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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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#1
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2" square stock strength question
Jeez, if it were MY bike on a trailer hitch thingy like that, I'd for sure use
1/4" wall! How much more can it cost? GWE wallster wrote: alright geniuses, (i actually mean that) I'm welding up a dirt bike carrier for the jeep and the hot rolled, mild steel 2" square tubing (that goes into the receiver) has a wall thickness of .125" Without getting too detailed (because there will be two stabilyzing tongues as well, then there's the length of the tube, weight of the bike, etc) but how much force (or weight) APPROX. does it take to bend a piece of this stuff? The details that i do have: the bike platform weighs about 30lbs, and the bike weighs about 215lbs. (length from reciever to channel is 30") thanks walt example of what the hell i'm talking about: http://cgi.ebay.com/ebaymotors/ws/eB...tem=4572979149 |
#2
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We tend to overkill everything we make, as a failure is often inconvenient,
at best. I'm with Grant, get a piece of 1/4" wall "Grant Erwin" wrote in message ... Jeez, if it were MY bike on a trailer hitch thingy like that, I'd for sure use 1/4" wall! How much more can it cost? GWE wallster wrote: alright geniuses, (i actually mean that) I'm welding up a dirt bike carrier for the jeep and the hot rolled, mild steel 2" square tubing (that goes into the receiver) has a wall thickness of .125" Without getting too detailed (because there will be two stabilyzing tongues as well, then there's the length of the tube, weight of the bike, etc) but how much force (or weight) APPROX. does it take to bend a piece of this stuff? The details that i do have: the bike platform weighs about 30lbs, and the bike weighs about 215lbs. (length from reciever to channel is 30") thanks walt example of what the hell i'm talking about: http://cgi.ebay.com/ebaymotors/ws/eB...tem=4572979149 |
#3
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Jon Grimm wrote: We tend to overkill everything we make, as a failure is often inconvenient, at best. I'm with Grant, get a piece of 1/4" wall It would be just as easy (and only about $10. more) to use .250" but if ..125" is more than strong enough, making this lighter would be nice for lugging it around when i'm not using it. I have a habit of adding all kinds of extra supports and brackets on stuff i make but sometimes it's just overkill. I guess i was really wondering how much weight or force it would take to bend the .125" stock. Thanks for all the comments so far fellas. walt |
#4
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hot rolled, mild steel 2" square tubing wall thickness of .125" (length from reciever to channel is 30") the platform weighs about 30lbs, and the bike weighs about 215lbs. From this, I ran one of the web beam calculators using as a calculation load 250#, and got just over 1/8" of bend, and 13.6 ksi bending stress at the receiver. With a yield stress of 36ksi, A36 would seem to be OK--BUT it is not unusual for bouncing and other momentary stresses to cause the actual forces to exceed that, so a common rule of thumb is to use four times the load for a safety factor. If we re-run the calculator for a 1000# load, we get just over 1/2" of bend and a stress of 54ksi, which would put you over. So my quick "back of the envelope" calculation would agree with your other two responses, use the thicker section. --Glenn Lyford |
#5
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I was going to make a luggage rack / platform that would fit into my 2"
receiver and was planning to use 2" square x .125 tube also. Just to get an idea of the strength my son and I stood on the tube about 2-3 feet from the hitch and we bounced up and down on it, tube did not bend or flex, (as far as I could tell and we weigh about 325 lbs combined). So based on that, you should be fine. If you don't have the tube yet, buy the 3/16 of 1/4 inch stuff. I'm a big fan of overbuilding when it comes to safety issues. YMMV, Chuck "wallster" wrote in message oups.com... alright geniuses, (i actually mean that) I'm welding up a dirt bike carrier for the jeep and the hot rolled, mild steel 2" square tubing (that goes into the receiver) has a wall thickness of .125" Without getting too detailed (because there will be two stabilyzing tongues as well, then there's the length of the tube, weight of the bike, etc) but how much force (or weight) APPROX. does it take to bend a piece of this stuff? The details that i do have: the bike platform weighs about 30lbs, and the bike weighs about 215lbs. (length from reciever to channel is 30") thanks walt example of what the hell i'm talking about: http://cgi.ebay.com/ebaymotors/ws/eB...tem=4572979149 |
#6
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Great info! sounds like it would probably be okay but questionable
