jointer problem

[jackl young]

I have a delta dj20 8 inch jointer. When ,making multiple passes to flatten a board I am ending up with different thicknesses on each side of a 8 inch board. The tables are within .002 of the cutter head and the blades are all within .002 os each other. Do I need to go end for end on each pass. I am jointing 8 inch wide mahogany. Any help will be appreciated.

[Mike Circo]

The age old question. And the answer is...

A jointer is not a thicknesser. A jointer only gives a flat surface to the face of a board, and a square edge to the adjacent side.

To get accurate thickness to all corners of a board, you need a planer.

Others may wish to give the complete engineering/scientific answer, but that is the short one.

M

[Frank Drew]

Jackl,

Assuming a correctly set up machine: If the board is no wider than your knives you don't have to flip each cut; changing feed direction can help with chipout, however. As for the thickness issue, it's as Mike said -- before face jointing, the board might be of even thickness throughout but not flat in all directions, so in order to flatten the board more has to come off some areas than others, and you end up with uneven thickness. The planer will correct that.

[Lee Schierer]

I'm assuming you are jointing the edge and not the face, though my answer actually works in both cases.

Creating a taper on a jointer is a common problem. Many times it is caused by poor technique rather than jointer alignment issues. As you start jointing a board edge all of the board is on the infeed table. Once you start the cut the nose of the board ends up on the outfeed table. As soon as you have 6" or so on the outfeed table you should transfer your grip to the portion over the outfeed table and only press down on the out feed table. The hand over the infeed table should only push the board forward and keep it tight to the fence.

[Tom Hintz]

I get this question contantly on my site and have been begged (literally) by jointer manufacturers to write the story at the link below on the jointer tapering issue. (You are not a bad person, honest!)

http://www.newwoodworker.com/jntrtaprs.html

[glenn bradley]

A bunch of you beat me to it but, I think we have a winning answer: Jointers make surfaces flat, planers make flat surfaces parallel.

[Mike Parzych]

The way I raed your question, you were asking about tapering in relation to jointing the face of a board. One of the primary causes is always starting with the same end of the board. Let's say you have a board where the first 6 inches of each end is "high" and the center is "low." So it's a concavbe surface.

If you keep starting with the same end, the jointer will take a full cut on that end. Shortly thereafter the high end will be off the outfeed table and is no longer function as the reference surface. In practice I've found that for this reason, less is taken of the back "high" end. By simply switching ends with each pass, you'll take them down at an equal rate until they meet the "low" spot. Obviously half your passes will be against the grain, but if your last pass is with the grain, you should have a good suface.

Then put it on the planer and you'll end up with the maximum thickness the board can finish at.

[keith ouellette]

The age old question. And the answer is...

A jointer is not a thicknesser. A jointer only gives a flat surface to the face of a board, and a square edge to the adjacent side.

To get accurate thickness to all corners of a board, you need a planer.

Others may wish to give the complete engineering/scientific answer, but that is the short one.

M

big ditto. Even if you joint the face and then turn it over to joint the other side it will not be a uniform thickness. When you run the face over the jointer you are making the face conform to the jointer table. Its thickness can vary. when you run it through the planer, the planer forces the flattened side down to the planer tables and the blades make the un flattened side conform to the other side of the board. Thus giving you a uniform thickness. That is if your planer is working correctly.