Universal built Lotus 7 Chassis

[ianashdown]

Does anyone have knowledge of the welding method used on the Universal built early Lotus 7 chassis.

 

I know Arch used, and still use, Nickel-Bronze Brazing using a Gas Fluxer, but I read the Universal didn’t.  So what method did they use?

 

I will be replacing a few tubes and making other repairs to my ‘61 S2 soon and would like to be consistent with the original build.

 

Thanks,

 

Ian

SoCal

[CarlB]

I never saw a English race car if the period that wasn't Gas brazed. It is easy to find out. Scrape the paint off a joint and see if you see the bronze. 

[IamScotticus]

The problem you might encounter with MIG/TIG on an area that has other gas welded joints is the the electricity may ruin any gas welds connected to the area.

A trained eye can spot the difference.

[SENC]

"Universal Radiator on the other hand, fusion welded their chassis using an oxy/acetylene set-up with the filler rod the same as, or similar to, the metal to be joined."

This from William Fayer's site, https://www.anglocanadianlotus7.ca/lotus-seven-parts-and-repair-notes/.  I've found his information reliable.

[MV8]

If it happens to be brazed, a fluxer can is not required but they are available. It goes between the acetylene tank and the torch, picking up liquid flux on the way.

[ianashdown]

3 hours ago, SENC said:

"Universal Radiator on the other hand, fusion welded their chassis using an oxy/acetylene set-up with the filler rod the same as, or similar to, the metal to be joined."

This from William Fayer's site, https://www.anglocanadianlotus7.ca/lotus-seven-parts-and-repair-notes/.  I've found his information reliable.

That must be the information I had stuck in my mind somewhere!

 

I’m trying to figure out the best repair method.  Tig absolutely cannot be used where it has previously been brazed, but I think it should be OK if it has been gas fusion welded.  I have a Gasfluxer and the correct rod as used by the English race car builders, and it should work with fusion/gas welding too.

 

I’ll do some tests before going ahead with the chassis repairs.  Should be interesting!

 

Ian

[IamScotticus]

who happens to have a gas fluxer on hand!!!

[IamScotticus]

I will dump my notes on the subject here.   These are all from various sources,  not my material.

 

SifBronze No. 2 
from Weldability Sif U.K.

Arch has been using the gas jet flux braze welding process since the 1950s. 
The Lotus Seven at Anglo Canadian
BRONZE WELDING RODS
By William Fayers  In Uncategorized  March 31, 2021  10 Min read 
BRONZE WELDING RODS SUITABLE FOR REPAIRS TO YOUR LOTUS
submit your comments or input here

Nickel Bronze Brazing Rod.

Contemplating some minor chassis frame repairs to my Lotus Seven Series 3, I decided to investigate the availability of suitable nickel bronze brazing rod to complete the repairs.

In January 2014, I commenced a search of the web for suitable sites regarding Nickel Bronze Welding. I found a forum whereby contributors were asking questions and receiving good advice regarding bronze welding on Formula Ford and other sports racing cars manufactured in the U.K. The name of Calor Bronzecraft No.3 cropped up a few times. One contributor noted that it was now unavailable (2011 post), but that it was the rod of choice for Lotus, Arch Motors, and a number of other U.K. manufacturers of sports road and racing cars until its demise.

I already had a good article on braze welding written by Bill Steagall, who had kindly forwarded a copy to me. It has been published in a couple of Lotus club magazines, describing how to braze weld with nickel bronze rod using a jet fluxer. Bill had also added a postscript advising that Calor Bronzecraft No. 3 was unavailable since writing his original article.

I found the Murex Company (U.K.) web site, and at the time of writing (March 2014) Murex still had the specifications of their “Saffire” Nickel Bronze rod (10% nickel content) displayed on their site. An email reply from the Murex Technical Section advised that Murex had ‘moved on’ from gas welding products, and their line of braze welding rods and associated fluxes were no longer available.

A rod called SifBronze No. 2 (from Weldability Sif U.K.) was highly recommended by a few of the forum contributors. These included an ex-Arch employee now living in New Zealand who still prefers a jet fluxer for braze welding, and a U.S. auto repair shop specializing in sports racing car repairs, likewise using a jet fluxer.

I have recently been in contact with Bruce Robinson at Arch Motors and although he is a busy man, he kindly took the time to answer a few questions regarding their history with Lotus. Bruce advised that Arch has been using the gas jet flux braze welding process since the 1950s. They initially manufactured wishbones, brackets, pedals etc., for Lotus, and in January 1968 commenced construction of the Lotus Seven Series 2 chassis frame and associated parts. This was followed by the remainder of the Seven line (Series 3 and 4 cars), as well as Formula Ford chassis for Lotus and other constructors. Colin Chapman fully approved of the braze welding process for tubular chassis frame construction.

Bruce noted that since the demise of Calor Bronzecraft rod, Arch now use SifBronze No.101, which is specifically formulated for use with the jet flux process. No.101 is a manganese/silicon bronze rod with no nickel content (according to the specification sheet on their web site), and has an ultimate tensile strength of 66717 p.s.i. (converted from the Newton/mm2 on the spec. sheet). For anyone interested in seeing how this product flows, please see the ‘YouTube’ videos “Ariel Atom Bronze Welding”; “Bronze Welding V8 Ariel Atom”; and “Bronze Welding” all by an excellent welder – Brian Ashcroft, using jet flux equipment and SifBronze No.101 rod. Brian Ashcroft advised me of the following: “I have used the Sif No.2 and it does weld very similar to No.101, it just doesn’t run quite as nicely. We found that No.2, although having a higher ultimate tensile strength, did tend to be more brittle than 101 which is why we prefer 101. I haven’t come across a weld failure with 101 yet in my 18 years of using it” (Note: Michael Costin and David Phipps allude to nickel bronze or manganese bronze welding in their book “Racing and Sports Car Chassis Design” published by Robert Bentley Inc.).
 

[anduril3019]

While we're on the subject...

Any rod and flux recommendations for brazing without a gas fluxer? I'm thinking non-critical things like tabs and brackets.

[MV8]

For steel on steel with some lap, any bronze should be fine bare (heated a little and dipped in powdered brazing (not soldering) flux) or flux coated. You can find some at the hardware and home improvement stores but I prefer to go to a welding supply store. There are a number of specialty rods that are very expensive, but you essentially have to call them to get a recommendation. You can read the MSDS to get an idea on the make up for comparison. Avoid cadmium and low fume zinc is preferred; both for health reasons. Working temp around 1500f.

 

Another consideration is that some alloys become very watery at the melting point which is good for wicking into pipes but bad for filling a lap that isn't very close fitting. I think the ones used for "braze welding" are less fluid.

 

You can weld around brazing if not using a torch that dumps a lot of heat into the area compared to mig. The higher than brazing temp heat from welding is what ruins an existing braze. You can also use wet rags or heat sink putty around the brazed areas to keep them cooler and weld an inch, let it cool, weld an inch, etc like when welding sheet metal.

[MV8]

Paul Brodie, craftsman and brazing guru. Two good videos to watch (includes gas fluxer design and use).

https://www.youtube.com/watch?v=OjRMbBl_Tbs

 

https://www.youtube.com/watch?v=Y2CnJ9lmlQo&t=135s