aluminum boat welding ?

I have a lincoln sp-170 MIG and everyone tells me it will be very hard to weld any amount of aluminum due to birdnesting. I local shop says thay can hardwire a miller spool gun into this welder. If I did this could it effectively be used to build a boat using a pre-cut kit consisting of 1/8" and 3/16" panels. I have been told MIG welded aluminum is very porous and it would be better to use TIG for water tightness, how true is this.

-I have been welding and repairing aluminum boats for many years and have not had problems of water tightness on boat hulls . 1/8" aluminum can prove to be a challenge to weld.as it is prone to burn through and warping. The equipment that I have used for lighter gauge materials is a pulser unit attached to a Miller XMT 300 and a Cobramatic spool feeder with great results

-I think Lincoln would be upset to hear that since they have spent a good deal of time designing it so the wire won't birdnest. Welding aluminum with a "push" MIG is not that hard. What causes the birdnests is the wire poping back to the tip and sticking. If the wire fedder is set too high, it will keep trying to push the wire even though there is no where for it to go. To prevent this you will have to use smooth drive rollers and set the feeder pressure so that if you stop the wire at the tip, the feed rollers slip. This way you won't get birdnests. You will need a teflon liner to decrease friction in the feeder.

The biggest problem is that with a "push" MIG the gas valve is about 12 feet from the gun, so when you pull the trigger, the wire hits before there is sufficient gas to protect it. This causes a barf at the beginning of the weld. You can fight this several ways. Every time you take your finger off the trigger, pull the wire out and snip it off flush with the tip. This will help add a small delay as the wire feeds. You can buy a second gas cup and solder a small tube onto the side. Connect a secondary gas source to this tube so you can have "pre-flow" gas shielding. All you need is a small valve on the line so you can turn it on and off manually.

Alternatively you could wire in a bypass switch to the gas solenoid in the machine so you could trigger the gas a few seconds before pulling the trigger.

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