I think I heard something today about flattening a board on a joiner that makde sense but is not something I had previously thought about. I think I have been doing this wrong.
When I have flattened a board I always attempted to end up with all “new wood” in view. Keep taking it off until it “looks done” or looks flat then put it thru the thickness planner to finish.
But what I heard seems a lot smarter if, in fact, it is good info. So the suggestion was to pass the board over the joiner only until it will lay flat then put it thru a thickness planer to “flatten” the second side, then flip again to finish up the first side that passed over the joiner.
Perhaps all of this affected by scale. Getting a 3″ x 2′ board flat is a different animal than at 10″ x 6′ board. The above makes more sense for a much larger board, but in practice maybe all boards should be done in the manner suggested above. I am sure there is a right and wrong way.
Tim
Replies
Lets say you flatten a cupped board on the jointer just so that it is flat on all four corners and lays flat, that is it will not rock back and forth when pushed on ends, sides or corners. When you run it thru the planner the rollers will press it down flat and you will plane off that side till it is perfectly flat but the board will still spring back to its cupped state when it no longer has the planner rollers pushing it down on the bed of the planner.
Understand. So the follow up questions:
1. as you run a board over the jointer should you be pushing down with some force or just push it along? Seems if you push down you are doing what the rollers do when planning and not flattening the board because you are distorting it?
2. so then one must work the board on the jointer until the entire face is worked by the knives; not just so judgement that enough is enough?
T
flat-flat vs. sorta-flat
I use just enough downward pressure so as to maintain consistent contact with the cutter blades, but not enough to actually flex the board across the width, running it through with the concave side down. That way, the two edges provide support across the width.
Usually, I run it until the entire width and length are planed, assuming the placement of the piece actually requires "flat-flat" as opposed to just "sorta-flat". Then, I run it through the thickness planer to achieve the desired thickness. All of that is based on having checked to make sure there is enough initial thickness to produce the finished thickness required, of course.
Tim, what you describe is pretty much standard practice in the business. Just flatten the first face until you get one of the following:
A rim flat with some hollows in the middle
Both edges flat along with most of the width at either end of the board. Some bits in the middle will have been picked up too, leaving hollows here and there.
2/3 to 3/4 of the width of the board flat with one edge sticking up
After this it's safe, as you say, to run the board through the thicknesser to get the other face parallel, finishing of by flipping from one face to the other if it's important to get both faces fully machined.
As long as the board is not too thin, ie, less than about 10- 12 mm thick, you're not likely to experience the hollows on the original planed face being forced down onto the bottom bed or the rollers of the thickness planer. Slainte.
After jointing the bottom flat and taking only enough wood off the top to make it parallel to the bottom, you might consider stacking and stickering the board for several days to adjust. Wood has been removed unevenly on the two surfaces, and the moisture content of the board probably was not uniform throughout. As the new surfaces develop a uniform moisture content some warping may occur. It seldom is significant, but a second flattening a week or two latger may produce a board whose long term steady state will be flat. Just an option.
Still getting traction
I appreciate that this post is still getting replies. Thanks
Tim
To answer your question on how hard to press down when putting a board through the jointer . . . You vary the pressure. Let's say you're putting through a 3 foot board. For the first half a foot you primarily push horizontally with the back hand. The front hand only puts on enough pressure to keep the board from "chattering" or bouncing off the cutter head. Then, as soon as you can put significant pressure on the board on the outfeed table, shift your weight almost completely to the left hand or front hand and press down firmly. Of course, on a 3-foot board you will probably have to shuffle hands once or twice, but you'll still be keeping the downward pressure on the outfeed and primarily feeding the board with horizontal movement from the infeed table. When you think of how a jointer actually works to flatten a board, this procedure or technique makes sense to me.
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