Mark Hoskins' HP 97 printer idler gears

[Dave Britten]

Fellow 97 owners/ebay addicts may have noticed that Mark Hoskins is now selling metal idler gears for the HP 97 printer. Naturally, I bought one almost immediately, since my plastic gear was stripped, and I'm happy to say that I'm pleased with the results so far.

Installation is fairly simple - open the calculator, remove the printer mechanism, and pop the E clip off the idler gear shaft. Remove the old gear (if it's still present), and slide on one of the included washers, followed by the new gear, then reattach the E clip. I also added a drop of synthetic oil to the bore and teeth for good measure.

I did notice that the gear I received was an extremely tight fit on the shaft in my unit. To fix this, I used a 3/32" bit on my drill to true up the bore, using my thumb and two fingers on my other hand to firmly hold the gear in place (probably not OSHA approved, but oh well). Just run the bit slowly while working the drill in and out a little. Shouldn't take more than a minute before it's moving more freely in and out of the gear. After I did that, the gear slid in place easily, with no discernible slack. I mentioned this to Mark, in case he's able to refine the drilling and boring technique.

After reassembling everything, I printed out a 224-step program listing as a test, and it turned out perfect!

So this appears to be the ticket to getting that printhead moving properly again. Just be aware there is a possibility (for now) that you may need to tune the bore very slightly with a 3/32" drill bit depending on tolerances. If you're comfortable digging around inside these old calculators, you're probably fairly comfortable with using a simple power drill.