When youre porting cast iron heads, do you use a single cut or double cut bit? And how (ie how many ports/heads) do your bits last? What kind of grinder speed do you use?
What about on aluminum?
My claim to fame? is that I started a machine tool business for the owner almost 20 years ago. Wonder of wonders, we are STILL in business! LOL. At any rate, to answer your question: Single angle carbide burrs are for aluminum. The flutes are wide apart and deep to evacuate the large chips that Aluminum and other "non ferrous" materials produce. A "double cut" is a carbide burr with shallow flutes, spaced close together. This is the burr to use for cast iron which produces a small, powder like chip. Also with harder materials, you want to have more cutting edges to take the maximum amount of material possible per revolution.
As for speed, a rule of thumb is 400-500 surface feet per minute in steel and iron. 1,000 surface feet per minute to 6,000 surface feet a minute in aluminum. The enemy of the tool is heat.
To calculate surface feet per minute (SFM) to revolutions per minute, use this simple formula: SFM X 3.82 / diameter. Example: 1/4" diameter burr in cast iron. 500 x 3.82 = 1,910 / by diameter (.250)= 7,640 rpm.
Aluminum: 1,000 x 3.82 =3,820 / .250 = 15,280 rpm. Now you know why your die grinder turns 30,000 rpm! If you stay within these recommended parameters, you should get the maximum life from your expensive carbide burrs. Also note that aluminum tends to stick to the carbide, gumming it up. In computer controlled CNC machines, we use a special coolant to help with this. If you could get a gallon of this from a local machine shop,(pre mixed right out of the sump of their machine) and put it in a spray bottle, it will extend the life of your tools. But, beware! It will sling coolant everywhere! especially at 15,000-30,000 rpm!