(especially factoring in time and fatigue) I'll go up a notch. thanks again! walt Capt. Tundra wrote: I was going to make a luggage rack / platform that would fit into my 2" receiver and was planning to use 2" square x .125 tube also. Just to get an idea of the strength my son and I stood on the tube about 2-3 feet from the hitch and we bounced up and down on it, tube did not bend or flex, (as far as I could tell and we weigh about 325 lbs combined). So based on that, you should be fine. If you don't have the tube yet, buy the 3/16 of 1/4 inch stuff. I'm a big fan of overbuilding when it comes to safety issues. YMMV, Chuck "wallster" wrote in message oups.com... alright geniuses, (i actually mean that) I'm welding up a dirt bike carrier for the jeep and the hot rolled, mild steel 2" square tubing (that goes into the receiver) has a wall thickness of .125" Without getting too detailed (because there will be two stabilyzing tongues as well, then there's the length of the tube, weight of the bike, etc) but how much force (or weight) APPROX. does it take to bend a piece of this stuff? The details that i do have: the bike platform weighs about 30lbs, and the bike weighs about 215lbs. (length from reciever to channel is 30") thanks walt example of what the hell i'm talking about: http://cgi.ebay.com/ebaymotors/ws/eB...tem=4572979149 |
#7
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Walt,
Having spent the better part of my 25 years as a welder/machinist in the army "field engineering" (usually field fixes for poor design "real" engineers put into play) I also am a fan of over building. Now...having said that...the good captain here has a point that stands at the very root of field engineering...find an equivalent field force test. That principle has NEVER failed me (when combined with my 0ver build habits. There is most definetly a down side to over building...namely stuff gets too %$#@!! heavy. In today's "over sue" world, you probably won't find anyone (myself included) who can promise you 1/8" wall tube will be O.K.. Especially when we don't have an actual detailed design to look at. I will tell you that if I'd done the test the good captain did & got the same results, I'd go ahead & use 1/8" (with gusseting & bracing whereever possible). Also, I'd tell you...next time look at using some 1/8" wall chrome-molly (4140) tube...it's good enough for stock car frames! Hope this helped -Wayne "Clutch" Glass- |
#8
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#9
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Before you go off and buy some tubing with thicker wall, do a bit more
thinking. The max bending is at the receiver. So maybe a six inch piece of smaller tubing to go inside the tubing that you have and then weld a foot or so of that tubing that you have under the other tubing. Since that changes the tubing from 2 inch square to tubing that is 2 inch by 4 inch, it will increase the strength more than going to .250 wall. Dan |
#10
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tomcas wrote:
Like you said 13.6ksi until he hits the first bump with the resulting equivalent acceleration load of 3g's. Then the bike is left dragging behind the car. Even 4 times may not be enough. Will not be so bad, because the bike has damping. But the load that is frightening me most is torsion. The way the rail is connected to the car (one tube in the center) is -in my eyes- the second most stupid way. It would be OK for a bicycle, but not for the wheight of a motorcycle. In my eyes, the construction is complete rubbish and doesn't need to be calculated. Nick -- Motor Modelle // Engine Models http://www.motor-manufaktur.de |
#11
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You guys are funny:
1.) I believe the guy said, "...there will be two stabilyzing tongues as well". 2.) "If we re-run the calculator for a 1000# load, we get just over 1/2" of bend and a stress of 54ksi" ---Where in the world did he get enough information out of what the guy said to come up with 1/2" of bend going on???...makes my head hurt! Now what Dan said, "So maybe a six inch piece of smaller tubing to go inside the tubing that you have and then weld a foot or so of that tubing that you have under the other tubing." & he makes a good point...sometimes heavier all the way around isn't any stronger...it's just heavier. In the end folks, we can't "over think" what the guy is doing...all we can do is guess (because we don't have detail put to his intent). He has been given some interesting points however, from all of you, to consider: 1.) Bending at the Tongue- Several factors will affect this including...Are there 2 "stabalizing tongues" that will absorb some of this?...How far will the load be placed from the bend point(s)? 2.) Torsional Stress- Again...will the "stabalizing tongues" absorb some of this? Also...how far out from the torsional stress point(s) will the load be? 3.) Consider thicker wall tubing (as well as gussets & bracing) at key stress points. 4.) Next Time (and I can't help this) consider 4140 chrome-molly Just some thoughts from an old "weldor" who's head hurts if he has to think too much without burning some rod along the way. -Wayne- |
#13
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Nick,
There is no way you have enough information from what has been said in this group to know where the center of gravity is (I am laughing)...also, you don't know enough about what he is trying to do to call his design crap.....you'd need to see detail first (i.e. does the bike mount at just one point...or more? and...do the "tongues" indeed mount in such a fashon as to help with the stress at all....or do they play as much a part as the hitch mount? Don't do a bunch of "assumed math" & call a design you know almost nothing about crap buddy. It makes you look silly. -Wayne- |
