Welding strength?

**Grahame Collins** · 12th May 2009, 09:18 PM

Originally Posted by Apples

You should now weld across the draw bar. That is if you are looking at it from the draw bar back. Never weld from left to right across those pieces of box section.

This I have heard from trailer guys and they say it weakens the draw bar or something and I think they mentioned that to get it registered that can void it...

What is the advice then? Weld across the draw bar or not.The two sentences seem to contradict one another.

I'll make it plain and simple.

NO! NO! NO! NO! NO!
Weld only parallel with the length of the trailer bar,never across it, PLEASE!

You have heard right from the trailer guys. For goodness sakes. You don'twant to be be party to advice that caused a runway trailer accident.

Imagine one of these hitting a bubble car head on.This stuff really makes the hairs on the back of my neck stand up

Why? The trailer will be loaded at some point. As it travels along the road the frame will flex ,including the draw bar .A weld across the the draw bar will cause a "hinge point " and the metal of the bar as it flexes up and down , ever so imperceptibly start to crack at the toes of the weld at the weld frame interface. At some stage in our child hood I am sure most of us got a piece of tin and bent it,one way ,then the other.After so many bends to and fro it broke.

Friends ,the situation with the draw bar could be like that. One hopes an observant driver might spot it it in time,but you just don't know?

If the welds(which will be fillet welds) have the slightest bit of undercut you may end up with staring a crack. at some point in the future the draw bar could quite conceivably separate from the rest of the trailer.

Trailers need to be inspected registered and must follow the ADR rules. I am sure any inspector worth his salt will fail a trailer with this defect.

Google the ADR rules and download them and read them.
http://www.infrastructure.gov.au/roa...pdf/vsb_01.pdf

While I can't see it in some many words there are some stress figures quoted and I believe that will be invoked against cross draw bar welding

This sort of activity by people who have not made a decent effort to find out exactly what is required is why we are being certified and licensed to ad nauseum to build or make an ever increasing range of basic stuff. At some point in the future one may well have do a course and pass some sort of certification just to be build a trailer.

Grahame

**montiee** · 12th May 2009, 10:08 PM

Originally Posted by Grahame Collins

This sort of activity by people who have not made a decent effort to find out exactly what is required is why we are being certified and licensed to ad nauseum to build or make an ever increasing range of basic stuff.
Grahame

I don't buy that. What I mean is that I don't think that is the reason behind certification or licensing. It's just industry using it as an excuse to gain exclusivity for their "professionals" to get more work. At the end of the day in any field and regardless of whether you are licensed or not you should get a 3rd party independent in to check your work and sign off. Licenses/certification mean jack #### i've foiund as plenty of license holders still do dodgy stuff and no one is around to know otherwise.

The guy checking the trailer for rego should be knowledgable enough and reject it. If you stuff up that's your problem. Costs you money for inspection and you need to redo the work. Lesson learnt.

Back on topic of the trailer even I have never seen a trailer that has that design on the draw arm. It just looks wrong no matter what. If it was me I'd be heading out to bunnings/servo/wherever a trailer is on display. Take a few pictures and replicate it.

**Apples** · 12th May 2009, 11:15 PM

Whoa, whoops that word "now" is supposed to be "not"

It can and will cause it to be a stress point and crack later on.

And make sure that the axle and wheels are slightly back from the center of the boxed part of the trailer. That is if it is 2000mm long, half way is 1000mm then from that point go back a few inches.

**montiee** · 13th May 2009, 02:39 PM

Just wanted to point out this thread https://www.woodworkforums.com/f184/trailer-build-ii-haul-64389 and it's subsequent forum as a good place for trailer info just incase the original poster wanted to enquire further about trailer specifics.

**motegi** · 14th May 2009, 09:58 PM

Montiee, I've read through Yonnie's trailer build thread many many times over! From what I read of his posts it was to not weld the top of the draw bar at the front (only?)

re: the commenst on the design of my chasis, I dont see a problem with design! it is a sound design...much more sturdy than you run of the mill trailer. When i designed it I've already considerd where the forces lie..ie torsional, lateral forces etc...

I may not be the best at welding but i know what I am doing when it comes to building structures. It is just a matter of considering where the forces lie and counter the forces.

I'd be surprised if a trailer builder said what i have there ( design not weld) is not a sound structure. It may be over engineered with a few too many braces etc but it adds only a few kilo's to the whole thing.

Rather than point out how this is not up to scratch, how about elaborating on where you think it is not sound or where the weak point is? that way anyone reading can also learn? And if you have not even build a trailer please dont tell me how not to build one.

I appreciate those of you (Graham, BobL and Fossil...to name a few) that have been subjective and shared their knowledge through giving advise in their field of expertise and experience...I dont mean to have a whinge but there's nothing more discouraging then people's negativity without elaborating to support their views.

cheers

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