This was from an article on the web (not that everything out there is correct) On metal Shapers by Kay Fisher.
Tool Bit Rake Angles
The rake of a tool bit is the angle (or angles) ground into the top. In the case of a round nosed tool the angle cut back into the tool is called top rake. Unfortunately this same angle is also called front rake and back rake. Its all the same. In the case of a left hand tool the angle cut sideways into the top of the tool is called side rake.
Tool Bit Rake Drawing by Kay Fisher
"Sorry the drawing didn't Paste from the article"
But no matter what you call it, rake is rake. With no rake the tool will tend to come out of the work and ride on the surface. With too much rake the tool will tend to dig in and pull the holder, and everything it is connected to, towards the work. Although rake is necessary, it is undesirable to grind rake, because this removes metal that would become the cutting edge in future sharpenings.
Armstrong style tool holders hold the tool bits at a 14 to 20 degree angle, eliminating the need to grind top rake. This way, a tool can be re-sharpened indefinitely. Also, the same tool can be used in a conventional tool holder for brass, which cuts best with no top rake.
Rake angles for steel and aluminum should be between 14 to 16 degrees. Rake for cast iron should be 2 degrees and for brass and bronze 0 degrees. My advice is to ignore rake and always use an Armstrong style holder except for brass and cast iron.
On a side note Steve you've never said HOW you managed to bust something as tough as a shaper. Kind of like busting a Sledge Hammer isn't it.
Tool Bit Rake Angles
The rake of a tool bit is the angle (or angles) ground into the top. In the case of a round nosed tool the angle cut back into the tool is called top rake. Unfortunately this same angle is also called front rake and back rake. Its all the same. In the case of a left hand tool the angle cut sideways into the top of the tool is called side rake.
Tool Bit Rake Drawing by Kay Fisher
"Sorry the drawing didn't Paste from the article"
But no matter what you call it, rake is rake. With no rake the tool will tend to come out of the work and ride on the surface. With too much rake the tool will tend to dig in and pull the holder, and everything it is connected to, towards the work. Although rake is necessary, it is undesirable to grind rake, because this removes metal that would become the cutting edge in future sharpenings.
Armstrong style tool holders hold the tool bits at a 14 to 20 degree angle, eliminating the need to grind top rake. This way, a tool can be re-sharpened indefinitely. Also, the same tool can be used in a conventional tool holder for brass, which cuts best with no top rake.
Rake angles for steel and aluminum should be between 14 to 16 degrees. Rake for cast iron should be 2 degrees and for brass and bronze 0 degrees. My advice is to ignore rake and always use an Armstrong style holder except for brass and cast iron.
On a side note Steve you've never said HOW you managed to bust something as tough as a shaper. Kind of like busting a Sledge Hammer isn't it.
Free advice is worth exactly what you payed for it.
Greg
Greg