What process & prep.

[imagineer]

Small project for the weekend.

I’m going to be welding 2 pieces of ~3” x 8” x .345” thick steel channel, 10” long, together to make a short rectangle tube. It’s going to be a trolley chassis for a 1000lb shop hoist. The welds will not be subject to the weight being lifted, but will just be holding the chassis together.

Available weapons of choice:
- Miller Diversion 165 TIG with Argon & 3/32” ER70S-6 filler
- Lincoln Weld-Pak 155 MIG (with gas kit) using 75%Ar/25%CO2 & .035” ER70S-6 wire. Also available E71T-GS Flux-Core wire (I believe it’s .045”).

Questions:
MIG or TIG? If MIG, should use straight MIG or dual shield (DCEN and weld with flux core and shielding gas)?
Would it be better to bevel and weld both inside and out, or just bevel and weld from the outside? Note, the weld along the bottom will be ground flush.

[Shade Tree Welder]

Well it looks like there will be some lateral load on it as the wheels and I beam
are beveled. Any of the processes will work. I would weld both the inside and
outside for complete fusion. Weld the inside first get 100% penetration then
welded the outside to complete.

It is a critical component, so overkill is good.

[JohnBoy]

I think I'd grind the top flat and weld a strip of 2" flat bar on top of the weld.

It would probably add little or nothing in engineering terms, but it'd make me feel better

[imagineer]

Originally Posted by JohnBoy

I think I'd grind the top flat and weld a strip of 2" flat bar on top of the weld.

It would probably add little or nothing in engineering terms, but it'd make me feel better

No available clearance above the tube. I'll have about 1/4" or so clearance on the inside if a strip of material is needed.

[LKeithR]

Originally Posted by Shade Tree Welder

...Well it looks like there will be some lateral load on it as the wheels and I beam
are beveled...

While this is true think about how most crane trolleys are built. They use two pieces of plate held apart the right distance by two spacers with a couple skookum bolts to hold everything together--no welds at all.

It is a critical component, so overkill is good.

Yup, when in doubt add a little more material or a little extra weld. For a backyard engineer it's always a good maxim to follow.

Originally Posted by JohnBoy

I think I'd grind the top flat and weld a strip of 2" flat bar on top of the weld.

It would probably add little or nothing in engineering terms, but it'd make me feel better

On the contrary, it would add significantly to the strength. The purpose of the welds is to keep the two pieces of channel from separating. A strip of flat bar spanning the welded joint would would add greatly to the strength.

To me this seems like an awkward way of doing this. Personally I'd make the trolley in the conventional way by using two pieces of plate with tiebars. Pretty simple and already proven to work. I'm a huge fan of "don't reinvent the wheel unless it's absolutely necessary"...

[imagineer]

Originally Posted by LKeithR

To me this seems like an awkward way of doing this. Personally I'd make the trolley in the conventional way by using two pieces of plate with tiebars. Pretty simple and already proven to work.

Cant use a conventional trolley in the regular way. The existing trolley has a large bolt that ties the two wheel plates together and also provides a single lifting point (to which a chain-fall is attached).

I need a flat, non pivoting surface to mount an electric hoist. Using the rectangle tube to restrain the wheel plates in lieu of the large bolt keeps everything together and provides a flat surface that doesn't pivot. If I could have found a piece of 8" x 6" x 1/2" wall rectangle tube, dimensionally it would have worked perfectly for this application. However in the essence of time, I could only get my hands on 8" x 4" x 5/16" wall tube, so I'm cutting it and making the larger rectangle tube I need.

[milomilo]

What Shade said.

[Oscar]

Originally Posted by imagineer

Questions:
MIG or TIG? If MIG, should use straight MIG or dual shield (DCEN and weld with flux core and shielding gas)?

I think you have your "dual shield" mixed up. The correct terminology is Gas-Shielded Flux Core (FCAW-G). "Dual Shield" is actually a trademark name used by Esab for this wire/process, where as FCAW-G is a generalized terminology. This is [completely] different from attempting to use regular ol' Gasless flux core wire E71T-GS or E71T-11 (DCEN) and [incorrectly] adding a shielding gas (which should not be done, according to the Lincoln Electric Inner-Shield Guide, page 21).

FCAW-G is ran on DCEP, and is specifically formulated for use with either 100% CO₂ (E71T-1C) or 75/25 Argon/CO₂ (E71T-1M) or either-or (E71T-1C/1M).

That being said, the Lincoln weldpak 155 doesn't have the balls to run true gas shielded flux core wire, even in a thin 0.035" diameter. This is because there is an amperage and voltage threshold that must be crossed to properly run this wire in spray-transfer mode, which is when the proper penetration and deposition rate are obtained. With C25 gas, the minimum is approximately 185-200A with about 25V to get it into the optimum spray-transfer mode. Not gonna happen with the weldpak 155.

That being said, the best option in a spooled wire will be Gasless Flux core ran as intended, without gas, in 035 diameter. It will burn substantially hotter at the same WFS than ER70S-6 with C25 shielding gas, due to the exothermic reaction of the flux in an electric arc. Even then, beveling the 0.345" thick sections would allow better fusion given the power limitations of the machine. A stick welder with some 5/32" 6011 at 140A will do even more damage since it produces a deep penetrating arc that is quite forceful in digging into the steel. Even if it won't be subject to carrying the load on the trolley, you still need some resemblance of weld integrity, I say.