Competition -- Rigidity
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How rigid is rigid enough?
On the left is a competitor's rotisserie holding a '57 Chevy body and frame. Their whole unit is built from 1/8" wall tubing, and center connector is so small, it can't keep the wheels on the ground here. Notice the sagging arm holding the car.
On the right is Accessible Systems 1500 lbs. rotisserie holding the same 57 Chevy body and frame (1200 lbs). Our 3/16" wall tubing is 50% thicker. Ours doesn't even need the center tongue connector to keep the arms straight.
Any structure will move if stressed, it just depends on how much. The movement may be so small you can't see it, but it's there. Gusseting helps if the gusset is in the direction of the stress. One manufacturer uses larger 1/8" wall tubing and gussets to achieve similar strength of a 3/16 wall tubing of a slightly small size. We use no gussets on our T-bars, as they are strong enough without the gusset, due to the tubing size. The side gussets on the axles are mostly decoration as there is no side-to-side stress on the upright post, as the car is balanced right over the center of the post.
The one place you can't gusset is the rotation pipe. One manufacturer talks about the 3" tower post at each end of the rotisserie as proof of strength. However, that 3" is the outside piece, the inside sliding piece is 2.5", which is welded to the 2.30" outside pipe, which holds the 1.90" inside pipe, so the 3" means nothing in the actual strength of the system. I would be surprised if these pipe sizes have not been increased as a result of our evaluation, so be sure to ask when your evaluating.
The idea that the 3 caster T based design is more rigid is proclaimed by some might be true if the car is never rolled up on a trailer or used with a pneumatic caster set. This design does not lend itself to a pneumatic caster version being rigid, because the center tongues aren't strong enough, at least in the version we reviewed. As we have shown before and below, we put about 3000 lbs. on our 1500 lbs. lift and the center tongue stayed straight. That seems rigid enough for me.
We only use the jam bolt tightening collars on the 1500 lbs. series and a 4 bolt clamp plate system on the 2000-4000 lbs. version, to assure rigidity in the T-bar and attachment arms.
1500 series on bottom with competitor's on top.
2000-4000 series T-bar adjustment plate system.
Here is part of a manufacturer's instruction sheet received with a unit. I've blanked out the name to protect the guilty. Notice the advise about only doing a body or frame but never the two together. You surely won't exceed the "3000 lbs." rating doing that! Also note the warning about the rubber tired version, due to the poor center tongue system on the unit. I've rigged our 2000 lbs version with a trailer hitch tongue tongue and a 65 Mustang. I wired the tail lights on the Mustang and towed it about 7000 miles to car shows in the early days. I had no springs but the tires. It went 70 mph on good roads and bad, with the body still being sound after two years of that.
The "Two Center Tongue" manufactures claim that the 2 rails on the outside are better because the two outside perimeter connectors keep the ends parallel. One manufacturer in the next sentence claims you can remove the two connector at any time to have access to the middle of the body. These two statements are contradictory. If you need the two connectors to keep the ends straight, then you can't remove them without destroying the integrity that these two connectors provide. In fact, this one manufacturer advises never to remove the body from the frame. So what he is saying is that the frame on your car is so weak that it it will shrink on one side compared to the other. It's just that those two rails keep banging you in the ankles as opposed to this.
Indeed, there are certainly times that you should not remove a body from the frame until some structural work is done on the body, if it's a basket case. However, thousands of 100 pt show cars have been built with the body removed from the frame.
As with all things in life, you'll have to make up your own mind about these conflicting questions. Ask more questions; get answers; then buy the one that is right for you.
