Roll Cage: Main Hoop & Harness Bar

Today is the day I get started on installing the cage.  I ordered this tubing notcher from Northern Tool (Ole Joint Jigger).  Plus I bought two 1 5/8” hole saws down at Lowes.  It is clamped in my woodworking vise on my workbench.

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The first job was to fit the Main Hoop.  The hoop lays back at about 14 degrees, it basically wedges in between the hard-top latch mounts.  So, I wedged it into place, and set the hard top on top of it.  Then I measured the height difference between the hard top hold down and the screw hole.  I marked the bottoms of the main hoop to remove the measured amount plus 1/8”.  I removed the top, remove the main hoop and used a saws-all with a metal blade to cut the waste.  After I fit it back in the car, I put the top back on.  There is about 1/8” of clearance from the top of the hoop to the hardtop.

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I used the grinder to fine tune the ends of the hoop where they meet the footings.

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Next up….the harness bar.  This is one of the trickier bits because the bar has two 45 deg bends and meets the main hoop at about a 15% angle.  That makes it a compound miter joint on both ends…and it has to fit exactly between the uprights of the main hoop.  There isn’t much room for slop.  Plus its hard to measure where the cuts are going to go, exactly.  So, you just have to get close and sneak up on it.

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I used a construction square to measure the distance from the seat belt tower to the main hoop.  Then I removed the main hoop and placed the harness bar into place…and marked the location of the seat tower edge onto the harness bar.  Then I transferred the distance I measured above onto the harness bar.  The trick here is that this is a compound miter.  You can’t just set the 15deg on the notcher.  The easiest way to do this is to hold the harness bar at the desired angle against the main hoop.  Then mark the point where they touch…it will be a little-bit outside of the verticle centerline.  This is the point that should be aligned with the axis of the hole saw.

You could do the math…it works out to about 14deg of tilt on the notcher, and 1.5deg of twist (of the tubing in the clamp).  1.5deg is hard to measure.  But, its easy to mark with a pen by eye.  I didn’t get the fit perfect.  I didn’t intersect the axis exactly right.  I may try and trim it a little closer…but, I don’t want to leave it too short, either.

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Next the main hoop diagonal.  This is a straight bar, so it’s a relatively simple job to cut these notches.  The bar is already cut to length.  So, I cut a 45deg notch in one end.  Then I put the tube back into the car, with the notch carefully held flush.  Then, as before I marked the point where the uncut end met the main-hoop…to mark the axis of the notch.  Then I held my protractor up to the joint to measure the intersection angle.  As it worked out, it was 43deg…not 45.

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Next up…the cage sides….

2 comments to Roll Cage: Main Hoop & Harness Bar

  • Hi
    I notice that you left the diag and harness bars separate. In Dave Wheeler’s rollbar instructions, he integrated them by cutting the diag into two pieces. Someone commented to us that this isn’t legal, but the way I read the GCR’s, it appears OK.
    Is that why you left the diag in one piece?
    KG

    • Hi Keith-

      Dave and I discussed this. NASA requires that the main hoop diagonal be a single unbroken tube with no bends. SCCA does not. So, that’s probably what your friend was referring to. Dave’s instructions are legal per SCCA. Verbally he suggested that I keep the diagonal one piece. So, if you want to be sure of getting a logbook in NASA, then you are best advised to build it the way I did with the straight diagonal. You loose about 2-3″ of seat room on the passenger side. You’ll also want to be careful that the diagonal doesn’t interfere with the driver’s seat. My seat wings and halo are just barely forward of the diagonal, but I wouldn’t be able to move the seat back much if I were any taller (or had longer legs). I’d have to remove and re-position the diagonal to move the seat aft.

      I’m 5’11” tall with a 32″ inseam. YMMV.

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