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Nelno

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  1. Thanks. I have a 4K resin (SLA) printer on the way that, supposedly, will print with an accuracy down to 0.01 mm. Even though I've got the PETG ones working well, they still need a bit of sanding. I am hoping with the SLA printer I will be able to simply print them and be done without any sanding. I was able to also fabricate the copper contacts used for each key to replace the one that I broke. I purchased a 0.15 mm thick copper roll and basically cut these pieces out with a tin snipper and bent them into the shape of the one original that I removed without breaking it. I actually received 0.25 mm copper roll, but it worked perfectly well. The original contacts are 0.16mm thick and that is extremely hard to source. I only found it one place after hours of searching, but I went with 0.15 mm that had a somewhat sooner arrival time (still took about a month to get here). Attached are some pictures of the contacts. Probably the most useful is the profile pics that show how the contacts need to be bent to actually work correctly (touching when the key is depressed and separated when it is not). You can see from the pictures that I didn't bother with the tabs on the outside, or the retaining clip that is punched in the middle of the original. I couldn't find any way to reproduce the clip with the tools I have, and I tried the tabs but accidentally cut them off. My tin snips are very unwieldy. I don't think this will be a problem, however, once I solder the copper strips in. The clip really only keeps the strips secure when the solder is removed, but it doesn't prevent them from wiggling around like the solder does. The tabs on the side just prevent the copper strip from going too deep, but the same can be achieved by careful sizing of the part and the notch that is cut on the bottom to make the solder pin. To be really useful I need to figure out a way to reproduce these with more precision, though I would recommend not breaking them as the best solution. My current thinking is to make a 3D model of a form that can be printed, then the copper strips can be bent to conform to that. Another possibility would be to make a 3D model of the contacts, make a mold from that and then poor in molten copper to make the contacts.
  2. Update: Printing these with PETG works much better: - it is more flexible, which helps when inserting the plungers, which are designed to flex a bit to allow the nubs to go in. - it seems to print more accurately and though it's more "stringy" it ultimately requires much less sanding an prep to get the pieces to fit. I've attached a slightly updated file with the "nubs" fixed to match the original (affects depth after insert) and made minor adjustments to the wall width to accommodate (what I found to be) more accurate PETG printing. hi-tek_key_plunger_B_3.zip
  3. I've been wondering... has anyone tried to fabricate a replacement stainless steel exterior for the TI-99/4A? I have two 99/4A's and my original one is missing the lower metal exterior piece. I have no idea what happened to this. I seem to remember it was slightly bent and was always coming up and getting in the way so I just removed it. I was probably < 12 years old then and didn't care what happened to it. It seems to me these could be fabricated from some sheet metal and a form, though I have no actual experience doing that. Another option would be creating entirely new pieces from plastic, sort of like the custom XBox 360 face plates you used to be able to buy, to customize your 99. Also considering getting back into TI-99/4A assembly programming and making a game. I spent 18 years in the AAA video game industry and there's an argument to be made that I owe my career to my TI-99/4A. I could never afford the expansion bus when I was younger, so my only option then was the mini-memory, which had some pretty terrible limitations, iirc.
  4. Replaced the 10K ohm thermistor (temperature sensor) in my spa heater, made some minor changes to the Hi-Tek keyboard plunger and uploaded it here!
  5. I was considering the entirely new PCB approach, too, but that would involve a fair bit more learning on my part. The PCB for these keyboards is pretty simple, though, so I don't expect designing a new one with the same functionality would be very difficult. However, since the modern switches are quite a bit shorter than these Hi-Tech High Profile switches, and because you want the switches to be held in place by more than just the soldered contacts, some sort of support structure to snap the switches into would still be required. In the end my guess is I wouldn't save anything by designing a new PCB. It might make such a project easier overall by removing some restrictions and limitations, but the extra freedom in key placement might also require a lot more prototyping to get things right. Still, I am intrigued by the possibilities here. I just doubt I would have the time for such a project right now and I'm not sure it's really how I should spend my spare time, considering my work and some of the other projects I have in flight. But honestly, the things I could learn doing it do make it attractive...
