Indestructible TI-89

Sometimes, expensive calculators hit the floor. It’s happened to almost anyone with a graphing calculator from TI or HP. Sadly, they don’t always bounce. After this happened to [Howard C.], an Industrial Engineering student from U. of Iowa, he decided to spend $50 on milling his own replacement case out of aluminum rather than trashing the device over a broken battery compartment. [Howard] chose to send us the story rather than write his own blog, so we’ve included all the great pictures he sent us after the break.

63 thoughts on “Indestructible TI-89

  1. Wow, that looks pretty sweet! I think if I was modifying my TI-89, I would put in a better battery system such as lithium. Then when I grab my calculator after months of no use, it will still be ready for me.

    I wonder how hard it is to read, in person, the text above the buttons?

  2. If he would have only known…
    Anodizing is fairly cheap and would have increased the cool factor a bit. But another really nice thing about anodizing is that laser etching after it comes out white and crisp, and often it is pretty cheap too at the right place. So the lettering on the case could have been really slick-looking and easier to read (more contrast).
    Maybe on case v2.0

  3. @vinito, i second your thoughts and as an engineering student he probably has or at least knows someone who has access to the schools CNC equipment and could do it for him, possibly even get some extra cred for themselves out of it too.

  4. wipe the case with black paint… it will fill in the engraving with the black and wipe clean everywhere else.. all the lettering will be high contrast.

    It’s like most of you here has never actually built anything that has engraving or etching.

  5. I’ve got a TI-85 that I use as my calculator (when opening Windows calculator or reaching for my iPod is too much effort). I’m pretty sure it’s about as indestructible as the IBM Model M keyboard.

  6. What total overkill for a calculator case, I love it! The world needs more robust case designs, things that are built to last years beyond their original warranty.

    @Jeremy, if you use normal rechargables in your calculator then take a look at the Low Self Discharge NiMH batteries on the market now, they’ll hold 70 to 85% of their charge after a year of not being used.
    I only buy those types of AA/AAA battery now because I can use them a week/month after charging and they’ll work as if they’d just been charged.

  7. Fun project, looks nice.
    But I can’t believe an Industrial Engineer did more than the CAD drawings. He probably hired one of us Mechanical Engineers to do the actual manufacturing!

    I also refuse to belove that the original casing actually broke. Back in high school we had to climb lots of stone stairs to reach our math lessons. We regularly dropped our TIs from a floor or two into the stone floor but none of them ever broke. Not even the battery cover.

  8. I don’t see how a TI calculator is worth this, but eh, I guess he really likes his calculator? I have a pile of 85’s, 86’s, 89’s, and 89 titaniums that I’ve accrued over the years, they don’t really seem to be worth much…?

  9. All you guys making fun of Industrial Engineers, I suppose you learned all your relevant skills in EE/ME courses? No? Amazing, you picked them up by tinkering and learning on your own, just like the rest of us.

    Modern engineering degrees have nothing to do with practical skills, I know plenty of MEs who would have freaked out at “OMG circuit boards!” and plenty of EEs who could do the maths but would be baffled by the engraving process.

    Of all the engineering degrees, who is expected to know a little bit of every single discipline? Oh yeah, industrial engineers…

  10. @Mechanical Engineer

    I also go to Iowa (literally typing this from the Iowa engineering building) and I’m pretty sure I know this guy (I know a Howard C.). If it’s the same guy, he started out as a ME and must have switched to IE.

  11. Hey Guys… I’m Howard (the geek that built that calculator) Thanks for the comments.

    Jeremy- Thought of rechargeable batteries, but I think a set of AAA’s last for almost half a year, so I don’t think it was necessary. The text on the buttons are easier to read than how it seems in the picture. however, having them color-coded would be better since I would know which secondary functions correspond to the diamond key and which secondary functions corresponded to the 2nd key. However, I’ve used the TI-89 long enough that it doesn’t really matter.

    Reno- Thought about it, but Titanium costs significantly more than Aluminum.

    SteveO- You’re probably right… I have a Bachelors Degree in Mechanical Engineering.

    Aaryn- Yes it does! I have the file all set up so it says TI-89 Aluminum, but it doesn’t not fit on the bezel, which is quite ashame.

    Vinito- Yes, I thought about it. But there comes a time when the new school year is about to begin, and I just want to finish my summer project. Not to mention its going to get scratched up anyways.

    Brennan- One of the best machinists I’ve met actually has a degree in Industrial Engineering, believe it or not!

    Nes- Yes, the stylish taper was deleted, which is a shame. This was done for ease of machining.

    Kyle- Yes, I do have access to a machine shop (Haas Mini Mill), and though I have made many parts before, this is my first serious machining project, and learned a lot doing it. There were 3 versions machined from plastic before I machined the aluminum version. Total machining time for the final piece was around 10 hours. Total time time spent on the project? probably around 60 hours.

    Mechanical Engineer- I dropped my TI-89 on numerous occasions, and what finally happened was a little piece of plastic that was part of the battery compartment snapped (see the 1st picture), so the calculator was fine, but wasn’t getting any power.

    Jake- I needed a TI-89 pretty bad, so I ended up buying another one, but needed a summer project that would get me more machining knowledge.

  12. Very nice. Wish I had access to a CNC mill!

    I’m sure the case is indestructible (for all practical purposes), but I hope he padded/shock-mounted the inner workings; aluminum won’t absorb some of the shock like plastic will. Otherwise, another drop could break the LCD and make it beautiful, but useless.

  13. @stevO: wtf? I’m in my first year of industrial sciences and I can mill.. *-) it’s not like it’s rocket science. I don’t say I can do it as clean as [Howard C.] but still. I studied Industrial sciences in secondary school to and believe me, I did learn how to mill.

