Technical Shrinking Disk and the roof of the '58 Biscayne

I had a good sized dent in the roof of the '58 Biscayne that I hammered and dollied out to just having high spots. I bought a shrinking disk off of eBay and went to town on it. I used a 9" angle grinder from HF and hit the high spots for 5-10 seconds and let the disk come to a stop on the metal, then quenched it with a spray bottle of water with a little soap in it. I just patiently worked the metal until the metal was smooth. As it is I will have to put a skim coat of filler over the area, but when you consider that it was a sizeable dent and the roof has been brought back to life with only a barely perceptable difference from when it was not dented.

 

I was really surprised at how easy it was, just takes patience.

 

I've heard good things about shrinking disks and I've been wanting to try one.

 

Shrinking discs are a valuable tool.
I'm curious about your use of soap in the quenching water though. What do you think the soap did?

 

I used the soap because that is what the instructions said to do. I reckon it did not boil off as quick as straight water would. Plus it made it clean and springtime fresh!

 

got to love the shrinking disc. I worked on an OT car that must have had a fat girl sit on the roof and collapse it, then they pushed it back out and there was stretch marks all around where it was caved in. all the experts came by and told me Ill have to cover the whole roof in bondo, one of these clowns actually worked at a body shop. shrunk the stretches down to almost nothing and high build primer perfected it.

 

The soapy water helps minimize the chance of the metal galling and messing up your disk.

J.

 

Shrinking discs are amazing by they have their limits. If you see sparks, you are removing metal. Keep it lubricated with soap and be patient. It will shrink eventually.

 

I got one a few months back, used it a few times, its a bloody awesome tool. As stated soapy water is used as a lubricant.

 

Lubrication might be the intent, but I don't see that happening for longer than a nanosecond because of the heat buildup of metal on metal. After all, the metal requires the heat in order to change it's form. I'll ask one of our metallurgists and see if they know.
Also, get a pad that fits your angle grinder. The one that came with the disk that I bought did not give me enough purchase to use the supplied nut that came with it. The wrench I had for my angle grinder would not fit the nut either (one of those two pin wrenches) so do yourself a favor and save some $$$ and just buy the disk and everything else from somewhere else so you know it will fit and stay on.

 

The soap beaks the surface tension of the water molecules so it doesn't want to 'bead up' as much and will flow out better. This gives better contact/cooling to the metal.