So I picked up my new machine last night.
The second I got home, I hooked it all up.
Comming from someone who has stick welded since high school, I am at a loss
This machine ROCKS!!! Thats about all I can say... My welds are sooo much
cleaner, virtually no splatter, and
getting excellent penetration... I can't say enough about the mm210.
Again, I only used it for one night, but based on what I have seen now, My
stick is going to collect dust until I need to
yank out the 7018's.
Thanks everyone for your feedback on this unit, I am VERY happy with my
Let the projects begin :0)
ps. How do I calculate how much amps/wire speed for the ammount of
penetration I require?
This is a critical piece for me, since I am going to be building a rollcage
for my buggy.
Also, this is good to know, as it applies to everything I am going to weld.!
I'm not going to say it, but "I told you so."
Your machine should have a guide that comes with it, or inside the machine's
cover panel. A lot of MIG welding is listening for the sizzle sound of a
good burning electrode, a lot is what looks good, and a lot is just getting
For things you want penetration on, you will have to learn torch head
movement, root preparation, and what to watch for in the puddle. For most
else, it's just like using a glue gun.
Do what you're doing. Do lots of welding with it. Become familiar with it.
Spend some time welding with it, and when you feel confident, do the frames.
Get some metal thicknesses of the frame, and do a lot of test welds. Break
them, or try to. Critique yourself, and particularly look at the backs to
make sure you got penetration. Watch for cold lap.
Congrats on new machine and empty wallet!
As for the roll cage welding. The last full tube frame we MIG welded (1"
x .083 and .065" wall) took a fair amount of setup to get it just right.
The machine is normally loaded with .035" wire, we got a spool of .023
S6 wire especially for the roll cage. We worked up weld schedules for
both the venerable Miller as well as a Century (the one that no one ever
wants to use) and found that the Century seemed to do better at the
requisite lower amperage. (Got a lot of raised eyebrows on that!)
We finished the frame fabrication up with heavy tack welds, then ground
down any excess tack weld. My welder came in fresh, did a handful of
practice welds, then did the whole frame in one session. We had a helper
to allow the frame to be flipped after each weld, going corner to corner
to minimize warpage. Most of the welds could be done downhand. Took a
bit over 2 hours to get the 40 or so joints done.
Whole thing came out really nice. This year we switched to .049" x 1.25"
tube and TIG welded everything, took MUCH longer to get it done. Rule
changes will force us back to .065" wall for next year, we'll have to
consider using the MIG again.
Make sure that you do several (many!) practice joints on scrap material.
Have a helper tweak the dials while you weld. Listen for the crisp sound
when it is set just right.
I am designing a frame/roll cage for a lightweight (~1,500 lb) 3 wheel
hybrid we are designing.
I note that you used (1"x .083 and .065" wall) . That seems quite
small and thin.
I am planning to use 1-1/2" x 0.095 square mild steel tubing. (DOM not
What material did you use and what was frame for?
Is there a photo available?
They weigh around 300 to 400 pounds without the driver. They need to be
able to withstand 3' of air every few hundred feet for a 4 hour
endurance race. You need to do some serious flight testing, nose down is
NOT a good way to land.
Square tube is nice to work with but you will shortly find that square
tube really confines your design to mostly orthoganal frame members. The
rules we run under REQUIRE 1020 or higher steel for the roll cage, mill
certification sheets are part of inspection. DOM is normally the higher
carbon stock, square is rarely found in this material.
A comparison of 1.5" square tubing to 1.5" round tubing.
.083 wall Round has a Moment of inertia of .093
Square has a Moment of inertia of .158
Round weighs 1.256lb/ft and 50 feet would weigh 62.8
Square weighs 1.6 lb/ft and 50 feet would weigh
If you thinned down the 1.5" square tubing to 0.065 the moment of
inertia 0.128 would still be greater than round at 0.1256 it would
weigh 1.2685 lb/ft and 50 feet would weigh 63.43 pounds compard to 62.8
pounds. Are the 17 pounds so important?
In other words, for the same weight square tubing is .128/.093 or 37%
stronger in bending moment and much, much stronger with the same wall
The round tubing could be of a higher grade steel than 1020 and it
could make up the difference in strength, but at a greater cost.
What are the reasons that square tubing is restrictiver to design? I
can imagine any design possible with square tubing.
Your strength numbers are a function of the Section modulous, not the
Moment of inertia. (Stiffness is proprotional to the moment of inertia.)
Tension strength is proportional to wall (and weight)Compression
strength is proportional to wall (and weight) as long as you stay inside
Ulhler's constant. For steel this means length MUST be less than 89
times the diameter. (safety factor says no more than 30 to 48 times!)
