I've done valve jobs many times on my fathers Black/Decker valve machine. I've faced the valve facing, and valve seat stones many times, but over the last 20 years I've forgotten if the valve facing stone needs to be faced flat, or at an angle? I just got the Snap On machine a few years ago, and finally got around to ordering a new valve facing stone. The new stone, out of the box, has an angle already in the stone, but giving it a try on an old junk valve at 44 deg valve angle, it donesn't look right. Here is some pictures of the valve machine model. Here is the new stone installed where you can plainly see the bevel, inrealtionship to the valve set at 44 degs. Here is the old stone in the foreground where you can see the bevel actually in a reverse angle to the new stone [yes, the new stone is installed correctly I double checked]. And, a shot of the whole valve machine.