Pulled the trigger
- Thread starter nathane
- Start date
Thanks Rover, we wanted something really solid, Mogs are high off the ground and I'm no lightweight (6'4 and 230lbs (or 1.96m 105kg)) so we want something that's solid and not going to feel wobbly when we're carrying a loaded bag or climbing gear etc in. They're not the lightest as a result but that's a trade off I was prepared to make.
Anyway, once the shell and frame of the base was all made it was time to foam line. We are using Airex C70 foam in 55 kg/m3 density and 50mm thick. Because of all the corner reinforcements and the joint reinforcements on the floor we needed to do some profiling of the foam to get it to fit properly:
The plan is to bond these in under vacuum and so when all the foam was cut we went ahead and bagged the base. This was a real fiddly job - I've not done much work with vacuum formed composites before and to be honest we would have been better starting with smaller components, but this was what we needed at the time - you live and learn:
All the various holes in the base. like the gap the stairs would fit into, the voids in the container lock receivers and the tops of the pro-lam corner joints, needed filling with plugs to prevent the bag from being sucked in:
Then all the foam was removed, parts numbered for fitting - the resin we are using is EasyComposites EL2 with a 95 minute pot life (https://www.easycomposites.co.uk/#!...e/epoxy-resin/EL2-epoxy-laminating-resin.html), but the bagging job was going to be a real fiddle and when you're under time pressure you don't want to be forgetting which bet fits where:
again pics of the profiling to make sure everything fits nicely:
and the edges cut at an angle to avoid the glue squeeze out getting in the way:
again pics of the profiling to make sure everything fits nicely:
and the edges cut at an angle to avoid the glue squeeze out getting in the way:
So then it was a final check of the bagging:
before mixing a bucket full of epoxy (actually several buckets full):
spreading a nice layer of epoxy everywhere and fitting the foam:
and finally a top later of bagging material (the top surface was dry so we didn't need any other layers of release film etc although we ran breather fabric around the edges to help with the vacuum):
before turning on the pump:
The vacuum wasn't prefect - we had to leave the pump running, but it was enough to exert a fair clamping pressure on the foam to get everything stuck down.
before mixing a bucket full of epoxy (actually several buckets full):
spreading a nice layer of epoxy everywhere and fitting the foam:
and finally a top later of bagging material (the top surface was dry so we didn't need any other layers of release film etc although we ran breather fabric around the edges to help with the vacuum):
before turning on the pump:
The vacuum wasn't prefect - we had to leave the pump running, but it was enough to exert a fair clamping pressure on the foam to get everything stuck down.
So that leaves us with a foam filled base. I sealed all the internal foam joints with sika 552 (https://usa.sika.com/dms/getdocumen...fd5796e9ba/pds-ipd-Sikaflex552-us-6.11.12.pdf) our glue of choice for joints requiring more flexibility than the SG300 allows due to differential expansion or whatever.
and then it was time to create the inner skin - 600g/m2 carbon fibre:
this stuff looks lovely ?
lots more vacuum bagging stuff to cut:
then wet out the whole shebang with more resin, bag and suck!:
We got a better seal second time round and ended up with a nicely bonded inner skin. I was pleased with the bond to the aluminium as well as the foam.
I didn't take pictures when I debagged - but you'll see more of the floor later when the whole thing comes together.
and then it was time to create the inner skin - 600g/m2 carbon fibre:
this stuff looks lovely ?
lots more vacuum bagging stuff to cut:
then wet out the whole shebang with more resin, bag and suck!:
We got a better seal second time round and ended up with a nicely bonded inner skin. I was pleased with the bond to the aluminium as well as the foam.
I didn't take pictures when I debagged - but you'll see more of the floor later when the whole thing comes together.
Thanks Sitec, I really appreciate the comments, in fact I have to say that this is one of the most positive and supportive web communities that I have been a part of over many years. It's fantastic to find the depth of encouragement and enthusiasm that I've observed here.
It's also worth noting that there's no special skills here. I studied engineering at college, but that was 30 years ago and I ended up working in very different fields ever since so whilst I have a practical side to me, all the technical stuff has been learned on the internet through resources like this forum, youtube, etc. Anyone who is able to spend a bit of time learning could do this stuff.
I thought it might be interesting to see the CAD "build" in parallel with the real thing so a bit of CAD catch up.