  6. I feel like the plunger is in a pretty good place to release the source files now. I decreased the width of the internal bar from 1.6 to 1.5 mm and I changed the lower cut-outs to have a tapered top which I think provides a little extra strength. In printing with some gray filament I picked up I had issues with these snapping right at the top of those bottom cutouts, so I decided to try and reinforce that a bit. I haven't had any of the ones I printed in white snap, though, so I think that other filament is just poor quality. I don't think I have the notches quite right. After inserting a polished one, these sit maybe 1 mm lower than the original and I believe it's because I've got the side notches a little too high. I've attached a zip file with the FreeCAD source file, plus two STL files, one with filleted edges and one without. The walls are so thin that slicing may cause some artifacting with the filleted version, so I included the non-filleted one just in case. It should be rotated to the correct angle for printing. If not, make sure the protuding nubs are on the top. All of the overhangs are angled from that direction so they should be printable. If it fails on overhangs it's probably rotated the wrong way for printing. Any feedback you can give would be helpful. See the readme file in the zip for more details. hi-tek_key_plunger_A_17.zip
  7. It might, but my printer isn't very modifiable in that respect. It's a Flashforge Adventurer 3 Lite, and while the quality is really quite good for a $299 printer, the nozzles come as a proprietary piece sold only by that company. I like the printer a lot, but in retrospect I would have bought something a bit more upgradable had I known.
  8. The main issue I'm having is that FDM printing just isn't precise enough to do this without a lot of cleanup on the parts afterward. The tolerance is about 0.2 mm and the width of the plunger walls is 0.6 mm. Both the inside and outside diameters of the plunger are important. Too small or large on the inside and the key won't fit or won't stay in the plunger. Too small or large on the outside and the plunger will be wiggly or stick. After having a bunch of failures with what is apparently some inferior gray PLA filament I switch to the other day, I've gone back to printing with white and I was able to get a piece sanded and working tonight. Unfortunately this is as small / thin as I can go with the piece before I start seeing artifacts in the print and this was maybe 10 minutes of shaving / sanding to get this piece fitting. In the pictures / video, I've replaced the cracked 1 key with the newly printed part. If you listen closely to the video you can hear the difference in the new plunger vs. the old. I think there are a couple of reasons: outside could still use a little sanding / smoothing, but it's close; inner bar is a little wider than the original so it has more friction on the copper contacts; I didn't do much, if any, cleaning on the lower inner cavity that holds the spring and I think that the spring is scraping on some of the imperfections I left there. I will continue making minor adjustments to the CAD file, but and upload that here for others to use. Ideally this should probably be printed in nylon so it's not quite as rigid, but my printer only gets to 240C which is the bare minimum for nylon. With the CAD file it's possible to also get injection molded pieces done, but the minimum batch I've found for those is 50 and I didn't follow through with getting a full quote on what that would cost. I probably should move this into the development sub-forum at this point. I didn't plan on making a whole new piece when I was starting on disassembling the piece. 20201221_015148.mp4
  9. After breaking the contact I did start to look at how I could replace the entire keyboard with standard switches, going as far as measuring everything and getting specs on some Kaihl switches. I'm confident that I could 3D print a waffle structure to go on the PCB and that the switches could be mounted to match the height of the originals. They are significantly shorter (around 10 mm compared to 25 for the TI keys) and smaller horizontally / vertically, but it would require some additional wiring for every single key because the standard switches of today don't have their contacts right in the middle like these Hi-Tek switches do. In addition, some sort of adapter would have to be printed for every TI key to attach it to the top of a standard switch. It looks like that would all be doable and it would be pretty cool to have a keyboard that looked 100% TI but was using more modern switches. I'm still thinking about this, but I suspect it would be at least a couple of weeks of work, on and off. I'd also have to order a bunch of switches to experiment on and I wasn't able to find a good source for those yet that wasn't overpriced and allowed me to get some reaosnable number.
  10. Yeah, I noticed they were brittle even before snapping one. I was trying to be very careful with the contacts on the back that I had de-soldered, because they bend easily and once the PCB is off, they're very easy to hit accidentally. However, once I figured out how to remove one (there's just a small tag on the copper that you can push in from the underside while pulling from the top) I measured it at 0.16 mm thickness. It's easy to find 0.15 mm thick copper sheets and they should do the trick. 0.15 vs 0.16 may change the feel of the key slightly, but it's much harder to get 0.16 mm (34 gauge) copper than it is to get 0.15 mm so that's what I have on order.
