KIM Uno /PiDP-11 plans...

[Ethan Dicks]

On Fri, Oct 23, 2015 at 5:26 AM, Alexandre Souza
<alexandre.tabajara at gmail.com> wrote:
>>> But a 11/70 replica needs two physical 'cosmetic elements': proper
>>> switches, and the white bezel/frame.

>>> The switches *seem* to be feasible to
>>> produce cheaply (I will know in a month with PDP-8/I switches...).

I had a sample PDP-8/L and a sample PDP-11/70 switch toggle printed
from Vince Slyngstad's models on a Form1+ SLA printer. They are very
nice.  I am not certain that the pivots won't break off - the resin is
quite brittle, but Form Labs does now make a "tough resin" that's more
resilient, at a 50% premium ($180 per liter?)  The printer is just shy
of $4,000.  The cost per switch toggle is around $1 in resin, but
operator time makes it much more expensive.  I'm trying to work out a
deal with other members of my hackerspace who own the printer... if I
do the part washing and the support clipping, it might be possible to
get switch toggles for a few dollars each.  An alternative is I think
they can be bought from Shapeways for around $5-$6 each (SLS format).

>>> The white
>>> bezel though brings me into unknown territory. 3D CAD (based on Museum
>>> Measurements), then injection molding or vacuum forming. Or any technique to
>>> produce a plastic object in medium quantities. All I know so far is that
>>> it's very feasible - and much cheaper to do than just a few years ago.

Yes.  All cheaper than it was a few years ago.

>    Can't it be 3D printed? Or done with vacuum forming? Resin molding?

Could be 3D printed, but not in one pass on any normal printer - it's
19" wide and 10" tall.

Vacuforming is also a possiblity, but the logo wouldn't be as "crisp".
We have a 2'x3' (600mm x 900mm) vacuformer at our hackerspace, but it
does very thin styrene sheets for custom 1-off signs (the plastic
comes on rolls and you form it over hard letters and logos to make a
"3D" sign - very 1970s tech).  We do not have a vacuformer strong
enough for, say, Storm Trooper armor.  Such a vacuformer could
probably handle a bezel.

>    Are you talking the white bezel on this photo?
>    http://www.psych.usyd.edu.au/pdp-11/Images/11_35_draw.jpeg

Yes.

>    It can be done easily:
>
>    - You can do it in a 3D prusa-something printer, if you divide it in
> printable blocks, and glue it afterwards.

Yes.

>    - You can easily do that in Vacuum Forming. Since I never saw a 11/70 in
> front of me, I don't know the size/hardness requeirements, but I believe it
> is feasible

It's a solid metal casting, not for strength so much as, I think,
durability (from when chairs and other things whack into the machine),
and manufacturability with techniques of the day.

>    - You can create a cast mold in some material and use liquid resin (epoxy
> comes to mind since it doesn't shrink/expand on cure). Probably it would
> need a two-part positive/negative mold. Easily done if I had the original
> part on hand

It could be fairly easily cast, I would think.

>    - I haven't seen all the details, but I believe it can be 3D-cut into a
> suitable CNC machine, in wood or plastic.

Having worked with it before, I'd recommend trying to CNC it out of a
dense PVC foam.  It's plenty rigid and sturdy, but carves nicely, and
is not particularly expensive.

It might take 2 passes - one for the outline, and one for the
"digital" logo with a smaller bit.

You'd need a CNC with at least a 500mm x 300mm bed, but a little
larger would be an easier fit.

I do have this frame to measure for CAD parameters.  As it happens, I
have a PDP-11/70 front panel PCB minus the switches, a couple of
bezels of my own, and a complete, borrowed, PDP-11/70 front panel that
I was already taking measurements from for a repro plexi.  I also
happen to have infrequent access to a Faro Arm ($80,000 3D scanner -
http://www.faro.com/products/metrology/faroarm-measuring-arm/overview)
and I'll see if I can get a scan of the bezel at my next opportunity.

-ethan