CStan
Here is a post from another forum by Gary Blum. It's is posted here in its entirety:

Great video and great discussion. Regarding the different effects at various planing angles, I have been doing a lot of experimenting lately with bedding angles, chipbreaker angles and chipbreaker distance settings. I recently made a 35 degree ( I can't get Alt 241 to work ) frog for my low angle block as well as a miter plane, so have been able to try the close chipbreaker setting with it. Amazingly, it works just as well even at that very low angle. All this has made me rethink my standard bedding angle for my planes. I just recently went to 47 degrees from 50, and probably should have just went to 45. Gee, maybe the old boys actually knew what they were doing.

I have seen references in some old sources of the chipbreaker being called a 'shaving thickness regulator'. This always puzzled me somewhat. However, now that I have 'discoverd' setting the chipbreaker much closer, suddently this makes sense. If you set your shaving thickness at .002, and you set your chipbreaker at .002 from the edge( or even further back because of the blade angle versus depth difference) , you are then limited to a .002 thick shaving. The chipbreaker then becomes just like the mouth, pressing down right at the cut. As the blade wants to dive deeper from hitting reversing grain, the downward pressure on the wood right at the cut actually increases and makes the chipbreaker even more effective. This is the opposite of what happens with a really tight mouth. The tight mouth is working just fine in normal grain, but when the blade hits that reversing grain, and the edge dives down some or the plane bed deflects down some, the tight mouth becomes LESS effective because the distance from the blade edge to the mouth increases.

In my experience, a tight mouth seems totally irrelevant when you are using your chipbreaker. I never bother changing mine and in fact am considering removing the mouth adjusting screws as this just adds another layer of complication, especially for a beginner.

When you get into heavier shavings, I think the chipbraker is still very effective if it is matched to the shaving thickness and wood species. I think this is what Warren has been referring to when he's talking about the learning curve in using them. There is no learning curve when using fine shavings, just set that sucker as close as you dare ( or even closer ) and you will be amazed at what you can plane. And I have found that the shaving can be thicker than you would think. I set my chipbreaker where it just barely shows any blade, and I can still take a nice shaving.

As to the chipbreaker angle, for my shop purposes I refer to the total angle from horizontal, like you refer to the bedding angle. This eliminates the differences that are caused because of different bedding angle of the blade. Most Stanley planes I have are about 90 degrees. This is quite steep. Most of my old wooden planes are more like 60-70 degrees. When I was first prototyping my plane, I started milling the chipbreak portion of the frog at 100 degrees. It wouln't cut at all. It wouldn't cut until I had lowered it below 90. However, like the video shows, you can get by over 90 if it is a very small microbevel. I use about 110 degrees on that microbevel, but try to always keep it small. In the video they may get by with that extreme negative bevel because of the power feed of the planer.

Well, now that Isee this written down, it's no wonder I can't sleep at night trying to figure out all this 250 year old technology.

Gary Blum

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www.blumtoolco.com