JordanPatterson

Jointer Issues with Edge Jointing

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I have a 6 in'" harbor freight jointer that has been setup with a veritas straight edge to within 3-4 thou co-planer, the fence is at 90o to the table, the tables are flat, the knives are even-2 thou proud of the out feed table, and the knives are brand new.

I am milling 40" long 5-6" wide poplar for a project and the face comes out great. Edge jointing results in a convex edge every time. To get this project done i made a table saw sled to edge joint the boards but I want to fix my issue.

Even though the jointer is "setup correctly" it seems that lowering the out feed slightly should help but i am so frustrated that I have lost confidence that I know what to do. Help.

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There is always a bit of back and forth on knife height.  Personally, I set my knifes a bit proud. With my straight edge laying on the outfeed, rotating the cutter head will move the straight edge back about 1/16"

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I suppose mine are a bit proud, in that they will just catch the straight edge. But 2 thou seems like a lot. And if you think about the geometry of the cut, having the knives too proud would lead to a convex edge.

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I have a Shelix head but the same principle applies...I have my head set not even a thou higher than the outfeed.  Any more than that can cause issues like snipe and the problem you're having.  2 thou is too much IMO.

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Cutter-head arc around 0.5thou to 1.5thou above out-feed table height works for most...

This is about the best guide I've come across: https://woodgears.ca/jointer/knives.html

 

Note: the height changes over time with the sharpness of the edge (I'll let you noodle on that). So you can follow a 'process' to set height, but ultimately it'll need a fine tuning jointing actual stock.

So it's not a 'set it once and forget it'...

 

 

 

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2 minutes ago, Brendon_t said:

Are you applying  the downward pressure on the infeed side? 

Initially yes. Once about 10-12" are past the cutter head i apply pressure on the out feed side

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I start applying pressure to the outfeed side just as soon as the stock is on the outfeed table. The part that's just been over the cutter head is the most correct surface on that board, so you should try to keep it registered to the outfeed table. That is a generalization of course. Different warps, cups, twists etc call for different strategies.

And no, knives too high won't necessarily cause concave. It could, depending on where the pressure is applied. But it is more likely to cause a convex edge.

When you say the tables are 3-4 thou out of co-planar, where are you taking those measurements? And what direction does which table slope relative to the other?

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What point of which bed are you focusing your attention on while passing the board across the cutterhead?

What is the depth of cut, and how straight is the edge of the board to start with?

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So after a little noodling with the jointer i have a few more things to report. 

My jointing process was to apply pressure to the infeed until the wood passes the cutter head by a few inches. Then all of the downward pressure is applied to the outfeed table. When focusing on this the results are acceptable but still not where I want them to be.

 

For grins I moved the fence toward the other edge of the cutter head and ran another board. This time the results were almost perfect. This leads me to believe that the either the in or out feed table is closer to coplaner on the near side of the cutter head as compared to the far side.

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1 hour ago, JordanPatterson said:

So after a little noodling with the jointer i have a few more things to report. 

My jointing process was to apply pressure to the infeed until the wood passes the cutter head by a few inches. Then all of the downward pressure is applied to the outfeed table. When focusing on this the results are acceptable but still not where I want them to be.

 

For grins I moved the fence toward the other edge of the cutter head and ran another board. This time the results were almost perfect. This leads me to believe that the either the in or out feed table is closer to coplaner on the near side of the cutter head as compared to the far side.

Or is it possible that the knives are higher on one end of the cutter head than the other?

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That's probably what it is.  I set straight knives by feel with a very hard thin strip of wood (I use Boxwood probably 3/16" thick, about 5 inches long, and 1-1/2 inches tall-joint a hair off of it after you set knives with it), so you can feel when the knife brushes the wood.  It can't be done with a 3/4" board as accurately. 

I do away with any jack screws and springs.   Just tighten the end screws in the bar barely tight enough to hold the knife in place, but not too tight that you can't push the knife down into place with the strip of wood.  Get the knife height right over the outter screws, and then tighten, and you're ready to move on to the next knife.  Use the wrench to swing the cutterhead back and forth while you are feeling what's going on. 

I can install a straight knife in less than 30 seconds like this.  You can feel less than a thousandth of an inch.  You want it barely brushing the wood without raising it.

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