Hey there, I need a bit of help getting started, I’m new to CNC and am currently testing different 2D operations with Fusion360.
I have a Shapeoko XXL with a Dewalt DWP611 and am currently testing cutting 3/4 MDF with a quarter inch flat end mill (the ones sold by carbide 3d )
I got the feed rate, plunge rate, and depth per pass from the carbide create program and used them to create my feed and speed in Fusion 360.
The automatic speed settings from Carbide Create when set for MDF with 1/4" flat end mill were as such:
Depth per Pass: 0.111"
Stepover: 0.113"
Spindle Speed: 12500
Feed Rate: 75"
Plunge Rate: 12.5"
What I set in Fusion360:
I also set in Fusion “Multiple steps” with “Maximum Roughing Stepdown” to 0.111".
The one thing I did alter is the Spindle Speed. It came to my attention that the lowest speed on the Dewalt router is 16000 RPMs, so even though the recommended speed in carbide create is 12500 I input 16000 in Fusion and lowered the speed on the router to its lowest setting.
Once I launched the Gcode though the router was obviously working way too hard and the CNC seemed to be snagging and getting caught up in it’s motion. Anyway it wasn’t looking good at all. So what’s going on? I thought I was on the right track here!
It looks to me like your settings should work fine in MDF and definitely not be as bad as you describe on the machine. Did you cut other things successfully ? If not there might be something wrong at mechanical level, loose belt, loose setscrew,…
Also, do things improve if you reduce depth per pass by, say a factor of two ?
@WillAdams In the carbide3d document you linked me to under the MDF category I am seeing DOC of .3", am I correct in assuming that this is the number to set my Depth Per Pass to (or Maximum Roughing Stepdown in Fusion360)? That seemed to me very deep for one pass, I launched a test with these new numbers and it was really loud, really rough, I’m scared to break the machine. That said maybe I just don’t know what to expect.
Also I am only seeing these numbers for a quarter inch flat end mill, is there charts for other cutting tools?
@julien I was testing yesterday with the 1/8" flat end mill and things seemed to be working pretty good, I can give it a go reducing the depth but this is becoming even more surprising since the chart I am now looking it says to increase it beyond what Carbide Create indicates. I will check hardware, but at first glance everything seems ok on that front.
Always take any feeds and speeds table with a grain of salt, carbide3d’s included… especially on depth of cut values. I would not cut MDF at 0.3" depth per pass as they recommend, myself I use an overly conservative 0.05 inch per pass to be safe, with very similar settings as yours for the other params, when slotting.
Come to think of it, the 0.3" recommandation even violates the rule of thumb to limit DOC to about half the endmill diameter…sure MDF is soft, but still…
@Julien, yes if slot cutting means simply cutting the outside perimeter of a 2d shape, I am doing a 2d contour in Fusion 360. As far as DOC the website provided by @WillAdams recommends 2 x the end mill diameter for soft wood and half the end mill diameter only for extremely hard woods such as ebony. (info found under the initial feeds and plunge tab).
That said I will try and see how it behaves at 0.05 as you recommend.
The 2x endmill diameter for soft wood is a guideline for a testing cut, but you shouldn’t do that on actual production cuts in most cases. The usual guideline is much more conservative:
Cut Depth/Step Down: The traditional guideline is 1/2 the diameter of the end mill. Another school of thought is to start shallow and work deeper until the sound of the cut changes (typical values this way are 0.3mm (harder plastics (acrylics)) or 0.6mm (wood)
I’d probably use settings pretty close to what you have…sounds like something else might be going on mechanically. You can always double the feed with real time overrides, so I’d recommend starting slower and working up to uncomfortable. I’d always cut slower and/or shallower in a slot than a pocket and try to clear chips as you go.
In the words of @WillAdams (the benevolent angel taking care of our community ), “slotting is hard” and MDF surface is often harder than its core, so this first slotting pass in MDF can be a bit hard on the machine if DOC is “too high”.
This is what of those things that no one tells you are a beginner and you try to make sense of the many tables/rules/black magic recipes out there to figure out proper feeds and speeds for a given material: RPM and feedrate are quite important to get nice thick chips, and the tables are usually correct there, because it’s simple math/geometry. But DOC is another story, it directly influences the load that the machine sees, and there is no definitive rule for how deep one can push it, because it depends on so many factors (slotting versus pocketing, machine rigidity, tool deflection, upcut or downcut endmill, chip clearance…)
My approach is to trust the RPM & feedrate from the theory/rules/tools, and then experiment to see which DOC I can pull off on MY machine, starting with a shallow cut (there is no downside to initially being conservative on DOC, just a loss of time/productivity) and then increasing it until I feel (hear) that the machine starts to complain. But that’s only me, braver members of this forum push their machine way harder and still get beautiful cuts (spoiler alert : some if not most have customized/ruggedized their Shapeoko over time though…)
Ok I’m starting to get a good idea of how to deal with DOC at this point. Now I’m getting maybe a bit more technical with feeds and speeds but it’s really just to get a better understanding of how to determine all this.
What I’m seeing in the documentation is that Chip Load is important and will help you determine the feed speed. I’m currently working with a 1/8" 2 flute flat end mill, the one sold by Carbide. In the wiki page I’m seeing a chip load of 0.02" for a 1/8" end mill in softwood.
(Note that it includes some settings from Carbide Create which arguably should be removed)
Discounting those, it ranges from: 0.00043478″ (aluminum) – 0.010416″ (linoleum) — the Nomad has a low powered spindle by traditional standards, but it’s carefully balanced against the rest of the machine, and the speeds which one can expect to get to moving within its working area — even on a diagonal one can’t move much more than 11", and can only accelerate for half that, so need to slow down at the halfway point.
), “slotting is hard” and MDF surface is often harder than its core, so this first slotting pass in MDF can be a bit hard on the machine if DOC is “too high”.