A solution for cracked Hi-Tek switches (VT100, Hazeltine, HP, etc.)

afan

05 Dec 2018, 04:07

I'm restoring my Hazeltine terminal, which has Hi-Tek High Profile keys which are known to be fragile. And I think I've found a good solution on making these cracked keys work with a small modification.
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Here I posted my illustrated story on how to fix them: https://imgur.com/gallery/lgZZZJ5

And here's the video:
Hope this will help others in bringing old terminal keyboards back to life.
Last edited by afan on 13 Dec 2018, 06:41, edited 1 time in total.

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Darkshado

05 Dec 2018, 04:49

Neat solution, do you plan on sharing the source files or selling these yourself?

afan

05 Dec 2018, 05:25

I don't mind sharing them for free.

Designs I made are suitable to be printed on ponoko.com. When printing, choose either white or black Delrin plastic, 0.8mm thick, P1 size sheet (181x181mm).

Option 1: 64 collars on one 181x181mm sheet:
https://www.dropbox.com/s/zj1z1xpnik11j ... 4.eps?dl=0

Making them on Ponoko will cost you $16.10 + shipping.

Option 2: 144 collars on one 181x181mm sheet:
https://www.dropbox.com/s/ag78jvzme8mrj ... 4.eps?dl=0

Making them on Ponoko will cost you $30.63 + shipping.

You can also edit the file and leave just the right number of pieces on the sheet, which can shave off a few dollars from your order.

If you find them useful and if using these will save you some money (on e.g. buying a donor keyboard), feel free to donate me whatever you feel reasonable: https://www.paypal.me/iafan

afan

12 Dec 2018, 08:14

Just a quick update: after picking the right size, I ordered a full set of laser-cut collars for all the keys, and had the keyboard fully restored. The process of installing keycaps and collars turned out to be a very easy one, and I was spending just 10 seconds per key (to put the collar and install the keycap). I did have to remove the top part of the shell to work with the keyboard and then put it back on.
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The keyboard now works flawlessly. I'm very pleased with the result and with the fact that you can fix even severely cracked key sliders with no keyboard disassembly and without using any donor keys.

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Hypersphere

12 Dec 2018, 20:13

Nicely done! Just the sort of thing that ought to be well archived on DT per the recent thread on the future of DT.

Engicoder

12 Dec 2018, 20:51

Smart idea. The slight loss in travel seems very acceptable to have a functioning key.

afan

13 Dec 2018, 06:56

Hypersphere wrote: Nicely done! Just the sort of thing that ought to be well archived on DT per the recent thread on the future of DT.
Do you think it makes sense to add the link to this topic on Hi-Tek switch wiki page?
wiki/Hi-Tek_High_Profile

I could add it, just don't know what the policy is around editing the wiki and linking back to forum posts.

caseybea

02 Feb 2019, 05:33

Well.... CRAP.

I have a vintage VT100 I literally pulled back into service last week, and came across this post!

Aha! Cool solution. But, I have a problem.

It seems that EITHER:
(A) the hi-tek posts on the VT100 are ever so smaller by a hair than on the hazletine terminal,
OR
(B) There's a flaw in the cutting process at ponoko and

....whatever the cause, the collars are too big. I cannot put them on and have them stay put.

In the video, it appears that the collars fit nice and SNUG. TIGHT almost. Which would be awesome.
In my version, the collars are loose: in some cases they sort of stay on top, but with the SLIGHTEST touch they fall down. In other cases they don't stay at all and just slide down to the bottom.

Super frustrating. I'm trying to discern what to do. glue them on? SOMEHOW get a new pattern? Have them printed elsewhere (where)?

My first thought is to use loc-tite and glue them on.

caseybea

03 Feb 2019, 02:22

What are the exact measurements of the collars supposed to be? Going to measure what I have as soon as i can find my measuring tools

afan

05 Feb 2019, 03:27

caseybea, just measure one side of the rectangle (the stem) with a caliper, and make the collars with the same size of the opening. In my case, the outer size of the stem was 8.2x8.2mm on each side, and this is exactly how the inner rectangle hole of the collar measures for me. You may want to find one non-cracked switch to get a better measurement. When you put these collars, they are not really a snug fit, they fit pretty easily on top and require almost no pressure. But they for sure don't fall down the stem. As you put the key cap on top, it will try to push the sides of the stem outwards, thus securing the collars. It may take a bit of practice to put them on. Feel free to post pictures (here or in a private message) of it doesn't work, since your key caps / stems might just be different.

Also, if you're 3d-printing the collars, its actual dimensions might be a bit off from the original design. If so, adjust your design to account for this. In my case, I made the collars laser-cut, so they all have exact dimensions, and clean edges.

caseybea

05 Feb 2019, 23:52

Did you print YOURS at ponoko?

Sorry, got distracted from making measurements. Hopefully tonight.

I'm also going to experiment with the glue. I ordered a 2-part plastic bonding system (loctite), and will experiment with one key. The collars (once set) DO seem to work, but without any adhesive, at lest for me they move and in some cases fall.

The measurements I come up with will tell all..........

afan

06 Feb 2019, 03:37

Yes, I ordered mine at Ponoko.

caseybea

06 Feb 2019, 06:12

The dec VT100 hitek posts (white, main keyboard) seem to be averaging 8.1mm
The black hitek posts (keypad) seem to be averaging 8.2mm
The inner width of my collars seems to be about 8.25mm

Looks like I have to glue them.

There appears to be some variance in the hi-tek posts (white vs black).

The collars are not a tight fit (they should be in my opinion?)

afan

07 Feb 2019, 06:38

I experimented with different options, and found that the best fit is when the sizes match exactly. So in your case you'd need collars with 8.1x8.1mm opening for the keyboard and 8.2x8.2mm for the keypad. Making them a tighter fit will just result in keycaps being too hard to put onto the stem.

caseybea

14 Feb 2019, 06:11

I ended up just gluing the collars in the proper position with loctite plastic bonding system. A pain to do, but it actually did work. While the collars weren't exactly perfect for some keys, once held in place they still do the job keeping the crack from opening, and voila- no sticky keys.

I actually like the reduced travel of the keys, makes for easier typing on the vt100 keyboard.

Thanks ton for such a creative solution, as there's just NO donor keyboards out there these days!

Wish I had bought a few of the terminals tho. When I got it, it was at a garage sale of sorts at my uncles' GE plant where he worked. They had racks of them for sale. 30 bucks.

afan

14 Feb 2019, 06:28

Glad it worked out for you!

$30, wow, I'd definitely buy a few as well!

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