23 Oct
2015
23 Oct
'15
8:14 a.m.
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