g_boxwood
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Dear gentlemen,
I thought I could share with you my common tech for making composites molds that will last a lifetime.
I hope you don't mind if the following tutorial doesn't refer to rocketry-related parts but that's the one process I documented the best!
Let's get started!
Mold-Making
Generally speaking mold-making deals with a sequence of known operations:
0. Plug finishing
1. Plug polishing
2. Plug waxing
3. Release agent (PVA)
4. Composites mold lay-up
5. De-moulding
Even if much of the work and materials belong to step .4 it is the precise and lovingly care exercised during .0 to .3 that leads to a satisying result!
The items needed to complete steps .0 to .3 are pictured below:
Polish (up left), PVA liquid release agent (up right) and Partall pasty parting wax, plus cloths and 'special' brushes for the PVA.
0. Plug Finishing
It may happen that some dust particles collect in your final coat of paint: it happens often as I paint in the outside so it could happen to anyone else as well.
Do not panic but do not leave any surface defect that will mirror into the molds and then into the finished part! The finished product should need little or no sanding & filling at all! This is why we invested time and patience and money in a good quality plug finish!
Inspect the plug surfaces carefully and find all the little defects: sand them down using 1200-grit WET sandpaper. Limit the sanding to those 'affected' areas as the scratches the 1200-grit leaves will fight with the overall glossy finish you gained with the painting.
Anyway do not dispear: the polish will clear those scratches later on...
1. Plug Polishing
Get a good quality polishing compound from your local automotive store or from your paint supplier. Usually it is a one-part viscous liquid that you rub onto surfaces with a soft cotton cloth. Apply the compound with a swirling motion and apply it with a generous pressure: insist on those areas you previously 'scratched' with the 1200-grit sandpaper until they shine as much as the rest of the plug.
The polishing will bring your already glossy piece to a mirror-like object! it amazes me everytime...
Consider the job done when you're satisfied with the overall appearence and remove any trace of the compound that got stuck in the recesses. The following pic doesn't do justice to the 'look' of the plug:
2. Plug Waxing
I hate waxes.
If you know what you're doing then go ahead and spread the Partall or similar pasty waxes.
If you're new to waxes then choose something such as R&G Priming wax: it is a lot easier to work with and it leads to consistent results without much experience (it is also referred to as beginner wax).
Generally speaking parting waxes may be liquid or pasty.
Liquid waxes are generally brushed on, let dry and then rubbed to a good shine with a soft cotton cloth.
Pasty waxes are spread with the same soft cotton cloth, let dry and rubbed to a good shine as well.
When you rub the wax to a good shine don't rub too much or you'll remove it!
Many coats are applied with long overnight drying times in between. That's time consuming on its own...
When you add coats be careful or the solvent of the wet coat you're applying may thin the dried coat and remove the wax you previously spread...
You know, you have to experiment on your own!!!
3. Release Agent
The liquid release agent, the PVA, is what really makes the difference between leaving the molds stuck to the plug or not.
It is a water-soluble liquid that you simply brush onto the parting surfaces: the above pictured brush (Moltopren sponge) should avoid 2 bad tendecies of the PVA coat: a lot of tiny air bubbles trapped in and the typical striping left by common brushes.
Even if the PVA is water-soluble it requires a night to dry. If you aren't in a hurry I suggest you apply 2 coats, the double coat builds up stronger and peels off easier.
Let dry overnight between coats!
Please remember that the PVA collects every possible dust particles in the air so brush it on in a 'clean' enviroment...
Here is a pic of the 2 plugs drying (darker areas are dried):
I thought I could share with you my common tech for making composites molds that will last a lifetime.
I hope you don't mind if the following tutorial doesn't refer to rocketry-related parts but that's the one process I documented the best!
Let's get started!
Mold-Making
Generally speaking mold-making deals with a sequence of known operations:
0. Plug finishing
1. Plug polishing
2. Plug waxing
3. Release agent (PVA)
4. Composites mold lay-up
5. De-moulding
Even if much of the work and materials belong to step .4 it is the precise and lovingly care exercised during .0 to .3 that leads to a satisying result!
The items needed to complete steps .0 to .3 are pictured below:
Polish (up left), PVA liquid release agent (up right) and Partall pasty parting wax, plus cloths and 'special' brushes for the PVA.
0. Plug Finishing
It may happen that some dust particles collect in your final coat of paint: it happens often as I paint in the outside so it could happen to anyone else as well.
Do not panic but do not leave any surface defect that will mirror into the molds and then into the finished part! The finished product should need little or no sanding & filling at all! This is why we invested time and patience and money in a good quality plug finish!
Inspect the plug surfaces carefully and find all the little defects: sand them down using 1200-grit WET sandpaper. Limit the sanding to those 'affected' areas as the scratches the 1200-grit leaves will fight with the overall glossy finish you gained with the painting.
Anyway do not dispear: the polish will clear those scratches later on...
1. Plug Polishing
Get a good quality polishing compound from your local automotive store or from your paint supplier. Usually it is a one-part viscous liquid that you rub onto surfaces with a soft cotton cloth. Apply the compound with a swirling motion and apply it with a generous pressure: insist on those areas you previously 'scratched' with the 1200-grit sandpaper until they shine as much as the rest of the plug.
The polishing will bring your already glossy piece to a mirror-like object! it amazes me everytime...
Consider the job done when you're satisfied with the overall appearence and remove any trace of the compound that got stuck in the recesses. The following pic doesn't do justice to the 'look' of the plug:
2. Plug Waxing
I hate waxes.
If you know what you're doing then go ahead and spread the Partall or similar pasty waxes.
If you're new to waxes then choose something such as R&G Priming wax: it is a lot easier to work with and it leads to consistent results without much experience (it is also referred to as beginner wax).
Generally speaking parting waxes may be liquid or pasty.
Liquid waxes are generally brushed on, let dry and then rubbed to a good shine with a soft cotton cloth.
Pasty waxes are spread with the same soft cotton cloth, let dry and rubbed to a good shine as well.
When you rub the wax to a good shine don't rub too much or you'll remove it!
Many coats are applied with long overnight drying times in between. That's time consuming on its own...
When you add coats be careful or the solvent of the wet coat you're applying may thin the dried coat and remove the wax you previously spread...
You know, you have to experiment on your own!!!
3. Release Agent
The liquid release agent, the PVA, is what really makes the difference between leaving the molds stuck to the plug or not.
It is a water-soluble liquid that you simply brush onto the parting surfaces: the above pictured brush (Moltopren sponge) should avoid 2 bad tendecies of the PVA coat: a lot of tiny air bubbles trapped in and the typical striping left by common brushes.
Even if the PVA is water-soluble it requires a night to dry. If you aren't in a hurry I suggest you apply 2 coats, the double coat builds up stronger and peels off easier.
Let dry overnight between coats!
Please remember that the PVA collects every possible dust particles in the air so brush it on in a 'clean' enviroment...
Here is a pic of the 2 plugs drying (darker areas are dried):