Good afternoon to all,

I am building a female mold that will beused to make a carbon fibre marathon canoe (18’6”). I have good skills working with fibreglass but this is my first experience in making a femalemold.

The mold is based on wooden slats lined with 1” foam and  lined once more with fibreglass. The fibreglass  is then finished with the usual body fillerand mold primer/hi-gloss coats to make it a glass finish. As you may realise,the front and back end of the molds are extremely streamlined and I find itimpossible to sand down to a glass finish.

The alternatives that I have come up withwould be to 1) cut the mold in half and work on each side separately thenreassemble to lay the carbon fibre cloth. The disadvantage might be that Iwould not end up with symmetrical sides. Option 2 would be to lay the carbon fibrein the mold as is but finish the exterior of the canoe’s ends to a glass finishafterwards. Finishing the outside to a glass finish after unmolding seemsdifficult to achieve. Any comment and recommendation would be welcome. 

Manythanks.

Z

I would definitely part the mold in two halves. It will make layup and de-molding much easier..

As to the symmetry, I would polish up and shape one side, then do a few "templates" by simply laying up a few narrow strips on the finished side, reinforce them to make them hold the shape perfectly, then use them to shape and polish the other side. (A bit like making one-sided rib for the canoe)

While it is a lot easier to polish up an outside surface, having a mold with as good a surface as possible, makes it much less prone to release problems, a definite worry with a CF shell to remove form the mold!
A demolding problem could become rather expensive ...

Have you given any thought to the types of CF cloth to use? I would recommend using a CF/Kevlar mix for the outside, to get a good impact resistance.




Good luck with the project .. 




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Post the pic of what you have actually built because I don't see the problem you are talking about


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Hi again...

From looking at the picture I can already see that you can not make that shape in a non split mold... there are at least two places on both sides where you have the shape going inwards towards the top edge. that will lock the body of the canoe into a single piece mold... even IF you can press the sides together enough to clear the top of the mold, you will have a lot of problems de-molding...

Even if you modify the shape to avoid the inward slopes on the top of the canoe, the very narrow places at either end will be very difficult to release, since you will also have great difficulty in polishing it in the very confined spaces in the bottom "corners" They WILL stick or lock solid ...

I certainly would much rather do this as a split mold, and avoid several problems at once.
You will have another problem with the split mold, you will have a slight edge along the seam of the split mold, but if you make sure that there is room for a bit of extra Gel-coat along the seam, that can be polished away.

I would definitely go for a clear gelcoat in the mold first.  Are you going to use Polyester?

@george:  I do not think the canoe in the picture is the actual one... it is what he is aiming to build, not having one to use as a "plug" to build a mold over, he is building the mold as a female mold, to use directly.. in effect "sculpting" the canoe "inside out" .. or should that be "outside in"

I have made a "plug mold" the same way, for the inside shell of a custom motorcycle seat.   since the underside of the seat shell is going to be the visible side, I decided to jump one step and laminate the seat shell directly over a reusable "plug"  made from MDF and coated with a thick layer of tooling epoxy resin with filler followed by a layer with only a bit of graphite powder and then polished and waxed ...  The "plug mold is looking great, but I haven't had time to try it yet.. 

"Sapere Aude"... Dare to KNOW!

The written word is the only truly efficient vehicle for transmitting a complex concept from mind to mind...

103% of all people do not understand statistics...

Do not adjust our mind, theres a fault in reality :-)

George, here are acouple of pictures of the project. As you can see the stern is extremely narrowand as Dravis mentioned, I will also havegreat difficulty in polishing in the very confined spaces. So split mould itis.

Presently,I am at applying body filler stage. The challenge thenwill be to split the mould after the fibreglass layers will have added rigidityto the structure.

Again, cheers for thefeedback.

Now I see what you did there, this should be built as a "plug" first, nobody builds shapes like his directly into a female mold


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Disclaimer opinions of others will vary depending on what they are selling

Well ... Now he IS kind'a stuck with it, since he has gone all this way, and it CAN be done... I have seen more complicated shapes done this way, but always as multi-part moulds.

So ... .somebody DOES do "direct female moulds"   

Personally I would have made a plug from cheap styrofoam blocks, closed them up with Epoxy and glassfibre .... It would be much easier to work on, and get a perfect shape and surface..

But:   Please keep this thread updated, we would all like to see how the project gets along ...

"Sapere Aude"... Dare to KNOW!

The written word is the only truly efficient vehicle for transmitting a complex concept from mind to mind...

103% of all people do not understand statistics...

Do not adjust our mind, theres a fault in reality :-)

Hi all,

Hi, I really admire you dedication for this project. You still have a lot of hard work ahead before you have a usable plug.