Making your own frame alignment jig.

Datum line clamp ready for welding

In this post, I’m taking a break from the car, and building a frame alignment jig.  My friend was telling about the one they use at their body shop, and said I could make my own out of HW store parts.  This post walks through the items needed, and what I did to build them.  We will build two simple tools, a datum line, and frame checking jig.  (Thanks Dennis!)

First up, is the datum line.  This tool allows you get a reference line that you run the complete length of the car in any position you need.  once level you can use it to take frame rail height measurements.

I built the clamps first, using the beam clamps, and two of the 1/2″ nuts.  Start by grinding off the galvanizing from both the clamp and the nuts.  nice clean metal makes for a much better weld.  I used the spare 1/2 bolt to hold the nuts in alignment while welding (See the first picture).  It does not take much to hold the parts together, I tacked each side of the nut to hold them in place.

Next replace the clamp bolt with the thumb screw to make it easy to position the clamp when you need to move it.  Now thread the ready rod in and use one of the remaining nuts to hold it in position.  Finally take the 1/2″ washers, and drill a small (1/8″) hole near the end.  install the last of the nuts and the washers (One below, and one above the washer) on each of the ready rods.

Install the datum rods at each end of the car.  On one of the ends install the “S” hook, and run the kite string between them, leave enough extra to tie the weight (3/4″ nut) to one end.  take the weighted end a slide the string in the “S” hook to act as a pulley. Tie the other end of the string to the other washer.  you can now level your line between the two rods, by threading the nuts and washers up and down.  to level the string you can use a length of clear vinyl tube filled colored water.  when the string is lined up with the water at both ends, it’s level.  you can now use this to take measurements on the car.  Make sure the car is level too.

Now the frame checking jig.  This tool allows you set the two pins to exact distance, and then move it to different parts of the car to check if it is square, or the same distance side to side.

This tool is even easier to build then the datum line.  To start I drilled a 7/16 hole in the middle of each of the threaded couplings.  I placed a nut in side the coupling, and one on top, grind away the galvanizing around the hole on the coupling and the outer nut, where you will be welding, then thread the bolt through both nuts, and tighten them down to hold the assembly square.  Check that the nut and bolt are centered in the hole, and square with the coupling (See pict. Frame-jig-Square).  Once your happy, weld the outer nut to the coupling.  do not weld the nut inside the coupling, this will prevent you from inserting the conduit later.

The next step is to make the pins.  First cut the heads off the long bolts, I beveled them end down to make it easier to insert it in to the holes.  Next I took the washers and cut them in half.  Now weld two halves of the washer on each of the bolts near the threaded part. (See pict. Assembled, with wings for tightening) to make thumb grips to help you tighten and loosen the pins for adjustment.

To use simply slide the coupling over the conduit, and tighten the pins at the desired distance.  You can see the last two photos I’m checking the frame for squareness, by measuring the diagonal in both directions to make sure they are the same distance.   One final note.  I chose the threaded coupling mainly because the threads will bite into the conduit when I tighten the pins.  this will prevent it from moving around as I move the jig from place to place on the car.

Materials needed:

  1. Datum line:
    2 – 1/2″ by 36″ threaded ready rod.
    10 – 1/2″ Nuts
    2 – large 1/2″ Washers
    2 – Conduit beam clamps 1/4 – 20
    2 – 1/4 – 20 thumb screws to replace the bolts in the beam clamps
    Enough kite string to span the needed distance
    1 – 3/4″ Nuts, or other weight
    1 – small “S” hook
  2. Frame checking jig
    10′ – 1/2″ metal conduit
    2 – 1/2″  threaded conduit couplings.  Check to make sure these slip loosely over your conduit
    2 – 3/8″ X 6″ bolts.  Get the ones with only about 1-2″ of threads, the less the better.
    2 – 3/8″ Nuts
    2 – 3/8″ Washers