On Fri, Oct 23, 2015 at 5:26 AM, Alexandre Souza <[email protected]> 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
