Heating Pulsar Glass

[retroleds]

I've been heating up Pulsars to 350 farenh, to remove the glass, and reheat the case and fresh glass to put back in. Done it at least a hundred times. Another member questioned why I would heat to put glass in - well, the glass seems to drop right in, presumably because the cae expands more than the glass. I'd appreciate some thoughts on this technique - pros, cons, problems.

[bruce wegmann]

It does take 350 degrees or so to soften the epoxy for removal [don't forget, the glue has had thirty years or so to cure]. You should clean all traces of the original epoxy from the case while it is still hot [if you wait until it cools, it has fully cured from the heating, and is much more difficult to remove]. To install new crystal, I first wash the crystal and case front with acetone [adhesion of the epoxy is greatly enhanced if the surfaces are free of any traces of dirt or oil]. Apply fresh epoxy around the bottom of the crystal recess and drop new crystal in place [there is no need to heat the case at this point; the crystal dimensions were designed to have a few thousandths clearance to allow for fitting, and a thin film of glue to create a full seal]. Once crystal is in place, I then heat the face of the watch for a few seconds with the heat gun. This does two things. First, it heats the epoxy and puts it in a temporary, low-viscosity state, allowing it to flow smoothly and completely around the crystal, creating a perfect seal [cosmetically looks better, too]. It also ensures a complete, full-strength cure. I have found that 200 degrees F. [about boiling-water temperature], maintained for a few seconds, is sufficient.

[charger105]

When I replaced the screen in my P3, as Bruce suggests, it just dropped straight in. If you clean all the old epoxy away, I don't think you'll have any trouble locating it in the recess.......it actually slides around a bit.

I used a tooth pick to carefully apply epoxy to the recess, dropped the screen in, cleaned up any excess (front and back) with acetone before it dried, and then held the screen down overnight using elastic bands.

Heating after placing the glass could be good for getting an even distribution of epoxy right around the recess ?

Very happy with my results.
Rgds.

[retroleds]

When I replaced the screen in my P3, as Bruce suggests, it just dropped straight in. If you clean all the old epoxy away, I don't think you'll have any trouble locating it in the recess.......it actually slides around a bit.

Like everything else, there were tolerances(size) and different suppliers. I'd agree, some drop right in, other don't - I'm not pushing one that is "close" and risking chipping or cracking the glass.

[bruce wegmann]

From an engineering standpoint, this is all about tolerances. For the glass, there is an "ideal" size, and a certain amount of variance [plus and minus], allowed in the manufacturing process. However, there is also a second part involved; the watch case itself, and there are similar variations allowed there, as well. If you end up with a piece of glass that is at the upper [larger] limit of variance, and a case recess that is at the lower [smaller] end, you could find yourself with a situation of what I call "dimensional incompatibility" [translation: the parts don't fit together]. Fortunately, Time Computer shopped those parts out to two very competant companies [Star for the cases and Corning for the glass]. Overall, they did an excellent job; I have seen only a single crystal [a P3] that I had to try in a number of cases before I found one that it would fit in. Heating the glass alone would tend to make this problem more likely; the crystal should fit with a bit of clearance when everything is at room temperature.