Landracing Forum
Tech Information => Technical Discussion => Topic started by: Greaseballracing on May 27, 2014, 05:45:12 PM
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Hey guys I'm in the process of building an aps-bf 650. It's rear engined with a 100" wheelbase, I'm looking for advice on the frame material. My local speed shop is drag racing based and they have in stock 1 1/4 x .0.82 cromoly or I can go to 1 1/2 x 0.155 mild tube not really sure and I can't seem to find a definitive answer as there seems to be no requirements in the rulebook. Any advice would be much appreciated. Thanks guys. Owen.
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The wall thickness you show for 1 1/2 doesn't look correct.
Pete
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Yeah it's been converted (roughly) from metric. As listed from the website is 25.4 mm x 3.96mm
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Decimal point is missing.
Regards, Neil Tucson, AZ
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Sorry guys from Australia, I'm not used to working in inches I'll edit it
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25.4 is one inch not 1 1/2 although 1 inch .155 wall should be sufficient for bike frame with the proper triangulation and design.
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1-1/2" sounds like streamliner material. I'd say 1" od x .095 is more than enough for a 650.
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Sorry guys from Australia, I'm not used to working in inches I'll edit it
You could use a combination of 38mm and 25mm tubing.
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Thanks for that stainless, vinsky & tauruck. The next deciding factor is chromoly or mild steel, does anyone have any ideas, I believe my headstock is chromoly so that is the way I'm thinking but if there is safety or legal issues with that I will machine a stock from mild steel.
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I build bike frames but I'm no expert knowledge wise on welding 4130 to mild steel.
I'm sure it could be done by the right welder.
My info over here in South Africa and from what I read is that Chromoly needs to be stress relieved in a furnace after welding to prevent it getting brittle.
Harley frames pre rubber mount get a pounding from the motor and they don't break so maybe there's an answer in that for you. :cheers:
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Check this link for info from Lincoln Electric on welding 4130 Chrome Moly.
http://www.lincolnelectric.com/en-us/support/welding-how-to/pages/chrome-moly-detail.aspx
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Thanks for the link.
I learned a lot. :cheers: :cheers:
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Chrome moly tubing that is usually used in building aircraft & race car chassis is 4130N. This is in a "normalized" condition. Welding normalized 4130 does not require stress relieving. Several FAA handbooks cover this.
Regards, Neil Tucson, AZ
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Mild steel......085........Bronze welding (Brazing)
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Thanks everyone that's the info I've been chasing. Looks like chromoly is the go, the shop stocks 1" x .120 or the next heaviest is 1"x .188 so I reckon the .120 will be my frame. It's planned with a double backbone and lots of triangulation so should be very strong. Thanks again for all the help.
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If going 4130 be careful of weld technique and the filler rod used.
This material was developed for the aircraft industry many years ago when oxy/acet was common.
Today we weld with much different techniques and filler materials. Plan on doing the torch normalizing after welding.
J
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Your "over building".......DOM Mild Steel with .085 to.090 wall ....1 to 1 1/4 is all that is needed....We build road racing sidecars that due to extreme cornering get a lot more stress on the chassis....your just going in a straight line (hopefully)......We have never had any problems using the above.........less material costs.........
No BS stress relieving.......Using a in-line-flusher do bronze torch welding (if you can find someone who knows how to do this type of welding)......Use the KISS system...(Keep it simple stupid)....Good luck on your project
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If you need proper filler rods for welding 4130N, check with Aircraft Spruce.Also, these may be helpful:
http://www.millerwelds.com/resources/articles/Best-Practices-for-GTA-Welding-of-4130-Chrome-Moly-Tubing
http://www.lincolnelectric.com/en-us/support/welding-how-to/pages/chrome-moly-detail.aspx
Regards, Neil Tucson, AZ
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Who is your frame guy Dale ?
i like the dom idea too, put your money into better body shape or more reliable power rather than exotic materials
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I just made my first run with a special construction bike. the bulk of my frane is 1x2 .062 mild steel. mig welded and in some places brazed. The thing that sticks in my mind is that when an space frame 4130 aircraft crashes you find a bunch of tubes that have all failed at the welds. If you have to make a repair on the lake, mild steel will be your friend. Yes, KISS
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Hey Owen
What motor are you looking to use
G
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Thanks again everyone. So general opinions are mild steel dom tube, good point zooterincm at least I can mig a mild steel frame if something does go wrong. Grumm441 I am running a late model 600cc triumph daytona engine with a turbo to put me in blown class.
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The thing is, unlike every other form of racing, it doesn't need to be light
G
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Very true. Just put the templates in to be bent I have gone with mild steel 25.4x 3.96 mm tube so will be machining a new head stock through the week. Thanks again for the help
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Thanks again everyone. So general opinions are mild steel dom tube, good point zooterincm at least I can mig a mild steel frame if something does go wrong. Grumm441 I am running a late model 600cc triumph daytona engine with a turbo to put me in blown class.
