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-   -   Welding Required (http://www.haynes.co.uk/forums/showthread.php?t=1991)

Tatey 21st May 2009 06:59 PM

Welding Required
What are the thicknesses of the steel required to be welded (im still waiting for WH Smith to deliver my build book)?

I know the chassis tubes are 1.6mm, can this thickness be changed? I know it will increase the weight and cost slightly, but im sure it would be cheaper than spending 200+ on a mig welder, would there be anything wrong with using 2.5mm box?

Bonzo 21st May 2009 07:22 PM

25 X 25 RHS box section
I would not even think of using 25X25 RHS box section to build a spaceframe chassis.

The weight gain would be unaceptable :eek:

Although I am not a race engineer, I can also forsee structural reasons as to why this material is not suitable.

If you really do not want to buy a MIG welder, why not tack your chassis with the stick welder, then hire or try and borrow a MIG to fully weld the chassis.
This will probably work out cheaper than the extra cost of RHS box. ;)

Tatey 21st May 2009 07:32 PM

I've done a few calculations based on using 1.6mm thick box and 2.5mm box. Based on using 36m of box and 1.6mm thick it comes to 42.4kg and using 2.5mm box it comes to 63.67. This is quite a large % increase in mass but in the grand scheme of things it isnt much since someone of the larger build than me could easily add double that mass.

There isnt that much of a price change. 1.6mm box is 14 per 6 m, i havent got a price for 2.5mm 25x25 but 3mm 30x30 is 20 for 6m so im guessing 2.5 25x25 would be about 17-18 so thats 24 more maximum for the steel used.

HandyAndy 21st May 2009 07:54 PM

i understand in a way what you are saying but have to ask WHY? the design of the chassis has had structural tests etc & has no need for the extra thickness steel that you suggest :confused:
i,m not knocking your thoughts just not sure why change a working formula.

as for the welding required... the way i see it its part of the ethos of the concept "build your own sports car".

i couldn,t weld until i started a course at local technical college in january this year, my welding might not ( i know its not ) be to qualified cert standard but feel confident enough to build my chassis & drive it once completed, & if you build your own chassis you will "know every inch " of it which when its on the road is something to be very proud of.
each & everyone that is building a Roadster has put there own little "touches" into it whether to everyones liking or not, its your car that you built.:cool:


Tatey 21st May 2009 07:59 PM

Hi Andy,

The reason i ask is because i already own an arc welder and loads of 2.5mm rods and im reasonable at welding with them, but its difficult to weld less than 2mm thick, which im guessing is why everyone recommends buying a mig welder. Im trying to cut down costs and 1 of the major expeditures was on a mig welder, which would be 200+, i've tried to find a cheap one but to no avail.

So i thought why not get rid of it and just increase the thickness of the steel box meaning i can just weld it with my trusty arc welder since there dont seem to be too many downsides that i can see, 1 being it adds an extra 20kg to the chassis and the other being it will cost another 30 for the steel.

Im just wondering if there are actually any major reasons im missing as to why 1.6mm thick tube was chosen, which would mean that 2.5mm thick tube would not be appropriate.

Bonzo 21st May 2009 08:05 PM

ERW square tube, 1.6mm wall thickness, is the material required for the chassis.

By all means use RHS box to build you chassis. :rolleyes:

Sorry to put it bluntly but if you are willing to make bad choices in the name of cost at this early & critical stage, where will it end up :eek:

Tatey 21st May 2009 08:10 PM

Ohh sorry i didnt realise it used ERW square tube, i've just been going on things i've read on the forum as i havent got my build manual yet. I'll give my local steel merchant a ring tomorrow and see what prices are like.

I have to say im not too much in the know about different kinds of mild steels, whats the difference between ERW and RHS?

HandyAndy 21st May 2009 08:11 PM

my apologies i may have misunderstood your thoughts/questions.
i,m not the person to answer why 1.6 steel was chosen for the design ( maybe Chris will confirm the reason ).
i,ll be totally honest & say i had the same thoughts as you whereas i had the offer of free use of an arc welder ( my brothers ) before i started my build & asked the very same question... can i use an arc instead of a mig, i decided once i,d done more research into the building of the chassis that mig was the way to go,
i bought my mig off the "mig welding forum" second hand for 50, its a 150amp & came with 2 large pub style gas bottles so the bargains do come up now & again, guess i was lucky as it works perfectly.
i,m trying to build to a strict budget, ask Ash G :D ;) & as close to the book instructions that my ability will allow.
i think if you used the heavier gauge steel it may cause more probs than it alleviates at first.
best wishes for your build by the way.:)

fabbyglass 21st May 2009 08:46 PM

Don't use 2.5mm wall, not sure you can get the precision tube in that guage anyway. If not then it will be that black rubbish with only one square edge if you are lucky.
Why nost ask a forum member to make you one

Land Locked 21st May 2009 08:46 PM


Originally Posted by Tatey (Post 14863)
I have to say im not too much in the know about different kinds of mild steels, whats the difference between ERW and RHS?

I second this question, I am now concerned about using the wrong material.:( :confused:

I hate TLA's(Three Letter Acronym's)!:mad:

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