I have a couple of carbide burrs that we use in a die grinder. They are made for aluminum for fast stock removal and do not load up. you can get them in different configurations and diameters. M.S.C. industrial supply or Mc Master-Carr have a good selection. I hope that helps (R.C.)

You are probly using the same grinding wheel to grind the aluminum as you did for steel. Get and keep one wheel just for aluminum, possibly a wheel MADE for aluminum, and do NOT let it touch other material. If you used a sanding disc, you are screwed because the adhesive that holds the abrasive to the disc is now in the metal you are trying to weld.

I have a whole different perspective on your problem here.

First off; Safety brief!
Grinding wheels are not to be used on Aluminum, Brass or other non ferrous metals that will load up on the wheel surface. The out of balence condition created by the smeared (loaded) aluminum on high spots of the wheel will cause the grinding wheel to part (explode). Eyes and lives are lost from this unsafe practice.

Secondly; The notion that sanding discs are not capable of producing quality work with aluminum is wrong.

Repairing a thin aluminum boat hull does not require expensive custom carbide burrs (that will load up anyway)

A quality 3 inch 80 grit aluminum oxide disc and a 18,000 rpm angle die grinder will be the optimum tool for surface prep and weld blending on aluminum sheet. X-ray quality welds are produced by the thousands on a daily basis using this technique. Here is a link to a selection of high quality discs.
http://www.ind.nortonabrasives.com/Media/Documents/S0000000000000001035/Norton%20Stock%20Catalog%202005-2006%20Speed-Lok.pdf 3M also makes high quality abrasives.

Carbide burrs are a good way to route aluminum castings. My tip for the day for carbide burrs is to buy a block of parafin wax and periodically dip the bur into the wax. This will keep the tool from loading up and extend the tool life up to 10X. This technique will also apply to reenforced cut off wheels of less than 3" dia. A little parafin will allow a 3 inch 1/16 cut off wheel to cut about 10 feet of 0.125 inch inconel where unwaxed wheels will shrink to nothing in an inch or so.

You must prep your boat hull on BOTH sides. I suggest an 80 grit disc. Bring the metal to bright condition right before you weld.. Put a copper chill block behind the heat affected zone with a small recess for melt thru on your crack area. The tighter the fit on your backup the less burn through you will encounter in unwanted areas. Run your weld pass, remove the heat sink and blend any badly contaminated melt thru (down to 1/8inch with no sharp edges) The top should be smooth and transition evenly into the parent material, if not blend it down.

To avoid smeared metal or impregnation use a new disc and don't bear down hard. They will remove an amazing amount of material if the RPM is high (not above the rated speed of the disc) and the pressure is low. Use the edge of the disc to blend the metal down. When the edges of the disc are no longer sharp you can use the center of the disc to take down high spots like starts and stops.

The best repairs of aluminum less than 0.090 inch thick will be with the GTAW process. Mig will do in a pinch but its not the best.

Dear Sir

Please contact Pferd, and look your product POLIFAN®-Flap Discs - www.pferd.com/images/PferdProducts/206.PDF

Giovani Lopes

SC-Brasil

You can use a flapdisc or what we call our Polifan. I work for an abrasives manufacturer called PFERD abrasives. We have one specifically designed for use on aluminum called Polifan A-Cool. It is a coated abrasive product and will not leave any contaminant residues behind to disrupt the integrity of the next weld pass. They are available in 115mm (4-1/2"), 125mm (5"), 178mm (7"), diameter and are offered in 40, 60, 80, and 120 grit (depending on the desired surface finish) in your case a 40 grit would be suitable. If you are interested please contact our Brasilien subsidiary: PFERD Ruggeberg do Brasil Ltda.
Tel#: 0055 41 373-8222
fax#: 0055 41 373-8182
www.pferd.com.br
As this inquiry came from our Brasilian subsidiary we assume that you are located in Brasil. If not and you are located in the United States please contact PFERD of America at the following toll free number
1-800-342-9015, thank you.