Greaseball,
Sorry I'm a little late to respond on this thread, but I wanted to chime in; I've had experience with both 1" x .062"wall 1020 CREW (which broke) as well as chrome moly (which hasn't - - yet!). Don't let chrome moly scare you away. As Neil has stated, thin walled normalized Chrome moly tubing does not require pre or post heating, can be welded by oxy-acetylene or TIG, and is at least 25% stronger than mild steel. The important thing is to either know how to weld or to use a welder who does, but that applies to whatever tubing you choose.
The design of your chassis is just as important as the material. I doubt that many on this forum have built a bike with a 10' wheelbase and 200 hp. You're going to be in 200 mph territory (if I had 200 hp, my bike would be capable of about 236 mph) and your chassis is twice as long as a standard bike which means stresses are going to be doubled as well. Consider showing your design to a structural engineer for ideas, but don't expect any engineer to sign off - - because they probably won't (can't because of their code of ethics which prevents them from designing in a field in which they are not qualified.) But they may be able to give you some valuable pointers.
Tom
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Thanks Tom, sorry for my late reply I ended up with mild steel 25.4x3.96 and am currently working on the frame. I have a reasonable amount of experience in mig welding (currently work on cell towers and do a lot of fabricating to mount antennas and ancillary equipment) if I can figure out posting pictures from my phone I'll show where I'm at. But your input is very appreciated, especially given the speed I am looking at running. So thanks again. Owen
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(http://tapatalk.imageshack.com/v2/15/01/14/45108e7ee5da1825326f216b7f6b4858.jpg)
Ok try that hopefull there is a photo on here now.
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(http://tapatalk.imageshack.com/v2/15/01/14/45108e7ee5da1825326f216b7f6b4858.jpg)
Very nice :cheers: :cheers:. Lots of triangulation, should be strong. Keep posting pictures as you fill it in,
Sumner
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Hey, I build a sidecar not 10 feet....but 8 feet....with 250hp (turbo)......not 200mph....but it did go 187mph.....(with 2 people on board)....Mild-steel 1.250x.085 Bronze-Welded (Brazing to you none informed...).......raced it on the salt for 10 years......Now in the National Motorcycle Museum........
It is not broken or cracked and still rolls just fine.....................................................................
PS. Your frame looks great....maybe a little "over built"
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Thanks guys, I'll keep the photos up as it moves forward sumner.
Bak189 that thing sounds like it was fun... And durable. I am generally pretty good at over engineering things, but have gone a bit hard with this one just because of the target speeds. Would much prefer to over engineer this than under engineer it. Mtabike, thanks heaps man
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Top view of the frame would be instructive. Is that a single top tube exiting the headstock at the front? You will want to read recent posts about CP vs. CG, especially if you plan to add bodywork.
Tom
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(http://tapatalk.imageshack.com/v2/15/03/04/0e1ebd5bbdd9b76b3cc6afca23c2bdee.jpg)
Thanks Tom I'll look it up here's a veiw from the top it has dual top tubes, I kinda figured it would be stronger than a single.
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Couldn't see your top tubes well so I lightened it up. Two tubes twice as good in compression as one. Lots of cross bracing to increase torsional strength as well. Click on the photo to zoom in. Now we can read your license plate on the '59 Chevy!
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Thanks Tom yeah two has to be better than one in my figuring I have tried to over build this thing as much as I can the cross bracing is two in an x brace at the first uprights and alternating diagonals at every upright there will be plates to stiffen around the neck and will be fitting more plates at various intersections for mounting things like seat and hardware. The 59 is my sensible work ute. You know run to the dump pick up engines and steel and stuff.
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Another observation is that with that very long frame and extreme fork angle, you're going to get a lot of stress where the frame tubes meet the headstock. I would like to see some plating on the sides, using the same technique that is used to gusset roll cages. Lots of bikes use gussets at this point so I assume that this is a common place for frame breakage. That is, leave a little gap at the tube-to-headstock joint so that any crack that starts (that you may not see) is less likely to propagate, and weld the gusset to the headstock and both upper and lower tubes. Also, inspect this section often to ensure no visible cracks appear. I lost my drafting program when I upgraded to newer computer (ain't that great!) so I can't illustrate what I mean.
Tom
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Haha good thinking Tom I actually started making the gussets for that area last night at work I have 6mm mild steel plates on top bottom and both sides the idea is to gain more weld on the neck itself and as you said spread the load evenly into the frame they extend 200mm from the neck once installed I'll post some pictures, I had planned on welding them as per roll cage gussets with an inch of weld then an inch of gap as you said. I really would not like to encounter any cracking in that area especially.
