PiDP-11 plans...

Mark Matlock mark at
Thu Oct 22 21:45:55 CDT 2015

    I am very excited to hear about your PiDP-11 project. I also would urge you to go to 1:1 scale for the PDP-11/70 panel and also utilize the classic Purple and Pink color scheme. 

    I saw Henk's PDP-11/70 reanimation and dreamed of doing one some day, and then saw Jorge Hoppe's work and contacted him when I finally was able to obtain a PDP-11/70 front panel. It was one of the later DECsystem 570 styles in Blue, light Blue and White. My project is detailed on Jorg's website as well as his projects which not only include a PDP-11/70 but also a KI-10!! Anyway interested is learning about these projects or just want to see a virtual PDP-11/70 running RSX11M+ on their Windows or Linux PCs should check out:

   You hit upon one of the key needs for these projects, a good replica bezel. In my project I had to have a plexiglass bezel laser cut then used white plastic to frame that bezel. It works but I would love to have a replica bezel.

   So I have thought about two other approaches to thermoforming. One is to make a silicone mold which then can be used to make new bezels from polyurethane. A video about that approach uses a 3D printed part to create a silicone mold which is then cut in half and the silicone is now the mold for more rigid polyurethane which is poured into the mold sealed allowed to cure then the part is removed and a new part is cast. It's not extremely fast like injection molding, but it could be used to make a mold from an original part if necessary.


   The second approach is something I used many years ago to produce some solvent resistant two holed stoppers for a lab instrument. I found some PVC stoppers that worked very well but the lab supply house quit selling them. I have a M.S. in Polymer Chemistry and was familiar with PVC plastisol that when heated to about 180 C then cooled makes a tough somewhat flexible rubber like material. If you were a child in the 1960s you may have done this with a "Thingmaker"

   The "Plasticgoop" is the PVC plasticsol and it can be made with a wide range of hardnesses and pigmented to any color as the PVC plasticsol is clear (It is what Tygon tubing is made from). To use this approach you would need a metal mold but it would not need to hold pressure like an injection molding machine. The heating can be done on a hot plate and monitored with an IR thermometer. In the day we could get a part from the mold about every 8 to 10 minutes by quenching with cold water.

   One other comment I would make is that it would be great to modified the SImh V4.0 to work with the PDP-11 front panel.    Most of the code supporting the panels are either V3.8 or V3.9. These front panel reanimations should be part of the Simh development.

   Also, thanks for your wonderful PiDP-8 !! i would never have been able to afford a real PDP-8 to learn about them



>> Oscar is already working on another very promising product.
>> [..]He will
also pay a visit to my "museum" to take a few measurements.
Sorry, can't say more
>> I'll leave that up to Oscar. Perhaps he
want to stay "below the radar" until that project is finished ...

Thanks for the kind words on my strange replica mania! We all need to do silly things at some point in our lives.

No secret... I'd love to do an "Open Source Hardware" PDP-11/70 replica (or remake - whatever choice of words is preferred). Electronically, it would a simple variation on the PiDP-8 (i.e., simh brains on a Raspberry Pi, hiding behind a front panel PCB). It's just a different emulator from the simh stable with less LEDs.

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...). 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.

If anyone here *does* have know-how in this field, I'd love any advice. I got some preliminary quotes and recommendations on making a case replica using vacuum forming. Which is relatively cheap. Not perfect, but low cost is very important for such a gadget.

Kind regards,


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