|Re: My monster lives!|
Message #13 Posted by Randy Sloyer on 15 June 2002, 5:02 p.m.,
in response to message #12 by Ellis Easley
As I said in previous post, I really wanted to thank all those who helped. I think this is a truly great site and I would like to "give back" best I can.
As for the ultrasonic welding, I kind of doubt it. I think this is used more when trying to fuse two separate pieces together. I have always likened it to inertia welding without the motion. All that needs to be done here is soften the material and force it down in a controlled fashion. A short blast of cold air and its solid again. Here's my reasoning:
First, I think the case is some type of styrenic material. Probably ABS with some impact modifiers or other "engineering grade" resin with good impact properties. ABS is the same stuff on the inside of your refrigerator (the food liner and door liner) - it handles the cold well, takes quite an impact without cracking, bends before fracture, and most of all: It's easy to scribe your initials into! I'm sure that was in the spec somewhere.
Assuming the case is of some material in this family, its softening point is somewhere around 150°F. It never really truly melts, it only gets less viscous with higher temp. Since heating it past 450° or so only degrades it, which lowers its strength, I wanted to keep the temperature as low as possible, hence the powerstat. I didn't actual measure the temp at 200-250, I was only guessing. I could do this with an accurate thermocouple if anyone is interested. I tried my IR laser pyrometer, but its spot size was too big to get a good reading. The strong broad tip of the tool was easy to manipulate and roll the mushrooms back into a stubby pin. I found it better to roll the edge up, then back over onto itself. Trying to pull the sides up to form a tall pin resulted in the "ring" of the mushroom falling off after becoming a tall thin cylinder.
After now doing two units (I put the 20S back together first before the 42S!) I find the real problem is getting enough pressure with my fingers on the front plastic and rear metal plates to get the proper key "feel". I have been daydreaming of perhaps milling a female plate that has keytop recesses to drop the front of the calculator into and use several toggle clamps to get enough squeeze on the back plate to make a good keyboard sandwich. Then both hands are free to do the reheat and form. Since the heating element end of woodburning tool has a #8 or 10/32 female thread, I could machine a female mushroom tip and have the final product be pretty much indistinguishable from the original. Maybe....
Just a curious question: Has anyone here every offered a "no guaranties" repair service? I know Paul Bragger has repaired some, perhaps privately, but I don't know if it exists as a service to our community at large. I for one, would be willing to give time to this cause since "They don't make 'em anymore!" and my fingers will be cold and stiff before I use an AOS calculator! Okay - so I'm biased! Why else would I spend 15 to 20 hours to fix a throw-away calculator? And kill a working AOS unit in the process.