For the gurus among us

There are times that I get tremendous wins from my MPCNC and other times that it feels like I’m throwing myself against the same mistakes (my mistakes - not the machine) again and again. It puts me in mind of a Ted talk that I watched some time back. The talk was about learning new skills and how to pick things up faster.

In the spirit of that, I’m asking the people that do CNC work day in and day out, all day, every day out of love for the craft or for want of a paycheck - What are a few things that you wish you’d figured out sooner? The mistakes that you kept making until something clicked? This can be anything from CAM to Firmware to machine construction, motors, mills, spindles, stock material - whatever.

I realize that there’s wisdom spilled all over these forums - feel free to link a post but also feel free to wax all sage-like.


My advice, always do a test cut. At least cut a test of the difficult feature. Early on, I even suggest doing the entire program in foam. You will find often that you screw up and have to do it again anyway so you might as well only waste foam on the first shot. I always miss holes or features.

Watch it closely, make revisions to your CAM do it again. I made piles and piles of LR flat parts. I was constantly messing with the CAM. You can easily save time if you pay attention. I would watch it cut and make changes in the CAM on my laptop as I watched it. Easy way to learn while baby sitting the machine.


That’s a good idea - I always watch the cuts then come back to the CAM software to make changes afterwards. I often miss things that way too. Short of bringing a laptop to the machine, I should at least take notes while I watch. Now that I’m typing it, it really seems like a no-brainer. Oh man. This alone could have saved me a ton of wasted material.

Mine was figuring out TOOL OFFSETS!
All my cutting tools are zeroed at 3 inches above what I am going to cut. This is so if I miss something it my tool path it won’t plunge my endmill into the material or into my vice!
I draw a box 3 inches above my part and use that as my zero, anything above that is Z positive and anything below is Z negative.
The other thing is cutting direction.
If you are cutting a hole (no matter the shape) your tool goes counterclockwise. If you are cutting a circle (or whatever shape) your tool goes clockwise for a better finish.
I’m sure I’ll think of a few more and post them.
Believe me I have broken some expensive cutting tools by just being stupid and over looking something simple.

So you’re final Z is -3" + -3/4" if you’re cutting 3/4" material? I like the drawing an air box at the top of the gcode. Like a skirt in printing. I might even wait until the box is almost done to start the router…

This is conventional vs. climb cutting. I think you are advocating for climb cutting? The opposite of what you would use with a hand router, right? My brain is still half asleep.

Sorry, I should have said: 3" above the BOTTOM of my part.

The box is not part of the tool path. the top of stock is set to incremental not absolute.

Yes, climb vs conventional cutting (i was not sure if that would go over some peoples heads that are new). in my opinion it gives a cleaner edge.
I’m not sure with the hand router direction, believe it or not I might be one of the only people on this forum who has not used a hand router…

I didn’t start using a router until a few years back. I made do with a table saw, a set of chisels, and a drill for years. Of course other tools as well but those were my primary cutters/gougers/hole makers.

Write down your feeds and speeds. In the beginning, there is a lot of fiddling with the speed controllers (mm/s and rpm). Group tools by material, make a note of the speeds that made you happy, and SAVE it. Bonus points if you can make libraries by material (this is what I’m doing in fusion) or just create a new tool with the material (like ‘softwood 1/8 FL 2f up’ or something).


Thanks Tony - I’ve recently started doing this. This is one of my personal gotchas. Really frustrating to crank the feedrate up for one tool only to have the next tool (that was set for the right feedrate to start with) completely destroy a workpiece because I had the feedrate set at 200% at the control box for the previous tool.

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A piece of paper and a pencil /can/ replace the on-site laptop. jftr. On a higher class level, take photos and videos and analyse them off-line, specially in situations where you are not quite sure if it is still a feature or already a bug.

And before the test cut, a few air chips can be helpful too - iow, run a test without any material.
A userfriendly interface of your cam software is - well, useful :slight_smile: .