Angle or RHS for drawbar

Eaglemax · Guru

Angle or RHS for drawbar

Bagmaker · Senior Member

Angle is for artistic wrought iron, Tony, use the RHS.
I would be tempted to save weight on the thickness if possible, extending the vertical measure whenever you can

blaze · Guru

On the last box trailer I built I used 75 x 50 x3.2 for the A frame. the rest of the the trailer frame is 75 x 50 x 2.5 with the upper section made of 40x 40 x2.5. I suppose what I am suggesting is go heavier on the draw bar and lighter with good design elsewhere
cheers
blaze

-- Edited by blaze on Saturday 4th of August 2018 06:00:33 PM

Peter_n_Margaret · Guru

If you want more strength without a significant weight penalty, go 100H x 25W.
Using 35H x 75W is the wrong way around. The greater forces are vertical. The horizontal forces are lower and constrained by the "A".

Cheers,
Peter

swamp · Senior Member

HI
How long is the draw bar ,over 1200mm or above ,??
Are u going to put storage on the draw bar ??
Are u going off road ??

If answer yes to any of above go with 75 x 50 x 4 mm RHS at minimum. Ideally 100x 50 mm x4mm RHS

The height of the frame is critical 75 vs 100 mm . As long as the thickness is at least 4mm
A single axle see saws a lot or at least tries to ,another reason to go big.
Run the first draw bar attachment point to the front spring hangers .

As u would expect 99% trailers are designed with tow ball weight in mind
Longer draw bars tow better

erad · Guru

The RHS (Rectangular Hollow Section) section 65 x 35 x 2.5 has a Section Modulus of 98900 mm cubed. The equivalent figures for the 75 x 50 x 5 unequal angle iron is 6270 mm cubed. What this means is that the RHS is way stronger than the angle iron. It is also lighter, and provides an easy conduit to carry cabling inside the tubing. It is by far the better product to use.

PeterD · Guru

Have you consulted VSB1. You are responsible for the safety (design) of your trailer. You need to calculate, or get someone to calculate the strength of the drawbar according to Section 16.1 of VSB1.

16.1 Drawbars
Drawbars must be securely attached to a substantial portion of the trailer.
Drawbars must withstand the following forces applied at the centre of the intended coupling without
detachment or any distortion or failure, which will affect the safe drawing of the towed trailer:
Longitudinal tension and compression (N) 1.5 x 9.81 x ATM (kg)
Transverse thrust (N) 0.5 x 9.81 x ATM (kg)
Vertical tension and compression for rigid drawbar trailer (N) 0.5 x 9.81 x ATM (kg)
(For further information, refer to ADR 62/01 clause 14)

swamp · Senior Member

HI
For a basic camper trailer I dought most makes go to the trouble .
If u have built a colllection of trailers and driven some , repaired more , the design becomes easy .
65x 35 RHS /angle belongs on a light duty trailer .

The only reason u use angle is cost cutting and weight reduction .

Eaglemax · Guru

Thankyou everyone, all relevant replies.

Atm will be 850kg only, towball weight 70-85kg. Drawbar length 1000mm. On road only. 2xlpg cylinders on DBar and swinging jockey wheel.

Yes weight saving is critical to the project as was first van I made (avatar). But drawbar back to the hangers is good idea and rhs is the go. Weight saving was the motivation but I'll make it up elsewhere. Eg polystyrene internal walls with epoxy paint. Balsa or multipanel framed kitchen cupboards etc

I take the point also 75x25 better than 65x35 and yes 65 was to be the vertical. I havent seen 75x25 listed anywhere on www.

Regards Tony.

