Mill Marks Versus Chatter

Any rotary cutter will leave mill marks, but chatter represents a maintenance issue. November 13, 2005

Question
Can anyone tell me what makes a jointer produce chatter marks on a workpiece?

Forum Responses
(Solid Wood Machining Forum)
From contributor A:
Your question is really vague. There are a lot of things that it could be. First, is the tooling balanced (cutterhead, knives, gibs, screws)? Next, do you have the work piece supported correctly? How far away are the fences from each other? What is your depth of cut? Are the fences square to the bedplate of shaper? These are just some basic guidelines. If these are all ok, then I would look at the run-out of your spindle, and maybe the belts. You may need new bearings, but check all the small things before you go spending money on new parts. Sometimes it may be something very basic that you donít need to spend money on at all.



From contributor B:
It sounds to me like one or more of the knives are cutting deeper than the rest.


From contributor C:
I am going to take a risk here and keep it really simple. I think that you might be confusing mill marks with chatter. Mill marks are present on any wood cut with a rotary cutter. As the wood is passed through the cutter, some of the points along the board are at the center of the cutter head at the same moment that the cutter is at top dead center. Other points reach and pass by the center of the cutter head while the cutter/cutters are not at top dead center. This causes high and low spots in the woods surface. The slower the wood is fed through the cutters, the closer together the high and low spots are, and they become less noticeable. The only way to have a mill-mark free surface with a jointer or planer type finish is to use a hand plane or a scraper.


From contributor A:
You need to first let us know which one it is - chatter or mill- marks? Contributor C described mill-marks perfectly. Chatter would be uneven mill-marks that would be noticeable by touch, sliding you hand over the workpiece. Mill-marks would be even knifemarks and the finish would be smooth as a baby's skin. Mill-marks can feel like chatter is your feed rate is above 30 feet per minute for a single knife finish.


From contributor D:
Try putting a straight edge on the out feed table over your jointer head, to see if you have a high knife or two.