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It is common for drag bikes to use the frame as an air tank. Simple and you know if a crack starts to develop.
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Hey GB are we going to see you in a couple of weeks at the big white dyno ? , not expecting the bike just yet
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There are many stresses in structural design as listed from biggest to smallest. Tensile stress is the greatest and that is when things break. Yield stress is when they start to permanently deform after loading rather than springing back to original shape. Fatigue stress is when they start to crack under repeated loading. The stress creating maximum allowable deflection is less than all of these. For example, the typical floor beam cannot deflect more than 1/360 of its length under the maximum design load This prevents plaster from cracking on the ceiling of the room below and it does not feel bouncy when people walk, dance, etc in the room.
Elastic deflection in a bike frame is really scary and we instinctively design them so it is minimized. The stresses from loading are typically quite low within these beefy frames when we do this and they are far below the elastic limit. The metal's modulus of elasticity governs performance in this realm. The elastic moduli of carbon steel and chrome moly are similar and neither offers a big benefit in low stress design.
We are not enclosed in the bike frame. The frame is history after a big crash no matter what it is made from. A roll cage or car frame is different. There, we want strength and protection. Elastic deflection under typical driving loads is not the governing concern. Resistance to permanent deflection is. The stronger more exotic steels can provide benefits in this application.
The stronger mild steels are plenty good for a bike frame.
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There are many stresses in structural design as listed from biggest to smallest. Tensile stress is the greatest and that is when things break. Yield stress is when they start to permanently deform after loading rather than springing back to original shape. Fatigue stress is when they start to crack under repeated loading. The stress creating maximum allowable deflection is less than all of these. For example, the typical floor beam cannot deflect more than 1/360 of its length under the maximum design load This prevents plaster from cracking on the ceiling of the room below and it does not feel bouncy when people walk, dance, etc in the room.
Elastic deflection in a bike frame is really scary and we instinctively design them so it is minimized. The stresses from loading are typically quite low within these beefy frames when we do this and they are far below the elastic limit. The metal's modulus of elasticity governs performance in this realm. The elastic moduli of carbon steel and chrome moly are similar and neither offers a big benefit in low stress design.
We are not enclosed in the bike frame. The frame is history after a big crash no matter what it is made from. A roll cage or car frame is different. There, we want strength and protection. Elastic deflection under typical driving loads is not the governing concern. Resistance to permanent deflection is. The stronger more exotic steels can provide benefits in this application.
The stronger mild steels are plenty good for a bike frame.
Bo,
Although this is generally true, fatigue failures are the most common type of failure for motorcycle frames, and Chromoly (normalized is the only form you want to use) is almost twice as resistant to fatigue failure as mild steel for a given section size. Also, stresses that result in fatigue failures are not due to static forces but dynamic forces caused by impact loads that can be many times higher than static forces. Structural elements, especially those adjacent to motor mounts and other parts that may vibrate, are subjected to literally millions of cycles of these impact forces which will cause frame tubes to fracture, even when the computed forces seem low. I recommend the use of thicker sections or stronger steels for these areas and by all means, keep them clean and accessible and visually inspect suspect sections. Following are a few real examples of frame failures after just 2 years of land speed racing! The frame was 1" OD by .060" wall mild steel. It has been replaced with normalized chromoly of the same size and has at least survived 2 more years at higher speeds with no visible cracks........yet! I continue to monitor it.
Tom
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A rough estimate of the endurance limit for steels is 50% of the tensile strength, plus or minus 10%. Normalized chrome moly has a tensile strength between 95 and 100 ksi, as I remember. This is stronger than a lot of mild steels and the endurance limit is also greater. This provides more fatigue resistance, as Tom says.
The problem with the problems I dealt with was as the builder, often a well respected manufacturer, used much thinner wall tubing in the chrome moly applications. This is typical. Stress is force divided by area, so the stresses from the cyclic loads in the thinner wall tubes were as close, or closer, to the endurance limit as with the typical thicker wall mild steel frame. The dang things broke. Also, they flexed a lot under use and the handling was spooky at best.
Builders, and especially me, figured out that the welds needed to be normalized to prevent cracking. This sorta worked. Sometimes we normalized the weld area, other instances we annealed it, or we did not get it hot enough to do any good. One thing we learned is the thinner wall chrome moly worked best for trellis like space frames. Bending loads are minimized and replaced by tensile and compression loads in these structures. Why this frame type works better, I have no clue. There is a book by Carroll Shelby, "Engineer to Win," that has some hints on using this metal.
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The book is by Carroll Smith. He wrote a whole series of books on race car construction, preparation and tuning. They're all worth reading if a guy's serious about being competitive.
Pete
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Hard to find info.