Making a mould...

My journey has begun into the elusive world of vacuum moulding, I only hope I can ask this question clearly enough ....
I want to make a hatch for my canoe as an entry into vacuum moulding. I am making a male mould first out of wood to then fibreglass over it to produce a female mould which I then will vacuum mould into the hatch I want. My question relates to the size I should be making the male mould in order to end up with a hatch vacuum moulded from the female mould to create a hatch measuring 230mm by 320 mm and a depth of 20 mm. I guess what I am asking is how many layers of say 400 chop strand mesh should I allow for for the female mould and how thick would I expect the female mould to be as that would surely influence the male mould size. My goodness I do hope that makes sense. to try and summarise the opening is a 20 mm lip measuring 230 by 320 mm for which I want to create a cover for.

 

Okay... The first "male mould" is called a "plug" or "master" , it should be the exact outer size you intend your finished hatch to be. The "female" (actual) mould will be the exact same size only in reverse obviously. Neither should be soft enough that they will distort under vacumm. You do not want the mould to be super rigid because it has to flex to release the finished part (and even come off the plug). I would not used chopped strand for mould making myself, and vaccum bagging (which I what I assume you mean by "vacuum moulding") isn't particularly needed for this application. You just need a good thick surface gel coat and enough glass behind it to keep it together and prevent the mould from warping.

Lots of videos online that walk you thru the art of all this that would take thousands of words to decribe. Watch a bunch of them and then try it. You might get an acceptable part the first time or it might take you a few tries, but you'll learn something either way.

 

Thank you JamesG.... yes that is my point, trying to work out just how much bigger my plug (thanks for that correct term) needs to be when the female is to be as big as the "outside" of the hatch.... shoot does that make sense. To put it another way, the dimensions for the inside of the hatch I have, i.e. the opening size that the hatch has to cover. So was just wondering how much to allow for the fibreglassing. Yes I hear you about the vacuum bagging....(once again thanks for the correct term) not being necessary. But this is just my very first project knowing little or nothing about working with fibreglass or vacuum moulding. I have watched plenty and plenty of YouTube videos about the entire process but just have not been able to get an answer to the specific question I have, how much should I be allowing for the fibreglass that I will be ultimately using in the female mould (that is why I mention the fact it is to vacuum bagged) which I should be adding to my plug. If you get my rather strange logic.

 

You are making three parts in order to have one.
Unless you have a marketable product that will be mass produced from your mold, this method is extremely costly both in labor and materials, as two thirds of your effort will go into the trash when it’s done.
I have made some great hatches in place by covering the hole flush with a rigid material, then covering the whole area (over the lips and out onto the flats) with packaging tape, and laying up glass right in place.
Guaranteed to fit, and reinforcement or coring can be added to the underside if needed after it’s popped off.

 

Fantastic idea, sorry maybe I wasn't clear enough. Without sounding like a masochist I have intentionally taken this rather long winded route to gain the experience. I want to eventually build a (I will probably use the wrong terms here) vacuum infused pontoon boat. I have recently purchased the pump and al the equipment I think I need. I am starting off with the hatch so I get to understand the nuances of the materials I will be working with until I feel ready to build my boat. My next project is a helm for a small semi rigid. By then I am hoping to have enough experience to feel brave enough to start my boat. Have watched hundreds of videos and read many a book....time to put the theories into practice. Bit long winded but I trust that makes it clearer.

 

It would be a wild guess to tell you a required "gap" between the outer shape of the plug and the outer shape of the lip of your hatch opening, because you didn't state what will be its orientation (e. g. horizontal) what kind of burdens it has to carry and so on. Is the hatch to build only used as a light rain cover, or has it to be watertight in case of capsize. Are hinges and or a lock to mount on it, a sealing gasket or something else? All this will influence the necessary thickness, the number of glass layers and so the required gap.

 

How is this hatch attached to the openning? Does it fit around a combing (I assume) or is it set in or threaded? How strong do you need the hatch cover to be? If its just to keep water out, you can do that with just a couple of plys for a mm or so thick. But if you want it to take getting knocked around or putting things on it, then a few more for maybe 2 or 3mm. Its still not much and you should err on the side of too big so... 5mm? This will give you space for seals, paint, etc.

Beware that vaccuum infusion does not really like doing small and objects with lots of relief and complex curves like a hatch or cap. The various bleed and peel plies have a tendency to bunch and not strech down into nooks and crannies. You might be giving yourself a bunch of complications and headaches that will have little application to actual boat building.

 

The OP said it was a hatch for a canoe, so I’m assuming not very large.
If I were just starting out and wanted to experiment with vacuum technique, I’d do some flat sheets, they will come in handy when you start building other parts.

 

Make the wood 'plug' to the measurements of 230mm by 320 mm and a depth of 20 mm. The female mold will have an internal measurement of 230mm by 320 mm and a depth of 20 mm. The finished piece coming out of the female mold will have outer dimensions of 230mm by 320 mm and a depth of 20 mm. The amount and thickness of the fiberglass will depend on the planned loading on the hatch. For good strength to weight, I would recommend you mold in a few ribs into the underside of the hatch while it is in the female mold.

Post some pictures as you proceed.

 

Another thing to consider is the vacuum. Your mould needs to be able to be bagged, so it would be preferrable to have a wide edge for bagging. And this is a part of the mould.

So make the male plug/master and then when you build the female; extend the edges well out like 2" beyond where glass will ever go.

Then when you build the part; preapply the gum tape and leave the top paper on until the part is built. Wipe the tapes and any puddles and then bag to the mould. I am always worried about the mould distorting; so give some consideration to how, if it can. And then offer rigidity to the mould on reverse if needed. i.e. plywood or an extra layer of hand laid glass, etc.

ps-if someone mentioned already forgive me; medications are strong

 

Another thing to realize is you can also build the male plug with marine foam and avoid moulding and all the vac work and make the plug the part.

It will be generally stiffer and generally a preferred part for many, not all, applications.

 

Thanks Heimfried, in fairness to me I did warn everyone I was a total beginner.... It is just a simple rain cover closing a hatch which is used for storage of fishing equipment on the canoe. It is a simple hatch held in place by a bungee cord, so no hinges or catches. I am assuming it would be best to use a poly resin as opposed to epoxy due to the fact I would like to use a gelcoat as part of my learning process.

 

Thanks fall guy, I am planning to round all corners, outer and inner. I am maybe too keen to get my new toys up and running and this probably is not the best application, with that in mind I am prepared to have those "if at first you don't succeed try and try again....." moments. I have the luxury of the time to learn slowly. I have seen a few guys (youtube again....) using foam and will certainly be trying that for various parts as I do the build. I enjoy carpentry and have the equipment to do it in wood at the moment so that is the easiest route for me to go right now.

 

Thanks JamesG, thanks to your input going to give it a go this morning......will keep you posted....

 

Thanks kapnD. Agreed, I want to do a few flat boards of foam as the next step on my learning curve, and yes will definitely use the successful ones (not that I am expecting too much initial success) later. Jumping the gun as I want to move slowly, but I do have a question re the foam, can I do both sides at once? I plan to use a glass bed (actually a shower door) to see the resin progress on both sides, but I haven't found any guys on line doing both sides at the same time.....