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PostPosted: January 26, 2007, 1:47 pm 
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Joined: October 11, 2006, 4:49 pm
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what are the concerns over substituting a round tube in a lower a-rm for a square one. should the thickness be increased, is ERW the only square solution. if so what orientation should the weld seam be facing

andrew

edit. just found out about HSS. comments on this too please.


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PostPosted: January 26, 2007, 2:32 pm 
My understanding of the superiority of round tubing vs square tubing in the A arms is that of 3 dimensional triangulation. Because the A arms are basically a 2d part the round tubing is superior to square tubing. Square tubing is fine for use in the frame because the frame is triangulated in 3 dimension.

Sorry I don't have a better answer, but that is what I remember reading a while back on some website. Oh yeh and that is the non-technical answer if you didnt aready guess.


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PostPosted: January 26, 2007, 2:43 pm 
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Joined: August 15, 2005, 10:13 pm
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Location: Charleston, WV
Did you see that funky rectagonal lower front control arm on Kinetic's (Jack's) website? It looked pretty neato.

The obvious downside I see to using square is that you couldn't weld in the threaded bungs for heim attachment.

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PostPosted: January 26, 2007, 3:02 pm 
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chetcpo wrote:
Did you see that funky rectagonal lower front control arm on Kinetic's (Jack's) website? It looked pretty neato.

The obvious downside I see to using square is that you couldn't weld in the threaded bungs for heim attachment.


yep sure did. i wanted to do exactly what jack has done but unfortunately, 2.5x1x.065 is extremely difficult to track down in my area, no luck so far. ive decided to use a square tube for the front lower arm, with a round tube extending rearwards. it simplifies the fabrication. the front tube will be 1x1x.083 or .100 square as opposed to 1x.065 dom. yes a weight penalty will be incurred, but this is about managing comprises. i will use bushings, not rod ends/spherical bearings.

andrew


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PostPosted: January 29, 2007, 3:56 pm 
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Joined: July 29, 2006, 9:10 pm
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Location: Oregon, usually
airframefixer wrote:
chetcpo wrote:
The obvious downside I see to using square is that you couldn't weld in the threaded bungs for heim attachment.


unfortunately, 2.5x1x.065 is extremely difficult to track down in my area, no luck so far. ive decided to use a square tube for the front lower arm, with a round


If I forgot to post a how-to on my site...you make square bungs the same way you make round bungs, except you start with a bar and drill it. 7/8 x 7/8 bar can be cut to length for the 2.5 x 1 x .065, sanded down a bit on one side, and drilled and tapped through the other side.

airframefixer, the 2.5 x 1 tube is off the shelf around these parts--I could mail you some if you like.

Ps--"funky" eh?
PPS--the way to avoid torsion loads on a square control arm tube is to put ball joints on the ends. The comment re lack of internal triangulation is correct, but not an issue on short tubes sans torque inputs. IMO.

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PostPosted: January 29, 2007, 11:18 pm 
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thanks for the offer Jack, ive settled on a design using the 1x1x.100 HSS, and ive started fabrication. ill keep it in mind in the future though as you know how fast the plan can change

andrew


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PostPosted: January 30, 2007, 9:39 am 
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Joined: September 16, 2006, 10:57 am
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Location: Stuart, Fl
I never thought of making my own bungs using bar stock. I ended up buying 7/8 .156 DOM and tapping it but it is really heavy.


Randy


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