In a recent tour of collision repair facilities located in the southwestern United States, my friend, Toby Chess, and I were asked by a shop owner for our thoughts on repairing a unibody vehicle structure with the universal anchoring and measuring method (the most popular method today) versus the increasingly popular fixture method (or, as some call it, fixed point anchoring or jig). The shop owner also asked us, “Are we entering the age of the net-built vehicle of zero tolerance?” Suddenly we realized that both of us didn’t know much about the subject and weren’t qualified to explain the differences between the two methods. The old saying, “If you think you know, you don’t know; but if you know you know, then you know,” applied in this situation.
Tolerances Getting Tight
Looking back 30 years ago, tolerances were “close enough for government work,” to use the old cliché, or one-fourth of an inch in any direction. With the advent of the unitized vehicles, however, tolerances became the industry buzzword. I pulled out some of my old frame books and found that some points were as much as plus or minus five millimeters (the thickness of a dime is one millimeter).
Why are tolerances so important? As an example, an inward movement of four millimeters at the top of the strut tower can change a camber reading one-half to one degree. Moreover, the manufacturers are competing against one another to say that their vehicles have closer tolerances. The truth is that as tolerances get smaller, manufacturing costs decrease. But where does that leave a body shop? How’s a shop going to duplicate these tight tolerances when changing a frame rail on a late-model sedan? With self-centering gauges and a tape measure? I don’t think so.
It’s not uncommon for today’s vehicles to have a zero structural tolerance at the torque box control points and not more than one millimeter at the (front) strut towers. I was blown away recently after observing one of our technicians measure a vehicle where the tolerance from bumper to bumper was one millimeter. I never thought this was possible!
The bottom line is that these tighter tolerances require a more precise repair method than what was used on the vehicles of yesteryear. More and more manufacturers are now stating how their vehicles must be repaired and are specifying the types of equipment to conduct those repairs, particularly pulling and welding equipment. Tolerances do interact with the type and ability of equipment a technician uses, most notably structural correction equipment. Let’s begin by looking at the types of equipment available for correcting structural misalignment on damaged vehicles.
We’ve decided to put the pulling devices into three different categories: frame machines, dedicated benches and universal benches.
Frame machine: The traditional frame machine has a large platform with some sort of anchoring clamping system for attaching a unitized vehicle to it. The towers can be attached to the unit or are portable. It’s usually in a fixed location (due to its size and weight), but there are some portable units in the market. It’s loaded by driving the vehicle onto it or using some sort of winching system for non-drivable vehicles. Most have a clamping system available for mounting trucks and SUVs.
Dedicated bench: Dedicated benches are smaller than most traditional frame machines. Their tread assembly is machined to very high tolerances. Most are portable and require extra equipment (either special high-lift jacks or an asymmetrical hoist) to mount the vehicle. The pulling towers are usually portable. What distinguishes these machines is that they use dedicated fixtures for anchoring and measuring.
Universal bench: Like dedicated benches, universal benches’ treads are also machined to very tight standards. They can be portable as well as fixed. Again, the pulling towers are either portable or fixed to the machine. Vehicles are mounted in a similar fashion as they are on dedicated benches. The difference is that universal benches don’t use dedicated fixtures to measure damaged vehicles but some sort of universal fixture system or mechanical/electronic devices.
The second part of the equation is the measuring of vehicles. I don’t want to dwell on past measuring systems (self-centering gauges, tram bars, tape measures, etc. see I-CAR’s measuring class for details), but rather would prefer to concentrate on the newer methods
Universal measuring system: This system utilizes a track that’s centered beneath the vehicle. Three points are located in the torque box areas of the vehicle (a minimum of three points are needed to center the track to the vehicle). A measuring tape is located along the edge to measure the vehicle’s length. Cross bars are attached and placed at specified lengths. The cross bars are calibrated with markings to determine the width of the various points. A height tube is attached to the fixture along with some sort of locating cone or cup. With the measuring system in place, any point on the bottom of vehicle can be checked against a data sheet to determine the extent of the damage. The system also has a bridge to check the upper strut towers and other upper points in the
Universal laser system: This system is used primarily on the bottom of vehicles. It’s universal and can be used on a frame machine as well as with an overhead vehicle hoist. Some systems will furnish a computerized printout before and after the repairs have been completed. Some aren’t recommended for use during the pulling and repair process, while others can be used during the repair process but must be recalibrated each time pulling forces are applied to the vehicle.
Sonar or ultrasonic method: Sonar or ultrasonic uses probes placed at selected reference points under the vehicle. An ultrasonic signal is generated by the probes and the information is transmitted to the central beam, where data is converted to measurements. This data is then transferred to a computer, where it’s compared with known measurements of the vehicle being measured. A comparison of the two data is then made.
