How to maximize plywood edge cut quality in Fusion 360 CAM

[ryanjg11]

I'm using Fusion 360 to create toolpaths for various shop projects. I use a gantry-style CNC router (Avid CNC Pro 4896) with a 3hp water cooled spindle. My electronics are custom - I'm using Clearpath SDSK servos and a Centroid Acorn CNC controller. For workholding, I have a vacuum table to keep everything secured. 

I predominantly cut baltic birch plywood using a high quality solid carbide spiral down-cut router bit.

On most straight cabinetry cuts, my edge quality is quite good, especially if I slow cutting down to ~100ipm. (I'm usually cutting at around 250ipm). 

I generally cut with a 1/4" router bit, taking less than a 0.20" depth of cut, and usually leaving .01 or .02" of additional stock which I then cut in a single full depth finishing pass, with conventional cutting direction. Generally this has yielded the best edge quality for me, but it still needs to be sanded to remove vertical "striping." 

Where the results generally look lackluster is when I'm using this 1/4" router bit to cut larger arcs, or a hole diameter >.25". Poor results from using pretty much any ramping technique (helical, plunge, profile). The hole just doesn't look hole-shaped when it's done; more of a square actually. When I had some colleagues look at the GCODE, they noticed that what should be a simple single-line circle or arc commands were being split into hundreds of polylines by Fusion. Is it possible to force Fusion to use more efficient GCODE? 

I'm usually cutting without changing the Tolerance setting (.004") and I've usually enabled smoothing in Fusion, though I've been told for the type of work I do, smoothing really isn't necessary. Centroid CNC12 also has smoothing capability, but I need to spend more time experimenting. 

I was wondering, for those who have "dialed in" edge cut quality with baltic birch, what settings do you swear by and what am I probably doing wrong? 

Images attached of some recent examples.

[brad_francola]

Hi.  At one point in my life, I used do do a lot with the Centroid Acorn system.  I'm glad it's working out for you.  It sounds like you need to allow your post processor to make helical arcs.  It may be as simple as checking a box in your post properties UI:

[brad_francola]

Also, you may like to use this program to back plot you code before you take it to the router:
https://ncviewer.com/

[ryanjg11]

@brad_francola- I have "helical moves" checked.

This problem ended up being caused by poorly tuned servos. I was able to get Teknic to fine-tune and the result is shown in the foreground (pre-tune in the background).

[brad_francola]

Those Teknic servos are really nice.  Back when I was into the DIY CNC thing, I put them on a WorkBee router.  They were awesome, but there is some "fiddle factor" in getting them properly tuned.  I found that high quality closed-loop steppers were nearly as good and much easier to setup.  But, the Teknic do have the advantage of being a true servo.  

[DarthBane55]

Your code is still point to point tho, which could indicate that you are using 3d operation for finishing walls (not recommended on prismatic parts), or that your holes are surfaces that are not cylindrical perfectly.

On circles, you should get G2 and G3 for arcs, which would shorten you code dramatically and make a better finish too (even with your tweaking of cervos).

[ryanjg11]

@DarthBane55  - How do you know it's point to point? I don't think I've posted the gcode here... Maybe I did and just can't find the attachment within this terrible forum interface. 

[DarthBane55]

you wrote this:

When I had some colleagues look at the GCODE, they noticed that what should be a simple single-line circle or arc commands were being split into hundreds of polylines by Fusion.