Does anyone have a good reference for setting up some of the basic tools especially the speeds they are capable of cutting at.
I am using Fusion 360 and want to set my tools up to cut in hardwoods like oak, walnut, maple, etc.
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Below is a link to good info on how to calculate feed and speed to achieve a desired chip load:
There are equations and a chip load chart at the bottom of the page that are very useful for carbide router bits (there are many similar charts online… beware of paramaters that wildly diverge from the above chart). You may also have to consider surface speed with larger bits (>1/4"). For hardwoods you want to keep surface speed <1500 ft/min or so:
Surface Speed in ft/min = (pi / 12) * (bit diameter in inch) / (RPM)
Lastly, you generally want DOC to be less than or equal to bit diameter, and stepover slightly less than half bit diameter to start.
[edit: So for example, 1/4" diameter bit on hardwood… lets take the lower chipload of 0.009". If the router is set <24500RPM for the cut, surface speed is OK. Let’s use 16000RPM, the slowest our router will go, to go easy on the gantry. So calculating the feedrate using 2-flutes, we get a feedrate of 7315 mm/min, at 16kRPM. You may have to slow down to 5000mm/min if you use 12V for steppers. That should be good to test, and the feedrate can be adjusted during the cut if needed.]
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I ran my first full project from start to finish this weekend. Fusion 360 was estimating just under 5 hours with the speeds I had set up. In reality, it was almost 10 hours. Has anyone else run into that? I would assume it is probably something with machine setup in Fusion 360 that is calculating wrong, but I haven’t dug in yet to see if I could figure out why. I don’t feel like the machine is running particularly slow, but I also don’t have any experience to compare it to. This is my first build.
Anyone have any calibration strategies to check to see if the machine matches the software?
There are a lot of ways to do that estimate, and the usual sources of error are:
- The smaller estimate doesn’t include accelerations. You may be travelling at 50mm/s, but it starts at zero and grows to 50mm/s only after some acceleration. Simpler estimators don’t know the accelerations, or they pick a value for the accelerations that they think are reasonable, but are wrong. The default firmware uses 180mm/s/s for XY and 80mm/s/s for Z (which are conservative).
- The CAM includes move speeds higher than the speed limits in the firmware. The default firmware is pretty conservative, and has a top speed on XY at 50mm/s and on Z at 15mm/s. If the CAM includes speeds higher than that, or if it assumes the jog speeds are higher than that, then the estimate will be lower than reality.
On a CNC, that is pretty much the only source of errors. Things like homing or pause moves obviously add some time that CAM can’t predict. On 3D printers, there are also things like heat up times.
If you’re comfortable running your machine (which it seems like you are, because you ran a 10 hr job on it!), you can adjust the accelerations and speeds. It can probably go a lot faster. We have the defaults set up for beginners, and to reduce pain when people are learning.
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You are lightening fast on replies 
That explains a lot. Thank you. Just saved me a lot of time digging for that answer. I am still using default firmware so I bet that is a big chunk of it.
The speed calculator was suggesting surface speeds in the 150 to 160 mm/s on a 1/4" 2 flute endmill. Before I go triple the limits in the firmware, does that sound reasonable?
No. That sounds way too high. Can you reduce the rpms on the spindle (in the calc and on the machine)?
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I too would love to know how to adjust Fusion 360s calculations so the machining time matches. The estimates for some toolpaths are pretty accurate, for others way off. In particular, I find adaptive clearing takes 2X as long as estimates, but contour cuts, even extensive ones, had reasonable estimates. I suspect, as Jeff indicated, that whatever acceleration numbers are used in the estimates are the root of the issue. I’ve never found where to adjust them, but I never looked too hard either. Note that Lightburn (software I use for Laser work on my MPCNC) has an explicit page for entering this kind of information so that estimates are accurate.