Multiple pass method question...

Hi,

I'm going to be cutting plastic and wood and have a question for when you do multiple passes each one deeper than the last.

Let's say I am cutting through 1/2" and I am going to do 4 passes at 1/8" depth.

Would you perform one pass at 1/8", then 1/4", 3/8", then finally 1/2". Between passes the Z would go deeper 1/8" all at once.

Or would you begin at 0 and transition Z to 1/8" during the entire first pass, then transition from 1/8 to 1/4 during the second pass, etc. This would be sort of a spiral or would look like a pulled spring.

Is either method better or more commonly used?

Thanks,

Alan

The usual way is the first way you mention, which is what they call "z-level profiling." The profile is completed in the increments specified in the program.

The second one you mentioned is usually called "spiral profiling" or "helical profiling." Maybe not as common since not many basic CAM packages support it.

I don't know if there's a distinct advantage to either other than with the second, the tool doesn't retract until the end, which may mean a faster cycle time. It also avoids "plunging" which may be necessary depending on the tool you're using (non-centercutting.)

If you're cutting material that can easily chip on both sides, I'd be inclined to used the first method, with a compression spiral with an upcut length shorter than your DOC, since the second method could lead to tearout.

For machining holes where the diameter is less than twice (and preferably 1-1/2 times the bit diameter) I'll "helix" in; this is usually faster than pocketing.

The shape of the part may come into play here as well.

I personally prefer the second method. But rather than ramp down during the entire first pass, I'll ramp down in one section of the profile. But as Louie says, a lot of CAM programs don't offer that method as an option.

This method takes longer to program, though, so I'll often use the first method.
I try to never plunge straight down, though.
Even with the first method, I'll ramp in and ramp out, so each pass is separate. This can take a bit longer to cut, though. So when doing a lot of identical parts, I'll spend the extra programming time for the faster cycle times.