Replaceable Cutterheads Versus Re-Sharpening

      A quick discussion on the pros and cons of resharpening your own tooling on the planer. April 18, 2015

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

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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.



From contributor G:
You might want to make sure you have plenty of life left in the grinding wheel and if not, can get new ones. We have a 93 Casadei with a grinder, and it was a bit of a workout to find a solution to the fact that they aren't made anymore.


From Contributor O:
I have had planers that were capable of grinding the knives in the head, and a Tersa planer, as well as the kind that could only do replacements. After all three, I am a fan of the Tersa for speed, and replacement knives second. The Tersa just takes a few minutes and is the only thing you need to fiddle with no adjustment at all. But it does have bit more limited feed rate and overall bite since the chip size is limited. Not much pf a problem in the real world.

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.



From contributor F:
I have a SCM planer with the grinder which your EMA is very likely a copy of. Unlike the Powermatic planers you do not adjust anything after grinding. There's actually a warning label under the hood not to tinker with anything. I respect the label and haven't had any problems with my machine. You'll have to check your manual to be sure, but I wouldn't be surprised if it was similar. The key is you set the knife height with a jig. Then you grind down to get the knives to the same height at which point they are where they need to be in relation to the rest of the feed works. After several grinds the knives will start to get too low at which point you re-set them and are again at the right height and nothing ever needs adjusting. Tersa heads I'm sure are nice, but you'll have to shell out a couple thousand for one. Same, (though possibly a bit less expensive), for the carbide insert heads. You have the machine now and I'll assume you have knives in it? I recommend using it and see how you like it before spending cash blindly.

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.



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  • KnowledgeBase: Knowledge Base

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  • KnowledgeBase: Solid Wood Machining: Tool Grinding


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