I’ve been running my Ooznest cnc for a month or so now and have come across a problem that someone may be able to help with.
When I mill thicker stock at the start of the program the z axis raises up then tops out on the frame, crunches, then cuts (be it far to high).
I think it has something to do with the Z raise level or ‘safe’ height, but being a n00b in this I’m not 100% sure.
If someone could offer some advice it would be great, thanks.
Mach3?
Yeah should of maybe included that… so I’m using Vectric Aspire to make the tool paths and Universal G-Code sender to cut.
On a random note can you use Mach 3 with a CNC xPro?
Disable G28 at start of program, or be sure your machine home for Z is something where it can actually go…
Yes if you use a mach3 compatiable breakout board instead of an arduino
Oh sorry. I thought you meant CNCRP pro. That control board is only for GRBL
I normally home on the centre of the work piece then begin the cut from there I see that g28 is absolute, not sure if i have that turned on tbh, but I’ll check when i get back out
No I’m using the grbl CNC xpro board that ooznest supply with there kit.
That’s your work home, not the machine home. Machine is wherever your limit switches are or where the machine was turned on
So would i be better pulling the router to say the bottom left corner with z at the very top then powering on the machine then jog it to the work piece setting the work home then starting to cut?
If you want, but it’s easier to disable G28 or remove it from the code
Ok I’m being stupid here, i just set a gcode file and there is no G28 commands in it, or are you referring to the controller setup
It’s in your CAM. Is there a strange Z command near the start then? Change your Z safe/retract height to something your machine can actuAlly travel
“Safe above workpiece” ?
Ah found it under the “rapid z gaps” for z1 / clearances.
Thank you for the help guys
Not sure if anyone will find this helpful, but here goes… There’s a lot of different practices from one user to the next. Find what works for you and run with it. originally my machine coordinates for z0 was at the spoil board. I always had to bear in mind what the max height was. I reconfigured z0 to be about 0.5cm below the max height, so all machine coordinates have a -Z value. I load the work piece, and set work Z0 to top of work piece. To each their own. Hope someone finds this helpful
Most CAM programs used to generate g-code have a setting for “Z Safe Height” or something similar. This is simply the height the Z axis is raised to when doing G0 fast move commands. You need to set this high enough to clear your work and any hold downs, but not so high as to crash the Z axis into the upper stops. Obviously, this is related to your Z axis zero point, so it must be correct as well. Crashing the Z axis into the stops will possibly do 2 things:
Certainly it will cause the A axis to lose steps and its positioning information, causing subsequent cuts to be the wrong depth
Could damage or loosen your Z axis leadscrew, and cause slop in all subsequent Z axis operations. In general not a good thing.
As to zeroing your Z axis, most people zero the axis at the top of the work. Some like zeroing it at the table, which in my opinion is not advised, and will cause no end of problems, especially for inexperienced users. In either case, your CAM program must know the reference point for the Z axis height for it to properly move the Z axis.
MG
Depending on your CAM software there may also be a out of the way tool height setting when returning home at the end of jobs. Ex : with SketchUCAM I have it at 1/2" (default ?) above the work piece zero … Fine until I started working on pieces which are at the limit of Z travel (ex: surfacing thick slabs).
The “Safe height”, used for rapids (ex: G0), I usually set to 1/8" (3mm). Could be less when using top of (flat) material as zero on a level work surface. Working with wood, this may not always be true. ;( Reason why some also work the entire top surface of a part.
You will also need to check your maximum travel settings, including in some CAM a maximum depth of cut. The latter had me scratching my head for a long time when myOX refused to go deeper than 1/2" when working I started working with 3/4" thick material. I forget if Universal Gcode Sender also has a parameter for this (added safety measure).
Zeroing the Z axis to the table can avoid cutting into the (waste) table, but you need to control material thickness and your Gcode. If you 0 to top of material, you might cut a bit deeper into the waste table OR not enough into the material as ‘standard’ wood dimensions can vary … A lot of people overcut to compensate for slightly thicker material or for a “clean cut”. If you work thin material, it may not lay flat on your table (unless using a vacuum holding system or a floating pressure plate).