Frame machines. What do they do, how do they work?
Simplistically they, through hydraulic force pull bent/dented/twisted metal close to their original measurements.
I'll use the one I used for my blue car as an example.
First off, loading a vehicle is done with the rack in it's loading position, meaning it's angled down so you can drive the vehicle onto the base. Once on there, the base is leveled out with a push of a button.
Look at the rocker pinch weld area. There are two clamps on each side to hold the vehicle solid. These clamps are bolted to the base of the frame machine.
You also see the four booms that are around the base. These glide into position and lock in place.
This particular frame machine is rated at ten tons of sustained pulling pressure (actually a little over 22k). In short, it could rip my car apart. I won't need anything like it's capacity for my little tweak.
I actually had to use one of the booms with a different clamp to pull the rear of the pinch weld straight on the left rear just so I could hook up the main clamp. A hammer wouldn't budge it. 60 seconds later and it is straight as can be.
This is a computerized measuring frame machine, though of course we do have the older hangers and rods for doing manual measurements as well. We also have a laser measurement system that we use as well.
Look directly under the car between both sides of the base and you'll see a sled that has the computerized flexible measuring arm on it. This is used to measure your base measurements prior to pulling at predetermined points on the vehicle. These points are all found in the computer. So when you move the pointer to one of those points and push a button, the computer loads that and begins to determine what your frame looks like as you measure to the other various points, then compares that to factory measurements. It tells you exactly where the measurements are off the factory specs. Luckily our computer still has a complete listing of measurements for fox chassis cars! Yay me!
If you ever have collision work done on your vehicle and it needs frame time, you'll see a separate time for setup. Setup means putting the vehicle on the frame machine, locking it down with the clamps, bringing up the base measurements and comparing them to what your vehicle measures. In the case of my car, that took longer than the actual pull.
For my car the right rear had received a hit down low at one time in it's life, that knocked the right rear frame rail up about 22mm above the left rear subframe, almost an inch, and pushed it out 5mm, less than 1/4".
To bring it closer to being even and to pull out the buckle in the right quarter/sail panel area the right rear subframe needed to be pulled down and in a bit.
The frame rail itself was tweaked starting at the forward bend toward the front of the wheel tub area. Easy peasy pull. I attached an additional chain to the right torque box to the base, then hooked up the boom to the rear of the frame rail. I angled the boom chain to pull slightly down and inward.
The hydraulics are electronically assisted, so all i had to do to make the pull is press a button. I pulled in short blips and kept remeasuring as I bumped the hydraulics. When it was slightly past both points I was wanting, I realeased the pressure to allow the metal to do it's springing back and remeasured.
Bringing it inboard was easy and quick and the first pull brought it back to exactly where it should be. Bringing it down required a couple more times. When I got within 7mm, I decided that was good enough. The buckle in the sheet metal disappeared and 1/4" is nothing on a fox mustang. When they were new they would be tweaked more than that at times.
Let's say the frame rail had been crushed, what's to be done then?
While you have the rail under tension the crushed area can be heated with a torch and adjusted with a bfh. This is done slowly since the frame machine can exert enough force to rip my little car in two. Now, if it were really compromised in it's integrity I would remove the subframe and replace it.
The wonderful thing about technology here is that to check the measurements while pulling is so simple. I release the pressure, swing the measuring arm over to the original measuring point and the computer tells you what you've done. It takes about five seconds to release the pressure and swing the measuring arm over.
Once I replace the right front frame rail I'll bring Scuby back to the shop to check what I've done and adjust it if necessary.
If you got any other questions concerning frame machines, let me know.