-- Edited by Eaglemax on Sunday 5th of August 2018 10:42:21 AM

erad · Guru

Whatever steel you use, make it galvanised. Reason is that any black steel has to be painted and any paint will be sandblasted away. I had a painted drawbar on our camper years ago, and I tried everything to keep the paint on it. We had sales reps coming to sell paint to pint turbine spiral casings and they all offered samples. Finally, I got one paint which seemed to work. It was an epoxy paint and was doing well, until the RTA complained about a duplicate chassis number on my van (the other was a White Truck - nothing like a caravan), but I had to change the number... This involved welding additional letters onto the chassis number, and away went the magic paint in the process. My current caravan has about 140000 km on it, mainly on sealed roads, but the galvanising on the chassis is still in perfect order.

swamp · Senior Member

HI
Eagle max 75mm x 50mm RHS Dura gal .

Donot make the draw bar to short u will regret it . Draw bar mounted gas cylinder /storage box etc etc . Remember to make the draw bar long enough so the trailer can go close to jack knifing b4 contacting the rear of car . Every one makes mistakes backing up occasionally.

Footprints · Senior Member

RHS every time. RHS resists bending under load, angle does not. Tube either square, rectangle or round is far stronger than variations of "flat steel" and weight will be lighter. A classic example is the shape of the fuselage of an aeroplane or hull of a submarine.

skins · Senior Member

Eaglemax wrote:
Doing some research atm on drawbars.
Going to use an "A" frame type in new caravan to be built.
Van wont be over 850kg ATM 650kg tare
towball weight will be around 70kg
Angle I'm looking at is-
75 X 50 X 5 BLACK ANGLE AS3679/300
W: 75mm
H: 50mm
T: 5mm
Kg/mt: 4.4
or RHS
65 X 35 X 2.5 RHS AS1163 C350 LO
H: 35mm
W: 65mm
WT: 2.5mm
Kg/mt: 3.6
Angle used to be used extensively on caravans. your thoughts?
Tony

Tony, I'm an ex-boilermaker - go with the RHS, maybe even make the draw bar a bit longer to make it easier for reversing & run the wires up inside the RHS. Maybe even consider the next size down in wall thickness also. But may depend on how good a welder you are. Just a thought.

Eaglemax · Guru

Thank Skins. Yes I'm aware that woth the little weight of the planned van 2.0mm thick rhs 65x35 would be strong enough. I take the AS that PeterD posted swriously but easier to compare drawbar manufacturers of yeardrops of similar ATM or dmall caravans...even 10x5 trailers using the same size.

However, 2.5mm thick is far easier for me to arc weld nicely along the corners lengthwise of the drawbar to joists and runners. 2mm I'm likely to make holes lol. Ive got a mig but dont like it.

2.5mm will give me more confidence in the drawbar also.

Thanks footprints.

Swamp- yep...1200 maybe 1300mm drawbar. Medium toolbox for wet items like hose, drain hose, mullet, bait, lol not heavy stuff. Good idea.

Erad - definately going gal on all the frame.

Blaze- I hear you.

swamp · Senior Member

HI
Eagle max
The longer the draw bar the more flexing
Has to be bigger in dimensions ,you`ve got that covered .
Thickness of steel 3mm light duty up to 4mm for your application . 2.5mm is to light for a slightly longer draw bar on a camper . 2.5mm is best used for small to medium box trailers only .

Eaglemax · Guru

Thanks again Swamp

skins · Senior Member

Galvanised steel - is an absolute b*st*rd to weld eaglemax, even for experienced boilermakers. I would avoid it like the plague. If you do use gal. use a grinder where your going to weld to take off some of the surface gal. You will run a much better weld that way that sticks to both surfaces. Naturally paint it with gal paint when your finished.

You will find that your first run will look like "bird ****" (as we called it in the trade). If you put a lot more welds down to cover the first weld cause it looks crap and hasn't stuck to anything, you run the big risk of the area next the welds cracking owing to too much heat going into the welded area, if you subject the area to strain etc.

In other words I would not use galvanised steel and I will now get a lot of replies saying well, I welded a trailer & used gal and it was OK - never any problems).

By using either Mig or Tig you wont put as much heat into the job, but I know you stated that you don't like Mig & that's fine.

The professional trailer frames are all welded together and then hot dipped in gal.

