On 7/14/09, C. Sullivan <feedle at feedle.net> wrote: I'm part of a group building one in Columbus. We are still at the "gather parts" stage. Cool. I look forward to your design. I'd personally want to print replacement PDP-8 and PDP-11 toggles, among other things. I agree. -ethan

On 7/14/09, Dave McGuire <mcguire at neurotica.com> wrote: Oh, yeah. I've got a pile of broken ones in a box in storage (most of the "good" ones are bolted to the face of various racks). If the plastic is amenable to (solvent) welding, it might make sense to turn some replacement stalks on a lathe or to mold them, then drill out the broken plate and weld the fabricated part in the hole. I'm guessing that the parts are either polystyrene or ABS, both of which have solvents. I wouldn't expect just gluing the broken bits back on would work because of lack of mechanical at the break. Perhaps I'd feel differently after making a few things in a RepRap, but the layered construction technique might not be the best method for manufacturing these sorts of brackets since the stress happens (usually) when you want to remove the blank cover from the rack, and this would apply the stress between layers of the printed replacement part. Finding a couple of cases of NOS in a warehouse would be great, but I have to think if it was going to happen, it would have happened in the past 10-20 years. -ethan

Chuck Guzis wrote: I think we're talking about these little <insert expletive here>s: http://www.cosam.org/images/pdp11-35/filler_bracket.jpg Those two countersunk holes take screws which thread into cage nuts to hold the thing on the front of the rack. The two protrusions plug into holes on the back of the blank/filler panels. What you often see is that the balls come away with the panel when you remove it. I also have a fair few which have been snapped at the screw holes, presumably due to over-tightening. It can take a bit of leg work, but if you're lucky you can find self-tapping screws with nice rounded heads which fit in the holes on the panels. Just trim/file the stump flush with the bracket, drill out a pilot hole and screw in said self-tappers a few turns. These replacement ball joints are much sturdier than the originals! Cheers, -- Steve Maddison http://www.cosam.org/

Ethan Dicks wrote: Not so much of a problem in my case as I don't often move stuff around. I did think about using a plastic bead, a narrow screw and a bit of tubing as a spacer, but never got the parts together (and I happened to have the nicely-fitting screws lying around). -- Steve Maddison http://www.cosam.org/

From: "Ethan Dicks" <ethan.dicks at gmail.com> Sent: Tuesday, July 14, 2009 2:56 PM I have cast those with pretty good success. The way that seemed to work best was to cast the RTV mold with the thing laying as pictured. Then when the RTV sets up, flip it over, and remove the original, exposing the whole whole back. Then fill with the 2-part plastic resin, being careful not to leave air bubbles in the recesses that will form the bulbs. I also like to fill it slightly over-full, so that the back is bulgy, then sand the face that bolts to the rack nice and flat. I run the part over a block of MDF with half-sheet of sandpaper, as the MDF has the nice flat surface I want to end up with on the back of the new part. (Sanding may expose bubbles inside the part, they shouldn't be large enough to compromise the part so you can ignore them.) The bulbs will fatigue the mold as parts are removed, so each mold is probably only good for 6 or 8 good castings. I have tried that, and did notice some fatigue of the sockets. Since the sockets looked even harder to repair that the bulbs, I quit using that technique. Vince

On Tue, Jul 14, 2009 at 4:15 PM, Chuck Guzis<cclist at sydex.com> wrote: I went grubbing around on Google and I checked through Bitsavers. I couldn't find any catalog PDFs that might have H960 accessories, but it _must_ be in a handbook somewhere. Everything was in a handbook. Essentially, if you look at the black blank panel covers on a photo like <http://www.digitalbits.org/data/media/pages/1170-1.jpg>, you can see there are no visible mounting screwheads etc. The white frame is a complex molded part with the black face glued to it. On the left and right edges of the white frame are a series of hollow open-ended cylinders, about 3/8" across, that line up with the holes in the 19" H960 rack. A 10.5" panel has 8 holes, 4 on the left, 4 on the right. What you are meant to do is to use 8 clip nuts to bolt 4 small black plastic bits to the rack semi-permanently. Each plastic bit has 2 screwholes and two plastic studs with knobs on top. The plastic bit is about 1/2" wide, and about 3-4" long. The studs are about 3/4" long, with a shaft diameter about 1/4" and a knob on the end about 3/8" diameter (from memory). When you have new plastic brackets, there are 8 studs that line up with 8 cylinders in the blank plate. You press them on, and the friction between the knobs and the cylinders holds the blank in place. What happens is when you remove them repeatedly, they rarely come off cleanly, and the studs get stressed, eventually leaving one or more knobs in the receiving cylinders of the blank cover plate. The plate will stay on with as few as two surviving studs, but 4 is better. *Some* blank cover plates were meant to be screwed onto peripheral devices with bolts through the black face of the plate, but most commonly, even for, say, a BA-11 Unibus chassis (which frequently had blanks attached to the face, but that stayed attached when the BA-11 was slid in and out of the rack), the blanks are friction-fit to what they are covering up. I took a couple other stabs at finding a good picture that's already online but am coming up dry. Perhaps someone else has a link to a good photo. -ethan