Cutting help

[studysession]

I recently bought a lathe. I am learning as I go.

I have a round stock of aluminum about 1.5 inches thing. I shape and cut down for the shape I need with no problems. Now I have shaped maybe 3 inches of a 12 inch round piece. What is the proper way for butting off the 3 inch cut piece very neat/cleanly without wasting to much of the round piece of aluminum.

Hope that sounds right. Many thanks!

[nervis1]

Get a cut off blade, and holder, KBC and every other big supplier sells them pretty cheap.

[studysession]

Thanks - I was using a cut off blade and it broke - not sure if it was just a cheap quality cutter or what. Figured I must of been doing something wrong.

[BigDaddyG]

Studysession,
A quick note: If you broke the cutter, there is a good chance that is was not centered on the work piece.
Good Luck
Glen

[nervis1]

Yea you want the tip of that thing at the dead center or just a weeeee bit below. Use the shortest overhang possible, and try a little cutting oil. Correct feed and speed doesn't help either.

Giver' another go.

[HuFlungDung]

What kind of cut-off tool are you using? There are high speed steel blades and carbide tipped (or insert) models.

The high speed steel blades pretty much suck for everything except cutting off brass and cast iron, where a neutral rake angle is called for. This is the angle that the top of the blade makes with the tangent to the work: 90 degrees.

This is not optimum for parting off aluminum or steel. Grind maybe 5 degrees top rake on the top of the tool (never grind the sides), so that there is a gentle slope that facilitates the chip sliding back over the face of the tool.

If you get a lot of chattering going on, this may indicate too much front clearance on the front of the tool. This should only be maybe 3 to 5 degrees, too.

The nicer avenue is carbide insert tools. These generally have a chip former pressed into the top of the insert. This helps wind the chip up like a clockspring, and also narrows it down a slight bit so that it comes out of the groove more easily.

Lube is very important, too. So is feedrate: a properly set tool likes to be fed in at about .003 to .004 per revolution. This is quite fast when you are hand cranking the tool. Slow down the feed as you approach the center for the final cutoff.

Carbide tooling is really the only way to cut steel. The spindle rpm is important for steel, too: the critical speed must be maintained in order for the tool to cut a smooth chip. Slower speeds leave a rough cut surface: when the speed is right, a nice shiny chip and surface result. But, in aluminum, you can seldom ever go fast enough to achieve this, so lube is the way to get what you want. Of course, constant surface speed on a cnc lathe is something you can dream about, too