[Herptastic]

I've got a relatively simple part I'm trying to cut with my new CNC router it is a leg for a bookcase with rabbets for the shelves to slide into -- I have designed in ArtCam Express, my machine is running Mach3 (4 x 8 Green Lean vertical machine). I've made the vectors, I've set up the tool paths for both area clearance for the rabbet and the profile for the cutting out. I've figured out bridging which is super important on a vertical machine as well. The problem is with the 1/2" wide rabbets. The machine is making them 0.41 inches per my caliper, and while in ArtCam they do show 0.5, also I'd like to get the CNC to mill them a hair past the profile cut so that once cut out the rabbet runs edge to edge rather than leaving a sliver of material for me to cut out later manually. I am going to guess these are probably related to tool offset but I'd like to find out before I move further. I thought it might be a calibration issue as well, so I tested that, and its spot on. The distance between the rabbets is also correct so that would lead me away from it being a calibration issue as well.

Please let me know what to look at. Any help is appreciated.

Merry Christmas to all

Chris

[LeeWay]

A couple things to look at. Check that the cutter is the actual size you are thinking it should be. I have had cutters sizes vary with router bits.
Then check to see if you are leaving material for a finish pass and are just not programming that pass.

[Herptastic]

Well I certainly appreciate the quick reply -- I would never have thought to measure the diameter of the bits considering most my bits are Onsrud which I was told is the diamond standard, but 1/4" = 0.223 and 1/8" end mill is 0.118 so I'll create tools based on the tools already in Artcam but adjust the diameters and stepovers to adjust for their slightly narrower than advertised nature. Going to need new endmills anyway though the ones I have now leave the plastic I'm cutting not so nice when I'm doing the cut outs - the face touching the table comes out rough.

[ger21]

It's nearly impossible to accurately measure a spiral router bit. My guess is that your Onsrud bits are the size they are supposed to be. I've used a lot, and they usually come back after sharpening around .22-.23. If they're not .25" when new, they should be very, very close.
Cut a slot and measure the slot width. That's the size you should be using.

Also, try making your cuts in the other direction. "Build Your CNC" machines are not terribly rigid, and the lack of rigidity can result in a big difference between conventional cutting and climb cutting. If your climb cutting a pocket, the pocket will usually be slightly smaller. Conventional cutting will give you a larger pocket.