Mold making

Making a fuselage mould

To make a fuselage mould you obviously need to first have a pattern to mould called a plug. This can be made from wood for good strength and durability, glass over a foam core which is a lost foam fuselage with the foam still in, or you could use a previously made fuselage. It is important when deciding where to have the seam joins, that you consider the relase of the part from the moulds, any undercuts will make the part difficult or imposible to remove. Joining method of the fuselage parts needs some thought also, I prefer tapered wet seams for which I need access inside the mould to roll out all seam joints, so some form of canopy opening or wing seat as well as an access point at the tail helps me with this. Once I have thought this out and decided on where abouts on the fuselage my parting planes will be, I lay the fuselage on my parting board and draw round it, aiming for a gap of about 2mm all round. I do this while at the sanding stage of the plug preparation to avoid scratching or damaging the final glossy finish of the plug.

I like to bed my plug into a foam sheet under the splitter plate, and as I have plenty of ordinary house plaster knocking about use this to form some seats for the plug to sit on so that the splitter plate/parting board intersects the fuselage exactly on the centre line. There are lots of ways to do this, making a wooden structure under the fuselage with some supports jigsawed out, hot melt glue ect. This is just the way I like to do it for making 2 part moulds with a parting plane through the centre of the fuselage. I would next finish off my plug and polish with 10 coats of release wax then put some pva release on with a damp sponge and leave to dry. Putting the prepared plug onto the pre moulded plaster dabs means the plug is already at exactly the right depth in the splitter plate, so I can mix up some epoxy with micro balloons and push it into the gap between the splitter plate and plug, just squash it in there with your finger or put into a polly bag and snip off the corner and ice it in there, then smear round with your finger. The neater you do this the easier it will be to sand it off later, and the reason I like a 2mm gap is to allow plenty of the filler splooge to get down below the parting plane and stick to the parting board. Some people use car body filler for this which is quick to harden, but I have found it to be too soft and often crumbles when removing the plug, it also reacts with my plug finish when I use g4 pond varnish, though I am experimenting with other plug finishes. After leaving the epoxy for a couple of days to harden, I can give the splitter plate a good tap while holding on to the plug and it will pop out nicely. Just sand the filler down level with the splitter plate and it will form a perfect edge to give a nice sharp line to your Mould. Plasticine as a filler works but will sink while waxing and you rub part of it away when polishing also, ending up with a sunken half filled gap that will put ridges in your mould along the edge. These can be removed by poping the plug out of the first mould half and sanding back, before moulding the second half. The way I do it seems like a lot of work but its all easy stuff and is just spread out over a couple of weeks with an hour here and there, I am not in a rush, it saves me work later on and gives a very nice enge to my moulds.

 

Sometimes I use polyester tooling coat and a light chopped strand mat for the first couple of layers of the mould, then finish off with heavy chopped strand mat or woven rovings to build up thickness. This is ok and fairly cheap, but the mould edges will start chipping after a few pulls, the mould is also more likely to warp over time than an epoxy one. It is quick to make though as the polyester cures quickly, just avoid using too much mekp and build up the thickness gradually. A friend told me he starts off like this with his moulds, then switches to epoxy to build thickness, means he can get a lot on in one go, sounds interesting but not tried it yet. My prefered method at the moment is to use an epoxy tooling coat from R&G, two layers of 110gm twill glass which conforms to the plug shape very nicely, then build up thickness with woven rovings, but have recently started using biaxial glass which I am very impressed with, wets out easily and very flexible, also uses half the resin of equal weight rovings or cloth.

Forgot to mention in the video that I use chopped glassand resin to fill out any problem areas where I think the 110gm glass will struggle to go round, this gets done after filling the edges with glass tows. The locating lugs on the mould second half is a prime example of where I do this, as these are dips in the splitter plate surface which the glass cloth will never conform round.

Now comes the hardest part of the whole proccess, leaving the mould alone for at least a week to cure before trimming down the edges and drilling out holes for the bolts, which is best done before breaking the mould apart to see how it has turned out. Because I have used pva as part of the release system, would expect there to be small iregularities over the mould surface, like very shallow dimples, these will need to be sanded out with some fine wet and dry before final polishing of the mould surface. Before I learned about pva, I did make a couple of moulds using just wax as a release, which worked well, so it is possible to transfer that shinny plug finish straight to the mould but be very careful, I have had plugs stick to the mould and it is soul destroying. I think of pva as an insurance policy, creates more work but the parts always release. Thre are some hi-tech release agents out there now which might be worth looking into, but they are very expensive and very toxic. 

 

 

Making an inner nose cone mold

 The inner nose boat or inner nose cone, whatever you prefer to call it is one of the trickiest bits of molding on a glider I think....it has to fit. Having made three or four of these now for different glider fuses, I have ironed out a few bugs and am beginning to get the hang of it. Still a long way from perfect, but willing to have a go at explaining how I do it. Brian Laird did an article about it on rc groups, which just about tells you everything, will see if I can find it and add a link.

The baisic concept is to lay up a nose piece from each half of your original fuselage mold, from nose to wing saddle, not joining them but keep them separate and trimmed flush or slightly proud with the edges of the main mold. Three to four layers of 10 oz  cloth works best for me, but whatever you have handy really. Once they have cured, pop them out of the mold and sand the edges so that when placed back into the mold they are flush with the main mold flange.

     Now fill the weave of the cloth on the inside of the molded parts with filler, and sand back until you see the cloth weave showing through, I like to then paint on some thickened and coloured resin, couple of coats with red pigment first, sand back then couple of coats with black pigment. Sand back with wet and dry until the red starts to show through, progressing down to 400 grit, no need to get too perfect as this will be a one off mold.

    At this stage I bolt the main fuselage mold together and cut into two pieces, separating the main fuselage from the slip off nose about 20-30mm in front of the wing saddle, either straight or angled its up to you. I can then use the nose mold to hold the temporary inner nose mold in place once the inner nose plug is laid up and curing. Sounds confusing but it isn't really, watch some video, kind of like peeping over my shoulder as I do it.

 

   Nose boat mold part 1  mpeg4 15.3mb video download file covering the making of a temporary inner nose boat mold, and preparing it for laying up an inner nose boat plug.

 

Wax up all the pieces with around 10 or so coats, then apply some pva mold release, again to all parts, to get a nice release with no sticking. It seemed a good idea to paint on two coats of polyester gel coat with some pigment to give me a sanding layer, before laying up the temporary inner nose boat mold allowing for a wet seam join of the two halves with 3 layers of 10 oz cloth. Join them together, put into the main nose cone molds and bolt together. Once everything is in place you can consolidate the seams with a small roller, put aside somewhere warm for a day or so, then pull it all apart to hopefully reveal the basis for an inner nose boat plug.

    Nose boat mold part 2  mpeg4 32.2mb video download file covering the lay up of the inner nose boat plug.

I now need to lay up the main fuse and nose before making any more progress, so will probably be a week or two until the next update.