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Steel or aluminium?
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Ray White



Joined: 02 Dec 2014
Posts: 6286
Location: Derby

PostPosted: Fri May 22, 2020 10:51 pm    Post subject: Steel or aluminium? Reply with quote

I am raising this question because I seem to be getting differing views as to whether it is better to panel a car in steel or aluminium.

My new MG TC body tub is due to be panelled in steel by a blacksmith with a great deal of experience. The frame builder says it would be better than aluminium - despite the extra weight. However, I imagine (but don't know for sure), that a steel panelled frame would be stronger than an aluminium one which presumably for an open car is a bonus.?

Does steel impart strength to a timber frame in a way that perhaps an aluminium one might not? I would appreciate an informed opinion on that question.

On the other hand an aluminium panelled car would benefit from being lighter - but with steel wings and other panels would it make that much difference?

What about the advantages of a weightier car in helping with traction and perhaps a general feeling of solidity?.
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lowdrag



Joined: 10 Apr 2009
Posts: 1585
Location: Le Mans

PostPosted: Sat May 23, 2020 1:32 am    Post subject: Reply with quote

I am not qualified to go into torsional rigidity and so on, but Jaguar produced their first aluminium-shelled modern car in 2006 - the XK. And since you have a chassis it, at least in my head, must be the same as the Jaguar C, D XKSS, all of which had steel chassis and alloy bodies and later the Lightweight E-types which were monocoque and all alloy. I built the 1952 C-type which had an all-alloy body to clothe the steel chassis. So, until someone comes along who really can give you a detailed answer, I would have gone with alloy.
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Keith D



Joined: 16 Oct 2008
Posts: 1127
Location: Upper Swan, Western Australia

PostPosted: Sat May 23, 2020 3:02 am    Post subject: Reply with quote

This is not a technical answer, but I would go for steel simply because of the difficulties of repairs to damaged alumimium panels. I would think that the strength of the bodywork would be in the wooden frame, not the panel that is nailed onto it.

Keith
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ukdave2002



Joined: 23 Nov 2007
Posts: 4100
Location: South Cheshire

PostPosted: Sat May 23, 2020 8:01 am    Post subject: Reply with quote

Hi Ray

The main advantage of aluminium is weight (about 1/3rd the weight of steel) and better corrosion resistance.
Looking at an MG TC tub, I reckon it would save about 20kg in weight using aluminium; about 2% of the cars overall weight.
The disadvantages of aluminium are; about 40% less shear strength, so worth having a think about any part of the tub where this may be important ; clearly the ash frame will provide much of the strength here, aluminium will damage more easily than steel and as Keith points out more difficult to repair.
In terms of making the tub; aluminium is more easy to form than steel, but trickier to join (panels are often made in sections and butt welded) if your body-man is used to working in aluminium this shouldn't present a problem, however the aluminium tub will be more expensive.

In summary if you were building a light weight special, aluminium would be my first choice along with the other body components, but given the minimal overall weight saving in this example I think I'd stick with steel as it would have been originally. I have assumed it was steel originally?

Dave
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Ray White



Joined: 02 Dec 2014
Posts: 6286
Location: Derby

PostPosted: Sat May 23, 2020 11:56 am    Post subject: Reply with quote

A wonderful response. Thank you everyone.

I have had a chat with Andrew Denton who is the guy building my body frame and he can't remember anyone having a conventional TC panelled in aluminium. That is not to say there are not some such cars about - and no doubt their owners will extol their weight saving virtues - but I have my own views on that matter. With an up rated engine and supercharger I don't think the power to weight ratio will be an issue and I would have thought that there are advantages in terms of traction and tyre adhesion especially under braking with having a bit of weight holding the car down.

The MG Midget is just that. A small car. A Jaguar is will never be... but thanks Lowdrag for your contribution.

I have also been told that the cost would increase considerably.

The good news is that progress is being made with my body tub. I was surprised to learn that there are just four 3/4" x 3/8" BSF bolts holding it to the chassis.! The reason for this is that the tub has peculiar shaped angle iron sections each side and it is these which bolt to the chassis outriggers.

At some point my car had it's original body violently ripped off and the mounting points have been damaged. I have spent the morning putting these right in readiness to receive the new body.

As I have said before this is no cherished classic so originality is less of an issue. Having said that, I am doing nothing that would prevent a future owner from pursuing a matching numbers, concours mission if they wished; it will just not be me.


I forgot, of course, that the tub will come in primer and I will need to paint it first so I will be crossing my fingers that I will be able to get it through the doorway into my painting shed. Confused
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