Landracing Forum
Tech Information => Technical Discussion => Topic started by: willieworld on October 13, 2008, 05:28:17 PM
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Outside dia. Advertised wall Actual wall At the bend outside
1 1/2 od .083 cm .083 .081
1 1/2 od .125 dom .126 .122
1 5/8 od .120 ew .118 .115
1 5/8 od .125 dom .126 .123
1 1/4 od .134 ew .124 .122
Straight section was sonic checked, outside of bend was sonic checked.
Some tubing not as advertised(nominal wall thickness). The smaller the radius on the bend equals the thinner material on outside of bend.
And the more degrees of bend the thinner material on the outside of bend.
This is just some testing I did today on a few random pieces of tubing I had around the shop. They are not all exactly the same bend and each tube size is different and some of the radius are different. But I think you get the idea.
If you need any testing in particular done let me know.
Willie Buchta
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Willie,, thanks that helps.. I was going to use .120 DOM... may use 1 3/4
.134/.135 DOM instead.
Charles
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charles--the mininum requirement is 1 5/8 .120 nominal wall ( THERE ARE SOME EXCEPTIONS ) if you use .120 wall dom you will be above the mininum----if you can break up the long pieces of tubing with diagonals --bracing you will make the cage much stronger than going to a larger tube size --dont lull yourself into a false since of security with your roll cage it is actually the other safety equipment that keep you safe in an " upset " ---the cage only keeps the car fron caving in on you ---and dont forget those gussets they make all of the connections twice as strong-----just some thoughts willie buchta
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willie, got it ... Gussets and Braces.... X Bracing, Diagonal Bracing, Cross Bracing, Sill Bars, Pro Stock/Funny Car set up, Think we will be ok on the cage once we decide entry and exit (with my size) need some well thought our drivers door swing outs (or lower x or y bracing so I can slide in and roll out ..lol)
The Chassis and Suspension is the big project... Have not decided on type of front suspension...Several Ideas floating around, but nothing final..
Not sure how much caster adjustment can get with a trick coilover Mustang II, or Tubular A arm IFS set up will yield..or how bump steer may come to play. The dropped straight axle like the Vicky is another idea, but using parallel leafs, but not sure how low we can go that way and how adjustable it can be..??
Almost certain will use 4 link and coil overs in rear with Panard Bar and sway bar. (Vicky has Pete and Jakes long ladder bars, and Panhard set up with adj coilovers)
Well my brain hurts thinking of all the possible combinations...
Charles
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Great information, Willie. Thanks for posting it. :-)
What kind of sonic tester do you have and what do they cost? I would like to get one primarily for engine blocks. Any thoughts or experience using them...
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saltfever---i bought the sonic checker in 1993 --at that time it was expensive i think about 1200 dollars--they are probably cheaper now---it is made by the staveley instrument co in kennewick wa.---when i bought it they had 3 options for the pickup ( concave--convex--flat ) the pickup was 300 dollars so i just got one (flat) it works well on flat and round tubing --it is accurate to .001 in 2 inches close enough for me ---i use it on tubing and cylinder head ports -keeps me out of the water jackets --even on the harley heads it lets me know how much meat i have left--i use to build nhra chassis and they required a sonic check--never had one fail --it is very easy to use --i will bring it to el mirage in a couple of weeks if anybody wants anything tested look me up willie buchta
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....................Not sure how much caster adjustment can get with a trick coilover Mustang II, or Tubular A arm IFS set up will yield..or how bump steer may come to play. .............................................................................
Don't forget that if you add weight like we have that you will need springs that will handle it. Hooley has some kind of odd-ball coil overs for the mustang like suspension on the front that take springs that come in only limited spring rates. I would design the front and rear in a way that you have a large spring rate selection available.
Great stuff on the tubing thickness Willie, thanks for doing that,
Sum
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saltfever---i bought the sonic checker in 1993 --at that time it was expensive i think about 1200 dollars--they are probably cheaper now---it is made by the staveley instrument co in kennewick wa.---when i bought it they had 3 options for the pickup ( concave--convex--flat ). . .
Thanks for getting back to me, Willie. :-) I'll look them up.
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Sum, thanks for the heads up on the springs. My plan if going Mustang II or other IFS was to use QA1 coilovers, they have at least 10 spring rates and full ride height, preload and dampaning adjustments.
Oh any luck on getting the spill plate and spolier templates for me... If you get them let me know and I will send you my address and postage.
Thanks
Charles
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panic could you do a couple more of those one with an upright in the middle with diagonals running top right to bottom left and one with one diaogenal running from top right to bottom left and the other diaogenal running from bottom right to top left ---smaller triangles with about the same amount of material -thanks willie buchta
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Guys, I am following this thread with a lot of interest. Great stuff and thanks to you both. However, I'm a little confused about Panic's last post. You are referring to an Excel program. Was this program posted in another thread and is public? (If yes, please point to it). Or is this a program you created and is personal? Great example though, on the effectiveness of geometry vs. mass. :wink:
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Willie,
I am new to tubing bending. What tool are you using for your bends? I may have a project coming up to build a frame with 1.5" OD tubing and may need to buy an (affordable) bender.
