I just finished setting up my new 48x48 and got the tramming pretty dialed in with no ridges in either direction I am cutting. However, I made a test pocket cut of 1"x4" in a piece of 3/4" oak and got tool marks at both the far left (X-) and far right (x+) of the each pass,. I was using a brand new Whiteside 1/4" spiral downcut bit at 90ipm and a cut depth of .1. I tried both one and two passes with the second pass as a .015 cleanup cut with the same result. I also tried using a 2" spoil board flattening bit on MDF making passes along the X axis (right to left) with the same result. If I run the bit off the board as it moves up the Y+ axis I get no marks since the bit is not touching the wood when it moves up. Since I am getting smooth cuts everywhere else, I am wondering if this could be a mach 4 setting or maybe the table moving just slightly as the bit moves up. I am new to Avid and Mach 4 so my troubleshooting skills are in the beginning stage with this machine. Any suggestions would be appreciated.
If you wouldn’t mind, post your gcode. Easier to get an understanding of what your tool paths are trying to do.
When I had to do pockets like this for a project, I used an up-cut bit for the “floor” but left some around the edges, and cleaned those up with a down-cutting bit. I thought using an up-bit would result in tear-out along the floor but (1) it didn’t, and (2) the down-bit left a “mushy” bottom.
As for your tool marks, my only thought is (1) the gcode is forcing a stop at the end before it changes directions; you might be able to soften that with a G64 to turn that stop into a tiny up-curve, and (2) the down-bit might be pushing the table down and the spindle up - if even a tiny amount - and when you stop, it has time to “relax” and dig into the wood. A down-bit would do the opposite.
So if you use offset instead of raster with a 40% stepover it should look better.
Here is the gcode and the bit settings I used. It is the same toolpath settings I used on my previous Axiom CNC. I would occasionally see these on the Axiom but nothing like this. thanks to all for the help.
GCODE:
(VECTRIC POST REVISION)
(886B9102B8853D0A478FC5DB337B40D5)
( test )
( File created: Saturday September 23 2023 - 01:37 PM)
( for Avid CNC Machines, post processor v3.0 )
( Material Size: X= 30.000, Y= 3.750, Z= 0.750)
( Z Origin for Material = Material Surface)
( XY Origin for Material = Bottom Left Corner)
( Min Program Extents: X= 0.000, Y= 0.000, Z= -0.750)
( Max Program Extents: X= 30.000, Y= 3.750, Z= 0.000)
( Home Position: X =X0.0000 Y =Y0.0000 Z =Z0.8000)
( Safe Z = Z0.2000)
()
(Toolpaths used in this file:)
(test)
(Tools used in this file: )
(1 = End Mill 1/4" Down Cut Spiral {Whiteside})
G00 G94 G20 G17 G90 G40 G49 G80
G91.1
T1M6
M07
G00 G43Z0.8000H1
S18000M03
(Toolpath: test Tool: End Mill 1/4" Down Cut Spiral {Whiteside})
X0.0000Y0.0000F85.0
G00X5.1393Y1.5000Z0.2000
G1Z-0.1850F30.0
G1X3.6393Z-0.2225
G1X5.1393Z-0.2600
G1X1.3893F85.0
G1Y1.6000
G1X5.1393
G1Y1.7000
G1X1.3893
G1Y1.8001
G1X5.1393
G1Y1.9001
G1X1.3893
G1Y2.0001
G1X5.1393
G1Y2.1000
G1X1.3893
G1Y2.1999
G1X5.1393
G1Y2.2499
G1X1.3893
G00Z0.2000
G00X5.1393Y1.5000
G1Z-0.0750F30.0
G1X3.6393Z-0.1800
G1X5.1393Z-0.2850
G1X1.3893F85.0
G1Y1.6000
G1X5.1393
G1Y1.7000
G1X1.3893
G1Y1.8001
G1X5.1393
G1Y1.9001
G1X1.3893
G1Y2.0001
G1X5.1393
G1Y2.1000
G1X1.3893
G1Y2.1999
G1X5.1393
G1Y2.2499
G1X1.3893
G00Z0.2000
G00Z0.8000
G00X0.0000Y0.0000
M05
M09
M30
%
Thanks I will try that and see how it looks. Does it matter if the offset is climb or conventional for the pocket?
IMHO a climb cut is better in brittle woods (like red oak) as you can splinter or tear the cells below the cutter if you’re “ripping the chip away from the wood” instead of “squishing the chip against the wood”.
Another suggestion which will remove the step-over/cusp issues is to change the “Profile Pass” option which you have set to “No Profile Pass” to “Last”. This will do a full circuit around the pocket interior (profile) once the pocket is cut to depth and get rid of the remaining cusps along the Y axis. Check it out in the Vcarve preview with and without profile pass and you will see the change.