NB Q #3 - No "grain" when cutting plywood, MDF?

[IBBugsy]

OK, you use the SMT when you crosscut and the rip fence when you rip. What about plywood, MDF, etc. that don't have a "grain" to go by? Rule of Thumb - rip along the length and crosscut across the width?

I want to make sure I'm using the right tool (SMT or Rip fence) for the job.

[softop41]

You should 'read' and cut plywood according to the direction the grain on the face is running. That way you will have the least tear-out and the best looking stock after the cuts. MDF doesn't matter, just be prepared for a lot of very fine dust when you cut it!

[LarryG]

With respect to wood, a cut with the grain is ripping and a cut across the grain is crosscutting.

With respect to operating a table saw, however, a rip is parallel to the long dimension of a workpiece and is made using the rip fence; a crosscut is parallel to the short dimension and is made using the SMT or miter gauge. Grain direction does not matter.

IOW, there will be times when you are cutting parallel to the grain -- "ripping" -- but are using the SMT. Conversely, there will be times when you'll make a cut across the grain but will guide the workpiece using the rip fence. In both cases you <s>always</s> usually want the longer dimension of the workpiece against whichever fence you're using. EDITED TO ADD: But there are exceptions to this, as Loring explains below.

These guidelines work for any material: ply, MDF, or real wood. After all, the blade is still meeting the wood the same way. The only difference is the means used to guide the workpiece, which is always done using the safest possible means. Safety trumps all else.

[LCHIEN]

I would add to what people have said previously,
I use the rip fence to guide a cut sometimes with the short side agaist the rip fence.

Now this will not work if you have a 4" by 36" piece of wood, the short side is too short to keep the long piece from twisting.

But if you have a plywood board say 24 x 36 and you need to make a cut across the 24" side, well 24" is too wide to use the miter fence but it will be good enough to ride against the rip fence w/o twisting.
So I would cut "Rip style" the short side of this board.

Say I also have a 4" x 6" piece of 1-by with the grain running along the 6" length and I want to cut the thing square (a 4" x 4" piece).
Now this is a crosscut in all sense of the word. But I don't really like hanging two inches off the end of the miter fence, you have to hold the 4" remnant against the fence less than 4" from the blade, and it wants to twist off the miter fence not being directly in front of the center push point.
So I will put away the miter fence, and put the rip fence 4" from the blade. Now I will ride the 4" end against the rip fence, use a push SHOE (not a stick) that I can bear down, and push that sucker through with good down force all the way until its past the blade by two inches or more.

With the 4" side, but being a short piece,there's enough to guide it well without its wanting to twist. Now for the important part: a 4" square board between the rip fence and the blade is the absolute most likely kickback combination in the world, bar none. This is the size that is just small enough to get twisted in a bind. That's why its key to use firm downward pressure to keep the workpiece from lifting, If it lifts, it's going to jam and kickback.

Now, if it were a 8" x 4" piece, I would say there's enough length to hold it safely against the miter fence And I'd cross cut it normally and avoid the kickback possibility since the rip fence will be parked way off to the side.

So those are the ocassions I would consider violating the obvious cutting conventions.

[LarryG]

Good addition the the thread, Loring, and I agree. I should not have used the word "always" and will go back and edit my previous post accordingly.

The exceptions you have cited are essentially what I was trying to say in my closing sentence: "Safety trumps all else." Whatever you do, however you're doing it, it should always be done in the safest possible way, and all the other so-called "rules" be ****ed.

[lcm1947]

Excellent reply Loring. Wish you'd said that back when I was first starting out. and that advice about the 24x36" cut reminds me to get busy building a sled. Oh and as far as the 4"x6" cut well the Gripper is perfect for those size cuts and extremely safe. Seems like I reach for the Gripper more and more now over any of my other sticks or push devices. It's truely a neat and safe jig.