Monday, March 18, 2013

V4.11 - Setting those pesky knives.

Let’s see…last week we talked about the cutterhead and how to loosen the knives. Now let’s talk about why to change them and how to properly set them.

First the why. Simply because using them makes them dull OR you might put a nick into the knife edge from hitting something harder than the knife. When a nick is there, they will not remove any material; therefore, it will leave a raised line on your workpiece. This also happens with nicks in planer knives. Now that I think of it, there is an old trick that you can do that will let you get more life out of your nicked blades before you need to sharpen them.

So, let’s say that you are jointing a piece and happen to hit a nail that was imbedded in the wood. (note: always check the wood over and look for nails or staples - anything that might nick a blade - BEFORE you run it thru the jointer) this puts a nick in all three blades.

Bad news, but all is not lost. For our lesson, let’s say the nick is one-sixteenth of an inch wide. So, here’s the deal, loosen one blade and move it one-sixteenth of an inch to the left and retighten. Then loosen the next blade and move it one-sixteenth of an inch to the right and retighten. The third blade stays the same. What you have just done is to introduce two un-nicked edges into the path of the original nick. Those two fresh edges will remove the nick line and your board will be nice and smooth.

The limit on moving the knives sideways is decided by the jointer itself. There will be a point at which you cannot move the knives far enough to remove the nick and then you will need to change the knives.

Now the how. Keep in mind a few things. 1) The tip of the knife edges MUST be dead level to the surface of the outfeed table at the topmost point of rotation of the cutterhead. This is a must. As your work passes over the blades, the freshly cut surface needs to lay on, and be supported by, the outfeed table. 2) Never remove more than one knife at a time. 3) Fresh knives are extremely sharp. Number 3 might sound like a no-brainer and it really is, but you would not believe how many people I have heard from that, just for that ONE moment, forgot how sharp they truly are. A few stiches later, they are reminded…over and over.

Ok, so you need to get the knives dead level to the outfeed table…but how?

Ah, that’s the hook to tune in next week.

See you then.
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