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A hole in the casing

2017-01-30 20:50:00,  In: DIY, Retrocomputing

Sometimes old computers come with broken plastic parts. When only cracks are present, it's easy - we can fix them with glue or staples melted into plastic using soldering iron. Even totally broken casing can be fixed this way. The bigger problem is when the casing lacks some part which cracked off. Recently I purchased an old computer with broken front panel. From photos it can be seen that damages aren't so big and two parts can be glued together, but if you look closer you will notice that a whole bottom-left corner of panel is missing. How to fix it?

I decided to try with hot-melt glue applied from pistol-type hot glue applicator. First, I found that front panel is made of porous, well-glueable plastic, so I glued broken parts together using cyanoacrylic glue. I found that this panel is painted with something similar to white acrylic paint. Next, I started to apply hot-melt glue to form a patch. The key factor here is temperature. The glue comes from the gun very hot. When hot, the glue is liquid and pours on everything, so it even won't form a wall. We want a semi-liquid state, so if you apply a layer, just blow on it constantly. This way, the glue will stick to the crack/previous layer, but it will be solid enough to form quite thick wall-like layer. Now, slowly, layer by layer like in a very coarse 3D printer, the patch can be built replacing part of panel.
After it cools down, by applying thinner lines of glue, flatten spaces between layers. Don't make it higher than fixed surface. If you need to flatten still warm glue, wet finger can be used. When glue solidifies, it will come off finger easily. Now we need to make it flat, and the most typical mistake here is machnining the glue. The only machining you can use is cutting with a very sharp knife, but the glue will stick to this knife after few millimeters. Never use sandpaper, file or saw, as you will heat the layers by friction and they will stick to the tool, making it move slowly. Moving slowly will cause the glue to solidify again and you have a tool embedded in patch you can't move at all. Wrong way.
The proper way is to flatten layer using moving hot plate. I used an old table knife heated on a burner, but a candle is sufficient if you heat it longer.

The proper operation is to heat the surface up, then use the other side of plate (to avoid transferring soot) to flatten the patch by repetitively rubbing it over patch's surface. Always end on the edge of patch and make it flat, but a bit lower than the rest of fixed surface (paint layer!). Then heat up again and flatten more. With careful moving, even rounded corners can be made. In my case it took about 30 minutes of forming. The last part of fix was painting the patch with white acrylic paint to make it correspond to the rest of surface. It doesn't look brand-new, but looks sufficient for a completely repaired computer.

It is definitely visible, but is not a hole.

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