Finally got to try out my 2.5" slab slayer bit on a 49" round mesquite/epoxy table. The bit cuts great still at the end of 6 hrs of chugging through the mesquite.
1 Like
What feeds and speeds did you end up using?
I ran around 0.080" deep, and 60% step over most of the day. I had it set to18k rpm and 100 ipm most of the time too.
On the last pass I run about 0.040" deep to clear out any of the epoxy chipping.
BTW, AVID now has instructions on the spindle over torque setup here: VFD Parameters - Plug and Play Spindle / VFD System Manual
This sets up the VFD to shut down and emergency stop the system when you get an over current. I tripped it once when I was cutting the bottom side pocket out for the steel baseplate. The toolpath took a 100" cut into pure epoxy and overloaded the spindle and it shut down very nicely without stalling the motor completely. Just had to hit the reset button on the VFD and continue on (at a slightly lower feedrate) to continue. So that feature works nicely. I’ll probably raise the overcurrent percentage a little more, but this is a great feature. I used to stall the spindle a few times cutting something big like this, and it sounds pretty bad when you lock up the motor and the CNC keeps trying to push along.
3 Likes
Ok, I’m drooling now 
I got a cheap surfacing bit just to flatten my spoilboard:
https://www.amazon.com/gp/product/B086QP537S
But based on internet math and no advice from the manufacturer, I ran it at 1200 rpm (yes, twelve hundred) and 130 IPM at a depth of around 0.030".
I had run it at higher RPM previously, but there was as much burning as cutting.
Despite buying the “more torque at low speed” VFD, it did not like it. It even overheated the spindle at one point - at least, that’s what I guessed happened after the fact. Spindle stopped, servos did not, and when the bit stopped, the servos had to too, and it all ground to a halt. Stupid machine jumped a foot when I jogged the Z up and the bit let go (I need to add a following error signal to the setup).
On my setup, the vfd is controlled over modbus, so I have access to all the data therein, with the vfd alarm hooked into the estop. Well, now it is
I wonder if it would make sense to have a near-overcurrent automatically slow down the feed rate…
All of the big surfacing bits I have showed a max rpm spec of around 18000 rpm, so thats where I run it. A lot of spindles (for sure the AVID ones) have a pretty flat torque curve, so that means hp is directly proportational to rpm. So at 1200 rpm, your 4hp spindle is only capable of about 0.2hp…its not gonna cut very fast.
I started with an expensive Amana RC-2263, and it cut great. However, the carbide cutters are like $25 or more each! The slab slayer overal bit costs about the same, but the cutters are about $6.90 https://www.ripprecisiontools.com/product-page/slab-slayer-replacement-inserts-10pc-box
They are also not flat, they have a angled (or maybe hooked?) profile more like some of the metal lathe tooling. It seemed to cut a lot cleaner, and they lasted all day. I had previously milled an aluminum cylinder head from an old skid stear with this bit and it cut the aluminum beautifully. When I told RIP tools about that they told me they have used them on cast iron, so I guess they are tough 
That would be awesome if you can pull it off. I know with a mesquite river table, there are sometimes some super dense knots that will slow it down, and then if you are doing a pocket profile with an offset profile, Vectric will create a toolpath that jambs the cut towards the corner as it widens the path and that is a 100% width cut for a short time and can bog things down. If you could drop the feed rate for like 5 seconds until it got through the tough spot, you could probably make it through the whole thing with a more aggressive feedrate. On a stock AVID, you can’t do that, the only thing the alarm at the VFD can do is trip the alarm on the maching…but that did actually work well today. Just had to reset the VFD and start the file again.
Great project!!
What I run:
Maple , Walnut, etc all wood slabs: CD- .25 IPM- 300
Epoxy filled: CD- .125 IPM- 180 (IPM also depends on the epoxy as I notice chip out if the IPM is too fast, (I also sand the slabs with the CNC so the chip out is not usually a factor)
I raster cut most of the time
Running the larger AVID spindle
I also sand the slabs with the CNC so the chip out is not usually a factor
What attachment are you using to sand with?
Made by cnckitmill. Works awesome. coupled with dust boot from raw woodworking.
How about yours?
I don’t have one - hadn’t occurred to me that I could use the CNC, so it’s a new thing to try
Are they balanced pretty well? I’m a little afraid of ruining the spindle bearings with a random orbit head.
Jim: I have two shafts one for random and the other for only circular. Most of the time I only use the circular motion on the CNC down to 180 then hand machine sand to the final grit. I too am concerned about the bearings. I have used the random on the CNC at the fine grits thinking it would be easier on the spindle. When I first ran the orbital at low grits on the CNC the vibrations were significant, they are way reduced at the finer grits. I am going to get a random action shaft with a smaller circular pattern soon. As a test case I did a walnut dining table 4 X 8 all the way to 1000 grit; never touched it by hand. The head I have is floating with pressure control by an internal spring with can be change allowing control of the disc to work piece pressure.
I notice that is does clog up my dust collection filter much quicker (running a 5hp Onieda vortex).
Interesting. I can see how that would really save time on big panels, and give you a very flat surface.
Where did you get the circular only shaft. I don’t see one offered on the CNCKITMILL site.
I made the circular shaft myself