Slimy38
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| posted on 18/4/14 at 05:35 PM |
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Curve in wishbone plate
Just a quick question, what's the reasoning behind the curve in the wishbone plate? Does it actually do something or is it decorative? My plates
are currently straight edged from one side to the other.
I noticed Talon's MX5 wishbones replace the curve with a horizontal bar;
although he keeps the curve in for the Sierra wishbones;
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jacko
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| posted on 18/4/14 at 05:40 PM |
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I seem to remember reading if straight it puts strain on the tubing
Jacko
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Slimy38
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| posted on 18/4/14 at 06:00 PM |
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quote:
Originally posted by jacko
I seem to remember reading if straight it puts strain on the tubing
Jacko
Seems reasonable. If I simply cut a curve out of the plate now that the wishbones have been made up, will that suffice? Is there any 'golden
rule' as to how much of a curve is required?
I've just been reading the 'bent wishbone' thread, British Trident talks about dressing the welds to prevent any sharp corners,
should I do that at the same time?
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twybrow
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| posted on 18/4/14 at 06:45 PM |
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I am not a stress engineer, so can't help on rules off the top of my head, but it is all about reducing stress concentrations where the two
pieces meet. A sharp corner will typically give you a stress concentration, whereas dressed welds, and a curve to the joint will help to reduce
this... I wonder also if Talon does this to reduce weight too?
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mark chandler
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| posted on 18/4/14 at 06:59 PM |
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Curve reduces the stress point, you should also weld in the middle of the tubing not top or bottom.
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Slimy38
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| posted on 18/4/14 at 08:22 PM |
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quote:
Originally posted by mark chandler
you should also weld in the middle of the tubing not top or bottom.
Yep, already done that bit even if it was a complete pain to get everything fitting perfectly!
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coyoteboy
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| posted on 18/4/14 at 08:36 PM |
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Curved gussets spread the load down the weld more evenly rather than concentrating at a point.
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PhillipM
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| posted on 27/4/14 at 11:47 AM |
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quote:
Originally posted by mark chandler
Curve reduces the stress point, you should also weld in the middle of the tubing not top or bottom.
Welding a brace/gusset to the middle of the tube makes the stress even worse, it really should be almost flush with the top/bottom of the tubes, the
middle of the tube is the weakest, least stiff part as far as a gusset is concerned. That's why when you see gussets on rollcages they're
generally two pieces rolled around and welded either side.
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Slimy38
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| posted on 27/4/14 at 12:18 PM |
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quote:
Originally posted by PhillipM
quote:
Originally posted by mark chandler
Curve reduces the stress point, you should also weld in the middle of the tubing not top or bottom.
Welding a brace/gusset to the middle of the tube makes the stress even worse, it really should be almost flush with the top/bottom of the tubes, the
middle of the tube is the weakest, least stiff part as far as a gusset is concerned. That's why when you see gussets on rollcages they're
generally two pieces rolled around and welded either side.
Mmm, I have to admit that's the first time anyone has suggested that, and the only time I've seen plate welded to the top or bottom was on
the 'bent wishbone' thread which certainly isn't the best example.
Even a quick google image search for rollcage gussets shows both being used, although it does appear that the top/bottom gussets are much thinner
metal than the centre gussets.
Would anyone else care to weigh in?
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PhillipM
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| posted on 27/4/14 at 12:36 PM |
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If you weld them in the centre your putting the stress into just the wall thickness of the tube - running the risk of kinking the tube (and hence a
big loss of strength) with an impact, and cracking with fatigue if the ends off the gusset aren't rounded and ground flush.
If you weld them on the outside you're effectively using about a quarter of the tubes diameter as the effective wall thickness.
[Edited on 27/4/14 by PhillipM]
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Slimy38
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| posted on 27/4/14 at 02:03 PM |
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quote:
Originally posted by PhillipM
If you weld them in the centre your putting the stress into just the wall thickness of the tube - running the risk of kinking the tube (and hence a
big loss of strength) with an impact, and cracking with fatigue if the ends off the gusset aren't rounded and ground flush.
If you weld them on the outside you're effectively using about a quarter of the tubes diameter as the effective wall thickness.
[Edited on 27/4/14 by PhillipM]
But conversely, if the gusset is on the top (which would be the most likely due to it being a suspension wishbone), you've got the weight of the
car (and the suspension) trying to do the same thing in a vertical plane. And suspension forces are guaranteed whereas an impact is (hopefully!)
unlikely.
I do see your point, but for now I'll stick with the Haynes manual design.
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britishtrident
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| posted on 27/4/14 at 02:19 PM |
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quote:
Originally posted by PhillipM
quote:
Originally posted by mark chandler
Curve reduces the stress point, you should also weld in the middle of the tubing not top or bottom.
Welding a brace/gusset to the middle of the tube makes the stress even worse, it really should be almost flush with the top/bottom of the tubes, the
middle of the tube is the weakest, least stiff part as far as a gusset is concerned. That's why when you see gussets on rollcages they're
generally two pieces rolled around and welded either side.
A roll cage is an entirely different load case, if look back 10+ years to the early days of as per book Locost building you will find horror stories
of bent wishbones, after a bit of discussion among the group a consensus was reached that welding a plate with nicely tapered ends along the neutral
axis of the wishbonebtubes was a valid solution.
Experience has shown that it works as stories of catastrophic failures in wishbones are pretty rare these days although there are a lot more cars on
the road..
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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garyt
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| posted on 27/4/14 at 02:58 PM |
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Hi if your after the plates.. I just copied the drawings to craig at plazcut waiting for costing to do the mx5 wishbone plates if anyones interested
will post it when I get a reply
Gaz
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PhillipM
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| posted on 27/4/14 at 08:48 PM |
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quote:
Originally posted by Slimy38
But conversely, if the gusset is on the top (which would be the most likely due to it being a suspension wishbone), you've got the weight of the
car (and the suspension) trying to do the same thing in a vertical plane. And suspension forces are guaranteed whereas an impact is (hopefully!)
unlikely.
I do see your point, but for now I'll stick with the Haynes manual design.
Yes, but if you're putting a vertical load through a flat, horizontal plate and expecting it to be stiff, you've got more issues than
welding it to the wishbone...
The very reason those talons ones you pictured have had to fit a horizontal bar is to spread the load to the top and bottom of the tube to stop the
gusset kinking/cracking the main tubes in the centre.
[Edited on 28/4/14 by PhillipM]
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Samuele
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| posted on 3/6/16 at 10:24 AM |
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s
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