Thoughts, comments wanted about jointer knife settings

Hey Gang, I was reading over the knife setting section in the instruction manual for my jointer (8 inch Delta DJ20) and was a bit dismayed about the height specified. The manual recommends setting the blades 0.015 inches (approximately 1/64 th inch) above the circular portion of the cutterhead. If I want to take any cut larger than 1/64 th the woood will contact with the cutterhead circumference. The manual states not to take more than 1/8 inch cut but it it looks like taking more than a 64th I'll be hitting the cylinder. Of course I'm noticing this now and not during work time to discuss it with whomever is representing Delta these days, but you guys and (maybe,..., hopefully ) gals may be able to chime in with your own thoughts. If you have another brand jointer could you post its recommended blade settings here? Thanks, Marc
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On 2/12/2012 11:55 AM, marc rosen wrote:

Seems like that would depend upon the diameter of the "circular portion of the cutterhead", and the speed at which it's turning, and the rate at which the wood was fed (which would probably have to be pretty fast to exceed the design parameters).
IOW, unless the diameter of the cutter head "cylinder" is pretty large, and the speed at which it was turning is extremely slow, it should not be a problem to take the recommended cut depth.
Take a look at the angle at which the cutting edge enters the leading edge of the wood during the cut ... the smaller the diameter of the "cylinder" holding the knifes, and the faster it spins, should insure that the wood would never contact the "cylinder".
I'm pretty sure this is taken into account in the design. Have you had a problem with this in the past?
Perhaps misunderstanding your problem?
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Marc,
I am not an expert on this, but every jointer maintenance book, article,etc. that I read say to set the knives at about the height equal to the top of the outfeed table. That way when you drop the infeed, you get a bigger cut.
I'd have to go into my reference books, but at the top of my head this morning, that's how I remember it.
Here's a great article on it:
http://www.woodcentral.com/bparticles/knife_adjustment.shtml
MJ
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Hi MJ and Swingman, Thanks for the article from Woodcentral and your comments. It has some similar details to the procedure I am using. MJ, in the Delta manual it instructs you to set the outfeed table 0.015 inches above the "round portion " of the cutter head. Then using a straight edge or a magnetic jig (my approach) you set the blade height off that table when the cutterhead is at top dead center. It is as you suggest the same height as the outfeed table but that table height is much smaller than the allowed cutting depth. I think the head's diameter is 3.75 inch and I can't recall its speed but I recall it is about 13,000 cuts per miinute. Swing, I see your point (no pun intended) very well now. As soon as the wood is cut by the blade(s) and passes over the head its bottom should be at the height of the outfeed table and not touching the head. I am sure I was incorrectly analyzing this while I was staring at the stationary head while adjusting the blades. Damn, after using it for 6 years I can't believe I was analyzing a dynamic part of it while it was being static and not realizing what takes place in real time.
Anyway I think I'm back to normal again. Thanks for helping me think properly. Marc
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On 2/12/2012 2:17 PM, marc rosen wrote:

Hey, understand perfectly ... I do a "doh!" forehead slap at least once/shop hour. The further from the problem, the easier it is to see the solution. :)
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Swingman wrote:

Especially, if it's somebody else's problem!
A friend used to comment that the more engineers he invited over to help, the less any work got done! Everybody is ready to offer an opinion about the way it ought to be done, but no one reaches for a shovel. : )
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This .015 adjustment thing with a round head is also a safety feature in that it does limit the material removed if you jabbed the wood into the cutter... With the tables adjusted for a heavy cut the old square head machines let you ram a board in so deeply that the board could basically explode. I understand it could also flip the board out of the user's hands or if you were lucky the belt would slip and it would stall the cutter like a catch while wood turning.
I took advantage of this cut limiting feature on my shaper today. I was using the shaper with a straight "safety cutter" to flush cut edging on plywood. The edging slid along under the fence while the fence was adjusted so the straight cutter removed just the edging and not the veneer. After the edging was flushed on the long edges I stuck the ends of the edging under the fence and carved them away with the cutter. It would only cut a limited amount at one time as the round body of the cutter only leaves a small cutting edge exposed. In normal use the cutter would remove wood before it would hit the cutter body but in the manner I was using it the wood was contacting the cutter body at times as I fed it in. This worked just fine... would have been a disaster with a non-safety cutter design!
John
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marc rosen wrote:

No, the cutter is ploughing out an arc...cutting forward of as well as at the top of the arc as it spins.
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I think you are confused, see the reply from MJ. He has it right. WW
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I've had your jointer's baby brother (DJ15) for about twelve years. I set my knives with reference to the level of the outfeed table, not the cutterhead -- not only is it much easier to measure that way, but height above the outfeed table is the only thing that really matters anyway.
Set them about 0.002" above the outfeed table, 0.001" if you can manage it, regardless of whatever that happens to be above the body of the cutterhead, and you'll be golden.
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It might be that 1/64" above the cutter head happens to be the outfeed table height. I don't own the machine and haven't looked at mine that closely, but it could be coincidence and the manual writer went with a non-standard point of reference.
Puckdropper
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Puckdropper <puckdropper(at)yahoo(dot)com> wrote in

I imagine that's the case -- I just wanted to make the point that the actual point of reference should always be the outfeed table, since that's what the wood rides on.
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I would suspect the knife setting of about 1/64" above the cutter head is correct. This is basically the setting for my Powermatic 8" jointer, as well. Probably a similar setting for all such jointers (and planers) with similar heads. The recommended setting of the blade, top-dead-center, above the outfeed table, for my Powermatic, is what Doug mentions, .002". I would suppose this is applicable for your Delta.... and other similar jointers. If you can set yours less than that and be okay, great.
I have a (newish) Delta 15" planer, but haven't had reason to change blades, yet, so not sure what that knife/head setting is. Eye-balling it, looks to be a good bit more than 1/64". My brother has a 12" Powermatic planer and, if I recall, that knife/head setting is a tad more than 1/64", also.
As for as I know/understand, 1) the knife relative to the head setting has nothing to do with nor is dependent upon 2) the setting of the outfeed table relative to the knife/head unit. Those 2 settings are independent of one another.
Sonny
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