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Welding strengthening sections


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#1 Pavel

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Posted 20 April 2004 - 05:53 PM

Okay, welding of the clubman's strenghtening bracing will commence in a week or two, and I need to figure out what I have to do and how.

Roof will be cut off, and doors will be removed.

I want to put long sections of box-section steel running just above the bottom of the doors, and another section running the entire length of the car front to back along the sills.

There will then be 2 box sections running the car from left to right, one directly behind the front seats, and the other along the seam of the rear bulkhead/parcel shelf. They will join the top of the car (bottom of where rear windows would be).

Then I want to weld in round door bars about half way up the door opening, these will be cosmetical more than anything but i still want them to hold.


Finally, any ideas on how I can make simple roll hoops? I'm thinking of just making the following sort of shape, with one end of it being mounted on the parcel shelf/bulkhead piece of box section that i mentioned above, and the other end on the box section behind the front seats (again, mentioned above).


How should I weld this in, I'll be using a MIG welder?

#2 Pavel

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Posted 20 April 2004 - 05:57 PM

OOps, forgot picture (excuse messy pen drawing :))

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#3 siggy

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Posted 20 April 2004 - 09:08 PM

Remember to do all the stenghtening before you remove the roof.

Siggy

#4 Pavel

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Posted 21 April 2004 - 11:56 AM

Yep I'm quite aware of that :)

What i wanted to know are there any techniques I need to be aware of, or places that I should(n't) weld the strengthening to? etc.

#5 Bluemini

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Posted 21 April 2004 - 11:59 AM

Mighty Mini may be able to help, his parents have a cabrio conversion.

#6 CharlieBrown

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Posted 21 April 2004 - 12:11 PM

Siggy or anyone,

Am I right in thinking you have to do the strengthening befor you remove the roof so that the bodywork dosn't move?

#7 Pavel

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Posted 21 April 2004 - 12:14 PM

Yup, as said by siggy above :)

In fact I'm pretty sure if you chop the roof off and just leave it (dont kneel down in the car, no leaning, no driving etc.) nothing will happen to it, especially if doors are closed. But that would be taking a big risk...

#8 David_J

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Posted 21 April 2004 - 01:53 PM

Well, Just to add my twopen’th in…..

First the disclaimer- I haven’t actually carried out a conversion like you propose but I have thought about the various ways of strengthening bodies and chassis’ and I have looked at quite a few kit-car chassis’ etc.. So these are some of my thoughts.

1. If you’re welding in box sections as you propose then you need to make sure that the thickness of the steel matches the existing steel as closely as possible to make welding easier.

2. You need to think about the load-path through the body. The mini doesn’t have a chassis so loads from the wheels are carried from the subframe fixing points through the sheet metal of the monocoque body to support you in your seat. By removing the roof you will remove a major load path for these forces so you need to add more metal somewhere to balance out the loss. Simply welding in a new box section along the sill line will work if it is beefy enough but you must continue it to the areas at which the loads are being transmitted into the body. Otherwise the body will be fine in the middle where you welded in new steel but will be weak between the ends of these and where the subframe is mounted. Any new metal that you put in should really provide a continuous path between the existing load points (front and rear subframe mountings points).

3. Following on from above, at the points where the loads will be transferred from one member into another you need to make sure that you don’t concentrate the load too much into one small spot. If you do then you need to include extra spreading plates to spread the load. – A good example would be the feet of a roll-over bar, if these are just welded straight on to the millimetre thin floor panel then if the car should roll over then the feet of the bar would probably just punch through the floor! Not good.

4. I would think that you need to pay close attention to the front and rear ends of your new sill box sections to make sure that you make a really good structural joint that spreads the load and transfers it to the front and rear subframes. A ‘good structural joint’ in the case of box sections would mean welding the entire perimeter of the box section end to the wheel arches/body etc with extra strengthening plates to spread the loads out. Just having lots of weld in one small area is likely to punch through or rip out in a thin sheet.

5. For torsion of the chassis the box sections will help too and putting in more box sections across the car will strengthen it even more.

Why do you want to make the bars across the doors cosmetic only? With nice big spreader plates front and back they would take a lot of the load and make life easier for the sills and floor!

I admire you for actually going for it! Nice one. If you’re worried about the body flexing when you initially take the roof off but before you weld in new box sections then you could make up temporary braces to go between the door hinge brackets on the A-post and the door locks on the B-posts??

Hope that helps!
Must get back to work!