  11. I was able to get the copper contacts out, one of them whole, and I think these can be fabricated by hand with a little patience, so that's what I'm going to try next. I was able to get my printed piece installed into the keyboard, with spring, and I think it will work. Unfortunately it takes a fair bit of sanding and scraping with an X-Acto knife to get it to fit perfectly - my printer tolerances just aren't good enough to print something at this precision. I'm tempted to try Xometry.com but the turn-around on that will be a week or so minimum and I don't know for *sure* if the model tolerances are correct and the extra I'm having to take off is just due to my printer's low precision. Something printed professionally might just work from the model I have. Once I've done a little more prototyping on my other keys with broken plungers, I'll be happy to print you a couple of replacements and send them if you want to PM me your address. I can do some basic cleanup on them, but you'll probably have to do some additional work to get them to fit your own keyboard and keys exactly. They seem like they'll be durable enough.
  12. Unfortunately after sanding down my latest piece to where it was fitting nicely, I tried to insert it without making sure the metal contact had separated and I crushed one side of the two copper contacts, breaking off the small pins there. I had tested this previously and the contacts were being pushed aside by the internal bar. However, it turns out that I put the nubs on the wrong side of the plunger I designed and when I aligned the nubs correctly on the outside for inserstion, I didn't realize the internal bar was 90 degrees off and it crushed the contacts. This is a very minor fix to the 3D CAD design, but a major setback for my keyboard repair. I am really, really bummed about this. Nothing like breaking a nigh-irreplaceable 40-year old piece of hardware to ruin your day. There doesn't seem to be any easy way to get the broken contact out of the plastic waffle housing and finding (or making) a replacement seems like it's going to be rather difficult. I'm pretty unhappy about this, but at least (I think) the 3D printed plunger has a good chance of success. Hard to tell from the picture, but that bar is going the wrong way compared to the little nubs that allow the plunger to snap in, and that's basically how I managed to break my contact on my 2 key.
  13. I've created this 3D printable version of the plunger. An initial test print for sizing was promising, but I'll probably need another couple of passes to get all of the tolerances right, and my guess is each one will need sanding so the operation will be smooth. Also not sure that the PLA I'm using will be strong enough. My second prototype snapped at the bottom as I was testing the key fit. The original looks like it may be nylon and has slots in each side on the bottom but I'm not entirely sure all of those are necessary. I think they may be there to allow the piece to compress more easily when it's inserted. Ignore the burring... it's slightly brutalized by me having to pull it out of the keyboard slot with pliers. It's only very slightly too large, nothing some sanding won't fix. And it's purple because I didn't feel like changing my filament.
  14. I will let you know how it goes. The biggest unknown is if I can get the wall width just right, as the tolerances are going to be pretty tight for my cheap printer. I can do some quick test prints of just the hollow rectangular part to see. I suspect I could get these printed online from a place like Xometry.com with good enough resolution, but that might turn out to be relatively expensive.
  15. This did indeed require de-soldering 94-odd pins in the back. I wouldn't recommend this unless you own a de-soldering gun. With the de-soldering gun it was easy and the board then came right off the back. Starting here, I was able to find an old reference manual for a CDC IST II which also used Hi-Tek "Hi Profile" key switches which said to basically just grab the white "plunger" (aka "thingie") with some long-nose pliers and pull up to remove it. Well, that didn't work. Instead, I was able to use some needle-nose pliers to pinch the outside bottom of the plunger from the other side to compress the two nubs on it side and then pull it out. Take care after de-soldering the PCB, since all of the contacts are sticking out of the back of the keyboard "waffle" housing after the board is removed. It would be easy to bend or break them off when working with the keyboard. The de-soldered board: The "waffle" housing after the board is removed: The removed plunger and spring on the back of the "waffle" housing: The front of the "waffle" housing: After getting the plunger out I am fairly confident I can 3D print replacements.
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