Electromechanical system: This system employs a mechanical arm that rides on a bridge under the vehicle. The bridge is centered underneath and is parallel to the floor (it becomes the datum plane). A pointer is attached to the arm and, after the system is locked into position, every reference point can be measured for length, width and height. Various attachments to the arm are used for measuring door opening and strut tower locations. After the data is compiled, it’s sent to the computer wireless or via wires. The data is then analyzed and compared with standard values to determine the extent of the damage. Data can be received during the pulling process in order to monitor the current status of vehicle dimensions. The computer also stores images of the various reference points so that the technician doesn’t measure the wrong reference points.
Computerized laser measuring system: This system employs a laser generator under the vehicle and a series of flags or targets placed at selected reference points to measure length, width and height. These measurements are triangulated and the dimensions transmitted to a computer to be compared to the computer’s stored database. A misalignment is diagnosed and a document is created showing any changes to
What’s the Diff?
The first step Toby and I took to answer what the difference was between the universal anchoring and measuring method and the fixture method was to ask for some input from a cross-section of repairers from around the country. Let’s first look at the differences between the four designs of pulling machines most common in the market today.
Drive-on frame machine: This machine has evolved through the years to not only offer multiple pulling capabilities (with as many as five pulling towers), but also universal measuring systems (in recent years, the stand-alone electronic measuring systems) that work in conjunction with it. It was originally designed for the “body over frame” vehicle or “perimeter frame” as it was commonly called back then. A number of years later, when the unibody vehicle became more prevalent (and had different anchoring requirements), pinch-weld clamping was added to the drive-on frame machine, where a speciallydesigned clamp attaches to the rocker panel flange to anchor the vehicle. These adaptations to this machine led to the term, “universal anchoring and pulling method.”
The frame rack is approved by most OEMs because of its versatility and allows a repairer to meet those OEMs’ standards. It’s bigger and usually more powerful than its much smaller cousin, the bench, often having a total length of 25 feet or more and a total width of 14 feet. It’s also designed to be wider and longer than the vehicle, offering complete access to the vehicle’s underside. Another feature it has is a platform for the technician to stand on, usually at a height of two to two-and-a-half feet from the floor.
At last count, there were more than a dozen manufacturers of drive-on rack systems in the market, with many designs priced to meet the needs of small collision facilities. The widely used method of repair this machine offers has proven to offer time savings in setup and pulling, allowing the user to repair a wide range of vehicles with a wide variety of damage severity.
Universal drive-on bench: The universal drive-on bench entered the U.S. market a few years after the introduction of the traditional drive-on frame machine. The design originated in Europe, where cars had unibody designs. Being much smaller than traditional American vehicles, those cars
didn’t require a full-size frame machine.
Most vehicle manufacturers approve of the universal drive-on bench and repair method because of its accuracy and versatility. It’s designed to anchor the vehicle at the rocker pinch-weld flanges. Surprisingly, this design also offers many of the same pulling capabilities as a drive-on full-sized universal frame rack while consuming less floor space (some being mobile on wheels). However, these benches may be limited in the size of truck or SUV they can accommodate. Most are designed to be narrower than the vehicle and have a removable platform that allows the technician to work more comfortably by standing closer to the vehicle but limits his access to the underside. They’re most popular with collision facilities that repair light to medium hit vehicles, and also where floor space is at a premium. Their design allows the repairer to process a high volume of work.
Some universal drive-on benches can be used to repair larger trucks and SUVs by having anchoring adaptors attached to selected locations on the frame. Some universal benches also offer dedicated electronic measuring systems and/or universal ladder measuring systems, allowing the technician to pull and measure simultaneously with speed and accuracy.
Dedicated fixture bench: The dedicated fixture bench (or fixed point anchoring method) also comes either fixed or mobile and is designed as either a fixed location drive-on bench or a vertical-mount mobile design (requiring a two-post lift to lower the vehicle onto it).
This design and the unique method of anchoring it’s used for also originated in Europe. It was originally developed to address the demands of some European auto manufacturers, who required the dedicated fixture anchoring method of repair on their vehicles with a specific dedicated bench manufacturer. The OEMs that require this repair method believe it’s more precise and removes any guesswork on the technician’s part. Hence, a less than highly skilled technician can produce precise repairs.
The dedicated fixture bench is in many respects similar to the universal drive-on bench, but is manufactured to be used primarily with dedicated fixtures (fixtures that both anchor and measure simultaneously) instead of the universal anchoring method that attaches only to the rocker panel pinch-weld and uses electronic or ladder type measuring systems. Vehicle-specific fixtures are manufactured for each vehicle model type, with the fixture dimensions taken from manufacturers’ blueprint specifications. The fixtures are generally identical to the fixtures used to assemble the vehicle during the manufacturing process.
