Finally got around to milling the other half of this sailboat tiller I am making for a friends boat and we kept running into issues when trying to mill deep contours.
In certain lengths of the outer contour of our machining operation the bit seemed to bind and resonate quite violently causing the surface finish to go to sh!t and causing me to pucker-up a bit due to the combination of tool chatter and machine vibration.
You can see that in this stretch surface finish is satisfactory and there wasn’t any problems with machine vibration or binding…
And here is an image of where we had problems.
There were some specific locations where the bit would start to vibrate and would cause the whole machine to resonate for an instant, creating a gouge in our contour walls, and then everything would go back to normal after passing over this location.
Is this mainly due to the relation of feed direction and grain direction in the work piece (we are using red-oak)? Improper spindle speed? Improper feed rate? Insufficient chip clearing? Or are deep contours (this was 35mm, w/3mm stepdown) just not reasonable to do with a 1/4’’ up-cut end-mill without more clearance for chip clear-out?
We were able to mitigate the problem by increasing spindle speed and reducing the feed rate, but the problem still persisted, only with less frequency and magnitude.
What seemed to further solve the problem was using a compressed air nozzle to constantly clear chips out of the contour as the machine did its thing.
I think the problem is a combination of everything I mentioned, but I’d be interested to hear if anyone has recommended feeds/speeds for deep contour work in hardwoods, such as oak, that doesn’t require me to widen the outer contour or use a finish pass…