[catahoula]

Hi,

TL;DR: what are the practical limits on reducing IPT below tooling manufacturers' recommendations while cutting aluminum, for example?

I'm working on building a machine system for milling aluminum molds. I understand the need for rigidity in machine, tool stick-out, workholding, etc, and I'll be able to produce something a lot better than a normal CNC router but not as good as a VMC. As I research speeds and feeds, I come across wildly different values for acceptable feedrates, which in my understanding, the difference ultimately comes down to the chip load per tooth. I'll be using a router-type spindle, so ideally cutting rpm's won't drop between 10,000, although 7,000 may be possible. With this as a given, I see that following manufacturer's specs for chip load gives feed rates for some particular tools that are at or above the limit for my current design (150-200 IPM). I would like to be able to keep my feeds at 100 IPM or below if possible (based on selection of motion components etc.)

Here's where I get stuck: a lot of recommendations that I've come across in my research work out to chip loads much below what the tooling is specified at. Also, the Tormach for example, which is certainly marketed and used for exactly the kind of work I want to do, is limited to about 110 IPM. I understand that the tormach has a slower spindle so feeds don't need to be as fast. But in general, maybe in terms of percentage from the recommended chip load, how much can you reduce feedrate before getting rubbing on the workpiece? My understanding is that the potential for friction and rubbing is the main limitation on reducing chip load. When I do the tooling calcs, it seems like I need a 200 IPM machine, but when I read practical experience or advice on speeds and feeds, it seems like 100 IPM is fine.

Cheers,

Brian

[Jim Dawson]

I try to keep the chip load at a minimum of 0.001'' and up to the manufacturer's recommended load. Understand that the manufacturer is recommending chip loads for MMR under ideal conditions with a rigid machine and enough power to drive the tool at that rate. You have to back those numbers down based on your machine.

[catahoula]

Ok, that's helpful. I guess I was looking at the manufacturer's ranges as min-max for decent tool life. Thanks.