new welding obstacle thick and thin

[dvice]

Ok so I have my outboard bracket frame together, and I have to weld on the outboard mounting plate. I have a piece of 3/4" aluminum plate and I have 1/4" plate. I think Id rather use the 3/4" plate... but I will be welding it to 1.5 " square aluminum tube with a .125 wall. so thus the thick and thin.... should I try to machine down the thickness around the outside so the material is similar in thickness. Or do I try to JUST get ant kind of bead down from the tubing to the side of the 3/4" plate and then try to build on top of that??? I am thinking the first pass Ill get a good melt into the tubing, but I might not get any penetration into the plate...



the plate will cover the five sides center section

I will be using a Miller 250 mig with a 30 A spool gun and I have 4043( I think )( not 5356) wire .030"...
some advice before I try?

thanks

bob

[mlahonta]

Is that a typo? I don't know much, but that seems outrageous. Jeez-us! Three-quarters of an inch aluminum plate? On a transom?

[Hardrock40]

Yea that's a challenge. If it were me, and I'm no expert on this I would do some preheat on the thick. A lot of preheat.

I would use a MAP gas torch or something like that, not oxy act. Just a small bottle torch like you would use for copper water pipe to heat it.

I would also try and Tig it if you have that process if not you probably know more about Mig aluminum than I do anyway.

Just keep your puddle on the thick and flow it onto your tubing a little at a time. It should do alright. The heat will dissipate real fast but once you get is started it should stay hot enough.

Looks like some good cleaning might be in order first.

[MMW]

Will this be a flush fit around the edge or will it only over lap about half of the tube? Switch to .047 (3/64") wire. Preheat the 3/4" plate to about 300*. Concentrate your weld on the 3/4" plate & with your weaving motion bring it to the tube & quickly back to the plate. Watching the puddle will be crucial. Stay on the tube just enough to penetrate then back to the plate. You may have to preheat, weld, then preheat again for each of the five flats.

[Cgotto6]

What mmw said.

[dvice]

Will this be a flush fit around the edge or will it only over lap about half of the tube? Switch to .047 (3/64") wire. Preheat the 3/4" plate to about 300*. Concentrate your weld on the 3/4" plate & with your weaving motion bring it to the tube & quickly back to the plate. Watching the puddle will be crucial. Stay on the tube just enough to penetrate then back to the plate. You may have to preheat, weld, then preheat again for each of the five flats.

thanks... I could bevel the edges that I am welding at work before I weld. I will stop the 3/4" plate half way across the 1.5" width of the tube...mainly so I have room for a flat surface with no weld build up to weld the 1/8th sheet coming from the other way!!.. I had planned on some preheat, but didn't know if it would still be a nightmare or not.. I have the option of bringing it to work and tigging it. The plate was free, that is why I am using it....otherwise id have to buy a 1/2 " plate.....18 X18 . I have some 1/4 " put I think that is too thin for the stick up above the swim deck( 3" with two sets of holes).

I wonder why NOT OX-AC for the pre heat?? too much localized heat?? I have a propane tank with a torch, for melting ice on driveways it has a 2" od tip!! think that might be broad enough?

bob

[MMW]

I use oxy acet for pre heat. Just keep it moving to heat evenly.

[raferguson]

A great candidate for some test welds, first to make sure that you can do it, and then to make sure that the welds are strong.

Richard

[dvice]

I have been welding the sheets on and it was going great. i swear the machine gets warmed up and it runs better...and i dont think it is the heat in the aluminum, it just HUMMMS along after a while...i went through two spools of .030 wire.. getting great welds. then it came time for the 3/4" plate!! I stepped the edges that ill need to weld down to 3/8ths " thick X .300" long. I warmed the plate good with a propane torch. I cranked the dial up about 75% and turned the wire feed to 7. I had been using 4-5 wire feed . I was meting the plate fine and it was pooling great and I flowed it into the 1/8" walled tube. I did about 2-3 " at several intervals to secure the plate, then went back over and ran a continuous bead on the bottom of the bracket and I even ran a second over lapping bead... looked great! I flipped it over to tack and weld the inside some...I ran about 2 or 3 3" beads..looked great.. then i went to a new spool and has trouble...I think the gun got hot and the liner melted onto the feed roll..and my wire burned back and clooged in the nozzle. I couldnt get the wire out so i went and installed a new tip. I ran 3 spools of wire and this was the first the wire melted back to the nozzle tip!! I jammed four times in a row after that!! not getting more than a ball out of the gun... before it jammed again. my wire keeps jamming up and smashing into itslef before it goes into the liner!!....I took the nozzle out and it says .023, but the .030 wire goes through it....it that my whole problem?? the guy gave me this package of tips with the unit.. i figured they were all for .030 wire...so i didnt look when i changed over..



the first welds on the 3/4" plate...


inside to the flat surface of the 3/4" plate



my spool gun liner:



before i started with the plate, i was getting welds like this on the 1/8"sheet to sheet and, sheet to .125 wall tube"



EDIT: I measured the ID of the tips and it seems they are oversized for their"size" so my issue would seem to be wrong tip...its probably heating up and closing the ID. the .030 tip measures .037, so it makes sense the .023 would allow the .030 wire to slide in with out heat...sorry

bob