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Thread: reproduction PDP 8e toggle switches?

  1. #41


    Good luck with the eye surgery Doug, and thanks for your efforts!

  2. #42


    I just did a quick setup and print of those two "thingiverse" switches (see post #9) on my cheap UV resin printer (an Anycubic Photon S).
    Pictures of the one that did not come unstuck from its supports during the print are presented below (you can probably print 6 full size switches at a time on the Photon S)! They both came unstuck on the first attempt (so the support attachments were increased for another go). Things needs tuning to get reliable printing and "best" quality.
    The surface on the test print is not as good as it sometimes is (this might be that old resin was used, the way I got the yellow colour, the way I "washed" it before the final curing, the "slicer settings", or a combination of those).
    In the images you can, possibly, just about make out some of the nubs caused by the supports (avoid having supports attached on the visible parts or where it will be most noticeable). This sort of thing can be trimmed, smoothed off. The print has to be cut off of the supports...
    Prints from both fused filament (FDM) and UV resin printers can usually be improved with a bit of after-print-effort.
    Both types can be painted of course - some paint might rub off, chip and so on, exposing the colour of the print. Acrylic paint seems to stick well to UV resin.
    3D printing tends to need a fair bit of effort and experimentation to get the best out of any particular model and resin/filament.

    UV resin
    The example seen below was printed in a white resin to which I added some yellow dye!
    You can also mix different colour resins, of the same resin type, to alter the colour (better than the dye approach; but the range of base colours to choose from is not that large).
    Sometimes colour mixing, as above, makes the resin harder to print with.
    Specialized custom resin coloring options have become available, but I have not had experience with them.
    I am not sure how stable the colours, modified or otherwise, are (I had one white resin print that quickly went a nasty yellow colour when left in the sun).
    Painting can help make the surface nicer, more matt or shinier.
    The resolution of the models can be seen in the print if they have a lower polygon count (this is normally much less noticeable in FDM prints).

    I feel painting might be the better solution for this particular print (PDP-8 switches) - look out for an example in a day or so! However, custom colour UV resins specifically for 3D printing is probably well worth investigating.

    Fused filament (FDM)
    Paint is the only practical option, at the moment, if you cannot get filament in the desired colour.
    Painting and sanding can help remove the filament lines that tend to be so obvious with FDM prints.
    "Vapour smoothing" of ABS can help get rid of the lines, but tends to make things very shiny and rounds-off edges if over done or is done sufficiently to completely remove the lines (we're dissolving the plastic in a solvent).

    Images of the UV resin example (print time was about two hours for this example, for however many could be placed on the platter in one go).
    Attachment 64100
    Attachment 64101
    Attached Images Attached Images

  3. #43


    Below is an image of the "reprint" mentioned in my previous post. The white resin again (no dye this time; which was better). The red colour is plastic primer (I couldn't find the yellow acrylic spray to go on top of that - it was probably not PDP-8/e yellow anyway).
    Some artifacts of the resolution of the model polygon are visible in places - but not on the paddle part itself, so that is probably okay; these might be slightly noncable when the switch is in the down position.
    Vince's paddle looks a bit nicer (I didn't remember about that model; so have printed the thingiverse one).

  4. #44


    Nice work, looks very promising - keep us posted!

  5. #45
    Join Date
    Jan 2007
    Pacific Northwest, USA
    Blog Entries


    Just curious--the little pivots would seem to be a point of failure. Any reason that you're not replacing them with a solid metal (e.g. brass) rod? It seems as if there would be no difference in appearance.

  6. #46


    Quote Originally Posted by Chuck(G) View Post
    Just curious--the little pivots would seem to be a point of failure. Any reason that you're not replacing them with a solid metal (e.g. brass) rod? It seems as if there would be no difference in appearance.
    Sometimes I feel alone in thise, but I'll argue against the metal rod.

