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

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

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

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

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

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

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-

wrote:
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

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.

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

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

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-

wrote:

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?

None.
The "tongues" will only help (partial) with bending in the horizontal
plane. But you have torsion in the vertical plane.

Scenario:
The bike is on the stand, you go around a sharp corner. Now some math:
CG of bike is about 500mm off the stand, bike wheights about 110kg. You
do have a moment of 550Nm if g is 10m/s^2. Now I'm too lazy to calculate
the stress, because it is a waste of time.
Don't forget that you have to add it to the bending forces.


BTW:
If it helps, you can laugh, but it won't stiffen the sick construction.
It will only work if you add 2 more connections (rear of bike + handle
bar connected to the car).

Nick
--
Motor Modelle // Engine Models
http://www.motor-manufaktur.de

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-

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

wrote:
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.

I called it a 30" cantilever beam with a 250 lb load multiplied by four
for bouncing, etc. and get
BeamOut(0 15 30)(30E6,1 I_sqr 2 .25)Beam 0(30 1000)
pos'n pt. couples shear bend. slope def'l
force stress stress

0 -1000 -30000 -1394 36170 0 0
15 0 0 -1394 18080 0.01356 0.113
30 1000 0 0 0 0.01808 0.3617

So I would say even .25" wall is marginal especially since going dirt
biking usually involves going over some pretty rough roads.

Ted

wrote:
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.

Better to just use heavier wall. Also note that with a cantilever beam
the greatest bending stress is right at the point of suspension so
welding another piece underneath won't help.

Ted

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...

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

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

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-

wrote:

Laugh at me if you'd like (I deserve it). No hard
feelings?

No.
If someone admits an error and asking for excuse, it is much better than
to shy away.

Nick
--
Motor Modelle // Engine Models
http://www.motor-manufaktur.de

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-

wrote:

So from one "shvitser" (welder) to another...thanks man.

Come on, let's have a beer! Prost!


Nick
--
Motor Modelle // Engine Models
http://www.motor-manufaktur.de