Don
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don--its a JD squared --the bender is great mine is 20 years old and works like new and ive made thousands of bends--the dies are sold seperatly-and are 125 to 200 dollars each ---check it out---willie buchta----------------www.jd2.com/
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.........Oh any luck on getting the spill plate and spolier templates for me... If you get them let me know and I will send you my address and postage.........Charles
Yes he said he would be glad to make templates. Send me an address, don't worry about the postage, remember he is a mailman,
Sum
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Ecentricity: This is a term that is used to discribe the actual weld joint of the diagonal tube at the corners of the two tubes that are joined at 90 degrees. For the greatest strength of the joint and the greatest stiffness the center line of the diagonal tube should intersect at the same point that the two tubes that form the 90 degree intersect. This means that you have to fit the diagonal tube to both tubes not just one. The difference in the strength of the joint and its stiffness can be as much as a factor of three.
Rex
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rex C² willie buchta
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rex C² willie buchta
Huh? What does that mean, Willie?
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c squared cc eccentricity willie buchta
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Ecentricity: This is a term that is used to discribe the actual weld joint of the diagonal tube at the corners of the two tubes that are joined at 90 degrees. For the greatest strength of the joint and the greatest stiffness the center line of the diagonal tube should intersect at the same point that the two tubes that form the 90 degree intersect. This means that you have to fit the diagonal tube to both tubes not just one. The difference in the strength of the joint and its stiffness can be as much as a factor of three.
Rex
That much of an increase in strength makes the additional fit-up time moot. Spreading the load across two planes @ 90 deg. seems like it will add torsional resistance as well. Jerry
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panic--i build chassis for a living and know exactly of what you speak --the diagonal coping (fishmouth ) into both the " main rail " and the upright--- the over all strength arnt just because of the tube placement but also because of the weld placement ---both help contribute to the over all strength----willie- i do better with pictures than words -buchta
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here is some information on that subject http://www.landracing.com/forum/index.php/topic,3837.0.html
thanks willie buchta
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I presumed that the quality of the weld, both placement and fusion, (something I'm not competent to evaluate) would always be of greater strength than the actual tubes!!
And that is the issue. Bisecting the 90 degree angle with another tube creates very small acute angles that are very difficult to weld continuously. You have to use a smaller torch cup, maybe extend your tungsten, wrap your arms around the back side to hold the filler rod, etc. Your get the idea. A competent welder will create a quality weld. However, I have seen a wide range of fabrication skill where the geometry was correct but the weld was poor quality. I'm not recomending it, but the non-bisected strut can be welded easier with less skill. The geometry may be inferior but because of easier to produce weld integrity, the joint may be stronger. That is a poor excuse for such a joint but that is the reality of what I have seen.
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It's something I wrote,download it from "Formulas".
Mr. Panic, thank you for doing that. Very nice.
You say to subtract 0.750" from total length for the pushrod. Just checking here. . . the pushrod is the diagonal and the .750" is because of the loss of material in the fishmouth area?
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I'm glad I asked.
What do you suggest to use as a total length for a fishmouthed diagonal? The the longest part of the tube or the shortest distance between the two fishmouthed ends?
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Sorry, I don't feel competent to answer a fabrication question - not enough with experience. Design is my stronger card, feeble though it may be.
Your sincerity is much appreciated. :wink: Great spread sheet . . .many thanx
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I`m thinking more along the X-axis. W/ the diagonal tube coped into the 90 deg. joint any twisting of the rails would put the diagonal into a compression/torsion load. J.B.
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One of the difficulties in fitting brace tubing is getting the tube to fit snugly against the other tube without gaps.
I found this program that lets you put in the tubing diameters and angle, then prints an accurate cut template for the tube.
Tubemiter (http://www.ihpva.org/people/tstrike/tubemiter.exe)
Text Instructions (http://www.ihpva.org/people/tstrike/tubemit3.txt)
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More complex version also posted to "Formulas", comments and error-debugging welcome.
Thanks for the good work and the update. That is a pretty sophisticated sheet from someone that is supposedly "learning" the software. :wink:
Any chance you could do a bolt strength calculator for tensile and shear? 8-)
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Rex brought up this, new word to me, with willie providing the correct spelling, :wink: resulting in a afternoon of reading white papers i.e. "Buckling of Imperfect Thin Cylindrical Shell under Lateral Pressure". :roll:
A number of thoughts on what eccentricity is from http://www.bendtooling.com/e-k.htm, Rex and myself.
eccentricity – The deviation of the center point of tube’s inside diameter from the center point of its outside diameter; normally in tube milling the permissible level of eccentricity is specified by a wall thickness tolerance. This applies to the tube wall being thick and thin resulting in the strong (thick) portion of the wall weaving back and forth as you travel down the length of the tube moving the center of strength as you travel down the tube as compaired to the center of the tube. Not something we worry about but the well drillers with a ten mile pipe do worry.