#14
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wrote:
There is no way you have enough information from what has been said in this group to know where the center of gravity is (I am laughing)... Haven't seen a motorcycle recently? No? So I bet you don't even know what a MX looks like, how much it weights (it was posted) and where the CG is. I have lifted (during 8 years of MXing and Hare Scramble racing) my bikes (Husqvarna, KTM, ATK, Honda, if that helps) enough times to make an estimate where the CG is. Trust me! also, you don't know enough about what he is trying to do to call his design crap..... I can see pictures, I can c&p links. If you can't I'm sorry for you. you'd need to see detail first (i.e. does the bike mount at just one point Well, I bet the bike won't just mount on one point. No need to think about this. YMMV. ...do the "tongues" indeed mount in such a fashon as to help with the stress at all Picture, see above. Don't do a bunch of "assumed math" & call a design you know almost nothing about crap buddy. I've seen the picture + there is just one location to connect the whole frame to the car. It makes you look silly. Whom? Me? Not in this case. Nick -- Motor Modelle // Engine Models http://www.motor-manufaktur.de |
#16
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#17
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Isn't anyone worried about the hitch? I hope the U-Haul kid used really
strong poprivets to mount the receiver to the sheet metal under the SUV g... |
#18
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On Wed, 07 Sep 2005 18:42:59 GMT, "Emmo" wrote:
Isn't anyone worried about the hitch? I hope the U-Haul kid used really strong poprivets to mount the receiver to the sheet metal under the SUV g... That was my thought as well. The only thing that gave me hope was the fact that it was a 2" receiver which is usually mounted properly now days. About 1 1/2 months ago I had a similar situation roll into my shop. A older couple from Arizona where coming through with the smallest camper I've ever seen in my life behind there car. Somebody had put a 1 1/2" receiver on the back of the camper and they had a bicycle rack in it. However due to the curve on the camper the bicycle rack had to be extended about 1' so that it stuck out from the receiver about the 30" mentioned here. The rack was holding up fine. However the receiver was just welded to a 2"x3" piece of about 16ga wall rectangular tubing which ran across the back of the camper frame. Of course it pulled and buckled in till the rack was able to drag the ground. I had to extend the receiver so that it went to the next cross member up the frame and reinforce the back cross member to repair it. This is the second absolutely lousy poorly thought out welding job to come from Arizona to my shop. The other was when somebody with no welding skills put a 30' dry box off a bob tail truck onto another camper frame made from 2"x6"x14ga rectangular tubing. The tongue pulled out twice before it got here and neither place that repaired it did as good a job as my dad could do welding it back (and my dad is NOT a welder by any stretch of the imagination). I ended up making a new frame from 6" channel with proper 6" channel cross members (the original had light weight C purlin type cross members which where broke) and a reinforced tongue before I would let it back on the road. The original welding on that frame was so lousy that I was able to take the 3" I beam off that they'd welded down the length (so they could U-bolt the box to the frame) by grinding one weld. The other welds where not stuck to anything. I'm starting to get nervous when I see a Arizona tag. :-) Wayne Cook Shamrock, TX http://members.dslextreme.com/users/waynecook/index.htm |
#19
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On Wed, 07 Sep 2005 16:11:25 -0500, Wayne Cook
wrote: This is the second absolutely lousy poorly thought out welding job to come from Arizona to my shop. I'm starting to get nervous when I see a Arizona tag. :-) And well you should... To describe just one example, a neighbor came up to my place (in AZ) to use my equipment. I just watched, somewhat amazed while he stick-welded two identical sledge hammer heads as spacers between the springs and axle of a pickup bed converted to a water hauling trailer (2400 lb. load). The rest of the project was equally ah, interesting. And he never touched the wire brush and chipping hammer I supplied. I keep waaaaay back when I see this kind of stuff on the road, no matter where it's from. Wayne |
#20
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Nick,
Um...er...gulp! here is the part where I eat crow pie & apologize. I actualy never noticed he put pictures up. I thought all that stuff you were saying was coming out of thin air. I was wrong & I apologize man. Laugh at me if you'd like (I deserve it). No hard feelings? -Wayne- |
#22
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Nick,
I spent 4 years in Gelnhausen (1987 - 1991). I very much enjoyed the culture and the people (not to mention krystal wiesen, wurst & shnitzels). I would try saying thanks for being so big in my broken deutch...but I'd probably butcher your language. So from one "shvitser" (welder) to another...thanks man. -Wayne- |
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