#9 Pavel

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Posted 21 April 2004 - 02:19 PM

Thanks, that helps a lot, its good to have it all summarized! :)

When I do the write up of this project for the site, I'll be sure to include the information from your post above!

Now just to get the car running so I can get it to the garage... :)

#10 Alburglar

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Posted 21 April 2004 - 04:24 PM

Talk to minispeed.co.uk as they have an identical demonstator to what you are proposing to do.
They should be able to tell you exactly what they did.

#11 Alburglar

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Posted 21 April 2004 - 04:26 PM

Or Paul Banham of Banham conversions because surprise surprise... he makes the Banham roadsters.

#12 Pavel

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Posted 21 April 2004 - 04:27 PM

Not very friendly folks from what I recall... I did try contacting them about something else previously!

I think I have enough info now to tackle this..

And, if i screw it up, it cost me about a tenner for the car (after subtracting the value of the alloys, GT clocks, halogens etc. that were taken for Stacy) :)

#13 Alburglar

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Posted 21 April 2004 - 04:32 PM

http://www.minispeed...ibackground.jpg

http://banmoco.co.uk...er/building.htm

I think this price is pretty bloody good aswell

ROADSTER KIT
Comprising: steel reinforcement parts, dual hoops in stainless steel with mountings, three-piece rear panel set with head fairings, tinted laminated-glass windscreen, upper windscreen frame, pair of side windows in toughened glass with safety markings, replacement dashboard to accept standard Rover instruments, assembly manual and video. £995

Hoodframe and hood assembly in black vinyl, including fixings. £345

Or in top quality black mohair £395

#14 Woody

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Posted 21 April 2004 - 05:28 PM

Right , how i would go about this is : put the mini in the garage , jack up and axel stands under the front subframe next to the bottom arm , if the floor is level you should be ok , if not put a straight edge across the wings (at the same hight) and use a spirit level and add small blocks of wood between axel stand and subframe untill level , repeat with the back end only this time use the spirit level on the door step lenthways and across the back on the boot lid mounting panel, if you do this corectly the car should be completely level and as you work you can check your levels and adjust as needed (if you weld too much on one side you can twist the shell )
before removing the roof, suport the front of the front subframe with a scissor jack and wind up the jack untill the doors close smoothly (both sides ) now measure your door appeture and note the measurments somewhere safe , then suport the midle of the floorpan both sides under the seat cross member (blocks of wood will do ).
you can now remove the roof , your welding and fabricating will be so much easier with the roof not in the way.
I would add the box section from the front shocker mounts (remove the wings and refix after)all the way to the top of the rear shocker mount and one between the rear shocks ,weld a box section at the top of the door apeture from the top of the "A" post to the top of the "B" post, cut the door skins off and weld them into the door apetures , if the floor is sound there is no need to streanthen it if you are not having doors .
I would surgest making a roll hoop from an old scaffold tube (a local engineering firm should be able to bend it for you for a couple of quid) and mount it to the floor in the traditional way and weld it to the leanthways streanthener on its way up and then two legs down to the rear shock cross member .
This is now a semi spaceframe shell !
I would remove the screen and fitt an aero screen and wear a helmet to keep my ears warm at night :grin:
Hope this helps , any questions dont be afraid to ask , i may even attempt to do a diagram :grin:

#15 Pavel

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Posted 21 April 2004 - 06:15 PM

Okay that is a good different idea woody, but a few problems with it:

I want to remove doors, want it to be open completely, no skin. Instead of the door I'm gona weld a nice big round tube in place as a door bar.

I never thought of having the box section running from shock to shock. Wouldn't that involve cutting bits out of the car (to get through the bulkheads?). Would it not be easier and have pretty much the same effect to have the box section running from the front wheel arch to the rear wheel arch or bulkhead (closer to the floor, as in my diagram?)

If that will not add enough strength, I'm considering welding a piece of scaffold tube down the middle of the car, from rear bulkhead to front dash rail if necessary, but i DO want the door aperture to be open apart from the door bars...

Also you didn't mention a box section going from right to left, apart from the one between the rear shocks. Surely it would be wise to have one in the middle of the car as that would twist otherwise? (i.e. behind front seats). This would also make mounting the roll hoops considerably easier as I could mount them to that cross member, and the other ends somewhere in the rear (depending on angle that the metal is bent for the hoops).

Basically for this project I'm trying to do what requires SIMPLE welds as far as possible. I rather do 10 simple welds, than 5 hard ones...

Thanks for your help, doc :)




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