08-27-2012, 06:13 AM
Gummy would be a good description of most piston material, exactly why it doesn't polish very. As any metalurgist's assistant will tell you polishing soft metals is very difficult.
The reason that gummy or chewy grades are used is simply that they absorb the shock loads much better than hard, short chipping materials do. Pistons most often fail as a result of the shock loading caused by premature detonation.
Unless you have access to good modern carbide tips specifically designed for ally the best tools for cutting pistons is HSS using a 0 degree lead angle tool with 15 degrees of clearance all around and critically 20-35 degrees of back and side rake, then rather than grinding a nose radius use a stone or diamond lap to polish both clearance and the top rake faces and finally lap in a very fine nose radius. Use 45fpm for speed and whatever feed that works for you. Above all else keep it lubricated I use wd40 as it is convenient but kerosene, Radiator coolant or even Diesel fuel works well, when using coolant I use it twice as strong as is recommended for use in engines as it lubricates better that way.
Regards
Rick
The reason that gummy or chewy grades are used is simply that they absorb the shock loads much better than hard, short chipping materials do. Pistons most often fail as a result of the shock loading caused by premature detonation.
Unless you have access to good modern carbide tips specifically designed for ally the best tools for cutting pistons is HSS using a 0 degree lead angle tool with 15 degrees of clearance all around and critically 20-35 degrees of back and side rake, then rather than grinding a nose radius use a stone or diamond lap to polish both clearance and the top rake faces and finally lap in a very fine nose radius. Use 45fpm for speed and whatever feed that works for you. Above all else keep it lubricated I use wd40 as it is convenient but kerosene, Radiator coolant or even Diesel fuel works well, when using coolant I use it twice as strong as is recommended for use in engines as it lubricates better that way.
Regards
Rick
Whatever it is, do it today, Tomorrow may not be an option and regret outlasts fatigue.