Hi There,
Im trying to make wooden spindles by carving out one side of a cylinder and then flipping the work piece and carving the other side. I need it to be quite precise but for some reason they keep coming out oval. The CAD measurements are correct, but the actual machined piece comes out slightly off, could this be something to do with tool path settings? Or a setting on the CNC itself?
Any help would be much appreciated
Hello Laurence,
Could you give us some more info?
How much is it out by and in which direction (width vs height)? What are you using to measure it with?
Have you cut both sides of one piece yet.
Do you have the means to check location/cutting accuracy of your machine ( dial indicator, calipers)?
I know this isn’t the answer you were looking for but it is probably the best solution in the long run. I made a basic rotary. Total cost was under $200. It can’t be controlled by the CNC so it can only make round shapes. But it works well. I did it using a drill press and the 1F.
Have you taken into account the actual profile of the ball mill, and is it cutting sufficiently deep to fully carve the steepest part of the semicircular profile of your geometry? If your two operations only mill down to the “equator”, if you will, then they will leave an oval like ramp along the edge of the spindle. If you want a perfect semicircular profile then the ball mill needs to plunge past the middle of the circle by a distance equal to the radius of the ball mill. If that makes sense.
however, it’s worth noting that once you cut through on the second side, then the workpiece is only going to be supported at thw two ends, and if the mill is upcutting along the edge of the piece, it is likely to flex and get pulled into the cutter and make a sadness. You could mitigate this with some tabs along the length, or you could just not cut all the way through and plan on cleaning up the seam/spine left behind afterwards with some sanding.
Or maybe you already thought of this and your problem is something else entirely 
Hi Bunkstaff, thanks for the response, yes that is what I thought initially, as I am using the tapered “Skinny Jenny” ball nose to finish. I do have the ramp along the seam you mentioned but on top of that the finished cylinder seems to have 1mm less in height (z axis) than width (x axis)
So the width is slightly over what I programmed (talking 10ths of a mm here) which I expect is due to the ramp/seam you mentioned but the height is about 1mm less than it should be.
Im using a 22mm thick piece of material, machining it 11mm deep and then flipping and doing the same on the other side. The aim being to have a perfectly round cylinder of 20cm (at its thickest point. Does that make sense? Thanks again
Hey there, sorry I didn’t reply sooner. I have a couple thoughts, but one thing I didn’t think about is the Z=0 situation. If the blank is accurately milled, then you might try setting Z to the bed surface instead of the material top. You just have to make sure your clearances are good to avoid any mishaps. I’ve done pretty good spheres this way in the past. I’ve also set Z to the top surface for the first milling, then set it to the bed surface for the flip milling- in order to maintain the same true reference point of the material. But in that case you need to have different toolpaths programmed for each and it’s probably more complicated than necessary for your purposes…
I haven’t used Carveco yet, but I’m guessing that 1mm top offset may be your gremlin? when you turn the piece over, it may be like pushing your material up 1mm closer to the sky, which would cause more of it to get milled away than you wish.
I’m used to rhino3d+rhinocam and I just received my 1f a couple days ago, still in boxes. I’ve been outta the saddle for a few months. But I’d look at simplifying your Z reference situation I think.
