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Jointer chatter --- bad bearings?9/17
I recently purchases a used SCMI F3A 12" jointer. This is a 3 knife, non-tersa cutterhead. The machine is up and running and I find it to be far louder, and produce far more chatter than machines I'm used to, especially considering that the knives are fairly fresh.
Cut quality is decent without a ton of tearout. I just can't believe how much downward pressure you have to put down in order to keep the board from chattering like crazy. It's a screamer, It almost feels like the machine is struggling to get through the cut, but then it joints true and the cut surface isn't poor. I'm aware that a common cause of this is a one-knife cut. Just checked with a dial indicator and all of my knives are within .02 in. of each other.
I read in another forum that this could be an indication of either bad bearings or an unbalanced cutterhead. I'm hoping someone could explain to me the best way to diagnose whether or not either of these is the case. Should I just take the cutterhead out to look at the bearings, and if so, what would the signs be? I have taken the cutterhead out previously, as I needed to take measurements to order a new Byrd head, which should be here in a couple of months. Figured I might as well replace the bearings when I install the new head but now I'm wondering if that should be done sooner than later. Any advice is much appreciated.
Within .02" is a ton out of alignment. That's more than 1/64". I shoot for .003" or less. Knives may be too far out of the head. I usually set them so the back of the bevel is around 1/16" from the head, but check with manufacturer. How much and how wide of a cut are you taking? Fairly fresh means nothing. Dull blades make the exact complaint you have.
Rich, my apologies. The knives are all within .002 in. of each other, not .02 in. Just checked knife height also. My bevel starts right at the cutterhead.
When I say 'fairly fresh' blades, I mean that we've been using the machine for less than a week now, with freshly ground knives at the start. They've worn a bit since then, but I noticed more resistance than normal when the blades were brand new. On our other SCMI jointer (granted, it's larger and more powerful), when you install new blades you can just glide a board though with little to no downward pressure. Maybe it's all in my head, and I'm just used to a more powerful machine that struggles less in the cut and makes less noise. We're not taking heavy cuts, and I even notice the issue when jointing edges.
I am not sure how familiar you are with knife etc., so let me suggest one remote possibility. Are you aware of the method used to check the rake angle of a knife? Measure the angle between the surface formed from the tip of the knife down the sharpened face and the surface from the tip to the center axis of the butterhead. The greater the rake angle, the more the knife acts like a plow and feeding takes more effort; the smaller the angle, the more the knife acts like a chisel or wedge. When a jointer head is manufactured initially, the slots have a rake angle in them, so we do not measure the rake angle of the knife out of the head but when it is installed in the head.
So, a large rake angle means hard feeding and the knives want to push the wood up and away rather than cut it.
If this ins't clear, I might be able to find a picture to help.
We had an older SCMI jointer that ate bearings. We replaced them twice a year until we could afford a better one. It was a 16" so it wasn't cheap.
What year is your machine?