SuperPID-help cutting aluminum?

CNC Machines Shapeoko
7

Yup, that one.

BUT It also depends on several other factors:

Machine:
Rigidity of your machine
Squareness of your machine

Cutter:
Quality (sharpness) of the end mill
Coated or non-coated cutter
Height of the Z (Higher (Z+) is weaker then Lower (Z-)
Length of the cutter
Amount that the cutter sticking out of the collet

Work Holding/Material:
How rigid is the material (sheet vs. flat bar)
How are you holding it to the table
Where on the table

I generally teach the 10/10, 20/20, 30/30 rule.

Start off with 10 IPM, and 0.010" DOC, if that sounds snd looks good, work your way up the Feed and DOC latter until you max out at 30IPM and 0.030 DOC (at about 80% Rad of the cutter.

That’s the max I would recommend for a S3 (for general roughing (material removal)

Finish cuts? Full width of the material (up to 1/2" thick material)) at 0.005 DOC

Clear?

8

Thanks for the replies.

To clarify

@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.

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9

@farmer
Lower speed equals lower temp.
More flutes, more temperature.

Check out Richards Shapeoko videos, he has covered squaring the machine and coolant and proper fixturing for metal work.

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10

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?

11

Because both the DeWalt and Makita have Hall-Effort systems that maintain the speed. Meaning that the hp is not speed dependent, so you do not need maximum speed to achieve the full 1.25 hp.

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12

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)

13

Will,

Here’s some links that seem relevant.

Gerald

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14

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.

15

The context of that is increasing milling spindles to speeds approaching that of the trim routers used in CNC routers.

16

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.

17

Yes, but they also require a more rigid machine and faster feed rates — the machine can only accelerate so quickly, and for the most part isn’t able to take advantage of the faster spindle speeds.

See: https://precisebits.com/tutorials/calibrating_feeds_n_speeds.htm for a testing methodology and https://www.cnccookbook.com/feeds-speeds-wood/ for a discussion of the tradeoffs.

18

As shown above, more spindle speed = less rigidity required, and faster feed rates are not required - certainly not for wood and apparently not for aluminum (based on the previously posted links). Also see https://www.precisebits.com/spindle_rpm_selection.htm. It’s unlikely that a hand held router would exceed the feed and acceleration capabilities of the Shapeoko 3.

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.

19

actually GW has about 126 different “soft woods” listed in the calculator. 135 under “hard wood”

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20

Yes, but what’s the point of that if the their hardness’ aren’t used in the calculations?

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I believe they are. At least i get a different feed recommendation for each one i choose. It also shows the hardness value (Janka) for each one.

22

See attached for what I get for Balsa (Janka 90) and Pumpkin Ash (Janka 990) with v4.45 of GW (no difference.) What do you get?Balsa and ash.pdf (604.8 KB)

23

not a big difference but balsa 9.237, ash 7.544. To be honest i don’t use GW for wood or even for the shapeoko. I do use it at work for the HAAS mill and lathe, and it is a must for me in that front.

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24

Where did 9.237 and 7.544 come from?

25

It was on my lathe machine profile because i was using it. On the dewalt profile its 4.412, and 3.603 ipm

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I’m confused! Can you please post screenshots of your GW calculations?