Jointer Will Not Cut When Approaching Flatness

[Mike C Smith]

I need some advice about what I can do to keep my Stanley #8 Jointer cutting when the board get close to flat. When it does cut, I seem to keep developing a high spot in the center of the board. When I attempt to remove the high spot with stop cuts, the jointer will not cut.

At one point when tuning the plane, I lapped the sole on sandpaper attached to plate glass. I believe the I inadvertently introduce some convexity to the sole with the high point just behind the mouth of the plane. Would this result in the cutting pattern I described above.

My question then is - 1) would the convexity introduce the cutting pattern described, and 2) if so, how should I go about tuning the plane?

[Robert Engel]

Glass (especially plate glass) is often not as flat as you think, so the first thing I would recommend is changing the surface.

I've had good luck using self adhesive sandpaper on a piece of melamine clamped to my benchtop (which I know is flat).
Draw lines with a sharpie and start with 80 grit.
If its pretty bad and you've got better things to spend your time on, the only other option is machining.

[steven c newman]

Usually has nothing to do with the sole. Too much pressure at the start and the end of a pass. Infamous Banana cut. Won't cut the high spot in the middle.....because a #8 is too long. Come back with a shorter plane in the high spots, then one more pass with the long jointer.

mark a line along the edge of a board. Try to plane to this line the entire length. Lots of pressure on the front knob at the very start, once the back end is on the board, transfer your weight to the rear of the plane. Pushing down on the rear handle.

A hollow BEHIND the mouth really does not matter, at all. As long as the toe, the heel and the area right in front of the mouth are all in the same plane. That is why at the start of a cut, all the pressure is on the front end, at the knob. Once the heel is on board, then you can transfer your weight to the rear of the plane.

[Pat Barry]

If the sole of the plane was convex from heel to toe (high in the middle), then wouldn't it tend to make a cut that is deeper in the center of a board? What you are describing is what sounds to be concave (low in the middle of the plane body - ie if a true straightedge is laid across the sole from toe to heel there would be a air gap near the center

[Mike C Smith]

Thx for the info. I remeasured the sole with a 4' machinest straight edge. Using a .0015 feeler gauge I could not find any hollow with the only exception being the very right corner of the toe for less than 1/2".

Question: Is that generally flat enough for a jointer. The board I'm surfacing is 30" in length so I'm a little confused why the plane would too long for the top cuts.

[Brian Holcombe]

Check the board for wind as well, if the wind is not removed it will drive you crazy as you approach flatness.

The last two pages of my cabinet build thread detail checking a board for wind.

[steven c newman]

Yep, flat enough for a jointer

Lay the plane along the edge of the board, and then look under the plane.

Jointer plane's job is to make an edge straight. That is why it is as long as it is. It can bridge over some smaller low spots, while bringing down the higher ones. If it is high in the middle, the plane may be turning it into a ramp. It will cut going up the ramp, but it will stop cutting once the mouth is over the high spot. If the back end is still on the ramp, that is. When it goes over the ramp's highest point, then it will rock a bit until it is going down the ramp. Iron would be in the air until the plane starts back down hill. It is cutting, just it is cutting "air"

I have a #5-1/2 that acts the same way.....that is why I mark a line to follow. It lets me know if and when a ramp starts to form in the middle. Then I can work just on the higherst point and plane it until the ramp is gone.

[Steve Voigt]

Thx for the info. I remeasured the sole with a 4' machinest straight edge. Using a .0015 feeler gauge I could not find any hollow with the only exception being the very right corner of the toe for less than 1/2".

Question: Is that generally flat enough for a jointer. The board I'm surfacing is 30" in length so I'm a little confused why the plane would too long for the top cuts.

Yes, it's more than flat enough. The only way flatness would matter in this situation is if the sole were concave; that could cause the problem you are describing.But if the sole is flat or a little convex, that is fine.

Brian's suggestion to check for wind is a good one, and you should check the plane's sole for wind as well, just to rule it out. But I'm betting the problem lies elsewhere. Three questions:

- How thick is the board you're planing?
- Is the underside flat?
- Is your bench top flat?

I'd bet that either the underside is convex or your benchtop is concave (or both), and the board is flexing under the weight of that massive no.8. So, it's flat at the moment the plane is passing over it, but when the weight is lifted, it springs back to convex. I think that's the most likely explanation.

[Pat Barry]

I'd bet that either the underside is convex or your benchtop is concave (or both), and the board is flexing under the weight of that massive no.8. So, it's flat at the moment the plane is passing over it, but when the weight is lifted, it springs back to convex. I think that's the most likely explanation.

Excellent point

[Mike C Smith]

My board is 4/4 by 6" by 30" quartersawn white oak.

I have not checked the flatness of my bench in quite some time. I appreciate everyone's input, sounds more like my technique than anything with the plane. So I'm planning on 1) sharpening the plane, 2) check my bench's flatness and reflatten if necessary, 3) I'll slighlty hollow the board with my smoothing plane, and 4) use the line section to avoid creating another ramp. I'll post later and let everyone know how it went. Thanks again for the help.

[Prashun Patel]

Hve u confirmed with a straight edge that you are devloping a high spot in the middle? When I'm misreading a piece, I may have a low spot where I think there's a high spot. When I therefore concentrate on the wrong area, it won't cut.

Test your plane on a piece you KNOW is flat, or on the edge of a board. Once you're convinced the plane and blade are flat enough and sharp enough, then in my experience, if it won't cut on a new piece, the error is in how it's being read by me - not the plane.