longrider1100 wrote:
These appear to be built on aluminum box frames, is that correct?
Yes , a lot of different frames and suspensions available.been a lot more composite structures added since that article was printed in 2011.
This is a very basic explanation of SOME techniques and materials
ALUMINIUM
Hugh Bailas – Millard RV
“Millard uses a 25x22mm (1in x 0.8in) and 25x25mm (1in x 1in) aluminium channel frame. Millard has used aluminium framing for almost five decades, which speaks for itself when you see the number of very old Millard caravans still going strong.
“We choose to rivet our frame sections together, rather than weld them, as this saves weight and allows the frame to flex as it travels over rough roads.
“Millard has chosen to stay with the aluminium frame because of its three main advantages over timber: it’s substantially lighter; has increased strength, especially at the joints; and eliminates the possibility of rotting wood problems in the frame, which means a longer life and lower maintenance for long-term owners.
“The disadvantage to the manufacturer is that an aluminium frame is much more costly to produce, both in labour and material cost. Our frames are not pop-riveted together. We hollow the sections, allowing the longitudinal and cross members to meet each other and give greater support than the average frame. We also place grommets within the frame to run the electrical wiring through safely.
“We place full aluminium framework around the fridge vents and windows and then insert timber into the aluminium to give added strength to the frame when these are screwed into place.
“In addition, the way we fix our cladding to the aluminium frame, with polystyrene foam underneath, gives added strength to the construction.”
Glen Gall – Kedron Caravans
“We use aluminium for our three models, with two different wall widths. The Cross Country is built for a mid-size 4WD with standard width walls, while the All Terrain Vehicle and TopEnder models are dedicated to remote travel and feature increased wall framing for added strength.
“All frames are interlocked and secured with a solid high tensile pin-punch. This allows for the slightest amount of movement (to minimise any chance of the frame cracking), and makes for a stronger structure.
“The frame sits on the chassis cradled into a Z-channel outer section, secured by ‘Huck’ bolts through galvanised plates, frame and chassis, both downwards and sideways.
“The aluminium roof is welded together and dropped in to become the base structure to build from, rather than other methods where furniture is the base.
“Aluminium frames are more expensive in terms of production and equipment, but they provide extra strength and have the added advantage of avoiding any moisture damage.”
TIMBER
Scott French – Designer Vans
“Designer Vans has been building vans for more than five years and provide a mixture of timber frame for their offroad units and composite walls for the touring vans. All our timber frames are glued and screwed, not stapled. We use timber because it provides extra strength and better fixing. We bolt the overhead furniture in place and screw the base furniture to the timber frame and floor. The way the walls are fixed to the chassis is also important and that’s why our walls are bolted not screwed, to give extra support.
“All our roof frames have a unique aluminium-section system designed to provide a stronger unit. Cladding is also important in providing strength to the frame, and we add a one-piece fibreglass roof sheet stretching from front to back. This method eliminates joins and significantly reduces the risk of leaks.”
COMPOSITE/STEEL
Mark Andrews – Caria Caravan Sales (Steel)
“We use our own 20mm box section welded steel frame with cross members and longitudinal, which combines with wood, polystyrene insulation, fibreglass construction and a handmade heavy-duty chassis to make a very tough caravan shell. We use this because our caravans are capable of carrying up to 900kg.”
Andrew Ryan – Jayco Australia (Composite)
“Jayco’s frame consists of five major ingredients which, when vacuum bonded, allow increased strength and detail when compared to conventional aluminium clad caravans: 19x19mm tubular aluminium outer frame; and four vacuum-bonded layers comprising fibreglass, ply (internal and external) and polystyrene foam.
“We also include galvanised plating to support the furniture fittings and an outer fibreglass skin that is 150 per cent thicker than standard aluminium with high gloss gel-coat finish.”
