Square Cuts

[ssmith1627]

When I was making my router table, I had an issue with a cut starting out right and then not ending up square. I thought it was the alignment of my sliding miter table but I think I've figured out my problem.

If you're using the rip fence......and the side opposite the side you're cutting isn't square, doesn't that basically trace that pattern right over to the side you're cutting ? Is there some way to avoid this problem ?

I was assuming that my piece sheets were square to begin with and I'd make a cut only to find things weren't coming out right. The same problem can happen on the sliding miter table if the side up against the fence isn't exactly perpendicular to the side you're cutting.

Not sure if I'm explaining that very well. Are there tricks to this ? How do you get back to square if the sides you're using to guide the cuts aren't square ?

Steve

[LCHIEN]

It's a little alarming to hear someone mention using the SMT and RIP fence in a single question about a cut. First rule of safety is that you should never use the SMT and RIP fence together while the blade is in the wood on any cut.

A fence that is allowed to move or flex at any time during a cut will result in a non straight edge. On the BT3x specifically, the rip fecne should be properly locked down front and rear. You can chek this by locking it down and wiggling by hand. The Miter fence needs to be properly assembled. In my experience here at BT3central, the common causes of miter fences not being square or changing squareness are: 1) improper sequence of assy where the washer is under the fence rather than on top 2) improper use of the orange angle indicator 3) improper seating of the bolt for the miter fence knob, 4) overtightening the miter clamp if used.

Now that all the above are fixed,
In most work, sheet goods are received with straight edges. Using the rip fence AND properly following a straight edge tight to the rip fence will make a straight edge on the opposite edge. With peices 2-3 feet long this is easy to do. With longer pieces, you may need a long auxilary rip fence to help guide the workpiece.

Provided your piece is not too wide, using the SMT properly can make a square 90° cut against the other side.

If you have a non-square piece with JUST ONE or more straight edges, the sequence would be to rip one side (opposite the good straight edge), now you have two parallel sides. Then use the SMT to cut the other two sides square to the first two sides.

If you have non-square, non-straight pieces, first thing to do is get a straight side, this with a jointer or by using a straight-edge guide clamped to the piece.

[vaking]

Steve,
Let me try to explain a little differently what you are saying.
when you work with boards (not sheet goods) you would use a jointer first to make the first side flat and the second side flat and square to the first. After that you use a thickness planer to make other sides flat and parallel to the first 2 sides.
Similarly to that in sheet goods you need to start with getting the first side straight. You can sometimes presume that factory edge is straight and it will work for some projects, but for the router table I would try for a higher precision. (My rule of thumb is that tools need to have higher precision than regular projects because any mistake in a tool will be transferred to projects later on). If you need to make your own edge you can use some jigs with the table saw, link below is an example:
http://www.newwoodworker.com/tsjointjig.html
Once you have one edge you can try to make the other edge straight and square to the first. For a small piece of ply you can use SMT (presuming it is well calibrated). For a bigger piece you will need a panel saw or at least a crosscutting sled for your table saw. After you have 2 sides straight and square go ahead and use rip fence for other sides.

[agent511]

I think I understand what you are saying. First of all, I don't think you are using the STM and the rip fence at the same time. I think you are saying that for some cuts you use the rip fence, and for some cuts you use the STM (which also has a fence).

I also think you are saying that your pieces are not ending up square. I think there is a simple explanation for this.

The rip fence should be checked for parrallelism with the blade. But the most likely problem is the STM fence is not 90 degrees to the blade exactly.

Take a longish piece of lumber, and cut it at 90 degrees. Remove the piece and flip one of the cut pieces 180 degrees and put the cut ends back together. You should be able to stand the pieces up on your flat table and see no light at the cut edge interface. If you do, then your 90 is not 90. Either the miter gauge is off, or the blade is off to the miter slot.

If this is too ambiguous to follow, let me know and I'll write it again differently.

[Tom Miller]

I think the others have you on track. I would just add that squaring a panel has been discussed before, so you might find more tidbits -- for search terms, I'd suggest "square panel".

I stopped assuming the factory edges of sheet goods were square from the factory some time ago, much less straight.

When you use the rip fence only, you can only assume your panel is a parallogram. Your SMT, or other techniques (see search) can make adjoining sides perpendicular.

Regards,
Tom

[ssmith1627]

I'll read back through this now -- thanks for all the quick responses.

But wanted to address that first point from Loring......no, I absolutely wouldn't use the rip fence and SMT together. I only mentioned both because I saw the same type of problem with each of the different cuts.

As Tom said, the rip fence could allow you to end up with a parallelogram.....and you can end up with a less than square cut using the SMT as well. Wasn't trying to combine the two for one cut -- just combining the two for purposes of this discussion and the "less than square" results.

It's not a matter of the rip fence being out of alignment. If I start out with a perfectly square panel, the new "rectangles" that I end up with are also square. Same for my SMT.....I have aligned its fence to the blade and I can come up with square results there as well.

What I'm trying to find the answer to is if the beginning piece is NOT square, how do you get back to square ? And not just end up with the parallelogram. You run a parallelogram through the saw against the rip fence and you just come out with a parallelogram right ?

I'm new to this so probably just making it harder than it has to be. Just wanted to talk it through with you guys. If I'm just being dense, don't be afraid to let me know.....haha.

Steve

[gimpy]

Steve, I think Loring answered your question in his next to last paragraph. Just make sure that your smt is 90*/square and you should be able to square everything up after you first ripped the piece.

Frank

[agent511]

Exactly. As long as the SMT fence is really at 90, then you can turn anything into a square.

Start with any one straight edge, which you can put against the SMT fence. then you cut the next edge, turn piece 90 degrees, cut, turn again cut . You can only have a square (or rectangle) at this point.

Unless the SMT is not at 90 to the table or the blade is not at 90 to the table.