Over the last few years we, and I am sure many others, have accumulated a large number of 18mm and 23mm Front/Rear Torsion Bars, most of them are in reasonably good condition.
We now have in excess of 70 bars and they are just getting in the way.
What to do?
If I bought a used set I would want to measure the spring rates and load them to be sure that someone hadn't installed them the wrong way round. Testing for these not an inexpensive proposition:
Perhaps an alternative use?
1966 911 #304065 Irischgruen
We "donate" them to the scrap guys when they start to get overwhelming.
-Marco
SReg. #778 OGrp: #8 RGrp: #---
TLG Auto: Website
Searching for engine #907495 and gearbox 902/1 #229687
I like the idea of the tent
I would think measuring the diameter and the effective length of the bar would be good enough to calculate stiffness to better than 0.5% as G for steel is relatively well established.
The spring rate of a torsion bar is, of course, the same in either sense of torque (Left or Right Hand Helix) and should be unaffected by previous loading history providing it is not taken beyond its yield point.
Once a bar is yielded in a specific torque sense then Bauschinger effects come into play and zero oints can be affected.
It is customary when manufacturing springs to carry out a scragging operation as one of the final steps in the manufacturing process.
This procedure is designed to remove any of the effects of microplasticity which could influence the ride height of a vehicle during the early stages of its life.
A torsion bar would be taken slightly beyond its yield point in a specific sense of torque which will cause it will develop a slight offset of its zero position. If it is then reverse loaded its yield point in the opposite torque sense would be at a slightly lower stress and this would change the initial zero.
I believe that this is the reason for marking bars as either Left Or Right Hand as this means a bar scragged in a Right Hand Helix could yield at a stress lower than its design point if used in a Left Hand Helix and this would affect static ride height.
The spring rate, however, would be unaffected as the Shear Modulus G is not affected by plastic deformation.
During the life of a torsion bar it is also possible that some fatigue softening of the material could occur and again this would influence ride height but again does not affect spring rate.
The developement of fatigue cracks and corrosion pitting can have an influence on spring rate but assuming that a bar looks to be in good order it is likely to operate correctly.
Sorry to have changed the subject but spring testing is an interesting subject.
I am not sure I like the Intercomp Torsion Bar Tester it looks a bit basic and I would worry about accuracy and repeatability.
It should be quite easy to hook this machine up to a PC and plot a curve of Force versus Deflection but it would be good to know bit more about the transducers being used and how they are calibrated.
Chris, fascinating, that does explain the left v. right dilemma. Made me search for "scragging," I come here to learn.
Perhaps you can ask Jim at EASY whether there's a support group. . . .
1966 911 #304065 Irischgruen
I've never bought anything from them that wasn't 1st class. Maybe pricey but still 1st class.Originally Posted by 304065
Testing for these not an inexpensive proposition:
Good luck with the dome.
Tom
Early S Registry #235
rgruppe #111
It is now quite clear that we must try much harder
Tom,
I guess I am picky when it comes to test equipment as I spent more years in the industry than I now like to admit.
I always like to be able to calibrate test machines so you can really tell what is going on and I am not sure how well these budget testers perform.
Last edited by chris_seven; 11-12-2012 at 11:34 PM.
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