Advice would be appreciated.

That sounds like the right tungsten.
For 1/16" mild steel (0.0625"), you need about 63 amps for a butt weld, or 30% more (82 amps) if you need to do any fillet welds.
These settings are from Ernie's guidelines, which are extensively documented in the archives.
I would use 0.045" ER70S-2 filler for this project.
Have fun,
Jeff Dantzler

Remember this rule.....are you ready?..... ALWAYS use filler....you always have to because you are always preping the joint.......right?? beveling is a must!!!
Doobie
corrections

Prepping a joint on 1/16 inch material? If you say so but I would think the only prepping necessary would be to fit the pieces as perfectly as possible. Not much meat to bevel with .0625".
I agree with using filler even if the joint is not prepped. It makes the joint larger and stronger especially since he mentioned building a cart for his child. .0625 material, if designed well, can make a cart that Dad can share too!
It is good to practice TIG or O/A welds without filler. It refines control of the torch and puddle. I can't think of a reason to do finished fusion welds for anything other than artsy pretty things.

Thanks, I appreciate the advice. I think I will have to find thinner filler rod as I only have 1/16th. The cart will be an electric vehicle with a surplus wheelchair drive and appropriately speed limited. I will first build it something like a tractor and then hope to add a semi-functional bucket to the front as my kid loves construction equipment. I just have to solve the problem of how I would lift and tilt the bucket/limited load. Hydraulics probably not a good idea for a four year old. Linear actuators quite expensive. Perhaps a manually controlled lead screw. The other thought I have is a manually operated enclosed winch where the cable largely runs in a tube to prevent injury. I really want limited lifting ability really more for show and allow him to pick up a little mulch. Safety is of concern. If anyone has any thoughts it would be appreciated. I have time to think as first I need to build the vehicle.
Thank
Barry

1/16th filler for 1/16th metal should be ok.
Why not? Just use low pressure to limit force.
Ted

I would love to use the hydraulics though don't know much about it. Is there such a thing as a low pressure pump? I could go either electric or manual. Everything I've seen is relatively high pressure. This would make me nervous in a power application and would probably require a lot of hand pumping with a limited stroke volume in a manual application. A low pressure solution would be great.. Any input would be appreciated.
Thanks Barry
Barry

metal so it melts before the base does otherwise you have to melt all three "pieces" at the same time.... .045 would be perfect

Usually the output pressure stated for a hydraulic pump is its' max operating pressure. An electric hydraulic pump (say 12V with reservoir, valving and pump all in one) usually has an adjustable relief valve to set the maximum allowed operating pressure. You could simply adjust the relief valve to your desired pressure. For example, a 2" cylinder would have roughly 1500 lbf if 500 psi hydraulic pressure was used, a 3/4" cylinder would have only 200 lbf at the same pressure. Here's an example of the type of pump. Shawn

The pumps are typically positive displacement. Assuming the driving motor hp at rated RPM is sufficient, they'll make somewhere in the range of 1500 to 8000 PSI at rated flow (actual pressure and flow depend on the specs of the particular pump). With insufficient driving hp, you'll have to lose some pressure or some flow to avoid stalling the motor. With lower RPM, you'll get lower flow. Etc.
But that's not really important in this case. What controls line pressure going to the load cylinders is the pressure limit set in the control valve. What this does is simply bypass fluid back to the reservoir in order to maintain a set pressure. You can adjust this to virtually any line pressure you want, analogous to an air pressure regulator, though this is a shunt regulator rather than a series regulator. So even though pump pressure may be 1500 PSI, you can set line pressure down to 1000 PSI or 500 PSI or 250 PSI, etc, as you desire, so that the rams don't put out more force than you consider prudent.
Now if you select a really high flow pump, you may find it difficult to set a really low line pressure. In other words, you're simply asking the control valve to bypass more fluid than it can handle. So you do have to use some common sense in sizing the system. For your project, you probably can't power a pump big enough to make this an issue. In other words, any pump small enough to be run from your battery supply, won't have a high enough flow to overwhelm a standard control valve's regulation.
Gary

Very helpful. Thanks
Barry