why does a jointer blade face joint a board but thickness planer does not?

[Greg Mann]

When you ust a sled, do you use shims under the gaps (or high spots)? If so, the reason for the sled working isn't because of its length, it is because of its ability to keep the board from succumming to the pressure that the planer puts on it. You could build a 2 foot sled and it would work (with shims). Without the shims it wouldn't work. The reason for the sled is to make sure the shims stay in place. If you put shims under the board without a sled, the friction of the table would move or dislodge the shims. By using a sled, there is no longer friction between the the shims and the table, all friction is taken by the sled.

Now, incorporating sliding table saw technology, if the bed of your planer "slid" under the cutters, then you could shim the board, in place, on the sliding table, and pass your board through. Thus jointing the one side of the board, then with that side being flat and now your reference point, flip the board over and thickness plane it.

Hey, what a great idea. Anyone make something like this? It would be simple and save so much space, I mean, you wouldn't need two machines. Oh yeah, except that you would probably need about a 12 foot table to accomodate a 12 foot board... I'm sure some manufacturer makes 'em.

I saw exactly this machine in the Henry Ford Museum, except that the cutting head was a vertical spindle with a big rotary facemill. Another issue: A sliding table will take up 24 feet to flatten a 12 foot board. When you make this machine use a traversing cutting head and leave the table stationary. You will need only slightly more than 12 feet.

Also, a facemill will give you rotary marks on your workpiece while a planer style cutter will not. The facemill will not generate nearly as much force upon the wood as a planer style cutter would so the board would not need to be suuported as much. The problem is the finish (and dust control), which is probably why I saw it in the museum and not in the Grizzly catalog.

[bob frost]

OK, Thanks to all for fellow wood workers at SMC for your input!
I am really pleased and somewhat surprised at the length of thread this has created. I think I may even become a contributor now.
I understand this much better now and I will print out this thread because some points of view have been expressed in ways that are clearer to me than what I had previously been exposed to . To Glen's point, yes, I think we all understand that there is good reason for the manufacturing and usage of both machines and could just stop there. However, I am one who likes to have more in depth knowledge about how and why things actually work, rather than just being satisfied that they do work. At least in many cases such as this one. It,s a little like turning on a light switch; most people will go thru life and never understand how it actually works and just turn it on. And thats Ok. But for many of us we will study the issue , as I did many, many moons ago and know why it does or does not light up when one throws the switch.
Again, Thanks to all
Bob

[bob frost]

OK, Thanks to all for fellow wood workers at SMC for your input!
I am really pleased and somewhat surprised at the length of thread this has created. I think I may even become a contributor now.
I understand this much better now and I will print out this thread because some points of view have been expressed in ways that are clearer to me than what I had previously been exposed to . To Glen's point, yes, I think we all understand that there is good reason for the manufacturing and usage of both machines and could just stop there. However, I am one who likes to have more in depth knowledge about how and why things actually work, rather than just being satisfied that they do work. At least in many cases such as this one. It,s a little like turning on a light switch; most people will go thru life and never understand how it actually works and just turn it on. And thats Ok. But for many of us we will study the issue , as I did many, many moons ago and know why it does or does not light up when one throws the switch.
Again, Thanks to all
Bob

[Glen Butler]

This thread makes me chuckle, and Glenn, where did you get that wonderful graphic showing the jointer and planer?

[Greg Mann]

However, I am one who likes to have more in depth knowledge about how and why things actually work, rather than just being satisfied that they do work.

If there is a single woodworking machine where it is important to know the how and why of how it works in order to get good results it's the jointer.

[Eddie Darby]

Ran into this in another thread.

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

What A Jointer Can and Cannot Do

A jointer can machine a face or edge of a board perfectly flat and straight. It can also make adjoining surfaces square to each other. What it can’t do is make any surfaces parallel to each other. That is the job of the thickness planer or in the case of edges, the table saw.
The jointer “sees” one surface of the wood at a time. The knives are set parallel to the outfeed table and the machined portion of the wood, sliding on that table is the only registration a jointer has. When squaring an edge, the fence comes into play but the outfeed table surface remains the only point of registration that keeps the edge straight.
The jointer has no way of keying of another surface to make a cut parallel to that surface. Consequently, while the jointer can make adjacent surfaces smooth, straight and square to each other, it has no way to make those cuts parallel to each other.
When working with edges, we often joint one edge straight and then go to the table saw to cut the opposing edge parallel to it. With the wide faces, after jointing one face flat, the planer is used to cut the opposing wide face flat and parallel to the jointed one. It this combination of machines that allows us to produce perfectly straight wood with square, parallel edges.

[Michael Weber]

Well I gotta jump in here and add my 2 cents worth. It's easier in my mind to consider bowed boards instead of cupped boards. A bowed board (bent along the boards length) will be flattened by the roller pressure underneath the cutter but after exiting will resume it's bowed shape. I can see how, and I have milled cupped boards on my planner by putting the concave side down and taking light cuts until I have a flat reference surface and then flip the board over and start taking the high edges off. Going back and forth gives me good results. YMMV. Of course it only works if the board is otherwise straight.

[glenn bradley]

Glenn, where did you get that wonderful graphic showing the jointer and planer?

That one came off of FWW online. The article, oddly enough, is entitled: "The Jointer and Planer are a Team" .