[RonnieT]

Ok, I weld every day for the past 30 years, tig or mig or stick.
I weld 1018, 1045 195 4140 and 4130 mostly prehard stuff.
I use an old Millermatic 200 that bought new in the 80s and never bleched, other
than a few torch changes.
The other welder is a Miller 180 SD , I bought both of these new and never had a problem with either even being turned on and off or 20 times a day.
I use a gas lens system on my Tig with the original torch, I use 2 % lathanated in it in different sizes.
I am self-taught out of necessity, As I live in a rural area and no one near even knows what a tig or mig is.
I watch the Jody videos and am amazed.
I use Argon straight on my tig with flow meter, I use C25 on my mig with a flow meter. I know when I get a bottle of bad gas.
I have tigged copper,
I now have to learn how to tig aluminum
I have a piece on my boat that needs attention
It is one of the cavitation fins on the outboard engine.
It starts out as about 3/8" thick and thins to about 1/4" and is cast. Crack about 6" long and is painted.
I need to know how to set my 180 SD and what amps I should use, what gas, and what tungsten .
I also need to know what size and number of rod I need for this.
Any tips on cleaning and beveling.
I have one shot at this and I need to practice some.
I probably can get a picture of it , I will take off the lower unit as I need to change the pump anyway so it will be in a clean environment and set up for level welding. I have the tools I need the know-how now.

It's an older 1989 Force 125HP outboard and I maintain it, I think someone tried to use it as a step to get in the boat.
Anyway please reply, I read them all and take them seriously.
Best
RT

[cj737]

You’ll need every bit of amperage your box will spit out, and then some.

First order of business is to clean the ever living crap out of it. Both chemically and mechanically. Bevel the edges. Preheat the fin with MAPP gas, propane won’t get hot enough.

You can use 4043, 4943, 4047 or even 5356 filler. Expect to run several passes and peen the weld between passes. I prefer to run 3/32 on both sides, multiple passes for these types of repairs.

60hz-120hz is all you need, and I prefer AC Balance of 65% on my box (more cleaning). If your first passes generate soot floating up, stop, grind it out, then run a pass without any filler. Clean, clean, clean every pass to avoid porosity and grime in the weld.

[sbaker56]

Yup, I wish this forum was large enough for overlap in members, I wouldn't mind helping nearby people get the hang of something hangs on in a lot of situations etc.

[RonnieT]

I hear you and thanks, I will gather some rod and metal and start prac-tizing my ability.
I didn't realize it took so many amps? crack is only about 4-5" long, I think an added "whale tail" caused it or a fat boy used it for a step?
Anyway probably won't weld long enough to run upon the duty cycle?
Can I clean it and bever with a grinding wheel? Maybe buff out the contaminants with a wire wheel?
Ron

[cj737]

I would shy away from a “grinding” disc and instead purchase an aluminum oriented flap disk. They’re plenty coarse enough to shape and grind away the cast (it’s pretty soft). It’s been my experience that cavitation plates are damaged primarily due to two causes: impacting something (rocks, piers, trailer bunks) or from the boat and motor porpose-ing across waves. Anytime the prop and can plate leaves the water while under open throttle, the stress and to the prop shaft and cav plate is immense. It can literally tear a prop off its shaft or break off an entire blade. Seen it many, many times.

After mechanical cleaning and grinding, chemically clean it and then heat it. You’ll drive more impurities out with the heat after driving them in from the mechanical surfacing.

[sbaker56]

YES, not just double emphasis on the flap disc but triple, get some one treated for aluminum or simply a cheap 10 pack of ZA discs in bulk from Benchmark abrasive like the boat shop I worked at did, they eat aluminum plenty fast but not gouging and chewing away the aluminum in such concentrated area. We had a few aluminum grinding discs hanging on the wall that were entirely untouched collecting dust and after using one thinking it would be the best way to remove tabs aluminum cutouts I realized how much easier a flapdisc was, just as fast and much easier to take it down flush without gouging deeper. We frequently used 80 grit and 120grit discs as often as anything else and not just for final finish work in order to have a bit more control over the metal removal. Aluminum is very gummy and the coarser the abrasive the quicker it'll want to dig in and tear up both the flapdisc and aluminum in equal measure.

[BillE.Dee]

IF you have a speed adjustable grinder, turn the speed down. The aluminum will gum up the disc. I usually use bees wax on the disc to help aleviate the the gumming. Wipe the area to clean the grindings...some use acetone and some use alcohol (the rubbing kind). You will also want to determine IF the crack isn't all the way to the edge. Also follow the directions of the folks above. Good luck and keep us posted.

[sbaker56]

IF you have a speed adjustable grinder, turn the speed down. The aluminum will gum up the disc. I usually use bees wax on the disc to help aleviate the the gumming. Wipe the area to clean the grindings...some use acetone and some use alcohol (the rubbing kind). You will also want to determine IF the crack isn't all the way to the edge. Also follow the directions of the folks above. Good luck and keep us posted.

I've also noticed that while regular coarser flap discs don't seem to gum or load up as much, they'll shred themselves instead due to it, I learned to generally go with at least a 60-80 grit or it would chew up aluminum REAL fast for a while, then it'd slow down and you'd realized the disc looked thinner than you were used to and realize it was mostly shredded fibers that were left exposed. Those will wear down obviously, but they seemed to do it at a rate that kept the flapdisc "dull" for lack of a better word.

[tweake]

for flap disks the trick is variable speed, just use slow speed and the disk will rip aluminum off and the disc will be fine.
however for crack repair i would be using a die grinder. either an aluminium bit or slow speed and a bit of lube.

actually i think jody has a video of an outboard motor repair.