Sometimes small fiberglass parts have complex shapes. The shape may not allow neat wrapping in gloss packing tape in order to facilitate mold release. You'll need to make a plug with a firm, slick finish of its own. So how do you do it quickly?
Start with a dense, small cell foam. You can order foam from the aircraft supply of course. I just hit the local big box home supply and buy a sheet of dense pink or blue wall insulation board, usually available 2" thick. Not expensive, and a whole lot more foam for your money. Cut a few sections bigger than your intended part and laminate them together with dry micro. That gives you a solid foam block of any desired size.
How to shape the plug? I use an ordinary crosscut hand saw for the big cuts, then a hacksaw blade for the finer cuts. From there use 80 grit paper to rough it out, then 180 to detail the shape. If there's a critical outside dimension, make the plug about a 1/16" small.
When you have the shape nailed, mix some epoxy. Pour a little off in another cup and mix in some micro. Use a little plastic squeegee to wipe some micro mix into any surface flaw. Now, without waiting, paint the foam surface with neat epoxy. The idea is to form a thin epoxy shell and seal the foam.
Shaped and sealed plugs, unsanded:
When cured, lightly sand the epoxy shell until smooth. Little defects don't matter much. They will be duplicated on the inside of the finished part, but a little sanding will remove them later. Do NOT sand through the epoxy skin.
Now wax the surface, two coats, fully dry between coats, no buffing. I've used the same old can of carnuba wax for ages. When dry, spray or brush over the wax with some PVA mold release.
If the part needs a mounting flange, cover a sheet of aluminum or wood with packing tape. Screw the foam to the sheet with a few coarse deck screws or similar.
Do your layups. Three or four plies of 8.9 oz 8-harness is typical.
When cured, dig the foam out. The epoxy shell-wax-PVA combination will peel cleanly and leave a finished surface. A little touchup sanding will remove any raised defect. If you accidentally allowed a few air bubbles between the plug and the layup, fill the indentations with micro and sand the surface flat later.
A finished part after 10 minutes of trimming and sanding, and a plug ready for layup:
BTW, if this doesn't seem to fit your definition of "quick", consider how the work is scheduled. Cut and laminate a few foam blocks, ten minutes. Shape the plug and paint with epoxy, an hour. Sand, wax, PVA, and layup, maybe two hours, and some of that is waiting for the wax and PVA to dry. Remove the foam and trim, another half hour. Between these tasks you work on something else.
Have fun!
Start with a dense, small cell foam. You can order foam from the aircraft supply of course. I just hit the local big box home supply and buy a sheet of dense pink or blue wall insulation board, usually available 2" thick. Not expensive, and a whole lot more foam for your money. Cut a few sections bigger than your intended part and laminate them together with dry micro. That gives you a solid foam block of any desired size.
How to shape the plug? I use an ordinary crosscut hand saw for the big cuts, then a hacksaw blade for the finer cuts. From there use 80 grit paper to rough it out, then 180 to detail the shape. If there's a critical outside dimension, make the plug about a 1/16" small.
When you have the shape nailed, mix some epoxy. Pour a little off in another cup and mix in some micro. Use a little plastic squeegee to wipe some micro mix into any surface flaw. Now, without waiting, paint the foam surface with neat epoxy. The idea is to form a thin epoxy shell and seal the foam.
Shaped and sealed plugs, unsanded:
When cured, lightly sand the epoxy shell until smooth. Little defects don't matter much. They will be duplicated on the inside of the finished part, but a little sanding will remove them later. Do NOT sand through the epoxy skin.
Now wax the surface, two coats, fully dry between coats, no buffing. I've used the same old can of carnuba wax for ages. When dry, spray or brush over the wax with some PVA mold release.
If the part needs a mounting flange, cover a sheet of aluminum or wood with packing tape. Screw the foam to the sheet with a few coarse deck screws or similar.
Do your layups. Three or four plies of 8.9 oz 8-harness is typical.
When cured, dig the foam out. The epoxy shell-wax-PVA combination will peel cleanly and leave a finished surface. A little touchup sanding will remove any raised defect. If you accidentally allowed a few air bubbles between the plug and the layup, fill the indentations with micro and sand the surface flat later.
A finished part after 10 minutes of trimming and sanding, and a plug ready for layup:
BTW, if this doesn't seem to fit your definition of "quick", consider how the work is scheduled. Cut and laminate a few foam blocks, ten minutes. Shape the plug and paint with epoxy, an hour. Sand, wax, PVA, and layup, maybe two hours, and some of that is waiting for the wax and PVA to dry. Remove the foam and trim, another half hour. Between these tasks you work on something else.
Have fun!
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