How to Make Large Composite (Fibreglass) Patterns by Hand

hi paul here from easy composites with the first in a series of tutorials where we're making the lightest and most indestructible sledge that we can to be used in a north pole record attempt called the dark ice project if you want to find out more about the dark ice project we've got an introduction video where we speak to expedition coordinator alex hibbert in detail about the project itself and exactly what he needs from these sledges because this project involves an original design so we don't have an existing part to create a mould from or an existing mould we need to start by making a pattern a pattern is essentially the exact shape you want your final part to be although it's unlikely you'll be wanting to make a pattern for an expedition sledge the methods and techniques we use in this video are applicable to many other things whether that's car body panels or even boat holes there are many different ways you can go about making a pattern that might be freestyle hand shaping a block of foam into your final shape right through to five axis cnc machining model board but the methods we'll be using today are essentially just a scaled up version of the techniques we used in our airbox tutorial that involves creating section views from a cad model using those section views to create profile templates which are cnc machined on a desktop router in this case then filling the gaps in between those profiles with foam sanding those into a final shape before sealing the surface with filler and following that with a pattern coat primer and gloss coat and that gets us to this final end result pattern so let's take a look at those profiles you can see here all of the profile sections that we've got to produce this pattern the original cad model for this was done in fusion 360 and then these templates were referenced from that model we have been asked before whether there's a plugin or a piece of software that can be used to automatically generate these sorts of profiles unfortunately to the best of our knowledge at least there isn't and so it is a case of manually going through taking relevant cross-section views and creating drawings on these this does take quite a lot of time to produce the drawings for a set of profiles like this is probably one or two days in cad we then use these drawings to cut the profiles out using a cnc router because of the size of these parts we were actually able to use a small desktop cnc for this but of course if you don't have access to cnc machining it's perfectly possible to print the profiles out and cut them by hand using a jigsaw as i mentioned earlier you can of course machine directly from a solid block of foam or model board and in many of our other videos you'll see that we do just that however for larger patterns this can become quite expensive in both machine time and materials and so this hybrid method is very realistic for many projects to assemble the framework it's simply a case of slotting the various patterns together and then we're going to bond these lines using epoxy adhesive i'm using the five minute permabond et500 adhesive for this task but any suitable wood adhesive would be absolutely fine you've probably also noticed that this mdf has a green colour to it that's because i've chosen to use a moisture resistant mdf which although not necessary i like to use as i find that it cuts and sands more cleanly than conventional mdf these templates probably look a lot more complicated than they actually need to be the large round cutouts that you can see in many of the profiles are only there to reduce the weight of the final pattern as these were cut on a cnc router i thought that it might as well be included if however i was doing the profiling manually i definitely wouldn't have taken the extra effort to achieve the curved line in the pattern a thin six millimeter plywood profile is used as this will easily bend to conform to the curve careful planning and accurate cutting of these profiles really pays off when it comes to the assembly as the entire structure slots together without the need for much alignment adjustment or measurement any flat areas of the pattern are paneled with flat boards of mdf this will leave you with only the curves and radiuses left to fill with foam so here we've got the completed framework ready for blocking out with foam all the critical geometries are set now by this frame so we've got the seats for where the runners are going to go the flat sides there in place and set and we've also got a number of reference planes around the more complex compound curve areas like here at the nose to block this out with foam we've roughly pre-cut some polyurethane foam and this is set so it just bonds into place with polyurethane glue and then we're going to trim that to a closer shape and then finally sand it into the final profile we have two densities of polyurethane foam available here at easy composites although both would be fine for this project i have chosen to use the high density version even though it takes longer to cut and shape it does allow for an extra degree of precision and a stronger final structure the adhesive i'm using is an expanding polyurethane wood glue these foaming adhesives are ideal for bonding polyurethane foams as they form into a very similar material that will easily cut and sand along with the rest of the pattern after around an hour the adhesive will have cured enough to start shaping shaping the foam into the pattern is a really straightforward process it cuts and sands incredibly quickly using only basic hand tools the bulk of the material can be removed using a handsaw and then the last stage is sanded down using a block when doing this you need to take care not to remove too much material so a steady and incremental approach will normally get you to the best end result to make sanding long radiuses easier i've made a long sanding block by taping some paper to an aluminium profile so that it can bridge the reference profiles and maintain a constant shape after the foam has been worked into the final form all of the gaps need to be filled this is done with car body filler after the gaps are filled with the filler the entire surface is then skimmed the skimming is only to fill the porosity in the foam and it's done by pasting the filler on and then scraping nearly all of it away leaving only the open cells filled a very common mistake for new pattern makers is to try and cover all of the surface of the foam with the filler if you do this the surface will be uneven and you will have a very difficult time sanding this back so work with small batches of filler and level it