For the same OD and wall, square is 30% heavier and 60% stronger in
bending on the X and Y axis. (Good) I don;t have the numbers in front of
me but square does not handle torsion as well as round, it also fails in
a buckling moment differently than round. (Bad) But a properly designed
space frame (think experimental aircraft) has all members in tension or
compression ONLY. Bending monents only occurr if you hang parts (like
engines) in the MIDDLE of a tube rather than at an intersection. Or when
you have "unscheduled dynamic testing" situations.
As for the weight calc, compare your 1.5" tube with the next size larger
diameter and smaller wall. Section modulus goes up, weight goes down. So
thinner wall, larger tube is theoretically better. The flaw comes in
when the wall thickness gets too thin to resist side impact loads. A
dent will cause instant collapse of a compression stressed tube.
For the Mini-Baja that I deal with, the rules committee inspected some
"field tested" vehicles. (Consider rolling off a 30' embankment!) The
larger diameter/ thinner wall vehicles do not fare as well as
"equivilent" tubes of smaller/thicker. One collapses, the other bends
gracefully. Think failure mode.
As for the fabrication of square vs round: Square can be bent only on
the 2 orthoginal axis, round can be bent however you want. Consider a
joint: you can have a perfect multiple member joint in round tube as
long as the center lines all intersect. Try the same with square tube
with multiple members and multiple planes.
We build a new vehicle from scratch every year. First couple were square
tube. Quick and easy to deal with. Next was a small tube heavy wall,
easy to weld, weighed less than the square tube version. Next was a
larger tube thinner wall that shed more pounds, but was a stinker to
One thing to watch out for is hanging potential impact load stress
points in the middle of any piece of tube. Engine mounts are a great
example: lots of vibration stress as well as the possibility of a crash
where the engine mount folds up and takes a section of the frame in the
You have the right idea on your original calcs, you just need to work
through some of the operational details as well as the unseen "testing"
situations. I can tell you that for the Baja buggies that we compete
with, less than 50% of the cars finish the 4 hour race. This is a vast
improvement from some years back when 50% of the cars did not finish
HALF the 4 hour enduro! Touring the pit area was a lesson in failure
A little Google search and I found these 2 statements:
For the dimensions given, square is 1.7 times stronger in bending, has
1.7 times less deflection in bending and is 1.3 times stiffer in
torsion. It also weighs 1.3 times as much per foot. Note: Contrary
"popular" opinion, round is *not* stronger for it's weight.
A 1.5" OD square tube of the same metal area of its cross section as a
1.5" x 0.125" round tube would have a wall thickness of 0.09616". This
would then be the same weight per foot as the round tube and be 1.4
times stronger and stiffer in bending but only 0.96 times (4% less) as
stiff in torsion.
Deflection is a function of the cube of the dimensions, strength is a
squared function, both are linear with wall thickness. 1.7x bending and
1.7x strength are obviously wrong.
But square tube does NOT have the same numbers when measured on the
diagonal, round is unidirectional. And you seem to be confusing
stiffness and strength. Both are important, best to get stiffness with
frame design, strength with section modulous and material.
Keep in mind that your frame will have to be some sort of space tube
frame. You certainly won't be trying to do a 1500 vehicle with an
unbraced 1-1/2" tube running end to end like we see on a truck.
1) Modulus of elasticity is the same for all steel (4130's no better
steel is that spec)
2) Modulus of elasticity is what will control the strength in
3) That will be the factor that goes first, in a space frame (members
take more force to screw up than members in compression)
That all adds up to me, that mild steel square tube is as good as 4130,
frame is well designed (a space frame). It's certainly cheaper and
easier to get
- and it doesn't rust so easily.
Is his statement factual?
Roy, I'm still confused. If I were to use a square tube with the same
width and wall as a round tube that you would use, would that heavier
square tube be as strong as your round one? (assume equal steel).
First, and before I forget a second time, great work in your Mini-Baja
At the moment this is what I am thinking about building:
A 2F1R hybrid 2 seater which in Florida is considered a motorcycle.
(BTW see http://www.geocities.com/doolenthreewheelers/DoolenHome.html
for a 3 wheeled Buick and a Fox)
Not quite a Trihawk.
A 2 seater with about 10 cu ft of cargo space.
Not a short micro car but about 105" wheelbase.
500-600 pounds of batteries up front.
65/35 weight ratio
No power steering.
The jackshaft to mount the 3 drive sprockets will go through a hollow
swing arm pivot.
Regen and disk braking in rear.
Weight under 1,500lb (hoping for 1,200)
Roll cage protection using square 1018 1-1/2" .095 tubing.
Frame/roll cage designed to force the batteries and the engine/motor to
go underneath in a head-on collision.
Fabric or other lightweight body panels.
Engine/tranny is from a 1981 Kawasaki 550 GPZ. Engine on right side
with chain to jackshaft going forward.
Front end and manual steering from a Nissan compact pickup truck.
10-20 HP ADC motor on left side.
Performance goals: 45 MPH 20 miles on battery. 70MPH 40MPG on engine.
Your valuable comments are most welcome.
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