Also with your "A frame" try and take it back as far as possible to the axle. This will help with load carrying and overall strength of the trailer and A frame itself and try to just tack weld as much as you can and put it all together and then go back & weld. You will have less chance of the frame warping/twisting etc owing to the heat.

The black steel frame will still outlast you if you paint it properly & look after it. By black steel I mean the stuff that comes with the 'blue' protective coat.

Grandad5 · Senior Member

skins wrote:
Also with your "A frame" try and take it back as far as possible to the axle. This will help with load carrying and overall strength of the trailer and A frame itself

I concur.

and try to just tack weld as much as you can and put it all together and then go back & weld. You will have less chance of the frame warping/twisting etc owing to the heat.

Or, maybe consider doing what I did. I tacked the chassis together with my stick welder and then towed the whole thing to a machine shop and paid the professional MIG welder to perform his magic.

(As a welder, I make a pretty good Chippy.)

Jim

blaze · Guru

Eaglemax has already built a small van that's been around aust so must have reasonable skils
cheers
blaze

Eaglemax · Guru

Thanks guys. I did have reservations going gal when I built my current caravan, the difficulty welding the frame and drawbar hence went the blue steel with two coats of enamel paint.

My welding method was to tack weld the joists to the runners and turn the chassis upside down and weld the joists properly along the length of the runners on the corners.

I'm self taught but competent arc welder...I get those nice pools just right. But have to admit gal is a different story, so will go non gal come to think of it.

Pictured is the frame of my first van. It was made from 13mm square tube. With strengthening sections. No wonder it came out 450kg tare....but strong. The only problem with 13mm is tech screws wont penetrate as the screws are too long. One must screw them to create a thread then use one with the drill end piece cut off. Time consuming but going 15mm square steel tube adds to the weight significantly.

I'm itching to build this but relocating to SW Victoria in a home to be built so you can imagine the waiting time. Have to sell here in Strathbogie first.

Drawbar back to the spring hangers I think is essential. 3mm 65x35 would be more than strong enough for a 650kg tare van. My experience in the model airplane hobby has taught me weight saving ideas. Epoxy paint on polystyrene walls, lightweight floor ply, multipanel, plaspanel, even balsa one inch square rods can be used as uprights under beds (surprisingly strong) and things like a pull out pantry by innovations that weighs just 3kg are just a few I'll use. The current van had only one weak point- that drawbar. Once the pro's at WWW welding in Cloncurry got to work on it the thing would never break!.

-- Edited by Eaglemax on Tuesday 7th of August 2018 12:45:55 PM

Peter_n_Margaret · Guru

I know you are convinced that your construction method is the best (aren't we all?), but I suggest that a frameless glass/urethane/glass construction would be stronger and lighter.
The A frame could also disappear by bringing the body all the way forward as a tapered structural box. The suspension and hitch being mounted to aluminium supports glued directly to the underbody.
Too radical for some....?
This motorhome was built by a friend. He made it all, including the sandwich panel.
There is no steel in the camper body. The camper body has glass reinforced pads that are glued to rubber pads that are attached directly to the vehicle chassis.
There are no bolts or screws anywhere.

10-01-30 GM 002E.jpg

There is always more than one way to skin a cat.....

BTW, for the Landy fans, the vehicle is actually a LWB Defender with a body change.

Cheers,

Peter

Eaglemax · Guru

Totally out of my comfort zone Peter. Based on the weight of my 11ft van and some more weight savings, I know the the larger van, now plamned to be 14ft long will be under 750kg tare.

I am not confident in such uncharyered territory. But I appreciate the idea.

Peter_n_Margaret · Guru

Eaglemax wrote:
Totally out of my comfort zone Peter. Based on the weight of my 11ft van and some more weight savings, I know the the larger van, now plamned to be 14ft long will be under 750kg tare.

I am not confident in such uncharyered territory. But I appreciate the idea.

It is certainly not "unchartered" by others, nor is it a new technique for RVs.