  14. Howard, that’s overkill to the point of elegance – a great little project!

    Next summer, you could refine it further by milling the body from brass and making a set of replacement keys in black hard-anodised aluminium for a little bit of steam-punk goodness… I’m sure Jake would happily donate a few of his spare calculators to rob for the internals if you made a batch up.

  15. Wow massive over kill. Cool but massive. Looks almost like it should have CCCP written on it some where.

    Makes me wonder if you could take the pastic case and coat it with ceramic and the fire it. The plastic should vaporise and leave a perfect mold cavity behind.
    You could then cast a case for you calculator.

  16. Howard, thanks a ton for sending this in- I love that someone got fed up with every damn thing made of plastic and made a metal version!

    Think about it- all our precision machinists tools are made of things like seasoned cast iron, stainless steel, carbide- all tough stuff, yet the items themselves need to be delicately handled to keep them the precise instruments they are- one good fall to the floor for a set of gauge blocks, onto a metal grit covered metal work area, and I’d never use that block again.

    A T1-83 calculator is a precision measuring tool. It may be circuits instead of ground carbide, but it’s just as delicate to dropping. I can’t believe Texas Instruments doesn’t already do this themselves- like a calculator equivalent of a Toughbook.

    Harold- I think you just found a great niche market product. If you won’t make more, I just might! Add viton gasket seals and sealing plastic covers to make it 100% oil and waterproof, and I’ll be impressed even more!

  17. Pop on a rubberized outer covering with internal ribbing like a Fluke (yes, I’ve been watching to much EEVBlog) and you’ve got a ToughCalc, indeed.

    And the lettering should be reasonably simple. Use leaf foil in gold/brass and some ink for black and you’ve got your 2 color contrast.

  18. Hey Howard, Can you publish your solid model files for us/me? I’ve been meaning to make my own custom TI-89 Titanium case for awhile and having the key patterns would help me out… pplleeeaaassssse? :)

    I’ll even try making the case on a Mendel :) Though I’ll probably still CNC mill it out of stainless in the end. My intention is not to make it indestructible, instead I wish to make it MUCH slimmer by using LiPoly batteries. (I can deal with the self discharge)

  19. I”m surprised nobody mentioned already, how awesome it would be to do this to a HP 50g while adding a hard slide case that interfaces with the new housing. I love my 50g, it just doesn’t feel as durable as it could be (… china…) and the lack of a slide case is annoying when I lay my backpack down and it presses buttons through the soft case that put it into the never-auto-turn-off testing menu.

  20. Appreciated the many comments.
    James- Yes, it is on the blocky (and heavy) side. There will forever be this tradeoff between manufacturability and design elegance. Unfortunately, this being a machining project, the design elegance took a back seat. There’s always revision two.

    Jake- How much? do they work?

    lwatcdr- I doubt it. I could possibly make a mold from the original case and cast that instead. Also casting doesn’t leave a really nice finish. A lot of work has to be done after the casting to make it look nice.

    Jackman- no, no one is marketing this. At the moment, it the business does not seem profitable. The machining time was around 10 hours, and even if it could be cut down to 2 hours of machining time, the cost of the case would still exceed the cost of a new TI-89.

    Drew- Appreciated the comment. I would tend to disagree with you. This calculator has been with me for more than a good four years, and has taken many spills, including some onto concrete sidewalks. I would, without a doubt, say that TI calculators are extremely well-built. This fall was the straw that broke the camel’s back. And even after this fall, it was the plastic that chipped, the electronics were perfectly in tact.

    D- Didn’t make the lid. Never thought of a clever way of making it. Its kept in a sock for the time being. To tell you the truth, the days of this calculator living in my backpack are over. Its living on my desk as a testament on what happens when a geek has way too much time on his hands.

    qwertyphile- the mendel is not going to offer the precision to make this case. I have to resort to using a 1/16 inch endmill to cut the button holes.

  21. If you’re gonna invest the time and money, why the heck would you go with TI? It’s not that much more to get an HP, and you’ll end up with a much more useful item in the end…

  22. I don’t get the $50 figure at all. The metal probably only costs $5. If someone asked me to do the machining, I would probably be insulted by a $50 offer, and it’s certainly not a favor I would just give to anyone. CAD/CAM work is expensive too.

  23. When engraving stuff like the aluminium legends in the calculator we used crayon to fill the engraved words and clean off with metho. I’m not sure if the crayon was designed particularly for engraving or not.

  24. The idea of ME’s joking about IE’s not being able to run a mill is pretty funny to me.

    Around these parts: if an ME can machine a hole punch out of a block of aluminum in a week without losing a finger, THAT’S IMPRESSIVE!

    The local Industrial Engineering program recruits from the local trade school. 2 years of making parts and studying machine tool technology. Most of those kids work full time as machine operators or machinists.

    Next thing you know: Pogues are going to be claiming Special Forces can’t shoot.

    We leave school recognizing we still don’t know shit, and that we’ll spend the next 10 years worshiping someone who never graduated highschool.

    “Downing effect” much?

  25. @ qwertyphile

    Why don’t you use a piece of graph paper to measure the optical distortion of your scanner, and then scan in the TI?

    If you take a rubbing of the keys with graphite on a piece of graph paper, you may be able to get even more accuracy.

    Ultimately: It appears that you could simply read the mind of whoever designed the layout in the first place using a radius gauge/compass and a pair of calipers.(what I suspect op did)

    Tweak your code by testing on a piece of sheet metal/plastic/overhead laminate.(sheet material is easiest using double sided tape) Don’t be that guy who guts himself with a spinning piece of steel turned in to a weedwacker.

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