Rex's great description of the center line being offset from the right angle shared endpoints or vertex of the angle. The problem is creating an offset of the diagonal tube centerline or new ray to the angle, eccentricity, creates a lever from the right angle vertex to the offset ray point making it easy for the diagonal tube to break the joint. Eccentricity force increases for compression loading. You should make a complementary angle i.e. 58 deg + 32 deg from the original 90 deg angle. panic can you draw this?
My definition of eccentricity can be applied to an X joint of verticle angles made in the bracing with one long tube and two short tubes and the definition is the offset distance between the two centerlines of the short tubes. Either (1) the offset centerlines with parallel planes like the two rails of a railroad track or (2) non parallel centerlines creating two angled joints or knee joints. panic can you draw this? 8-) Would an offset less than the thickness of the tube wall be OK?
The two main parameters that control the static strength of un-stiffened knee joint under compression loading are the joint angle and the diameter thickness ratio. It is found that the joint strength is more sensitive to a change in joint angle.
My understanding is the joint should be directly across to make a straight line rather than making two knee joints or railroad track centerlines of the two short tubes.
To change the topic slightly back to the fantastic program by panic, thanks! Will the length of the tube change the force applied to the joint with shorter tube applying less force to the joint? Meaning we should keep the tube length short for this additional reason.
And just another term to think about: flattening – The reduction in the diameter of the tube as the lengthening outside radius pulls inwards while being stretched between the clamp die and pressure die. Reduction is mitigated by reducing drag at the point of bend.
I am changing a few of the tubes I have to make the cage stronger after this great thread!
willie can you tell us more about the gusseting? Every joint? Outside like the rule book shows or inside at the center? How big should they be?
Dean, thanks for the TibeMiter program by Giles Puckett of AU :-D
saltfever brings up an important fact about welding skill and equipment. I think the cage should be made correctly with some additional money spent having a pro weld the few joints that cannot be done buy the crew.
Geo
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geo i can tell you everything i know but its all theory --i will be glad to do some testing -- let me know what you want done --tube size-angles -gusset size and placement let me know willie buchta
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willie,
Would you do some of your welded tube joints with gussets to show us a good way to do it and have you tested any like you tested tubing previously. TIA
90 degree, 45 degree, 30 degree. How about an offset X joint. 1 5/8 inch .120 because I am a car guy 8-) or any tube just to show us what happens and to keep the tester, you, safe. Is there a point, angle, where gusseting is needed or not needed?
I do better with pictures than words too. :wink:
Geo
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Outside dia. Advertised wall Actual wall At the bend outside
1 1/2 od .083 cm .083 .081
1 1/2 od .125 dom .126 .122
1 5/8 od .120 ew .118 .115
1 5/8 od .125 dom .126 .123
1 1/4 od .134 ew .124 .122
Straight section was sonic checked, outside of bend was sonic checked.
Some tubing not as advertised(nominal wall thickness). The smaller the radius on the bend equals the thinner material on outside of bend.
And the more degrees of bend the thinner material on the outside of bend.
This is just some testing I did today on a few random pieces of tubing I had around the shop. They are not all exactly the same bend and each tube size is different and some of the radius are different. But I think you get the idea.
If you need any testing in particular done let me know.
Willie Buchta
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We were told at our LSR meeting that SCTA bought a sonic tester, Elmo next weekend sould be interesting. Hope they use it.
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:-D Do the rules permit us to use a smaller diameter and wall thickness for the struts and diagonals between the top frame rail and the bottom frame rail or would these items also be considered part of the "FRAME" and therefore have to be the same size as the top and bottom frame rails? :? :? :?
Terry :cheers:
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terry the rules permit you to use any tube size anywhere on your bike period--other than aero. there is no advantage with the smaller tubing ---you can use streamline tubing if that is a concern--it comes in C M if you want it in mild steel there are some companys that will make it but it will cost the same--i gave it some thought when i built sheris and my bikes but decided the expense wasnt worth it --as far as weight savings we both run 70 pounds of ballest on our sidecars ---it doesnt matter how light and fast it is if it breaks before you get to the finish line ( 2 times ) well you know the rest -----willie buchta
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when i started this thread it was because someone asked about material thickness on the outside of a bend (thought they might sonic check the outside of the bend )---i was cleaning the shop today and was looking at those bends and remembered the rule of bending--if the outside stretches the inside has to shrink (compact ) that would make the tube thinner on the outside but thicker on the inside ---any one have any guesses as to how much--none--as much as the outside thinned--more than the outside thinned-- i will post the results tomorrow willie buchta
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.......---any one have any guesses as to how much--none--as much as the outside thinned--more than the outside thinned--.........
d.) all of the above,
Sum
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willie,
I would say on a 90 degree bend, the inside would shrink and become thicker than the outside.
