How Much Cast Iron Do You Need To Peel Off Of Virgin Metal

Yes, the discolorations will disappear once you get past the skin on Dura Bar. That's the reason it is made oversized, so you can get past the "skin" as I mentioned above. The skin is part of the extrusion process. It cools quicker than the inner does. And you get a lot of impurities at the surface. You want to get rid of this, so you have good iron.
 
Hmmm! It had slipped my mind but I took a minimum off the 1" X 2" durabar I made into a prisom.
Probably a sixteenth off the large flats and 1/8" off the small flats.
Cussed it for some time as the bright lines were very soft and it was difficult to keep from digging in.
One whole end of the bar was harder than the other and there were spots of hard and soft elsewhere along the length.
Treating it in the oven helped to even it out but there was always hard n soft to deal with.
 
In smaller sections of Dura Bar, that is expected. Best to fully stress relieve before doing any machining.
 
As with other recommendations of stress relieving, I found the clean cycle in the oven to work quite well with this exact material. The size I bought is 6x1-1/4 (finish size). I've made one small dovetail straightedge, 2 laps, and the square I'm working on. It has all been ok to work with. Except those streaks, I've only had one piece that actually had cracks in it. When I was scraping the small straightedge it would move, and I had done a 550deg bake on it with no success. It stopped moving and both faces scraped in well after the clean cycle. I'm pretty anxious about how the square is going to turn out, there is ALOT of machining to do on it, which may require a professional stress relieve. Lol The g-code for milling the pockets in the square are around 130k lines per side.
 
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