December 14, 2002

Why is it so hard to reproduce what you did last week in the Winston Cup series?

One reason is the chassis and framework of the car. Many team owners and engineers have scratched their heads and wondered why they can’t build an exact duplicate to a car of which just won on the track last week.

A car that wins and was considered to be of good quality to the teams will be measured in an effort to duplicate what they have. Many shop hours will be spent in what will usually result in a futile attempt. The car that wins the Daytona 500 this season will be measured before it goes on display in Daytona U.S.A.

The chassis system of a Winston Cup car is much more complex due to its overall size and general configuration as compared to open wheel cars which offer a decent chassis repeatability rate from system to system. If you think about all the welded round stock that goes into the making of the Winston Cup chassis and roll cage you can begin to see why repeatability is at best, luck.

The chassis system is built on a jig which some shops refer to as a construction plate. Round tube stock is carefully fitted and tack welded together and checked for compliance. In most cases after someone signs off and approves the fitting process a certified welder will start the weld out procedure.

There are procedures for this type of welding which will usually consider a tig process. The welder will take a piece of straight filler wire in one hand and the tig welding torch in the other. The torch portion of the tig system considers a piece of sharpened tungsten surrounded by a ceramic cup. The tungsten carries the voltage from the welding machine. Argon gas is also introduced into this process through the torch head. The tungsten heats up and virtually melts the hand held wire into the weld area in question. The certified welder will manipulate the torch head in a rolling motion to create a pattern in the weld. There are several different patterns that are used to create the needed strength in the welded area.

The welding procedure that we speak of considers the fact that you don’t want to weld in the same location all the time thus you will skip around to other areas of the work in an effort to dissipate heat build up which will cause deflection and stress. On pipe such as what is used in this system you don’t want to weld in a continuous circle because you will draw the pipe. Drawing relates to the stock being pulled by heat out of square thus causing stress.

Let’s say for example that you were welding on a flat plate and you wanted to institute a welding procedure. The engineered procedure may call for you to preheat the metal as well as complete a two inch weld and then skip another two inches and then do an additional two inch weld. This would be called a 2 on 2 weld procedure.

The tig process carries the least amount of heat as compared to stick welding and the quality is much better. Tig welding is used for stainless pipe for the most part with that type of certified welder being highly in demand as compared to a stick type craftsman. Some coded welds will be x-rayed in an effort to look for pin holes which would weaken the structure. In most cases if a problem is found the weld is ground out and re welded.

Can you begin to see the complexity of what it takes to weld a roll cage and chassis out?

The chassis and roll cage assembly are a flexing system in and of itself. In most cases the chassis system upon its conception is put through a Finite element analysis (FEA) test. This process is a mathematical technique of doing strength analysis with the aid a computer program. This tells the engineers where the weak points may be in the system.

So now we have our completed chassis assembly that was hand crafted down to the most intricate fitting of the round stock tube. Let’s consider why it won’t repeat as to what you will build next week. I think you already know why at this point.

It’s the complexity of the whole process. There is really no way for a human to recreate every weld from system to system. The flexing of the system will be ever so slightly different than the last one. If there is stress on the tubing when you made a fit perhaps from forcing it to fit you will create an area of stress which may be different from the last one that you just built. Even though they may look the same they indeed are not. There are processes that consider stress relief but for the most part every hand welded system will be different.

There are machines that do perfect welds but once again in general they are used in areas such as boiler tubes and the like where there is ample room to fit the bulky device in place. There are also robotic welding devices used in auto factories that work day after day but most of those machines do spot welds. Tig welding and some higher forms of stick welding are art forms and take a skilled craftsman with a steady hand. I don’t see any way at this point to get away from hand working the chassis system.

There are firms that do a fantastic job in regard to out performing most chassis builders. Ronnie Hopkins located in Greenville, SC is at the top of the heap when you start thinking about a store bought chassis systems for the Winston Cup series. Hendrick Motor Sports has a chassis team that offers over 35 employees that can turn a complete chassis and body system out in one weeks time, if need be.

So I think what we are getting to here is the fact that chassis repeatability is among one of the highest problematic concerns in the Winston Cup series today. There have been technology gains but the stumbling point is the human factor. As long as you have humans cutting, fitting, and welding there will always be this consideration of moderate repeatability from this very complex custom built structure.

You can contact Joe at: Insider Racing News