I have a part from which I want to take a mould - it's around 50cm long by 46cm wide at the widest point.  I'm unsure as to whether the ready mixed epoxy fibre kit would be best or the uni mould kit, and which size to use if the former.  Guidance on this would be great.

It's a small motorcycle fairing and is curved so part of it touches the board and the top is about 6 inches of the board.  I've watched the video and saw that when making a small part, modelling clay is used to created flanges. I could do that with the part it would just need a fair amount of it (46cm across by about 15cm high) to bring the moulding cloth/putty down to the board. Is that the best thing to do? Or better to cut out sign board and make flanges that way? 

Hi Mikew,

Epoxy gelcoat and its putty is fine, I used it with with sucess in the past for small parts.

But if it was for me, i would use UniMold method. It's more like regular mold making method, gelcoat then layers of csm. Resins are filled to keep mold from retracting too much. Thickness of the mold will be more uniform (compared to the epoxy+putty), leading to less uneven distortion during cure. Plus you can even post cure it to a higher degree than the epoxy one (90°C for the Unimold and about 60°C for the epoxy if I remember well). Maybe not necessary, but you can if you ever want to try.

For the flanges i would use signboard. Signboard will conform better to your part and then u'll need less fileting wax, as opposed to laying your part on a flat sheet and fill enormous gaps. Do NOT hesitate to make flanges bigger than what you think you will need. Better cut flanges afterwards rather than having the joy to discover than you made them too "thin". I usually make 'em about 5 inches wide. It may appear as a waste of material, but I'm always comfortable with laying cloth and consumables. In some occasions, it leaves the stress out of the room

Hope it helps, good luck in your project.

 



 


    A $1000 electronic device will always protect a 10 cents fuse

Cheers Joe.  I guess i was trying to avoid the laying up etc. The part is quite thin so needs strengthening anyway on the inside to stiffen it up but as you suggest, best to do it right.

Hi Mike,

I think I'm with Joe on this one. Both systems woudl do the job well but if you're comfortable with slightly more conventional fibreglassing techniques then Uni-Mould would probably be the way to go. If you've not done fibreglassing before then the putty system tends you yield better results in the hands of a first-timer but neither are difficult and I don't think you would have a problem either way.

As for the flanges, again, this is a preference thing. If you did lay the part onto a flat board then you will indeed need a reasonable amount of clay to fill the gap from the part to the board (in places) but the clay is inexpensive and re-usable afterwards. The advantage to this method is that the flanges you're left with are flat which might actually make things even easier when it comes to laying your various bagging consumables etc. You can make them as big as you want (like Joe says, the bigger the better) by laminating plent of material onto the 'board', like a good 150mm. If you do it with signboard then again, make sure you make them plenty big enough. It will be just as easy to do it this way but you'll end up with flanges that come off at different angles which might just be a fraction less easy to lay your consumables down onto.

Both would be fine I'm sure.

All the best, Matt

Matt Statham
Easy Composites / Carbon Mods - Technical Sales

Thanks Matt.  With it being a fairing, it needs to remain pretty stiff at high speed, do you think two layers of carbon and a sandwich in between would be sufficient? Or more carbon? Its fixed at each edge with bolts so the bolt areas need to be robust as that's what carries the stress at speed.  The first couple I make will just be standard wet layups, not vac'd.  I plan to use peel ply on the back for a decent finish (I've done this before with wet layup to good effect).

Would you also use carbon tape around the edges between the carbon layers or not neccessary? I'm thinking that would give thickness and reinforcement to the bolt areas.

to clarify, I mean coremat when i say "sandwich"

You haven't specified what composite layup you will be replacing the part with/method of creating it but just in case...

Coremat is a lower end core that is used mainly in fiber glass layup. The main draw back is that it is compressible so if you are planning to use say an infusion method or any method that involves putting pressure on the layup then you will need a different core. Some to name are Soric or Closed Cell PVC which EC supply.

Dave.

Cheers Dave

First two I make will be standard wet layup with carbon fibre. For stiffness and cost saving I had the idea to use coremat as it won't be under vacuum.  A snag I came across is that there needs to be an aperture for the lights of course, and I dont think coremat can be exposed at the edges ie, the ones I've made so far have been in glass and I've cut out the aperture for the lights.  If I use coremat, I guess I'll have to cut a hole in the coremat first, then leave a decent carbon overlap so as not to expose the edges of the coremat?  Could just do with some layup guidance really to give a stiff but light result without a resin infusion method.

Hi Mike,

For none-vacuum use coremat will work fine and will add plenty of stiffness to your laminate; its inexpensive and easy to use. If you wanted something higher in performance you could use some closed cell pvc foam - the 3mm is very nice to work with and with a heat gun you can soften it and shape it in advance to follow the contours of your mould but coremat is still fine too.

I don't think I would worry too much about the exposed edge of the coremat for your switch appertures. You could also try to wet out and coat the cut edges with some more epoxy to seal them after you've cut them.

All the best, Matt

Matt Statham
Easy Composites / Carbon Mods - Technical Sales

Cheers Matt, I'll ring in the week and order the bits.