Monday, November 30, 2009

New grinding techniques applied

I've been having trouble with patch panels flattening out/shrinking when I grind them. I wrote Pete at South West Rod and Custom to ask if he had any advice for me. He said the heat from the grinder will shrink the metal just like welding will. He suggested I use a 3" cutoff wheel to grind rather than my 7" grinder. Also he suggested that I concentrate on grinding ONLY the weld.

I made sure to only use the edge of the grinding wheel rather than using the face. I also ran my hand over the work area every minute or so to make sure nothing was getting hot. I made a big effort to keep the wheel moving over the length of the welds rather than concentrating in a small area. I literally took one swipe on one line of welds, moved to the other side of the panel, took a swipe, moved to another area, etc. It made for about an hour and 10 minutes of grinding, but the panel looked perfect when I was done. The alternative is spending an hour beating the panel back into shape. Case in point; I'll be spending a few hours replacing a patch on the passenger side that I ruined by grinding too fast.

Thanks to all who thought nice things about my compressor... I don't want to speak too fast, but I think she's gonna make it. I did some reading on the interweb and found that it was just a loose belt. I tightened it up and changed the oil... She's running better than ever now!

Panel ground down and run over with 80 grit on a D/A


  1. Cool project! What a huge amount of work! I was wondering why you covered up the air vents on the front of the Karmann? Does that make it more aerodynamic? My Karmann ('71) has covered air vents too, but they aren't smoothed over with the contour. The air vent space covers on my car dip in and look like nostrils. I have no air flow so I just drive her with the windows rolled down.

  2. Pete-

    Thanks for taking a look at the project. I decided to smooth out the air vents for a couple reasons... When I started the project about a decade ago, I thought the vents were beyond repair. The ducts were rotted and I didn't think there was replacement sheet metal available. I was also sent a picture of the concept for Karmann. The concept had no air grills, just a smooth nose. I thought it looked cool, so I removed the vents and ducts... 10 years later I finally finished patching them up!!!

    In the end, I don't think I'll ever drive it with the top up, so I don't think I'll need any fresh air.

  3. What about flap wheels and flap disks? I was planning on using a flap disk with my grinder to smooth welds. Are they too imprecise?

    1. The flap discs are fine for finishing but rough grinding I don't like them as much. Using the edge of a stone lets you pinpoint the grind and reduce heat. If the metal turns blue you are in danger of warping the panel. Work slow and keep the panel cool as possible.


Let me know what you think about the project.