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  #1  
Old 06-16-2016, 08:45 AM
larryj larryj is offline
 
Join Date: Dec 2005
Location: Bellevue, WA
Posts: 165
Default Roll Bar bend

I've seen a couple RV-4's (and maybe others) with a non-Vans Roll Bar that was bent instead of welded at the top. The material is 1.50"dia X .049"wall 4130 tube.
Does anyone have a source for the bend ???
I've been chasing vendors and am getting quotes of $500 plus 20' of material and lead times of 8 weeks for just one bend.
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  #2  
Old 06-16-2016, 09:08 AM
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bret bret is offline
 
Join Date: Feb 2010
Location: Gardnerville Nv.
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I would check for a muffler shop that does custom exhaust, they use hydraulic tube benders that use dies that encapsulates the material to eliminate kinks.
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  #3  
Old 06-16-2016, 09:40 AM
JimRice JimRice is offline
 
Join Date: Aug 2014
Location: Collierville, TN
Posts: 99
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My -4 has a rounded roll bar. While it looks nice, it is several inches shorter than the stock Van's plans. I think it has to be in order to achieve the necessary bend radius. I have actually been considering replacing it. In the event of going over on its back, all the height possible on the rollbar will be a good thing.
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1994 RV-4 N4WJ (Purchased/Flying)
1946 J-3 Cub N7155H (Restored/Flying)
1946 Globe Swift N3368K (Purchased Restored/Flying SOLD)
1987 Starduster Too SA-300 (Purchased/Flying/SOLD)
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  #4  
Old 06-16-2016, 10:43 AM
SMRacer SMRacer is offline
 
Join Date: Feb 2012
Location: Leesburg, VA
Posts: 551
Default Roll bar

The roll bar in my RV4 was fabricated by a shop that builds roll cages for racecars.

Two problems exist. The severity of the bend at the top makes it very difficult to fabricate. We ended up doing this by bending two pieces as tight as we could without any crushing, and then cut and welded in an internal sleeve at the top to join the two pieces. If that doesn't makes sense, you can contact me and I'll try to explain better.

The second problem is that since it isn't pointed at the top (a radius bend instead of an acute angle) it ends up being wider near the top. So the tip over canopy can interfere. That's why they tend to be a bit shorter.

https://static.wixstatic.com/media/c...956203c4d3.jpg
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  #5  
Old 06-16-2016, 11:39 AM
Radioflyer Radioflyer is offline
 
Join Date: Nov 2009
Location: Boston
Posts: 154
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I've been considering this for a non RV airplane. You might find it worthwhile.
http://www.showplanes.com/ecom-prodshow/WD_814fb.html
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  #6  
Old 06-17-2016, 09:52 AM
larryj larryj is offline
 
Join Date: Dec 2005
Location: Bellevue, WA
Posts: 165
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Thanks for the input so far but none applies.
I'm scratch building a Rocket including a canopy system of my own design; a combination fixed windscreen and flip over. The layout work is done and I can accommodate the shortcomings discussed (height etc.). The standard mandrel bend radius for the 1.50 X .049 is 3.50"CLR (Center Line Radius). My experience with muffler shops is that their equipment is not fine enough to handle the thin-wall. Similarly, race car shop bending roll-cages are bending much thicker wall DOM and are not using a mandrel.
Still looking for a tube bending shop.
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  #7  
Old 06-17-2016, 12:24 PM
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Bob Kuykendall Bob Kuykendall is offline
 
Join Date: Sep 2006
Location: Douglas Flat, CA
Posts: 589
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Quote:
Originally Posted by larryj View Post
...Similarly, race car shop bending roll-cages are bending much thicker wall DOM and are not using a mandrel.
Still looking for a tube bending shop.
When I need 4130 bent I shop it out on mfg.com. But it's been a while since the last batch, so I can't remember who did it.

As to the wall thickness, you kind of have to decide whether you are making what the Miata guys call a "show bar" or an actual piece of rollover structure.

Thanks, Bob K.
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  #8  
Old 06-17-2016, 12:47 PM
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DanH DanH is offline
 
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Location: 08A
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http://www.showplanes.com/index.php?...z0o79i7rs7e215
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  #9  
Old 06-17-2016, 12:51 PM
gmkonrad gmkonrad is offline
 
Join Date: Feb 2005
Location: Howell,MI
Posts: 132
Default Roll bar bends

You might give this a look.
http://secure.chassisshop.com/partrelate/C42-290/
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  #10  
Old 06-19-2016, 09:04 PM
deek deek is offline
 
Join Date: Mar 2013
Location: Flathead Lake Montana - 8S1
Posts: 334
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Quote:
Originally Posted by larryj View Post
Thanks for the input so far but none applies.
I'm scratch building a Rocket including a canopy system of my own design; a combination fixed windscreen and flip over. The layout work is done and I can accommodate the shortcomings discussed (height etc.). The standard mandrel bend radius for the 1.50 X .049 is 3.50"CLR (Center Line Radius). My experience with muffler shops is that their equipment is not fine enough to handle the thin-wall. Similarly, race car shop bending roll-cages are bending much thicker wall DOM and are not using a mandrel.
Still looking for a tube bending shop.
Header manufacturers have the correct Eaton or Pines benders and ball mandrels ("spoon" mandrels won't give you the quality you're looking for on thin wall DOM tubing)
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