I’m not sure if this is the right forum for this, But I’ve been cutting EVA foam for the handles of LARP swords, and I had a quick question regarding the smoothness if the cut. I’m using the Makita 10-30k trim router as my spindle at 30k rpm with a 20-20 feed speed for finishing, ad I’ve had a lot of luck with this setup, and it would be perfect but this keeps happening: http://i.imgur.com/rnPM0hU.jpg On the way up the finish is smooth as butter, but on the way down it’s not as smooth with a little roughness. At this point this is mostly cosmetic, but I was wondering if any one knows how to mitigate this issue?
I’m not sure what you mean by the way up and the way down. Please explain further.
Well with the finishing path it goes along the X axis, and the handle is round, so when it’s carving it it goes up one side, and down the other. you can actually see the path it follows on the left side of the handle, while on the right side it’s just smooth. That’s the roughness, it doesn’t do it going up the curve, so I’m just wondering if I can keep it to a minimum when it the bit goes down the curve.
What program are you using to generate your G Code?
It sounds like you may want to try a different milling strategy.
Climb vs. Conventional
Spiral vs. Raster
See what your options are and give them a try.
I’ve been using meshCAM and they only give the climb/conventional option for the roughing cut, the finishing path doesn’t have any of these options.
It will increase the time it takes to do the finishing pass, but have you tried to overlap the paths more?
I’m already running it at .02 stepover with a 1/8" ball end mill. So I’m not sure how much more I could overlap them I guess I could drop down to .018 or something but this already is a 4+ hour carve for all the parts and I’m trying to not make it any longer. If that’s the cause though then I can deal with a little fuz if it means not increasing the time anymore then it already is
OK here is what I think is going on. If your cutting from left to right on the X axis and the tool is moving up or Z+ on the Y+ side of the part (the side away from you when looking from the end of the machine) and moving down or Z- on the Y- side of the part.
The tool is climb milling when moving up and conventional milling when going down. Then if X moves .02" and makes another pass from front to back it is then conventional milling going up and then climb milling going down.
What does this mean. If there is any play in your Z axis climb milling tends to move the tool away from the part and conventional milling tends to pull the tool into the part.
I’m not sure there is an easy cure for this.
Hope this helps
Also when cutting 3D ball end mills, the LARGER the bit you can get away with the better. A .25" ball end mill would likely remedy this AND cut down on your finishing time. Plus you will get a much smoother surface.
@DavidSohlstrom and @Earwigger make good points.
Here is what I was typing last night when the forum stopped letting me post, so it didn’t make the cut:
The roughness seems to be coming from something like tear out. On the way up it looks like the flutes are cutting into the material but on the next pass the roughness gets cleaned up, but on the down side the flutes are cutting on the other side of the bit so it is cutting away from the material and so aren’t getting cleaned up on the next pass.
Other than increasing overlap, you might try changing the direction of the finishing pass to be parallel with the length of the piece rather than perpendicular or some other angle that helps… just spitballing here though. You may even save time on in a longer more parallel strategy.
Here is a great primer on ball end milling: