HP-67 keys wanted

[Kees Bouw]

Hi Brad,

That is a very interesting idea, as a matter of fact I thought of this as well and I tried holding a key above a tea light (a small candle) at various distances and lengths of time. It had no effect, except for the last attempt where the key started to smell a little bit. I observed with a magnifying glass that the plastic did melt somewhat, but in small "islands" with the cracks in between. So the cracks did not disappear. Maybe with a very specific temperature at a prolonged time a better result can be achieved, but to be honest I don't think so. I would very much like to know what the white cracks are and why they only appear on areas that have been exposed to sunlight over the years. The soap water I used was quite hot, maybe that was a contributing factor. But I have done this before and this is the first time keys are damaged. Very interesting stuff, the ageing of plastics. Some plastic discolours to brown, some plastic disintegrates like the magnetic card drive rollers, some plastics become very hard like the paper transport rollers of a HP-97 printer, and now these white cracks in the keys. I would welcome a "plastic historian" to explain these phenomena along with some advice how to treat the various kinds of ancient plastic.

Kees.

(11-21-2017 12:47 AM)Brad Barton Wrote:  I don't have any keys but i wonder if a carefully controlled toaster oven could be set at just the right temperature to "reflow" the surface of these keys. You'd have to be very careful not to over do it.

I once saw an Instructable on how to do it. Here it is. It's not something you want to walk away from, but it looks like it would get you very good temperature control

You could take a single key and, starting at a low temperature, leave it in there for varying times and see if they can be saved. Someone with injection molding experience may be able to tell us if it's worth trying.

Brad