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 for words. 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 purchase.!! 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.! Thanks again,
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 the experience.
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.
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 jo> So I picked up my new machine last night.
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 f> I am designing a frame/roll cage for a lightweight (~1,500 lb) 3 wheel
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 pounds Square weighs 1.6 lb/ft and 50 feet would weigh
79.975 pounds
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 thickness.
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 weld up.
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 wrong direction.
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 analysis.
Cheers.
Boynt> A comparison of 1.5" square tubing to 1.5" round tubing.
First, and before I forget a second time, great work in your Mini-Baja frames. Congratulations.
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
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a 3 wheeled Buick and a Fox)
Not quite a Trihawk. Aero. 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. Disk brakes. 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.
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 to "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 than mild steel is that spec)
2) Modulus of elasticity is what will control the strength in compression (crumple strength),
3) That will be the factor that goes first, in a space frame (members in tension 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, if the 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).
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