Does anyone have a definitive explanation for the springs under jointer knives? They sure make setup a PITA. It seems more logical to me that gravity sould be used to let them rest on the jack screws, then the ends can be raised as needed before tightening everything down.
“I cut this piece four times and it’s still too short.”
Replies
If you've a guide that you want the knives to rise to (like a Jointer Pal), then you can tighten the gib bolts while the springs lift the knife to the guide. It can be much faster and easier than getting jack screws precisely set.
For two of my machines there is a setting jig that pushes the knives down while the springs push the knives up to the bottom of the setting jig.
Look at pages 10 and 16 in the manual found at http://www.general.ca/manuel/80-200an.pdf
That setup makes changing knives very easy and fast.
Usually jointers have either springs or jack screws for the knives, but not both, since they would work against each other. If your machine has both I'd be interested in knowing the brand and model number.
The springs or jack screws can be removed if you aren't using them, just be sure to remove the parts from all of the knife slots so the head stays in balance. It is possible that the manufacturer included both springs and jack screws so that the user could remove one system and use the other.
John White, Shop Manager, Fine Woodworking Magazine
It's a Grizzly G1182 (6"x47") and it came with a setup guide, which is metal. I see the same guide all over and have reservations about using it on a freshly honed edge. I just reset my knives after having them honed and with springs and screws, it was a royal PITA, so I removed the springs. I understand the point about being balanced but I doubt that having more springs in one slot than another will throw it off. Not much mass there and it's not very far from the center. Still, when I remove one, I do remove all when doing something like this. Good point about having a choice- I'll look in the manual again and see if they did it for this reason.
"I cut this piece four times and it's still too short."
I looked up that model in the Grizzly catalog and they advertise that the machine comes with "both jack screws and knives so you can set the knives the way you prefer." So my guess was correct, but I wouldn't be surprised if the manual left out explaining that you would have to remove the springs if you were going to use the jack screw method.
Lately, a number of Asian made jointers are coming with knife setting jigs that are meant for planers not jointers. These jigs have two end pieces that straddle the knives, with the two ends being connected to each other by a steel rod that serves as a handle. These jigs don't set the knives properly because the knives can end up not being parallel to the outfeed table, which they must be if the machine is going to cut properly.
The easiest way to set knives is to use magnetic jigs which can be purchased or shop made. Magnetic jigs don't require springs or jack screws to set the knives. The magnets serve to both hold the jig solidly on the outfeed table and to lift and hold the knives in place while the screws are tightened. In my experience, the magnetic jigs, when used with a little care, don't damage the freshly sharpened edges of the knives.
No matter what method you use to install the knives, you will probably need to fine tune the height of the outfeed table, after the knives are installed, to get a perfectly straight edge when edge jointing.
John W.
I talked to one of the people in Technical at Grizzly yesterday and he recommended setting the outfeed table to match the cutter head. I checked it and there's no misalignment between the two. I'll need a longer straightedge to check the whole length of the infeed and outfeed, but when I checked the 16" before/after the cutter area, they were fine. I then set the knives according to the outfeed and checked it- never better. I was using a dial indicator when I checked everything and while I did see a little light in some areas when I spanned it with a straightedge, it was on the order on .001" and this was with a clean feeler gauge. The only reason I needed to reset the knives is that after having them honed and trying it, I noticed that there was still a little of unevenness in knife height (same as before) and decided that I would adjust it. Since it came to me well adjusted from the factory, I'm pretty sure they were different heights because a couple of the lock-down bolts had apparently loosened from vibration. With springs and jack screws it was really annoying, so I just removed the springs and it was a piece of cake. Thanks for the reply.
"I cut this piece four times and it's still too short."
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