I’m getting close to pulling the trigger on a Shapeoko. I have a project in mind that involves aluminum, if it works out I would probably be cutting aluminum often. I’ve looked at the carbide speeds and feeds guide and it recommends speed 1.5 on dewalt dial i.e. +/- 17k for cutting aluminum. SuperPID seems to enable speeds as low as 5-6k rpm. Is carbide3d recommending that speed b/c it’s best case scenario for included hardware? Would slower speeds help with cutting aluminum?
You don’t need the PID, and both the Makita and DeWalt work great at cutting Aluminum. The slower speed of the Makita helps when cutting steel. Check out my InstaGram for some of my projects. I cut metal about 90%
If we work up the chip load and Material Removal Rates for the Dewalt feeds and speeds as was done for the Nomad at: https://www.shapeoko.com/wiki/index.php/Nomad_883#Feeds_and_Speeds would it then be helpful to go from those chip loads to work up an optimized feed and speed chart for the Makita where at suitably lower speeds, we calculate a feed rate which achieves the same chip load.
Is that the purpose / intent of chip load and is that a valid procedure / set of calculations?
If I’m understanding this, there would be some sort of torque rating for the motors involved which would show what torque it can achieve at a given RPM, and that one then needs to match that torque and speed to the expected cutting forces, and so not exceed the torque which is part of what causes problems when cutting.
As an experienced maker and an engineer and not the Manufacture (Apollo), let me tell you my findings:
I am going to talk about horsepower rather then torque just to simplify things. The Makita is rated at 1.25hp but consumes 700 watts and that means 1hp (100% available) with a little bit of reserve (1.25 total available for perhaps 10-25% duty cycle), and since the router has speed detection, it does in fact maintain the 10k speed at just about anything that I can throw at it (I am referring to the Router NOT the machine).
My Shapeoko (Spindle: Makita 0700 and an Shapeoko 3 (9mm belts), with a metal table)
During heavy machining, the Z Axis plate will flex considerably when taking a 1 1/4 hp cut (Example: 1/4 End Mill, 0.25 DOC (Axial), 0.22 DOC (Radial) with a 25 Inch/Min Feed rate) when cutting in the Y direction (Note 2 drive motors, which will produce about 36 pounds of pulling force). It will also stall (skip) the X Axis Stepper motor (Stalls at 18 pounds) when cutting in the X direction. (I won’t even go into the noise factor)
What does all these numbers and math mean: The Shapeoko cannot take advantage of the available horsepower that these (Makita and DeWalt) Spindles can provide. My recommendations for speeds and feeds are based upon the machine’s STRENGTH and are pretty much spot on with that is published in the recommended published document.
@ApolloCrowe you stated the makita’s lower base rpm of 10k would be better for 6061. Carbide speeds and feeds list higher speeds for dewalt and makita, is that for simplicity? If I plan to cut aluminum what would be primary benefits of using the lower speed, tool life, finish quality etc.? Is 10k speed enough of a reduction to use a 4 flute with aluminum? A part I’m looking to make has an undercut and there are a lot more options for spherical end mills in 4 flute vs 2. Appreciate all the info, thx.
Isn’t 1hp = 745.7 Watts? Isn’t the router’s output power further reduced from that 700W electrical consumption by the efficiency of it’s motor and drive electronics (likely 80 - 85%)? Isn’t the force on the machine (and workpiece) proportional the torque on the cutter and inversely proportional to it’s speed? So, why not maximize router speed rather than minimize it?
Also, you want to adjust the speed of the trim router to match the feed rate which you can reasonably achieve so as to get a chip load which is suitable to the material you’re cutting — this often wants a lower speed, rather than a higher. See Tutorial on feeds and speeds (which needs to be expanded upon or finished)
Assuming router motor horsepower is determined by output (mechanical) rather than input (electrical) power, a router with a 700 Watt input would provide about 700 * 0.85 / 745.7 = 0.8 hp of mechanical power.
Rotational mechanical power (hp) = Torque (ft lbf) * Speed (RPM) / 5252. Cutter (and workpiece) force (lbf) = Cutter Torque (ft lbf) / Cutter radius (ft). Since the required cutter hp is proportional to material removal rate, increasing cutter speed reduces forces.
Motor output power is proportional to speed and torque. Torque is proportional to motor (winding) current, which = voltage across the windings / winding resistances. Voltage across the windings = supply voltage - motor back EMF (which is proportional to motor speed). Those are the factors that ultimately limit motor performance, not the type of speed/torque controller used with it.
I believe that most/all motors power ratings are at the maximum design motor speed. Higher speed means less winding current and less heat generation for the same power output.
That was my point. Higher spindle speeds enable higher material removal rates (MRRs) and reduce forces on the cutter, spindle, machine and workpiece (all good things)! They also reduce spindle heating for a given MRR.
Regarding your CNCCookbook link, you should take a closer look at that. In particular, consider that softwood hardness “family” “alloy” Janka hardnesses vary by an order of magnitude, yet G-Wizard uses a single undefined hardness value for the entire “family’s” calculations (the same is true of other “families”). There are numerous other problems with G-Wizard.