The inside would become thicker by 33 to 50 % of the amount the outside thinned.
So on your 1 1/2 DOM, .125 it was .126 actual and when bent the out side thinned to .122 or .004... so the inside would grow to a max of 50% of the .004 so add .002 to the .126 and the inside would be a max of .128 but I wold say .1275
Just my logical deduction (not based in any fact or experience LOL)
Charles
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On the previous page we talked about having the tubes meet correctly. Here is a pdf marked to show the rays of the angles and how they should meet. Except for one that is about 3/8 inch off which creates the eccentricity and the levering between the connected rays at the vertex and the non-connected single ray. It's a short lever however the forces are huge.
Found out how to markup a photo to post :-D
Geo
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Using the type of bender that is most common in motor sports the thickness of the outside of the bend has to get thinner and the inside has to become thicker. The amount of the thickening and thinning is related to the bend diameter and the diameter of the tube. i.e. a large diameter tube bent around a small radius die will stretch more on the outside, therefore thinning the metal and will compress more on the inside, therefore thickening the metal. If we looked at a .75 inch diameter tube bent 180 degrees around a 6 inch bend radius bend block (the 6 inch radius is at the tube center line.) the lenght of the outside surface of the tube is 6.375 x PI= 20.0276 inches, the inside length is 5.625 x PI=17.6714 inches and the length at the tube center line, which does not change is 6 x PI= 18.8495 inches. So the % change for the out side is 20.0276 div. by 18.8495= approx 6.3% longer and on the inside the number would be 17.6714 divided by 18.8495= approx 6.3% shorter. So the material on the outside of the bend should be about 6.3% thinner and the inside should be about 6.3% thicker but if you measure the thickness this is not what you find because as you bend the material the outer gets thinner and the inner gets thicker so this moves the neutral axis of the tube closer to the inside radius so what happens is the outside actually thins more than the 6.3% and the inside thickens less than the 6.3%. Also these numbers are only somewhat close on very thin wall tubing. If the tube was .050 wall the amount of increase and decrease would be around .003 inches. It becomes pretty obvious that if you go to larger diameter tubing the outside radius has to stretch a longer distance and therefore thins more. On a 2 inch tube it would be almost 17%!
Now there are machines that can actually bend thin wall tubing at very small bend radii and actually increase the thickness of both the inside and outside walls. This is all part of the "art" of tube bending. These benders will have a mandrel that will wipe the inside of the tube to keep the tube from collasping and also a "pusher" cylinder that grips the tube just infront of the bend dye and wyper and actually forces the tube into the area being bent and can actually force extra material into the area of the tube that is being bent and prevent thinning of the tube on the outside radius! The F1 guys bend 50 mm dia (2 inches) with .5 mm wall (.020 inch) tubing made from 625 inconel at less than 2 inch bend radius and make perfect bends! That is tube bending "art"!
We also need to remember that when the tube material is stretched or compressed it can actually have enhanced material properties because of work hardening which usually means an increase in the materials yield and tensile strength.
I will be interested in Willie's information on his testing of wall thickness after bending. Willie be sure to give us the bend die radius and the tube diameter and wall thickness.
Rex
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well folks i checked the inside of the bends today and i must say i was a little suprised--also im not a very good speller and was also suprised that someone would make fun of that--i think thats why i know and do what i do i dont spell so good and i dont rely on someones opinion without some facts ---any way enough of that--when i get the chance i will go back to the first post and add this in----the 1 1/2 CM was .098 on the inside--the bend radius was 5 1/2 ( center of tube ) ------ the 1 1/2 dom was .137 on the inside -5 1/2 radius----the 1 5/8 EW was .129 on the inside -6 1/2 radius-----the 1 5/8 DOM was .136 on the inside -6 1/2 radius----the 1 1/4 EW was .135 on the inside -4 1/4 radius----now remember all of the bends were not exactly 90 degrees ( close though )--this was not a perfect experiment but i think we all have a better understanding of the bent tube--im sure that different benders will have different results sometimes i oil the tube to bend that might even make a differance also but i dont really think that is important--i think that us all thinking about it is the important part---i would like to thank charles for THINKING about it and posting his answer --GOOD ON YOU CHARLES----willie buchta
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Saved you the work Willie. This one blew me away. I've bent a lot of tubing and I always assumed that there was more effect on the outside than the inside. There's usually a slight flattening on the ouside of the bend with the types of benders we commonly use. I guess that's partially how the thickness is maintained. Bye the way most of us know how assume breaks down. (ass-u-me) Oh so true!
