Quote Originally Posted by Ross77 View Post
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Any one have any data on cutting forces? I seem to remember 20N for Ali for some reason :whistling:Probably wrong tho.
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Are we talking high-speed machining or conventional cutting? With high-speed machining you need special cutters and high feed rates if you dont want them to burn out... If we are designing this machine to be 'aluminium capable' we need to work that through and be realistic about our goals. Here is an example working as a starter for 10... dont take it as gospel, there are people who will say " I can cut a 5mm deep 10mm wide slot with my 30k rpm spindle on an MDF machine" maybe they are right, maybe not... but I go by my own experience...

The cutting rate for ali is ~100m/min. With a cutter of 10mm diameter you need a spindle speed of 320 * 100 / 10 = 3200rpm. (the 320 is a contant) (10mm assumes a 1/2" router based spindle)

Aluminium needs about 0.3mm/rev feed rate per tooth. If we assume a 2-flute cutter (1 flutes are hard to find) then we need a feed rate of .3 * 2 * 3200 mm/min = ~1800mm/min. With a 5mm pitch lead screw thats 1800/5 = 360rpm, 6rps = 1200 step/sec, thats going to need top end drivers... or we'll need to gear up 2:1 or 3:1. 1mm or 2mm pitch trapezoidal is probably not going to work. TR12x3 might just.

Aluminium is 17W per cc/min removal rate. So taking a 2mm deep cut 5mm wide with a 10mm cutter at 1800mm/min = 0.2 * 0.5 * 180 * 17 = 306W, say 600W input on the spindle.

Power = torque * revs -> torque = power/revs = 306/3200 = ~0.1Nm, which at a 5mm radius = 20N cutting force... (and thats where the number came from Ross). Remeber the torque must be available at that spindle speed, for many variable speed routers the torque falls off quickly as the speed is reduced.

Dont want this to be a blocker... just so people are aware of some of the design issues and recognise the limitations.. There are some good examples of router-style machines cutting ali.. they are all capable of high traverse rates and have adjustable spindle speeds. A high spindle speed isnt always a good thing, it can burn out cutters if the feed rates are too low... rubbing isnt cutting!

The question I suppose is... do you want the ability to do the occasional bit of small ali work or a machine truely capable of doing it as a matter of course?