The technician installs the fixtures to the vehicle and bench guided by a set of instructions, which are worksheet-specific to the vehicle and show the technician where each fixture is located throughout the vehicle’s underside. (Some benches also offer side-mounted fixtures to measure and secure side A, B and C pillars). Depending on the vehicle model and severity of damage, there can be as many as 16 different fixtures attached throughout the vehicle’s underside, securely holding each anchoring/measuring point in place.
For damaged vehicles requiring multiple pulls at one time, the dedicated bench can be limited since most are equipped with only one pulling tower. But with the dedicated anchoring repair method, a technician wouldn’t normally need more than one pulling tower. Some dedicated benches, however, do offer optional pulling towers.
Although this fixture repair method has been around for many years, it hasn’t been until the last few years that the U.S. collision industry has seen a slight shift towards it. Many repairers now want the option of repairing vehicles by the fixture method, regardless of the fact that some OEMs require their vehicles to be repaired that way. This is because of what more OEMs are beginning to admit publicly: With certain types of damage, the fixture method can be a more precise repair method.
Universal fixture bench: The universal fixture design (or fixed point anchoring method) has also been around for several years and originated in Europe as a result of OEMs’ demands as well. Many European auto manufacturers also approve the universal dedicated fixture method, with a few OEMs specifying a particular bench manufacturer.
In principle, there’s not much difference between the dedicated fixture and the universal fixture methods. Both benches are similar in design and have the same pulling capabilities. The one basic difference is the individual design of their fixtures. The universal fixture method has broader vehicle capabilities (you don’t have to rent or purchase fixtures) in that it can be used on all vehicle models, while the dedicated fixture method can only be used on a specific vehicle model.
With the universal fixture method, the individual fixtures have to be assembled by the technician, who must follow a set of instructions specific to the vehicle model. The setup instructions show how to assemble each fixture from a numbered set of universal brackets and attachments supplied with each bench. These instructions are produced by the manufacturer following its blueprints or by actual measurement documentation. The fixture is mounted to the bench and also to a known specific holding/measuring point on the vehicle, which shows the technician the precise dimension of the datum height, length and width. Another similarity with the dedicated fixture design is that there can be as many as 14 fixtures attached to the underside of the vehicle, both anchoring and measuring simultaneously.
So why choose one repair method over another? Or is there a need for shop owners to offer more than one type of repair method? Here are the opinions of a few repairers, whose names have been left out to avoid any potential controversies. Also, understand there’s always a level of bias when asking repairers about their views on the equipment they use.
Midwest repairer: “I think whether or not a repairer should embrace one method or the other will depend a lot on the vehicle mix he has. Our area has a lot of pickups and SUVs, so the drive-on machine and universal measuring seems to work best, not only for the time savings but also for the ability to do multiple pulls.
“Another factor to look at is job size. If the shop is doing a lot of ‘heavies’ involving a great deal of structural replacement, then there’s great value in the jigging capabilities of the dedicated or universal fixture bench. But if the mix leans toward less intense repairs, then the universal system makes more sense to me since the need for fixtures is less intense.”
Lower Midwest repairer: “To me, anything other than a light tug to gain a few millimeters gets loaded onto one of our dedicated fixture benches. The ability to isolate the damaged area that a dedicated fixture bench gives you is invaluable, plus the danger of causing collateral or unintended damage during a structural pull is greatly lessened. We’ve yet to have a customer return his vehicle with any body alignment or wheel alignment issues.
“The buzzword around dedicated fixtures is ‘integrity,’ and we’ve had no problem with that when loading medium to heavy hits on one of our dedicated fixture benches. But keep in mind that since electronic measuring can’t offer angle or isometric readings for proper parts placement and or alignment, it should only be a secondary source with heavier hit repairs.”
West Coast repairer: “For the last 25 years, we’ve had universal drive-on benches equipped with laser measuring systems. In recent years, we added universal dedicated fixture benches. In my experience, the universal bench excels in the following areas: multiple pulling capabilities; heavy side hits (loosening mounting bolts at pinch-weld beam and spreading both beams with ram relieves banana condition); and universal setup (you can set up and square any vehicle quickly without a data sheet).
“Some drawbacks I’ve seen are in the following areas:
Pinch-weld mounting. “It’s very hard to restore pinch-welds after a repair. We’ve done many pre-buyer inspections in the past and the first area we look at is the pinch-weld.”
Compensation for setup time. “In the past, the industry took a generic three hours to bench and setup. Due to ignorance and competition from the drive-on racks, setup time has now been reduced to two hours with measuring included.”