Outside dia. Advertised wall Actual wall outside inside radius
1 1/2 od .083 cm .083 .081 .098 5 1/2
1 1/2 od .125 dom .126 .122 .137 5 1/2
1 5/8 od .120 ew .118 .115 .129 6 1/2
1 5/8 od .125 dom .126 .123 .136 6 1/2
1 1/4 od .134 ew .124 .122 .135 4 1/4
Pete
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thanks pete --im not to good at columns---there is one more thing maybe you could do ---all of the bends had an outside length of 8 inches and a inside length of 6 inches( or close to it ) so thats a 4 to 3 ratio--using that ratio could some one figure the average wall thickness for the bends --that would be interesting to know ---the 1 1/4 tube was 4 inches on the outside and 3 inches on the inside ---thanks all for everything willie buchta
this is my bender http://www.jd2.com/
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Peter and Willie,
Great info and it is always great to get the real hands on information!! Pretty dramatic to see the amount that the inside wall thickness increased! This is probably a result of the neutral axis of the tube moving closer to the bottom of the bend .
Willie, I am like you never a strong speller but somehow both of us have mumbled through! and I am of the age right now that I really don't give a sh-t if I can't spell!
Rex
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Some of this is much ado about nothing,
So whatta ya gonna do if the outer comes out thinner than the inner on MOST any bender that u and I can access?
If yer worried, build it with thicker material. SCTA/BNI, to my knowledge doesn't YET have a sonic tester-even one like Willie's several year old one.
Structural design may be more important.
By the way, the neutral point (a general statement-meaning MAYBE -not exact- is about 41% of the radius.)
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Willie - I will take spelling errors and non-aligned columns any day as long as you keep good stuff coming like this.
If you look at a single straight tube you can determine the strength of that tube very easily. If you assemble that tube into a girder with proper supports and gussets it gets more difficult. Put that all together as a complete frame and the analysis becomes a problem. Solving for partial differential equations is beyond the calculator or spreadsheet.
To really detemine frame strength you need Finite Element Analysis software.
Here is a source that you can look at to get an idea.
Nastran Finite Element Analysis (http://www.nenastran.com/)
Wikipedia entry:
http://en.wikipedia.org/wiki/Finite_element_analysis (http://en.wikipedia.org/wiki/Finite_element_analysis)
I am pretty sure that the Ack Attack and Speed Demon streamliners were designed with FEA. There may be a few others, but it requires huge buckets of money.
This also assumes that you can correctly predict the stresses in an accident.
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Scta does have one and from what I understand it will be used, so over the winter people can fix there cars before next year. I think they may even have a list of cars they what a closer look at .
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when the nhra started sonic checking tube thickness (roll cage ) you would get your car sonic checked --if it passed you would get a sticker with the date stamped in ---if it failed the car was not allowed to race until all repairs were made --it sounds like to me the scta is headed in the same direction--that is just a guess on my part though--if you have tubing that you arnt sure of now would be a good time to get it tested ---the nhra had a mininum for .120 wall tube it was .118 and they had that mininum before they started sonic checking--- hope to see you all at el mirage --sheri well be making beef stew for sarurday evening around 7 everyone is welcome willie buchta
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Done with this.
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yes it means when the infraction is very very small compared to the whole that it shouldnt matter --it applies to criminal law--- just using cheating as an example ---your saying that cheating a little is o.k. or that lieing a little is o.k. or did i misunderstand you willie buchta ------ p s you spelled it wrong
the tubing wall thickness is an nominal size not an exact size ---im only going by the scta rule book its the only one i have
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Scta does have one and from what I understand it will be used, so over the winter people can fix there cars before next year. I think they may even have a list of cars they what a closer look at .
I can confirm that. There are a number of suspect cars on the list. Mostly older cars that rusting from the inside out is the area of concern. There have been problems in the past.
The other concern is the guy that makes his frame or roll cage out of muffler tubing. You can't tell by looking, so the sonic checker is going to be used if they have any concerns that the fabrication is suspect. I asked if the motorcycle guys would be using it and there are no current plans, but it is always available to them.
No plans to check every vehicle. Only spot checks are planned. New vehicles might be checked.
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Slightly off-topic,but...I don`t see a way to weld the verticle tubes 360 deg. and then fit the dia. pcs. into place w/out the uprights being at an angle. I wonder how much strength is lost in the joint if the parts are fitted/welded as 1 pc.? Jerry
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Iam sure that some maybe sent home ,but even more will be upset over the deal, if you built the car yourself you know what you used and didnt read the rule book, or you just have an old car that was built years ago by a farmer. good luck
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About eight years ago I was approached by an aquantance who had purchaised a ex-record holding roadster found in a ad in Bonneville Racing News, asking if I would update the roll cage and redo the front suspension.
