I have an accurate fence set up, so I can use (0,0) origin for repeatable cuts. Is there a way to get the machine to cut .05" past the edges of the spoilboard? Currently, I just lie to it and tell it that my 1.375" surfacing bit is 1.1" in diameter, and that seems to do the trick. I also thought about putting a spacer on the spoilboard next time I have to rebuild it so it’s 1/8" up and to the right of the origin fence.
Any better ideas out there?
I’ve moved away from frences mostly because the way I cut my stock results in the fences getting cut up very quickly. I’ve since moved to a dog hole based system with much better results (for my workflow).
Downside to surfacing bits and waste boards that extend to the extents, or past the machining surface of the machine is that you end up being able to put your stock in an area the machine technically can’t touch with typical sized machining bits.
I’ve tackled this problem in the past but intentionally surfacing the waste board so that the finished surface matches where the zero zero position of the cutter would be. I’ve also flattened the whole surface but used a removable fence system to achieve the same results.
I always found all of those methods annoying so I just moved to a dog hole system.
I manually surface. I find it’s much easier to deal with rough cut wood. If the wood has a low spot I can make a sight adjustment on the fly.
The other option would be to manually set the X and Y zero. I’ll do that on occasion. Just zero all 3 axis and then manually move over the amount I want, then just press the zero tile.
Yep, that’s the easy way. Manual resurfacing works but then you’re the robot instead of the machine.
Agree with Jim - that’s what I do 
I use a 1" diameter surfacing bit. My surfacing G-code goes to the physical limits (0,0, etc.), so the bit surfaces 1/2" beyond that.
I’m confused by this topic…Am I wrong in thinking that the machine will have just a bit more than 48x48" cut area? I’m not understanding how I might not be able to surface the entire waste board…?
Hey John,
If you manually (with gamepad, jog pane or Manual pulse generator (mpg) pendant or with manual data interface (mdi) commands) go to the outermost corners of the work area, this always refers to the center of the bit. You can then add the radius of the bit to this to know how much you can mill beyond the work area.
However if you create a toolpath, the CAM program will take the bit radius into account. You will then either have to manipulate (fake) the bit radius setting in the CAM program, or the postprocessor, to mill beyond the machine limits settings for the workarea.
Well, the 4-6 week lead time has come and gone and I still don’t have a machine so it’s hard for me to relate, please forgive my ignorance. But I can’t get my head around this issue. It seems to be discussed quite a lot within this forum and I’ve always found it confusing.
If my waste board will be 48x48…and the machine capacity is 48x48…
I’m still not understanding the need to “fake” anything unless you create a toolpath for exactly a 48x48 area while using cutter comp. But why would anyone do that?
I’m not trying to be an a$$…I’m genuinely perplexed about why this is a problem.
Hey John,
you will understand that easier as soon as you have experience. If your workarea is 1220 x 1220 mm, then you have the outermost positions
Front left: X=0, Y=0,
Front right: X=1220 Y=0,
Rear right: X=1220, Y=1220
Rear left: X=0, Y=1220.
You can move to these positions, and all positions in between, manually or with mdi commands like “G0 X1220 Y1220”. So if you have a bit with 8 mm diameter, which is 4 mm radius, then this will mill additional 4 mm outside the workarea at every edge of the workarea. So your wasteboard could be 1228 x 1228 mm big and you would still be able to surface it.
However if you use a CAD/CAM software, it wants you to enter the bit radius of the bit you use for the toolpath. So if inside the CAM program, the limits of the workarea is set to 1220 x 1220 mm, and you tell the program that you will use a 8 mm diameter bit, then it will stay inside the limits, which means, for generating the toolpath, it will subtract the 4 mm radius from the 3D model automatically in order to honor the bit’s radius which is responsible for the fact that the milling of the outermost 4 mm is already included.
So in fact on a 1220 x 1220 mm workarea, it will mill from positions X=4, Y=4 to X=1216, Y=1216, which are the positions of the center of the bit; and the outer 4 mm are still milled because of the 4 mm radius that surrounds the bit center. The CAM program always takes the radius of the bit into its calculations, to exactly reproduce your virtual 3D model. So it will not go outside of 0,0 and 1220,1220 mm if you have set the limits inside the CAM program this way. Except if you either tell the CAM program that it’s a 8 mm bit and e.g. use a 16 mm bit in real, or if you change the limits values of the workarea dimensions inside the CAM program.
30+ years as a cnc machinist, well versed in several cad/cam packages.
Thank you for the explanation, I see now what’s happening. I’m going to assume that whatever cad/cam package these folks are using, they either don’t know how, or don’t have the ability to disable cutter compensation…(?)
The most common, and arguably best, CAD CAM package for woodwoorking CNC is Vectric Vcarve, and that’s not an option. I don’t think it’s an option in any of the consumer products in fact.
I can’t imagine why you would want to do that, other than the specific instance I highlighted in the original post.
The focus of my work has largely become creating complicated inlays, so I think I’m going to go with the spoilboards that BROINWOOD and M&S use…3/4" PVC dogs and dog holes and wedge clamps.
I do it all the time. It’s like having the ability to remove your seatbelt while still seated in the car. Why would you want to do that? Depends on your situation, but imagine how limiting it would be if you couldn’t. I primarily use Mastercam and Gibbscam for everything these days so I’m very surprised that consumer cad/cam doesn’t have the option. However it does clear up the burning question I’ve had about why this is an issue for so many 
Thanks guys…enjoy the day!