Receiving accurate measurements while in the repair process. “Some electronic systems need to be constantly recalibrated due
to the vehicle shifting during pull-
“The universal dedicated fixture bench has been our favorite frame bench because it has been very accurate in the repairs we’ve done. Even so, it does have drawbacks, like when we repair a vehicle that’s not listed in the bench manufacturers’ database of vehicle-specific setup instructions. When that’s the case, you have to convert generic frame specification data from either the Mitchell or Chief Frame Dimension Guide. This can take a little more setup time to dial in the correct datum height and figure out what fixtures to assemble.”
Hawaii repairer: “I currently use drive-on universal benches and also a bigger drive-on frame rack. I chose these machines based on the kind of vehicles I repair (Asian and domestic cars and light trucks), and I don’t anticipate my market changing anytime soon. I agree that the fixed point anchoring and measuring system is superior to the more conventional means of anchoring and measuring. Fixed point anchoring allows the repairer to come as close as possible to duplicating the manufacturers’ specifications.
“Insurance companies refuse to recognize that the fixed anchoring methods are universal to all unibody constructed vehicles; this is how the vehicle was made. They only recognize what the OEM requires as part of the insurance approval process for repairs. The industry knows fixture rental reimbursements are difficult to get from insurers unless the manufacturer (BMW and Mercedes, for instance) requires the fixture method and provides a written statement to show that.
“I realize that setting up for the dedicated fixture method takes longer than setting up a universal bench or other machine. Therefore, getting fair compensation for a fixed anchoring setup and measure may not be cost effective for the reasons I cited above. I also feel that the learning curve for the frame repair theory and processes may be faster on the dedicated fixed anchoring method versus the universal bench or frame machine.
Northwest repairer: “One thing to consider is that many cars have no pinch-welds. There’s more room for error with a universal measuring system, especially if a technician likes to cheat a little.
“As I see it, the greatest advantage to the dedicated fixture method is that cars are built/assembled with the dedicated fixtures. While this method doesn’t guarantee a better repair, it’s harder to put things on in the wrong place. You almost have to work at messing it up. Additionally, you cannot pull a point you’ve anchored to that’s out of the specified dimension.”
West Coast repairer: “Dedicated fixture/jig-type repair systems may take longer to set up, but there’s peace of mind knowing that an average tech can repair the vehicle properly. Ask yourself why some automobile manufacturers require certain types of equipment. There’s a reason! But then there’s cost. Why some insurers resist paying for jig rental baffles me. They’ll accept higher premiums on these technically advanced vehicles but want to repair with improper methods.
“The universal-type clamping and electronic measuring continue to improve, but I think there’s a greater learning curve with the electronic systems. These electronic systems can easily be manipulated, so we as owners need to be diligent about ongoing training for our employees, considering all the aspects of the repair method we select. There will never be one system that will be all things to all repairs. Collision shops in the future have to decide which vehicles they’ll repair and figure out the vehicles they know won’t be cost effective due to equipment expense
What’s Best for You?
As you can see, there’s value in
both the universal anchoring and measuring method and the fixture method, but there’s no one method and machine for all occasions. The fixture method continues to become more popular now that vehicles are being manufactured with closer and closer tolerances and built with exotic (no heat) metals. Plus, many manufacturers are beginning to approve the fixture method. But don’t “throw the baby out with the bath water.” There’s still a need for the universal anchoring method of machine, especially if your mix is both full-framed vehicles and unibody types. With all that has been mentioned in this article about frame-racks and bench designs of structural equipment, it boils down to the two fundamental methods of structural correction to be considered: conventional pinch-weld anchoring compared to the dedicated/universal fixture method of anchoring. At the end of the day, you have to decide what’s best for you.
Writer March Taylor owns Auto Body Hawaii in Kailua-Kona, Hawaii. Not your typical shop owner, Taylor works alongside his employees as a technician. This, he says, gives him “the opportunity to see things how they really are. I’m not disconnected from production or management.”
Contributing Editor Toby Chess has more than 30 years of industry experience. Chess is an ASE Master Certified Technician, an Accredited Automotive Manager, an I-CAR instructor, the Los Angeles I-CAR Chairman and a technical presenter for CIC. He can be reached at [email protected].
The OEMs Speak
We asked the U.S. auto manufacturers about their opinions on fixed anchoring repair, and the summary of what they said follows: Information at hand prevents us from providing a position or an approval for any one method over the other. Research continues, recognizing the variables in damage severity and repair situations. The current conventional method is still supported, but with the advent of tighter and tighter tolerances and the Ultra High Strength Steel materials, we’re looking at the important points of the dedicated/universal fixture methods of repair.