Re: What Glue is best to repair HP 41-CX case plastic ? Message #2 Posted by David Smith on 27 Feb 2002, 5:07 p.m., in response to message #1 by Kurt Stauffert
I fix the broken screw bosses on the case back as follows:
1) Grind off the old remains on the screw bosses using a dremel type tool. Grind it flush to the rest of the case back. If you have old epoxy traces, make sure to remove them.
2) Cut some 0.25 x 0.375 pieces of 0.10 inch thick styrene rod (available at hobby shops as packs of five 0.10 thick rods of 0.25 inch thick strips about 12 inches long).
The thickness is important... (3/32" / 0.096 will also work). You want the blocks to be thick enough to just fit flush to the bottoms of the recesses in the battery contact assembly plus just a little bit (a few thousanths). Sand around 0.02 inches off the sides of the blocks so that they fit in the contact assembly recesses with a little room around the edges.
One problem with the original screw bosses in the case is that they did not seat to the bottom of the contact assembly. When you tighten the screws, the bosses bow inwards and place great strain on themselves... hence the cracks.
3) Using styrene welding cement (dichloromethane / methylene chloride) also available at hobby shops, wet the back of the case where the old screw boss was and one side of the styrene block that you just cut out. I like to make sure the plastic is very thouroughly wet. The solvent works by melting the plastic and drys very fast so work quickly.
4) Press the block onto the case back and try to align it so that it will fit properly into the battery contact assembly recesses. Hold it for a few seconds then quickly check the alignment by snapping in the contact assembly.
5) Remove the contact assembly and the clamp the block in place at let it dry at least 48 hours. You want all traces of the solvent under the block to be gone before you put any strain on it.
6) Remove the clamp and drill a hole though the block for the mounting screw.
7) Voila... if all went well your repair will be much stonger and more reliable than the old screw bosses.
The styrene welding fluid also works very well for fixing cracks in the screw posts.
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