(It’s such a hard decision, sort of)

Starting base

To start building the machine, we have to pick a base. If you were following my “RACS III” rebuild, I had my original system, and a few spares. (You can see that here). I also picked up a system from the UK on eBay. After much consideration (Ok, not so much, a little) I decided to go with the completely unknown system because it’d be the one I would have the most interesting time with. Ok, well, not totally true. Here’s why I picked it. It had no numberpad. Only one other machine I have has no numberpad, and it was a “D” series. This had no keypad and was a “G” series. I decided to work with a more current machine.

And off we go

So now that I had a machine, time to check it out. How bad was it going to be ? Actually, not terrible. It seemed it was a pretty stock machine and would make an –

starting place.

Opening it up

So, time to open it up, clean it up, and get going on Frankie. This is when the horror of this project actually set in. For as nice as it looked outside, and seemed to be just a regular (Though dirty) machine on the outside, this looked like the Mythbusters dropped it out of a helicopter onto pavement . It was a total mess inside.

Most of the top keyboard shell posts were broken, and , well, the same for the bottom. Marcel Erz hadn’t yet come out with his replacement shell, but what would have been the fun in that. There was no way I was going to beat him on it, especially because I have absolutely zero background or knowledge on 3D parts printing. What to do, what to do.

3D standoff reprint for the top

The top was in pretty bad shape. Being able to repair it just wasn’t in the cards. So looking around, I happened to find “TRS-80 Model 1 – Screw Standoffs Plate” by barrakuda. It was 2 pieces that when put together would be the complete parts needed for being able to have intact screw holes on the top of the case. Nice. So, I sent it off to be printed 3 times (I expected I’d “screw” up 2 of them, plus sometimes printing isn’t exact so I had a few to choose from.

In the mean time, it was expecting a perfectly flat surface. As you can see, mine wasn’t –

Ok, so I don’t have pictures. I was bad during this phase and don’t have all the pictures I might want. But just imaging it REALLY bad. So to start I did something I didn’t think I’d ever do. I took a grinder to the case and ground down any remaining screw posts. I took some sandpaper and smoothed everything out the best I could. But, there were screw holes still. I used “Vallejo Plastic Putty, 20ml” and filled them in and sanded it down again. I used a more coarse grit towards the end a little to give the glue I was going to use nooks and crannies to hold on to.

I needed to be able to know EXACTLY where I needed to have these units positioned so that everything would be totally aligned. I decided that since “A case is a case”, I’d take a known good bottom case and use it. I put the 3D print on the bottom which looked like –

They weren’t screwed down tightly, which I’ll explain later. I decided that the filler would also make a great glue, so I smeared it on and put the two halves together

I rubber banded it and specifically made sure the rubber bands went over the screws to push down on them to make sure they were as flush to the case as possible.

and waited until the next morning. I took the rubber bands off, and went to pick the case up by the top and was met with

Say it with me “Filler isn’t glue”. Meh, that sucked. Ok, so I sanded down the parts of the filler left on the top of the case, and then worked on sanding down the 3D printed screw posts. Yea, I know, I had 2 more left, but I wanted to keep them in reserve. I used a glue this time, and it worked! Top accomplished.

But what to do about the bottom? No one had a replacement for that. I was totally on my own for that. How was I going to be able to make replicas of posts/etc? Oh, I know!

Ms. Plaster Caster

So I could swear her name was “Lady Plaster Caster”, but according to Wikipedia she’s Cynthia Plaster Caster. This is a family oriented blog, so I won’t go into the total details, but when she wanted to copy something, she just made a plaster casting of it. I think it could work out for what I needed.

Off to the web I went, and found that “Oomoo 25-1A:1B Mix by Volume Tin Cure Silicone Rubber – Pint Unit” would be a good bet for casting, and then “Smooth-Cast 305 – Bright White, Ultra Low Viscosity Liquid Plastic – Pint Unit” for the reproduction.

Since I already had the good bottom, it gave me a place to start. I did a few test mixings to understand how this stuff worked. The first time, not so good. Eyeballing 1 part A and 1 part B wasn’t my forte apparently. Ok, time for mixing cups and popsicle sticks. Measured amounts in both, combined, stirred like crazy. No good either. :-/ Maybe you really gotta stir in the bottle first? Took like 5 popsicle sticks and stirred A for a good long time, 5 others in B for a good long time, poured into mixing cups for equal parts A+B, then put A into B… Or was it B into A. Yea, it was B into… no, I think that was…. ANYWAY, they got into the same cup, mixed with the stick for a few minutes, and then left alone. SUCCESS! 2 hours later I had the form of a popsicle stick. WHOO HOO.

