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Old 02-27-2014, 11:07 PM   #142
MP&C
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Join Date: Jan 2013
Location: Leonardtown, MD
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Re: 55 Wagon Progress

For dressing welds I use the 3" cutoff wheel for the bulk of the weld, to get it to just above flush. This has a minimal contact patch for about the least amount of heat buildup possible. It also gives you about the maximum visibility possible to insure you get the weld down as far as possible without inadvertently hitting to either side of the weld and thinning out the parent metal. The flap wheel fails on both these points as it causes too much heat buildup, and you can't see what you're doing. Flap wheels are not suitable for sheet metal IMO. After getting that far with the cutoff wheel, then use the 3" roloc sander to blend the remaining weld to the parent metal.

On the sanding drums, they are used in the same fashion when dressing inside radiuses. Save your cutoff wheels when they get smaller in diameter for tight spots, good for dressing welds in tighter spots. Then when weld is down to just above panel surface, revert to drum sander.

As far as cleaning up the rear of the welds, multiple reasons. First, the weld dots should have gone through the "initial" planish while the dots were still isolated by themselves. Then grind down to get rid of the bulk so it's out of the way for planishing the next. When you get done and have finished the weld with you roloc sander, now you have nice flat panels that are more receptive to metal bumping, and more predictable when it comes to metal bumping. Leave weld dots proud on the back side and you are risking panel distortion as the welds deflect off the dolly, possibly causing more distortion than left by the welding operation. Lastly, just like the lapped seam gives the possibility of a ghost line in a finished panel, leaving a weld proud, whether on the back side of the panel or a cold joint left on top and "hidden" by mud, thicker metal expands slower than thinner. Leaving weld proud on either side risks ghost lines just like the lapped seam does.
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