First the Pro-Lam frame that the panels will fit into, this is just so you get the concept - I build it from the base up rather than creating this completely up front:
The real build started with the floor parts of this frame built onto the aluminium "subframe" which incorporates the forklift pockets and container lock castings:
This was then foam lines with the laminated inner carbon fibre skin:
I have to say - it's much less messy and stressful building it on a computer than in real life as resin is setting!
It's also worth noting that there's no special skills here. I studied engineering at college, but that was 30 years ago and I ended up working in very different fields ever since so whilst I have a practical side to me, all the technical stuff has been learned on the internet through resources like this forum, youtube, etc. Anyone who is able to spend a bit of time learning could do this stuff.
I thought it might be interesting to see the CAD "build" in parallel with the real thing so a bit of CAD catch up.
First the Pro-Lam frame that the panels will fit into, this is just so you get the concept - I build it from the base up rather than creating this completely up front:
The real build started with the floor parts of this frame built onto the aluminium "subframe" which incorporates the forklift pockets and container lock castings:
This was then foam lines with the laminated inner carbon fibre skin:
I have to say - it's much less messy and stressful building it on a computer than in real life as resin is setting!
Next up was the roof. First thing was to assemble the frame - this one with reinforcing braces for the windows and solar:
This frame will then have foam glued into each aperture (leaving voids for roof windows) and skinned inside and out with carbon fibre. I don't have photos of the frame in construction but you can see it in the next photo when glued together. This photo shows the approach I started using for the foam panels in the roof. I initially thought I would wrap each foam panel in carbon before gluing it into the frame. Here you can see the first panel vacuum bagged to create a carbon/foam/carbon sandwich sitting on top of the frame (together with helpful Godson once again!):
This worked pretty well, but I realised when I then fitted it into the frame, that pre-making all these panels before laminating into the frame was going to be inefficient and the benefit over just gluing the foam directly into the frame and laminating the whole thing as a single roof panel would be quicker and sufficiently strong to mean I could save a load of vacuum processing of individual panels. As a result we then glued in the remaining foam:
You will notice that the foam only half fills the voids. I wanted 60mm foam, but couldn't source it without a ridiculous delay, so decided to use twin 30mm panels with a 200g/m2 carbon layer inbetween to help bond the two together. This led to a sandwich of (from inside to outside) 400g/m2 carbon, 30mm Airex C70/55, 200g/m2 carbon, 30mm Airex, 600g/m2 carbon. You can see the layup and the bagged component:
I was really pleased by how this turned out - we got great vacuum despite the large size of the roof and an acceptable surface finish given that this isn't going to be a panel that's highly visible. However, when we had done these we finalised the call that we would buy in the wall panels rather than building them ourselves. I realised that I wasn't going to be able to get a fantastic surface finish that we would want on the walls (both inside and outside) on panels of this size and for the price of buying in panels from a supplier in Manchester who builds refrigerated truck bodies it just wasn't worth me trying. We looked to source panels from the European expedition truck folks but they weren't interested in supplying panels to self builders, which led us into the truck body builder space - in the end I think we got an equivalent product and probably without a price premium for "Expo" kit.
This frame will then have foam glued into each aperture (leaving voids for roof windows) and skinned inside and out with carbon fibre. I don't have photos of the frame in construction but you can see it in the next photo when glued together. This photo shows the approach I started using for the foam panels in the roof. I initially thought I would wrap each foam panel in carbon before gluing it into the frame. Here you can see the first panel vacuum bagged to create a carbon/foam/carbon sandwich sitting on top of the frame (together with helpful Godson once again!):
This worked pretty well, but I realised when I then fitted it into the frame, that pre-making all these panels before laminating into the frame was going to be inefficient and the benefit over just gluing the foam directly into the frame and laminating the whole thing as a single roof panel would be quicker and sufficiently strong to mean I could save a load of vacuum processing of individual panels. As a result we then glued in the remaining foam:
You will notice that the foam only half fills the voids. I wanted 60mm foam, but couldn't source it without a ridiculous delay, so decided to use twin 30mm panels with a 200g/m2 carbon layer inbetween to help bond the two together. This led to a sandwich of (from inside to outside) 400g/m2 carbon, 30mm Airex C70/55, 200g/m2 carbon, 30mm Airex, 600g/m2 carbon. You can see the layup and the bagged component:
I was really pleased by how this turned out - we got great vacuum despite the large size of the roof and an acceptable surface finish given that this isn't going to be a panel that's highly visible. However, when we had done these we finalised the call that we would buy in the wall panels rather than building them ourselves. I realised that I wasn't going to be able to get a fantastic surface finish that we would want on the walls (both inside and outside) on panels of this size and for the price of buying in panels from a supplier in Manchester who builds refrigerated truck bodies it just wasn't worth me trying. We looked to source panels from the European expedition truck folks but they weren't interested in supplying panels to self builders, which led us into the truck body builder space - in the end I think we got an equivalent product and probably without a price premium for "Expo" kit.
