Cutting Square on the Table Saw
If I take a piece of 30” x 30” ¾ cabinet grade plywood and cut all 4 sides using the fence, I would assume the cut would be very accurate, but it is not. If I take a very accurate square and place it on the piece, clearly it’s not square. One side is less than 90 by 1/16 and one side is greater than 90 by 1/16. The gaps are bigger as the pieces get longer.
I’m frustrated with the performance of the saw and unable to solve this problem. My research and testing has led me to believe that accuracy of the fence in terms of parallel to the blade does not have to be perfect as long as it’s in the same state. For example, if the fence was .01 out of alignment with the blade in theory if I cut all 4 sides with the fence being out of align by .01 the piece should cut squarely, correct?
From contributor L:
I can tell you that getting square panel stock is hit or miss. The lower grades of ply (ie:c3) seem to be the worst. The higher grades of ply (ie: b2, a1) seem to have a better chance of being square form the factory, but not always. It varies from sheet to sheet, even in the same unit. I notice, as you cut a piece of ply, that like solid wood, it can develop a curve from relieving stresses. This can affect what is truly square. The best way to tell if you have a square cut is to measure from corner to corner. I try to have my results within 1/64", but 1/32" will past muster with me. You need to make yourself a dedicated plywood sled for cutting 90º. I also have one for cutting perfect 45º. You can never assume something is square until you have checked it with some sort of measuring. Keeping things perfectly square is one of the harder things to do, as it affects most things in a cabinet. Good luck, and just so you know, it took me about 6 hours to build and get my sled perfectly square; it was time consuming, but totally worth it.
From contributor D:
I always struggled getting square cuts on my table saw until I built an accurate sled for cutting panels. Now it's a matter of how I cut. I first use my EZ Smart saw guide (wish I had a Festool) to rip the sheet of ply oversized by about 1/4" (depends on what I'm cutting for). Then I'll take that piece and rip the factory edge off, keeping the piece oversized by about 1/8". Then I rotate the piece and rip it to final width, which leaves me 2 sides perfectly parallel. Then I'll rough crosscut them with my sled. I say "rough" because I find it hard to be accurate with an 8' piece. Then I'll trim one side square, and flip it and cut it to final length.
My sled is a 3/4" piece of MDF with an aluminum angle fence that can be adjusted by backing out the mounting screws and repositioning. The guide that runs in my miter slot is made by Incra. The adjustments on it work great. I'm going to add a self-stick tape to the fence and a stop block so I don't have to measure each time.
From contributor B:
First off, you need to be sure your square is very accurate. Most are not, no matter how much they cost. Measuring diagonal like contributor L said and measuring both ends of width and length carefully is the best, no matter what the square says.
Second thing is that with or without a sled, cutting on a tablesaw is never going to be perfectly consistent. The reason is that anytime there's movement, there's opportunity for slop. Moving the wood through the saw creates a big opportunity, and throw a human into the equation and you triple the chances of inaccuracy. So with a tablesaw, you can only expect a certain (lesser) degree of accuracy and consistency.
Third, keep on cutting around the test piece. With just 4 cuts, you've still got some "factory edge" influence in there. Maybe run the first edge over the jointer, then start cutting. A panel saw or slider will give you more consistent results, but there will always be slop. You just have to minimize it. Remember, it's wood. Shim it or trim it.
From contributor J:
I agree with a previous response - the panel must be square first, before using the fence. The fence alone only guarantees that the opposite sides are parallel (not square). So you get a parallelogram or a rhombus from the fence, not a rectangle or square. Measuring the diagonals is the best way to determine squareness. As mentioned by others, you need a sled, slider, panel saw, long guide for a skilsaw, or some other device (Festool looks pretty good for this) to square the panel first.
From contributor S:
As much as we would want, 4x8's of any thickness are not always square. Sometimes you get lucky, sometimes it's a 16th off on a corner. What I do (and I don't have a fancy panel saw) is quickly find a square edge or corner of the sheet and work from that. The fence doesn't ensure a square cut, and as others say, it basically duplicates or creates a parallel of whatever you have running along the fence. If it was me, and I do this often as over time machinery come out of square, I would pull the fence over and re-check everything, button things up, square up the fence to the blade, check the square of the blade guard, etc. Work off of a square edge always. If you square your table saw up, I doubt that the table saw is then to blame for the lack of true of your lumber and sheet goods.
I love my Delta table saw and wouldn't trade it (until I get my way up to a Sawstop) and I don't ever have problems like these, because I'm kind of a neat freak and always check twice on everything to make sure things are set right and always square. Time is money, but so is wasted lumber.
From contributor G:
When it's really important to have a square panel, I clamp up a straight edge square to the straightest edge of the panel and use a pattern bit to rout a little bit off the end of the panel. Then, with one reliable square corner, I can use the table saw to do the other edges. One way to check the squareness of the routing fence is the 3:4:5 triangle. Measure 3" (or 6, 9, etc.) from the corner along the fence and 4" (8, 12, etc.) along the reference edge. Then connect the marks. The hypotenuse will be 5" (10, 15, etc.) if the corner is square. It's the law!
From contributor Z:
I also made a sled, however I just bought the new Jessem slider attachment for my Delta. Check out the Mast-R-Slider; mine is just great. They did have some that had a problem, but Jessem has corrected the problems from what I heard. Really great item, up to 36" wide crosscut with flip stop fence out to 48".
From contributor O:
You did not mention what kind of blade you are trying to use. I have had blades heat up and start to deflect and cause the problems you are having. The giveaway for this problem is the start of the first cut is straight for a short distance, then it starts to deflect. Try a new quality blade. Another problem I have seen is the saw needs to be taken apart and everything cleaned. This includes removing the trunions, etc., and checking the arbor for end play. Also check your rip fence guides and make sure they do not have any play in them and that they are in line with each other, and do not over tighten the rip fence, which can damage it. If it is already damaged, it can still lock and be able to move due to vibrations.
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