More ridges

[ljdm]

any idea what causes these ridges? To test, I did a an area clear, raster cut, 1/16"tapered ballnose, only .06 deep. Did it in two areas of the bed. Rails looked good, cleaned, scraped, etc and also v-wheels. This is on a PR.
3989

[garyb]

Its cusping from the ballnose cutter, reduce your stepover

[ljdm]

It's not cutting in that direction though. If that was the case, wouldn't it have ridges running along the x-axis, the way it is cutting? Also seems more pronounced at the ends where it changes direction. Also, the stepover is already .0076, any less and it will take more than forever to carve. Got me baffled.

[cnc_works]

Lou, I cannot shed a bit of light on your situation. I can say that I just cut a walnut plaque with one of Gary's 1/16" tapered ballnose bits (though I have a hard time imagining the bit choice would contribute) and developed the same lines at 90deg to the cut travel. It was in an undetailed area and the lines were fine enough to be unobtrusive in the final job, but they were definitely there. I think my stepover was about .006".

Sooo, I'm curious too.

Donn

[bcammack]

Almost looks like the v-rollers aren't perfectly snug on the Z axis.

[ljdm]

Well, kinda got it under control for now. Had to drop move speed down along with move ramp speed. Going to really slow things down, but then again was losing time sanding ridges out.

[garyb]

The lines look very uniform, thats why I say its cusping, take your cutter and hold it vertically in the groove, does it match? if so its the cusp.
You more than likely can't see them in the x due to going with the grain.
Feel for them in the x, are they there?
You shouldn't get lines like that as a result of speed at least not on a pr machine!

[beacon14]

I just cut an 8" x 39" 3D relief last week and also got the same ridges, perpendicular to the direction of cut. I had vacuum on the whole time. The ridges are very regular which leads me to believe they have something to do with the rack and pinion system, although the ridges are much smaller than the rack spacing - something like 4 times smaller.

It can't be the cutter profile as the ridges are perpendicular to the cutting direction.

I plan to re-cut the file after making the motor and spindle upgrades, just to see what kind of difference it makes.

[ljdm]

I checked the cut at various speeds and ramps to find the best finish. The ridges were worst at ends of the cuts, where it changed direction. Absolutely no ridges along the x, not hidden by the grain. I made sure the z was level, perpendicular, etc. For now, gotta go with the slow speed, all that seems to cure it. It really hurts - 1 ips and .3 ramp. I was blazing away at 1.75 ips (real speed demon, huh?)Need to do the upgrade next, when finances allow. Have to try different machining strategies also. There were no ridges on the reliefs, just in the areas around them, probably due to slowing down to move the z up and down. I could probably get away with a 1/8 end mill to do the area clear around features if I figure it out. Just use the 1/16 for finish pass on the relief only. Oh well, there's always tomorrow to try more.

[garyb]

Lou, do you also get ridges with an end mill? & at different locations of your table?