Stupidly, without seeing the car first, I agreed to upgrade the car.
Upon looking the car over, I noticed that on the main (3x2) frame rails that every place a bracket or crossmember were welded, the frame was buckled. I also noticed that a bridge-truss type support was welded to the underside of the tubing from front to rear.
I told the owner that the only way I would continue on the car was to cut the frame off at the firewall and use new tubing for the front half.
Imagine my suprise when I cut the car in half to find it was constructed of .062 mild steel tubing.........thats 1/16th of a inch!
Needless to say, I built a new frame for him.
p.s. we used the existing rear radius rods, and three years ago on the rough salt, the heim ends both broke at the welds...............know what you are buying...........Bob
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when he bought that car he should have taken a sonic checker and anyone that buys a car now should do the same willie buchta
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since the late 70's and early 80's the mig welder was new lots of people went out and bought one,now everyones a welder. sure they have there uses but you still need to know how to weld. I just wonder how many cars are welded together with flux core wire. :roll:
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The nice thing about welding is that it is very visible. Someone that knows how to weld:
(http://www.ecstuning.com/stage/images/product/exhaust/GHL/GHL-BungWeld.jpg)
And someone who doesn't:
(http://i35.photobucket.com/albums/d171/saladtossser/gogogo/myweld.jpg)
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Maybe you sould show them photos to the tech guys at elmo! LOL :-o
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and I wish I could spell as well as I can weld (should)
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The problem with MIG is that it can look good and have absolutely no penetration. Typically this will happen on a fillet weld where most of the heat has been consentrated on one leg. On the other leg the molten weld metal will just lie up against the leg without actually penetrating into the base metal.
Pete
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I get a lot of sh*t because I bad mouth MIG welding (mud guns) but when you TIG something you can see the weld puddle and and you can see the penatration and make it right! Again MIG is for building trailers and TIG is for building race cars (and race bikes Willie!!).
Rex
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I get a lot of sh*t because I bad mouth MIG welding (mud guns) but when you TIG something you can see the weld puddle and and you can see the penatration and make it right! Again MIG is for building trailers and TIG is for building race cars (and race bikes Willie!!).
Rex
I now have both a TIG and MIG and love them both and feel that one is not necessarily better than the other in all situations. There are times when I feel much more comfortable with using my MIG on a structural weld on the car than the TIG due to the position of the weld. In fact over 90% of the welds on the cars frame and cage area are with the MIG and I feel very comfortable with those welds (most were done before buying the TIG).
Once you realize what Peter was describing you can make sure it doesn't happen with a MIG. You can see during the weld and after the weld if you have penetration. The major problem as I see it is that you are moving much faster putting the weld down with the MIG, so you have to pay attention to the weld puddle. I agree that with the TIG you are moving along much slower and do have more control over the puddle but you find situations on the car that it is hard to get into a comfortable position for both you and the torch with the TIG.
My conclusion is if you are new to welding and have a MIG make sure it is a 220 volt and take a class or get someone that is a good welder to give you some instruction and don't just assume that since your welds look good that they are. If I only had one welder that I could afford it would be a MIG and I would do more than build trailers with it :wink: ,
Sum
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At this years BUB event, we had a lot of new racers to the salt with a lot of "new builds".
Many of the frames were MIG welded.........and ground down to "look good"......................for 2009
a ground down welded frame will not be allowed to race...............so all you new builders keep this in mind.................in fact for 2009 a close look at
all the welds of frames and chassis will be the order................................................................................
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As far as I can remember back 15 - 20 years the rule book has always said " grinding of welds on the roll cage structure is not permitted."
As far as MIG vs. TIG. I have both and its the Indian not the arrow that makes a good weld.
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I get a lot of sh*t because I bad mouth MIG welding (mud guns) but when you TIG something you can see the weld puddle and and you can see the penetration and make it right!
Well, if you can't see the weld puddle you have no business welding in the first place! I don't care if it is oxi-acetylene, TIG, MIG, or stick. Seeing the action of the puddle, and knowing how to compensate is what welding is all about. VISION, is one of the most important attributes of good welding. Knowledge and motor-skill respond to what you see! In the case of MIG a good welder is looking at the erosion (or lack of) at the edges of the puddle, looking at both the front and rear of the puddle to see its action, can see the preheated glow in front of the direction of travel, can see penetration, repeat . . .can see penetration (as determined by the meniscus (or lack of), the flatness or sinking of the puddle, etc. In MIG you use different patterns like crescent, zigzag, oscillating to accomplish your objective. If you can't see the puddle then change the filter or get glasses. I agree there are a lot of ignorant MIG welders but that shouldn't condemn the process universally. There is no "one technology fits all". You certainly wouldn't TIG a 1" thick, beveled, 1030, butt joint, when the strength of the weld is mostly determined by the mass of filler material laid down. Submerged arc, or stick, would be used in that case. All welding techniques in the hands of the ignorant or inexperienced is suspect!
