Making a mould...

[JohnMarc]

Having just made the molds for the 2 hatches on my extend swim platform project, I can add a nitty detail that you will want a slight taper to the sides of the plug, so the mold can come off easily from the plug.

The hatches that I am making are 380 mm x 460mm x 50mm (15" x 18" x 2") and one of the molds had a death grip on the plug. It took a bit of prying on the flange area to get the mold to come loose. One the second one, I added some additional PVA to the sides of the plug before making the mold. It came off easier, but still could have been better.

My hindsight is that I should have given the sides a slight taper (2-3 mm) so the mold would want to 'pop' off of the plug.

I hear you thanks..... will do just that. In fact have now made the plug so will run a router around it .... many thanks for the tip.

 

[kapnD]

Your overcomplicating your mold with the addition of the second 90degree turn, which is just being discarded.
I’d just make the vertical sides a little longer, much easier to make the fabric behave.

 

[JohnMarc]

Your finished part does not reflect the radius formed by filleting and radiusing the plug.

It may be a drawing limitation or irrelevant, but you asked for nitty details.

I would draw a section picture of the final part to verify section detail accuracy. The section drawing is more important than the big 3D imo.

Sorry you have lost me...... not experienced enough me thinks to understand what you saying. I cannot really produce and accurate section detail as I do not know the exact thickness of the glass layup. I have had to assume a 4 mm wall thickness ... so yes it is a bit of a guessing game a section can be produced but might not to be an accurate reflection of my results. But hey we live and learn, as I said earlier more than happy to make a few mistakes......

 

[JohnMarc]

Your overcomplicating your mold with the addition of the second 90degree turn, which is just being discarded.
I’d just make the vertical sides a little longer, much easier to make the fabric behave.

Thanks and I agree but the main reason why I did this is because for the helm and drinks surface of the boat (which is what this learning experience is about) I have one or two situations very similar so I have decided to kill two birds with one stone as the saying goes and tackle the second 90 degree turn now rather than cock it up later ....

 

[JohnMarc]

I am still wondering if my thinking is correct, can I not do a gelcoat with epoxy? can I only have a gelcoat if I use poly?

 

[tpenfield]

Polyester gelcoats will not cure if applied to an epoxy surface. . . at least not without a lot of surface preparation to eliminate the 'amine blush' that remains on the surface of epoxy.

However, on your mold and finished part, you will be putting the polyester gelcoat down first, then doing the epoxy resin with the laminates. So, that will be OK.

You can also look into epoxy gelcoats, so there is no compatibility issues to worry about.

 

[JohnMarc]

Thanks to everybody for their help, going ahead today to try my first vacuum bagging ..... one last question if I may, any comments on using denatured alcohol to thin the epoxy?

 

[fallguy]

Thanks to everybody for their help, going ahead today to try my first vacuum bagging ..... one last question if I may, any comments on using denatured alcohol to thin the epoxy?

No thinning is done.

You can lower viscosity by warming the mixture, but this will hasten gel time.

 

[tpenfield]

Thanks to everybody for their help, going ahead today to try my first vacuum bagging ..... one last question if I may, any comments on using denatured alcohol to thin the epoxy?

I have thinned epoxy with acetone, but only slightly (5-10%). Not sure about denatured Alcohol. . . I am not sure how a thinned resin would do in a vacuum bag setup. I figure that the solvent needs to go somewhere. thinning may be better suited for an open mold situation (not sure).

Are you going to do resin infusion? (not sure if that was asked/mentioned already) or just vacuum bagging for the curing process?

 

[JohnMarc]

I have thinned epoxy with acetone, but only slightly (5-10%). Not sure about denatured Alcohol. . . I am not sure how a thinned resin would do in a vacuum bag setup. I figure that the solvent needs to go somewhere. thinning may be better suited for an open mold situation (not sure).

Are you going to do resin infusion? (not sure if that was asked/mentioned already) or just vacuum bagging for the curing process?

Very good point about solvent going somewhere? will not risk thinning ....weather warm here at the moment so should be good. I am doing vacuum infusion....I am such a newbie I had to google the difference between the two before answering you

 

[tpenfield]

Hopefully, the epoxy is thin enough for an effective infusion. The part is small, so the distance the resin has to travel is short and the cure time of epoxy is long, which will help.

Take some pictures and post them if you can.

 

[JohnMarc]

Okay so the journey begins..... As I said earlier made the plug just from MDF (particle board I think is another term for it) rounded the corners with the router and filled the inside corners with a bit of wood filler. I popped down to a paint supplier and bought some Auto paint, applied the primer after mixing with hardener etc. I will sand it down before applying the top coat which will hopefully give me a smooth enough finish for the inside of the female mould to ultimately give me a wonderful gelcoat (he says optimistically) finish on my final product....I will post a pic or two at every stage if peeps are interested, if not let me know and I shan't bother you with them.

 

[JohnMarc]

No thinning is done.

You can lower viscosity by warming the mixture, but this will hasten gel time.

Our average temperatures at the moment are in the high twenties .... (80 F) so all should be good as far as the viscosity goes..... don't know about the rest though time will tell.

 

[tpenfield]

Not sure if you are planning on waxing the mold or spraying it with PVA (polyvinyl alcohol) as a release agent for the mold.

 

[JohnMarc]

Not sure if you are planning on waxing the mold or spraying it with PVA (polyvinyl alcohol) as a release agent for the mold.

Just had a giggle, your use of the word "planning" assumes a plan right? ..... So what I have on my shelf of newly procured goodies are what I think they call "Ram Wax", I have a bottle of PVA as well. I am now doing some serious you tubing to find the best way forward. So far I think I am going to hand lay the gelcoat and Chopstrand fibreglass, four or five layers then Vacuum Bag to cure, creating the female mould. Then use vacuum infusion (hence the large lip on the plug) for the hatch itself. These are my thoughts at the moment although open to suggestions.
BTW if I use the PVA does that mean I do not need to wax?