I milled out a box that I designed in Solidworks and imported into VCarve. Everything looked great, and the model looks right, but today when I did a test run, something odd happened.
At the base end of the box, it decided to do a little extra milling on either side of the opening. Pics are worth a bazillion words here, so:
Because it did it on both sides, and both ends, I’m ruling out movement of the workpiece. It happened with the finishing 3D carve using a 1/4" Ball Nose bit.
Has anyone seen anything like this before? Did I miss a setting somewhere?
I was told to tag Brian Davis, but I can’t figure out what his username is, if someone else knows, please tag him here.
I’d need to look at the piece, but offhand, I’d say a couple of things happened.
The regular striations are a function of the “stepover” setting. On a ballnose bit, you’ll need to set the stepover to 8% or less to remove the little regular lines. Think of mowing your lawn. When you line up in the wheel track of the previous path, you are cutting at 100% stepover - that is, 100% of the mowers cutting width (cutting edge diameter). An 8% stepover means you’ll be moving sideways only 8% of the width of the bit, which keeps you beneath the radius of the ball, thus eliminating the lines. Be aware, that the bigger the bit, the more likely it is to leave some striation behind. The tradeoff is, that the job will take a lot longer, as the machine starts making a lot more passes.
As the cutter gets closer to the top of that arc you’re cutting, it starts to go almost straight up - producing the thicker lines as the side of the bit contacts the top part of the wall of the cut - milling in some grooves there. Use a roughing pass first with an end mill, and those should go away.
Good suggestion on the step over, I’ll drop that down a bit to smooth things out.
I may start at 20% or so as that should get me close enough without making it a 3 day cut.
I did a rough out with a 3/8 EM which worked great. I may have you (@Tapper) take a quick look at the part after I run the second test cut later this week.