Preparing the bottom

In order to prepare the bottom, I basically did the same thing as the top. Anything partially broken was taken down close to the case with a Dremel, and then hand sanded it when it got closer, and then finally a coarse grit to rough it up a little. This time, though, I have a picture!

As you can see, I had both screw holes on the bottom, all 3 rests for the keyboard, and 1 middle screw post. This was going to be a LOT of fun. 🙂

Molding attempt number one

*NOTE* – What follows could possibly end any friendships, love and marriages. PLEASE BE CAREFUL!! (You’ll see)

So I figured I’d work on one of the posts. I thoroughly mixed the parts separately, then measured exactly and mixed together quite well. I then set it on the kitchen counter, and took the bottom I had and put it in –

The cup on the right side has the material. I have it on a few sheets of paper towel, and things to prop it up and a bowl to give it weight. I let it go overnight, and ended up with –

The slits are from where it was part of the vents on the bottom. You can see there was a bit of an air bubble off the side of the post, but that’s actually not terrible. It give me a way to take it out, and a little place to pool the material to be able to adjust the height.

A bit more difficulty to do

While there was plenty of room to do that post, it wasn’t the case all around. Some of the others are pretty close to edge, have odd shapes, etc. How to do? Well, watching TV for oh so many years finally came in handy. I took a queue from MacGyver (And not that Lucas Till one, we’re talking the original Richard Dean Anderson one!). All I needed was a toilet paper tube and some dental wax. (This isn’t the first time I’ve used Dental Wax for a non-dental issue, so much so I keep it around all the time).

I put the wax in the slits to keep it from spilling out, and then put on the TP tube, and sealed it inside and out with dental wax. It looked a bit like –

Since I also had the screw hole to worry about, I put the screw in and then damed it with the dental wax. I poured it in and let it set. When it was done, I just peeled away the TP tube, scraped off the dental wax, and had myself a nice copy without any damage to the case.

Now its time to pour

So after I had all the molds I needed, it was time to pour. This is where you could lose your house, your belongings, and your love. THIS STUFF IS TRICKY, AND ONCE IT HARDENS, GOOD LUCK! I did this in our kitchen. I put MULTIPLE layers of paper towels down under everything I did. I think that just gave it all more of a reason to do its damage. The paper towel sucked it up and then proceeded to glue to the tile counter. Pour cups I swore were poured cleanly left rings on the counter. A bit I spilled that I thought I cleaned up got on the cabinets. I’ve spent hours trying to get it off and haven’t had any luck. On the bright side, the wife helped clean out 1/4 of the basement for me to build a lab if I never did anything in the kitchen ever again (Including soldering). It’s been 2 months since I did this and still am chipping off and scraping it. As for the cabinets, I’m afraid it’ll take the varnish off.

So when you pour out the 2 items they’re clear, but when they dry their white. So I shook vigorously and measured exactly and poured it in. You can see a bit dried where I dribbled it.

I let it sit for a bunch of hours, came back, and pulled it out of the mold. It looked like –

Came out pretty good, so I started my production line –

Left: Keyboard rest post

Middle: Front screw post

Right: Middle screw post

What you’ll notice is that there are screws in them. I first tried to cast them without the screws, and then drill out the hole. That didn’t work so well. So, since I cast them with the screw in it, I put the screw in and cast again. That was an even BIGGER mistake! I basically had to ruin the casting because I couldn’t get the screw out. Dental wax to the rescue again. I coated the screw in dental wax and now it was easy to remove.

Mounting them

Next came the task of mounting them in the case. This was a bit trickier than expected. The bottom of the case is slanted, and positioning was going to be difficult. So, I decided I’d mount them with the motherboard in. I also created a rig to make sure that it was straight. It’s too weird for words, so –

Seemed to work pretty well! The hardest part is that because the keyboard rests are slanted, keeping them oriented correctly. When all of them were in, it looked like –

I found that I had to be very generous with the glue to keep things in their place. But it worked and now the motherboard has all the posts and supports it needs!

Now that the case is in good shape, time to move onto the machine itself.