Question (WOODWEB Member) :
I have a 24" EMA planer with an attached knife grinder/sharpener. In order to get the best surface finish should I press this attachment into service? Should I use HSS or carbide blades? How do I decide when the blades need to be sharpened? Any advice on sharpening or should I replace the head with a Tersa, Shelix or other?
Forum Responses
(Solid Wood Machining Forum)
From Contributor E:
I had a Powermatic Model 180 years ago with the knife grinding attachment and ground the knives in the head with much ease and success. First, unless you have a diamond wheel, you can't grind carbide, only HHS. It is faster, and I believe more accurate then swapping knives out and trying to get them all set concentrically.
So stick with HHS.
One little tip I learned from grinding my knives was how to remove the burr which results from the grinding. In the Powermatic manual they said to take a copper penny and drag it along the back edge of the knife to remove it. I found that to be quite effective. The only problem is trying to find a 100% copper penny. Don't try to remove too much material and keep the wheel moving so as to not over heat the steel and you'll be ok.
As to know when it's time to sharpen them again, don't worry, you'll hear it. You'll be planing some lumber and think to yourself how loud the planer is. It's time. You will have to lower your chip breaker a little after grinding, but not too much, and the feed rollers after a number of times, but it's not too bad.
The regrinding of knives in the head means you have to adjust the pressure bar after the head to make a good quality cut. To do the grind and to adjust the pressure bar takes about as much time as replacing the knives. To do it properly, replacing knives means just that - you do not have to make any other adjustments to pressure bars or hold owns and your digital readout is still accurate. By the way, the 24" Ema Casadei I had was equipped with a jointing stone as well as a grinder. After grinding, it was possible to joint the knives on the fly (ever so slightly) making for a very smooth cut even at high feed rates.
As for grinding there's two different types of a grind. There's your full on re-set the knives and grind to height grind. Then there's your, knives are starting to dull so I'm going to touch them up a bit grind. I probably re-set the knives in the head once a year at most, the rest of the time I simply run the grinder just kissing the knives a bit and back to work! It takes probably five minutes to do a light touchup and go. A full on re-set probably takes me a half hour or less. Unlike changing the blades in the jointer where you need them set dead on, you don't have to be as finicky since your grinding them anyway. You want to keep your HSS knives vs changing to carbide for several reasons. One is because carbide needs different wheels than HSS does. Two is that carbide is toxic to grind. Third, HSS leaves a better finish when sharp than carbide does.