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Damn, I was going to learn to weld over the winter (even buy a Miller MIG)...Now I guess I will just have to re think that !!!!...
Charles
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listen everyone---welding is something that can be learned by most anyone--but like a lot of things that we all do only a few can do it well---if you plan on doing a chassis then there are times that you will have to weld left handed if you are right handed---upside down and plenty of strange positions--with the tig you have to do 3 things at the same time and you should be able to do it left or right handed---i know of no test to see if you are going to be a good welder or not ---i have taught many people to weld and my best pupil was a tattoo artist---some people no matter what just dont get it ---i remember i was having trouble with some welding i was doing so i went down to the local welding school and talked to the instructor there and for 20 dollars he gave me a 1 hour lesson --the best 20 dollars i ever spent--i would suggest if you are new to welding before you fire up that new welder go by the welding school or at the very least have a good welder get you started--but even if you find that you arnt a very good welder you can still fabricate things and tack them together and pay someone just to weld everything together---it will be much cheaper just some thoughts willie buchta
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I tend to agree Sum. I watch a MIG puddle really closely to ensure that it's getting both legs I also tend to use a little manipulation to help encourage the process. The problem is that until you've got a few hours in and the process slows down to the point where you can analyse as you weld the welds you make may or may not be structurally sound.
Pete
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Willie is absolutely right. Welding is something that you understand how it works and have the knack, or you struggle. Americas Funniest Videos could have an entire show on the weird positions you end up trying to get a decent weld in some odd place.
If you are going to weld a frame, then take some of the scrap pieces, or cut some test pieces and weld them up. Then band saw the weld and see what kind of penetration you get. If the test piece isn't perfect then keep cutting test pieces and welding until it is perfect.
If you don't have a 220 welder then go get one and stop playing.
If your welding looks like the second picture then you need serious help. If you pray some day that your weld will look like the first picture, then practice, practice, practice.
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:-D A few pages back Geo posted a pdf of a roll cage showing the intersection of the mitered tubes where they didn't quite line up. I have attached his pdf marked up where the high stressed going would be located on his tube. If this is a really big concern, why not just put a diagonal brace there to distribute the stresses? :|
Terry :cheers:
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Terry is correct about the place the tube will bend. I have another side of the “funny car cage” that should take care of that. 8-) The point being discussed is the importance of having the center lines of the tubes meet to eliminate the weak area. One side thought is that I plan to not have any tube meeting point aimed at my body! Terry, I would worry about creating other weak points by removing the meeting point with the addition of a short diagonal as the one tube is only off by 3/8 inch or so. And remember my pdf is on the side with the bar not meeting being the horizontal bar and the three upright vertical bars meeting. Willie, any thoughts on gussets? :-D
You must also think about creating a shear area where only one bar is located in the middle of a tube. Remember a triangle has intersections of the rays at the corner not up a little from the end allowing a “tail or leg” to stick out as a support. The place where the tube will bend, or worse shear off, is just up the leg where the rays meet so when you move the meeting point to the end of the tube the sheer is also moved to a stronger location or past the end of the tube. I will post another pic after the next weekend of the diagonal tube meeting the floor and upright tube.
A side intrusion bar or a shoulder harness bar does not need to meet another tube at the center of the angle, vertex, where the angle ray lines meet because these tubes are not part of the support structure. However, you can use part of the support structure for a side intrusion bar or a shoulder harness bar and then meeting the vertex of the angle is important. Hmmm, head spinning yet? :-P
Another consideration is where to place bracing and have it add needed strength rather than add weight and moving stress from a strong vertex to a weak area. I drew the cage and then checked for triangles. And then thought about what stresses the car will have in the event of not being on wheels. I did change a tube from my first sketch. This varies from Bonneville to sled pulling to Maxton to track days to drag racing to… Most salt cars end up on their top and do not strike an immovable barrier like a concrete wall or get hit by another high speed mass (fellow racer) so plan accordingly. McRat needs a slightly different cage in his truck than I do with added protection for the additional impact types that may occur in his different events.
Follow the rule book first and then add if needed. The cage specified in the rule book has been empirically tested and is good for what we are doing.
I am fortunate enough to have a certified welder in our team and I am still reading welding books as we work on the car. The comments posted are good about the different types of welding. Roll bar welding is near the max for tig and middle for mig, depending on machine so all comments can be correct.
My reading about welding brings up temperature being important and 90 degrees best with weakening at 55 degrees and below, gas choice, good quality wire from a major vendor creating a stronger weld than cheap wire, etc. Another point is how to weld tube intersections to eliminate warpage using tips found in ”Welders Handbook” by Richard Finch, page 38 and “Modern Welding Instructor’s Manual“ by William Bowditch, page 218.