I used this material 13 years ago. My first attempt at building an RV. One of the best decisions I ever made. The skills required are lower than conventional construction.

Cheers,

Peter

swamp · Senior Member

Hi
Short draw bar 65 x 35
Longer draw bar 75x 50 mm . Consider this heavy duty for a box trailer =similar to what u are building

Dura gal saves money on paint but takes longer to prep for welding .
Painting a trailer really requires frame to be blasted first to etch the steel to have the best adhesion .
Cost of blast/paint when new and when selling is $$

Cost of owner ship duragal wins hands down . I have built many a industrial plant trailer .

Eaglemax · Guru

Hi Peter

Budget is tight. The van is to resemble a retro van so wont have bodywork on the A frame. It will resemble a streamlined Franklin with retro parts like portholes. Budget is tight eg $12,000 total cost. Chassis, windows door total will cost around $6000 alone. Doesn't leave much left. In my experience with my little van frame, external stucco cladding ($2500)and frame ($1300) and poly insulation ($150)makes it really economical. I will investigate it though and observe the building techniques. Apart from the assumed cost I don't feel confident.

Swamp- what about 75x25x3? I noticed it was for sale, the same weight same weight as 65x35x3. Would it be preferable than 65x35x3 as it has more vertical. going to 75x50x3mm would increase the drawbar weight 8.4kg .

65x35x3 w/kg 4.2kg

75x25x3 w/kg 4.2

75x50x3 w/kg 5.4

Drawbar back to spring hanger is 3.5m (x2) is 7 metres x 1.2kg is 8.4kg total weight of drawbar would then be 20kg. On a caravan with tare of only 650kg I can justify this weight for such a critical part of the build and use 65x35x2.5 for the runners. what do you think?
Tony

-- Edited by Eaglemax on Wednesday 8th of August 2018 12:36:22 PM

swamp · Senior Member

HI
There is always some parts that should not be short changed and the Draw bar is one of those . To resist flexing and eventual cracking 75 x 50 x 3 mm . As I said , its not a box trailer . The weight is never less than specified .
The type of weight =sizable physical large places strain on bar also .
Constant minimum weight never runs empty box trailer weight
Weight from a van is unevenly spread compared to a trailer with a load of sand
single axle see saw motion occurs
extended draw bar
storage / load ontop of draw bar

75 x 50 x 3 is not a big draw bar
Fatigue on a draw bar cannot be under estimated

Eaglemax · Guru

Thanks mate tony

iana · Guru

Just remember Eaglemax, a chain is as strong as its weakest link. If you have weak joins, under cut or dry welds, then there is your weak link. There is one caravan company in Australia using "C" section with lightening holes, this is very strong and light, but you would need the manufacturing facilities and engineering to use it.

Good luck with the project. Ian

Eaglemax · Guru

Thanks Ian.

After much thought I've gone away from having a fully curved front at the bottom of the boot. As the roof comes down past the boot lid a 4ft centre section will go directly down to the drawbar. The outer 18" on each side of the van will still curve under for design reasons. This means a bigger centre boot area for the diesel heater and wet section for hoses etc.

This means that from the front of the van to the tow hitch will be 1100mm. With a 75x50x3mm drawbar this should be ample strong. My tare limit is 650kg or hopefully less. This I believe will be easily achievable based on my lightweight current van which since building it, I've noticed many areas I could have made it even lighter than the 450 tare it has and not sacrifice strength.

Gotta sell our home first, get another built and carport, sheds etc. So planning is well advanced.
Tony

rodrocket · Veteran Member

Just thought I would drop my $0.02 of advice in here

Do Not weld across the top of the A-Frame where it meets to the first cross beam of your van body as this creates a weak spot.

You have been given great advise about cross sectional area of steel members however weight is another important factor to consider, I will try to find the direct link later and post it up, there is a great steel formula from One Steel, it shows you all the weights per meter along with the torsional strengths on each axis, I used this in the construction of my first toy hauler and was able to reduce weight without compromising on torsional strength of the members.

regards
Rod