[Espie]

Hi All,
I have just bought a CNC router which I will be picking up on Monday. I already have plenty of 3D models that I have made ready to try out.
What I want to know is what feed rate should I be using for MDF? I am using Vectric Cut 3D for the CAM software
Also what spindle speed should I be using? Is there a chart somewhere I can look up for different materials?
I plan to use an end mill for rough out and a 2mm ball nose for finishing.
Any advice would be greatly appreciated
Thanks
Andrew

[awerby]

Speeds and feeds vary with the type of material being cut, the type of cut being made, the abilities of the machine, and the type of cutter used. The way to figure out which to use is to look up the recommended chip load per tooth for a particular tool in a given material and use math to determine a feedrate that will give you that chip load at a given RPM. Here's a chart that explains all this in more depth, and has suggestions for cutting MDF: Calculating Feeds CNCRouterShop.com

Andrew Werby
www.computersculpture.com

[mmoe]

In addition to what has already been recommended, I suggest using the largest diameter ball end mill that can fit into whatever project you are working with. Without seeing the parts you plan to cut, this may or may not be relevant, but I see a lot of new CNC users cutting with the smallest ball end they can get thinking that it must provide greater accuracy than a larger ball end mill. The truth is quite the opposite. Any ball end mill that will fit into the detail level of the part is going to provide the same detail, but not necessarily the same quality of finish.

You get three things by maximizing the ball size. First, you get the maximum surface speed possible for cutting the part. The greater the surface speed, the more flexible you can be with spindle RPMs (this relates to the previous poster's chart on chipload). I find that it's best for spindles to run in the 10,000-12,000 rpm range where ever possible. You get roughly the same lower current draw as you would at 15,000-20,000 rpms, but less heat in the bearings. Spindle RPMs below around 8000 rpms start to increase current draw, which also generates more heat and reduces spindle lifespan.

Second, you get maximum clearance for chip removal because the depth of each cutting edge is maximized. This increases the life of the tool and generally produces a better cut as well.

Last, you get minimum scalloping to the finish of the surface. The smaller the ball size, the rougher the surface will be. If a 20mm ball end mill will work for a given part, it will produce a drastically smoother finish than a 2mm ball end. All ball end mills will be cutting tangent to the surface, so if you can visualize the difference between a small circle with a tangent and a large circle with a tangent, and then step over the same amount, I think you'll see why minimizing scallop is wise. You could also draw this relationship out in CAD and it will illustrate clearly that the larger the tool, the less the scallop.

Have fun with your new machine!

[ger21]

I'd finish @ 200 ipm and 18000 rpm as a start.

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