I think this thread is going to result in better cages for all. Charles, join me in learning, again after a 25 year break, how to weld. I just got a setup for aluminum.
Geo
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Nobody has brought this up yet so I will-- it seems to me that one of the problems associated with structures built with bent tubing is that those bends then create a "pre- buckled" tube. A straight tube has higher compressive strength than one that is bent, all things being equal. I've never seen a roll cage fabricated with all straight tube members but it would seem to be stronger than bent tube hoops if the welds were all good quality.
Comments?
Regards, Neil Tucson, AZ
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neil i think that the arch is the strongest---i think a long tube as in a roll cage in a door car is very weak in the middle of the tube and the arch in a roll cage in a streamliner is 10 times as strong --if you are building a door car do yourself a favor and also do a funny car style cage --then you have a cage in a cage --if you still dont feel safe switch to a motorcycle doesnt get any safer than that ---think about it like this---i do a lot of street riding and i feel like a duck in a shooting gallery most of the time --when i get to bonneville or el mirage i have the track all to myself and my only worry in the world is if i can break the record --doesnt get any better than that willie buchta
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Willie, it sounds like you're trying to lure Franklin - and his rider-wear-a-parachute concept --- back to us.
I agree with you -- While there are certainly risks when riding a bike, I sure do feel comfortable riding on the racde track. I mean, not only is the riding area as good as you can get - no traffic or road obstacles, etc -- but I'm wearing the best safety garb I can afford and have safety and security workers all helping me have a safe ride. And as Jason (unfortunately) showed -- even a high-speed getoff is relatively safe under thewse conditions. I'd go on about bike safety, but I don't want to hijack the thread. Back to building a cage...
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Neil i think that the arch is the strongest---i think a long tube as in a roll cage in a door car is very weak in the middle of the tube and the arch in a roll cage in a streamliner is 10 times as strong
I think you are missing Neil's point. There are two kinds of material deformation. (1) Elastic. The tube does not reach its yield point and therefore springs back without loss of strength and (2) Plastic. The tube has been deformed past its ultimate yield and takes a "set" or does not return to its original shape. There are no exceptions. Plastically deformed materials are always weaker than their parent condition!
When you bend a tube you have plastically deformed and weakened it. The question is; by adding in struts or other geometry have you increased the strength of the structure to equal or exceed the loss of strength due to the bending? In most cases the answer is yes. If you don't know you are a test pilot. :wink:
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The arch, as an architectural shape, has good load bearing capacity in compression only. The curve transfers the bending load above the opening to compression of the vertical legs.
It's an improvement in this respect over the lintel (end-supported horizontal beam), but not over a simple triangle ending at mid-span of the opening - but it does give far more "open" area.
It has little resistance to side-thrust, and becomes a trapezoid-oid (sorry!) much like a rectangle, by morphing the arch radius into a partial ellipse when pushed sideways.
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Welcome back Mr. panic :-)
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Saltfever,
I agree that a piece of material that has been strained past its yeild strength is typically weaker but that is mostly do to the reduced material cross section and not the actual strength of the material itself. Most materials that we work with, steel, aluminum etc actually exibit improved physical properties once they have been stretched. This is a type of cold working that refines the metal grain sizes and increases strenght, but what happens, as Willie's test have shown, the material thins and the percent of thinning vs the percent of increase in material properities can make the part weaker.
Strain hardening is an important component of most of the "heat treatable" aluminums. To get 6061 to the T651 the material has to be stretched a certain percentage to get the desired properties.
I do agree that once you have a structure that has failed in "plastic deformation" it is junk and not repairable.
Rex
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Willie;
Sorry, you won't get me on a motorcycle. There seems to be something inherently wrong about draping yourself over the outside of a vehicle. You are then protecting the vehicle in a crash; I'd rather have the vehicle surrounding me. :-)
Yes, a long unsupported straight tube is not a good idea-- but that is solved by triangulation with intermediate bracing. If a tube is bent into a hoop, it is already partially collapsed-- that bend is where it will buckle in compression.
Regards, Neil Tucson, AZ
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this thread is 7 pages --read 3577 times--lots of time spent testing -lots of time spent posting---if we all rode motorcycles it would be irrelevent---the bike thing- some people get it some dont -to bad willie buchta
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Rex:
I was referring to the typical stress/strain curve (below) for structural steels that shows loss of strength after the "ultimate" is reached. However, as you correctly indicated, this loss of strength is due to the typical "necking" that occurs. Since "necking" in beams and coupons, or wall thickness changes (in tubing) always occurs in structural steel, my point was it is best if design loads are within region 4 (below) rather than at ultimate.
“Roger that” for the aluminum T651 condition. Good information. :-)