Planer Knives: Grind Yourself, or Send Out?
Both sides of the debate are represented in this thread. January 15, 2008
I recently acquired an old Northfield #7 single-sided planer. The grinder attachment is missing about $500 worth of parts. Before I spend the $500, I'd like to know if I can expect acceptable results from the Northfield grinder, or would I be better off to outsource the sharpening? I'm not financially ready to make the $5K leap to Shelix just yet.
(Solid Wood Machining Forum)
From contributor D:
I have an SCMI planer that had an onboard grinder. It never did near as good a job as removing the knives and having them sent out and ground professionally. If I were in your shoes, I would seek out two separate sets of carbide knives. One set in the machine and one on standby in case of an accident. When one set is being sharpened, you always have a good set in the machine. A solid jig and process for setting the knives in the machine is essential. You should have a jig that sits on the cutterhead and allows you to set them all to the same height.
From contributor R:
Spend the money on the parts. A spare set of knives and a setting jig will cost you $500, not to mention the cost and hassle of sending them out.
There are two operations to properly sharpen the knives in the head. First the knives must be jointed, then they are ground to reduce the size of the land left by the jointing process. When you are finished you will have all knives in the same cutting circle - impossible to achieve with a setting jig.
In short, make sure you have both the jointing and grinding attachment. Get an owner's manual from Northfield to make sure you fully understand the process. Use a dial indicator and magnetic base to verify the guide bar is parallel to the cutterhead. Also, after sharpening, the pressure elements will need to be slightly adjusted to the new cutting circle.
When fully understood and properly executed, this method is far superior to loose knives and setting jigs.
From the original questioner:
Interesting responses - one pro, one con. Thanks for your input. I have an owner's manual and have read it and understand the grinding process and re-setting the machine accordingly. I appreciate the level of accuracy gained by jointing the knives in the machine - seems to me it would be a real challenge to achieve such accuracy any other way.
From contributor R:
By the way, that is a great machine.
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