right back to the foam one area at a time after the filler has cured it should be denipped with a sanding block this is not really a shaping exercise and it's just taking away any of the slight high spots left in the filler real care must be taken not to break through that surface of filler into the foam underneath having done this you may notice a few additional low spots or imperfections in the surface if this is the case simply repeat the process until you have a nice consistent and even finish the surface of this pattern is now finished to the final dimension so there's no high spots or low spots so the next stage from here is to coat this in a pattern coat primer we're going to do that in the booth pattern coat primer is a high build and easy sanding pattern coat it's based on a polyester resin system and therefore needs to be catalyzed with mekp at two percent after a thorough mix it can be loaded into a gel coat cup gun and sprayed this is a fast and even way to apply the pattern coat but it's perfectly possible to achieve excellent results with a brush application it just might take a few minutes longer to flat it down at the end due to the high viscosity of the primer a cup gun is the spray gun of choice admittedly it doesn't offer the fine levels of control and finish of an hvlp gun but it rapidly builds a thick coat and it's very easy to clean each application of primer is done at around 500 grams per square meter after the first coat has been left to cure for around four to six hours you will notice with the uniform colour that a few imperfections like these low spots will become noticeable these can easily be fixed with some body filler so having addressed these the entire pattern can be flattened down to remove any high spots before applying the second coat again this can easily be done by hand but a da sander will make lighter work of the job here i'm using 240 grit abrasive [Music] after a quick dusting down the second coat can be applied this is simply a repeat of the first but should now leave us with a surface that is more level and with no low spots the second coat has now been left to cure and so now we can flat the pattern completely to remove any orange peel effect and minor irregularities using in this case a 240 grit abrasive compared to conventional resins and gel coats the patent coat primer is an absolute joy to sand i would say it's almost like chalk and flats incredibly quickly and doesn't choke or clog the abrasives if you don't require a gloss finish it is perfectly possible to pull a mold straight from the primer if you work through the abrasives to around 1200 grit but in this project i want a full gloss mold so i will continue on straight from 240 grit with the pattern coat gloss the pan coat glass is again polyester base so will require catalyzing with mekp as this is a lower viscosity than the primer system i'm going to use a conventional hvlp spray gun with a large 2.5 millimeter nozzle this will leave me with a better finish than i would have achieved if i'd used a cup gun don't worry if you don't have spray facilities as just like the primer this gloss coat can be very effectively be applied by brush and will self-level very very well full disclosure here i never checked the state of the gun before i used it and soon discovered that it had not been properly cleaned after it was last used so i did have some contaminated particles spitting through the gun which resulted in a few nibs in the finish even though i realized this pretty much the moment that i pulled the trigger i was catalyzed and loaded at this point so rather than wasting the material i put the coat down knowing these small nibs would almost instantly disappear when doing the final flattened polish having been left for 12 hours the gloss coat is now fully cured and all that's left to do is flat and polish so starting with 400 grit the entire surface is flattened with a da to remove any orange peel and nibs left by the spraying you can see here how quickly it's achieved this stage is best on dry as it's very easy to identify the unsanded and therefore glossy areas then i moved on to the 800 grade pad before changing over to wet and dry sanding by hand starting at 1200 grit the compound curved areas are done with the paper alone and then for the flat areas and single curvatures it's wrapped around a block to maintain a perfectly flat surface once the 1200 grit flatting is complete the pattern is cleaned down the water is exchanged and the whole process is repeated with 1 500 grit whenever you change through to a finer grade of abrasive it's really important that you do this by cleaning down the pattern and changing the water as it ensures that you don't simply rub around particles of the previous grade causing deeper scratches with the 1500 grit sanding now complete we can now move on to the polishing for this we're using the nw1 polishing compound which is specifically designed for composite resins now unless your pattern is very small this is definitely best done with a foam pad on a polishing machine but if you have the perseverance it is perfectly possible to do entirely by hand unlike many compounds the nw1 does not need water and does not quickly dry out this polishing process is essentially the same as polishing car paint and you should make sure to keep the pad moving and not focus on a small area to avoid overheating the surface this particular compound is self-diminishing so the more you work it the finer it gets and it should be able to take you from the 1500 grit paper to a mirror polish in one step once buffed the last residue of the compound can be wiped away with a microfiber cloth which should reveal a mirror-like polish so you can see after the final polish this pattern is now ready to produce a mold not only have we got an excellent surface finish but we've also retained all of the features and dimensions from the original cad model that's thanks in a large part to the profile method which keeps those dimensions true throughout the entire build in the next installment in this dark ice project series we're going to take this pattern and use it to create the mould itself so if you want to stay up to date with that hit the subscribe button if you're feeling inspired and you want to get going on your own pattern making project remember that most of the materials that we've used throughout this project are available on the easy composites website you

Channel: Easy Composites Ltd

Views: 740,320

Keywords: fibreglass, composites, pattern making, buck, GRP, sledge, arctic, how to, tutorial, guide, instructions, DIY, CNC, MDF, polishing

Id: Cusncs4GaFg

Length: 13min 3sec (783 seconds)

Published: Tue Sep 29 2020