and place it into the mold before you pour in the resin.

[KC9UDX]

A friend owned a small volume machine shop here in the Miami area. One of the things he frequently worked on, either making from scratch or repairing damage, were molds for injection molding of plastic parts like the ones you're trying to re-create. Those molds are made of steel or aluminum and large relative to the volume of plastic being injected. In other words, quite rigid. The plastic is injected, as under pressure, and heated. Also the molds were designed to let air out along the flashing lines.

I've never seen anyone re-create that process in a way that would work in a small volume or home workshop environment.

Making a plastic injection die at home is doable. But it's typically more expensive than if you were a high volume tool and die shop.

Running parts is the hard part. There are guys building their own injection machines now too. Again though time is money, and if you're making enough parts to justify all the work, you're not going to make money, or even come close to break even, making parts one at a time.

[KC9UDX]

But hey, for a first attempt I think it's nice

I think it's awesome. Great work!

[Roland Huisman]

Two possibilities come to mind. You could cast those pins separately, then glue them into a blind hole drilled into the switch handle body. Or you could drill all the way through the body and install a one piece steel pin that protrudes the correct amount on both sides. The pin could even be a nail of the correct diameter with the ends cut off. Now that I think on it, it might be possible to make the pin and place it into the mold before you pour in the resin.

I was also thinking to use an metal pin. But putting a little pin into the mold
right before putting in the PU might be a way better alternative indeed!

But I will try to get a better pump first...

I think it's awesome. Great work!

Thanks!

[daver2]

If you didn't see my previous thread a while ago - my son 3D printed me a full set of handles (excuse the poor photography) - see https://drive.google.com/drive/folde...EUxZElDYjdoeG8.

The colours are a bit 'loud' - but these are the 'standard' filaments.

We ran into the same problem with the mounting spigot - and went for a hole in the key with a metal bar in the end.

I was thinking of asking him about 3D printing some handles as well.

Dave

[Roland Huisman]

Hi Dave,

Nice, I've also been thinking about 3D printing. But with
thermal 3D printers you see the printing lines in your product.
(At least the 3D printing results which I have seen the last few years...)

But every way has it's disadvantages... You have to bring these PU on to the
right colour. And since I'm not a painter it is quite hard to get the right colour...

Does anyone know the RAL colours of these handles maybe?

BTW, I'm thinking to make those H960 front panel holders as well...
I have a few with only one pin left...