    I feel that injury to the front panel switches is an inevitability, as the paddles stick out the front, and are quite fragile, compared to, say, the bevel casting or the sides of the metal box.

    The little pivots are the weakest points. That's why we see so many broken ones. But, they are also the least expensive and easiest to repair bit of the thing. Even if you order a $5 replacement paddle from Shapeways, then paint it up to match, you got off easy, compared to damage to the switch body or the switch PCB. And of course, no one does all that. They do the easy thing, by drilling out the pivots and gluing in an axle. I'm OK with that -- it's an easy repair, restoring form and function.

    What I'm not so OK with, is strengthening the thing by using steel (paper clip) or brass rod to do it. Even solid copper wire seems dicey to me, because next time the injury happens, that spot won't give. That force will instead bend the pivot supports, or worse, drive them edge on into the switch body. If the switch body is also rigid, as is likely, the PCB may crack, etc.

    So I recommend using a plastic or wood cylinder of 1/16" diameter for this. In a pinch, take your flush cutters to a round toothpick. Hobby shops also carry 1/16" square stock, which can be quickly sanded round. I like the wood as it's cheap and easy to work with, and super brittle if (when) you hit the paddles again. The disadvantage is that the end grain can be difficult to make pretty, and tear-out there can make the pivot a bit less reliable.

    [A similar argument pertains to the plastic balls that hold front panel stuff to the rack. Replacing those with rods and screw heads or whatnot makes them very strong, and they proceed to damage the clips they mate with, which are much less replaceable.]


  7. #47
    Join Date
    Oct 2019
    Rapid City, SD USA


    On the topic of the pivot pin. It is certainly an easy fix to just drill out the paddle and put in a piece of piano wire. And as Vince points out the next time that handle gets bashed you have a much more difficult repair. I am pretty sure that I have seen aluminum tubing with the correct OD. Aluminum might actually be too soft. Copper or brass tubing with that OD should also be available. I know you can get a carbon fiber pultrusion in that diameter. Carbon might be a good choice as it is quite brittle and would probably shear but then again it is also stiff and could damage stuff before it does. Carbon is also abrasive and could wear the pivot holes in the switch body. You can get hardwood dowel stock although 1/16" is pretty small. Vince's idea of using toothpicks is a good one. Bamboo would be a good wood to use.

    Having said all that I currently am using a single piece of piano wire threaded through all the handles. It is retained in place with a pair of wheel collars I grabbed from the local hobby shop for holding wheels on small RC model planes. If it gets bashed the load will be spread across many switches but there will be damage.

    I will probably remove the front panel when I move the machine as a safety measure. This would not stop me from bumping them if the machine was mounted in a rack. But in this case it is on a table.

    My Straight 8 has the factory table in front of the machine so unless it is being moved without the table attached it is pretty safe.

    There is no perfect answer. I am certain that nobody at DEC would have guessed that any of these machines would still be around 50 years later, much less still operating.
    Doug Ingraham
    2nd owner of Straight 8 SN1173
    5 other PDP-8's including an 8/i and a DECSet 8000

  8. #48
    Join Date
    Jan 2007
    Pacific Northwest, USA
    Blog Entries


    FWIW, most hobby shops have access to K&S metal kits. Lots of good stuff there.

  9. #49
    Join Date
    Apr 2011
    Brisbane, Australia
    Blog Entries


    Hobby shops also have Evergreen styrene rod and tube:
    I use this for scale modelling and it's very easy to work with.

    As for carbon fibre, I use it quite a bit. I would not suggest it for such short pivot pins though. Even using a brand-new #11 blade and scoring right round before cutting, I have found CF rod invariably fractures into fibres right from the ends. It can be soaked with cyanoacrylate but for such a short length (~10 or 12mm) I am almost certain it will not hold together. Longer pieces seem to be ok.

  10. #50


    What is the $5 replacement paddle being referred to in post #46? I'm not familiar with this...paddles for PDP8e? are they available? I presume not or we wouldn't be discussing all this?


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