JMortensen Posted July 10, 2006 Share Posted July 10, 2006 I was looking for a calculator to tell me how much tubing of a particular wall thickness would weigh per foot. I found this site: http://www.thefont.pwp.blueyonder.co.uk/bikes/index.htm which appears to be a DIY chopper site out of Europe. The calculator on the "Selecting Tube Sizes" page seems to work, and he gives a good demonstration of bending stiffness. I thought the page about gusseting was pretty interesting as well. I was planning on gusseting my roll bar the "wrong" way with the gusset right in the middle of the tube. At least wrong according to his article. Now I'm thinking I should do it tangentially. Anyway, I'm hoping this might spark a conversation about how to gusset and maybe tubing length and thickness as well. The guy seems to know his stuff. Heres the jacking my own thread part - My own interest in this has to do with adding onto my roll bar, and I was considering using different size tubing for the brace parts which aren't part of the traditional 6 or 8 point cage. I used 1.75 x .120 for the main hoop, and was considering 1.625 x .065 for the bracing, but could get 1.75 x .065 if necessary at about 4 times the cost of the 1.625. Still don't know what to think about those options. In reading katman's ITS article it says in a parenthetical note: the rules essentially dictate the same tube everywhere However when I read the SCCA rulebook I can't seem to find any reference to cage tubing sizes other than for the basic 6 point cage and the shoulder bar. Maybe that rule has gone by the wayside, or maybe since the ITS rules don't allow the bracing that I'm going to do, they just don't have anything to say about this type of bracing. I really don't know. My car will be an autoxer and time trialer, maybe at some point might be entered in a vintage race or two. The added structure will be bracing to the front and rear strut towers, maybe down to the subframe connectors, that type of thing. Quote Link to comment Share on other sites More sharing options...
johnc Posted July 11, 2006 Share Posted July 11, 2006 The SCCA rule mandating the same size tubing is section 18.6.B/C - "Minimum tubing sizes... for all required roll cage elements." Basically, if SCCA specifies an element in a roll cage, that element has to meet the minimum tubing size listed in 18.6. This includes the front and rear hoops, rear braces, diagonal brace, door bars, front down braces, and forward braces. Anything else that the builder adds can be made from whatever the builder wants, although sticking with DOM is a very, very good idea. Tech can, on their opinion, reject a cage that they consider unsafe. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted July 11, 2006 Author Share Posted July 11, 2006 That's good news, thanks. What did you think about the gusseting info on that other page? I was curious to hear your take on that subject John. Quote Link to comment Share on other sites More sharing options...
johnc Posted July 11, 2006 Share Posted July 11, 2006 The gusseting info is interesting but I'm not sure how true it is. I would think that both types of gusseting create stress points. I"m going to refer the page to my mechanical engineering friend. Quote Link to comment Share on other sites More sharing options...
tube80z Posted July 11, 2006 Share Posted July 11, 2006 Prepare to Win, page 56 Straight Gusset Plate Not too good -- can be improved by flanging long side Shaped Gusset Much better I found some additional papers in seismic bridge design that were interesting to read by I'm not sure how much they align with what we're doing. I will be interested to hear what your friend has to say. I remember many, many moons ago when racing BMX bicycles the frames with the single gusset would break at the end of the guesst. And those with the guessets on the outside of the tube didn't have this failure. Cary Quote Link to comment Share on other sites More sharing options...
mom'sZ Posted July 12, 2006 Share Posted July 12, 2006 when Katman wrote that it was true, the rule allowing any size tubing for non-mandatory bars is new, this year I think Quote Link to comment Share on other sites More sharing options...
tube80z Posted July 14, 2006 Share Posted July 14, 2006 The gusseting info is interesting but I'm not sure how true it is. I would think that both types of gusseting create stress points. I"m going to refer the page to my mechanical engineering friend. I chatted with a friend who's a civil engineer and he gave me an answer but wanted to check with a friend that's a structural engineer. They both agreed a single gusset in the middle of a tube is a bad idea. If the joint is in tension or compression there will be more stress in the middle area (top and bottom). You'd be better off with a gusset that captures the neutral axis where stress is least. Both agreed a formed gusset (what I call a taco gusset) would be the best solution. Are they in agreement with your engineering friend? The explanation made sense to me. But I'm far from qualified to give a real answer Cary Quote Link to comment Share on other sites More sharing options...
JMortensen Posted July 14, 2006 Author Share Posted July 14, 2006 These taco gussets, what thickness metal is used? I've seen a lot of pictures that look like sheet metal. Also see a lot with a flanged hole. Is that hole necessary, or just better? Is it that much better to have the sheet wrap around as opposed to doing one separate gusset on each side? The BMX comment brought back some old memories Cary. Made me realize that my Supergoose had a flanged hole and two separate gussets. Quote Link to comment Share on other sites More sharing options...
johnc Posted July 14, 2006 Share Posted July 14, 2006 My engineering friend is traveling around the country checking bridges. I don't know when he'll be able to answer my question. Regarding gusset metal thickness, I typiclaly make it the same or slightly less then the tube thickness. But, that's for a single, in-line gusset. If I did the double gusset on the sides I would use material that was half the thickness of the tube wall. Quote Link to comment Share on other sites More sharing options...
tube80z Posted July 14, 2006 Share Posted July 14, 2006 These taco gussets, what thickness metal is used? I've seen a lot of pictures that look like sheet metal. Also see a lot with a flanged hole. Is that hole necessary, or just better? Is it that much better to have the sheet wrap around as opposed to doing one separate gusset on each side? I've been using the gussets from Joe's racing products. They are 0.065 (16 guage) if I recall correctly, which is essentially sheet metal. The hole isn't necessary but would save some weight. These need to be thin so if the joint is loaded in compression the gusset buckles before the tube. And in tension the larger surface area is better. At least that's how it was explained to me. Cary Quote Link to comment Share on other sites More sharing options...
JMortensen Posted July 14, 2006 Author Share Posted July 14, 2006 Wow that's convenient. Joe's is about 20 minutes drive from here. Thanks. Anyone know where to get the flanged sheet that people use to tie the cage to the A pillar like Mike Kelly's car has? Quote Link to comment Share on other sites More sharing options...
tube80z Posted July 14, 2006 Share Posted July 14, 2006 Anyone know where to get the flanged sheet that people use to tie the cage to the A pillar like Mike Kelly's car has? I just make my own. I've never seen panels that have flanged holes. Send me an email and we can chat about it. Cary Quote Link to comment Share on other sites More sharing options...
zlalomz Posted July 14, 2006 Share Posted July 14, 2006 I was going to use a hole saw and the flaring tool seen here. http://www.irvansmith.com/catalog2/parts/irvan_flare.shtml They have a hole punch/flare combo tool too for more dough. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted July 14, 2006 Author Share Posted July 14, 2006 Didn't Mike say that the place that did his roll cage was buying this stuff in pre made sheets? I guess I'll PM him about that. That's a good price on the flare tool for sure Steve, but I'd like to make this easy on myself if it is available in pre-made sheets. You'd think they could stamp these things out for next to nothing... Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted July 14, 2006 Share Posted July 14, 2006 Might try the WWII stuff (Marston matting) http://www.calumetindustries.com/lmats.html Quote Link to comment Share on other sites More sharing options...
JMortensen Posted July 14, 2006 Author Share Posted July 14, 2006 Looks a bit beefy for what I need. Its the right idea though! Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.