Sitec
Adventurer
Looks brilliant, but I guess quite time consuming. Being a glued composite, it'll be hugely strong. I guess I've gone with the metal frame, alli skin and insulation batts as It's stuff I can just potter on with on my own. Doing what you are doing there'd be a fair bot of forward planning and prep but then once done a large section has been completed. It'' be good seeing that body evolve!
Very time consuming, it's true, but I'm not in a hurry. It's partly been slow because it's a bit scary doing the laminating. Get it wrong and you can throw away £££s of materials. As a result I kept putting off doing the big jobs until I could avoid them no longer!
I opted for the frame approach because it would make the box assembly easier - it's almost impossible for it not to end up square and true when all the panels come together.
I opted for the frame approach because it would make the box assembly easier - it's almost impossible for it not to end up square and true when all the panels come together.
Sitec
Adventurer
I was wondering that too..
Lined with foam internally. The metal profile is 50mm deep and my panels are 64mm. There's just 20mm of "corner" exposed inside on each edge recessed 14mm back from the panel face so I just fill this corner void with insulation. I cut strips of 10mm thick airex to fit, glue onto the metal (sikaflex 552 used for all joints that are not straight metal/metal). All exposed internal edges (i.e. those not concealed by cupboards etc) will then have a finishing section of right angle composite bonded over mainly for aesthetic reasons. Upshot is absolutely zero thermal bridging anywhere on the box. Out of interest pro-lam do make profiles with insulated sections if you need them, but I didn't with this approach.
I'll take some pics to show as I get a bit further in the thread to illustrate!
By the way Sitec, just reflecting on your skills comment, I looked again at your build thread, hmm, there's real skills. That's some great fabrication work you're doing there.
I'll take some pics to show as I get a bit further in the thread to illustrate!
By the way Sitec, just reflecting on your skills comment, I looked again at your build thread, hmm, there's real skills. That's some great fabrication work you're doing there.
Iain_U1250
Explorer
Great work, love the carbon fibre
Sorry to dampen your spirits, but be careful building out of aluminium, as it will crack from fatigue, unlike steel, it has no fatigue limit, so corrugate roads and vibrations will cause cracks at stress point. Just a matter of when.
I worked out in North West WA, and our welders were constantly re-welding aluminium trays, roof racks, boxes etc. As long as you spread the load out evenly, you should not have a problem, but if there are any stress concentrations, be careful of cracks, as with a composite, you can't weld it easily. So far it looks like you are doing great
That is reason I build mine with a steel frame, rather than aluminium, and at most I would have saved about 150kg
Sorry to dampen your spirits, but be careful building out of aluminium, as it will crack from fatigue, unlike steel, it has no fatigue limit, so corrugate roads and vibrations will cause cracks at stress point. Just a matter of when.
I worked out in North West WA, and our welders were constantly re-welding aluminium trays, roof racks, boxes etc. As long as you spread the load out evenly, you should not have a problem, but if there are any stress concentrations, be careful of cracks, as with a composite, you can't weld it easily. So far it looks like you are doing great
That is reason I build mine with a steel frame, rather than aluminium, and at most I would have saved about 150kg
Good reflection Iain. I'm working on the basis that with an isolated sub-frame on the already well suspended mog, mechanical cycling will be limited. In addition things that hopefully mitigate this are that the main strength of the box actually comes from the composite walls - the frame is glued using very high fatigue resistant glue designed for applications like this. I think this will be much better than welding from a fatigue perspective.
It's the same stuff my lotus is built of and whilst I don't drive it on washboard, they survive many thousands of miles of track use with very high load cycling. I hope it will be ok!
It's the same stuff my lotus is built of and whilst I don't drive it on washboard, they survive many thousands of miles of track use with very high load cycling. I hope it will be ok!