Odd observation when trying to square up cross cuts via 5-cut method

[Larry Fox]

Group - wondering if I can pick the collective brain on a problem that has me a bit perplexed and I am at a loss to explain. I am trying to square up my cross-cut fence using the 5-cut method (which BTW is brilliant and I would have NEVER thought of on my own) - see link below.

http://www.thewoodshop.20m.com/five_cut_method_swf.htm

The piece I am using is about 11" x 11" and I make all 5 cuts and measure A - B and it comes up to be about 1/128" difference so I figure that is close enough for working in wood considering that the difference on any one cut is 1/512". The problem is that the 1 --> 2 angle is not exactly square but the rest of them (2 --> 3, 3 --> 4, 4 --> 1) are. How can both these statements be true?

Thanks in advance for your time. If it helps, this saw is a Euro Slider so the fence is attached to the sliding table and I am not absolutely certain the table is running parallell to the blade -- but it seems REALLY close if not dead on.

What am I missing?

[Prashun Patel]

One possibility is if either of sides 1 or 2 are not STRAIGHT along the entire length. If you torqued your piece near the end of the cut, this can happen.

Personally, I do my calibration cuts with 6" square pieces; they're easier to keep square through the cut, I can use my eng square to check for perpendicularity and straightness with one tool. To each his own.

[peter gagliardi]

The key to the 5 cut method, is to cut/ square the largest piece available or you are comfortable with- this is what shows and amplifies how much you are off. I like to use a 1/2 sheet of ply if available, if not, no less than 3' . You will have to determine if your sliding table has any runout toward or away from the blade first though. A very long straightedge nested against the teeth of the blade in the center of the edge, then check distance to sliding table lip with a caliper front and back , and thru the travel.
Peter

[Jay Park]

Althought I'm pretty new to woodworking, I like the method shown in this video better than the 5 cut moethod to square the fence.


http://www.youtube.com/watch?v=tZM1OBcC6ok

[John Schweikert]

Not really understanding the question. I used the 5 cut method on my table saw sled. The first 4 cuts serve only the purpose of getting to the last cut which is all that matters. Measure the difference in width at each end on the 5th offcut (not the main piece) and divide by 4 and that's how much your 90 degree cuts are off by. For example, my 5th cut piece had a difference of just a 2 thousandths, so my error is a half of a thousandths. I can't do better than that on the first try, so I was set. There is an excellent youtube video that made it all quite clear: http://www.youtube.com/watch?v=UbG-n--LFgQ

[glenn bradley]

Althought I'm pretty new to woodworking, I like the method shown in this video better than the 5 cut moethod to square the fence.

Cool method but, just to show how different people react to different things. I feel the video method is quite a bit more tedious and fussy than the 5 cut method but, a great deal of that reaction is that I am used to the 5-cut and can square things up in just a few minutes. I'm a lot slower with a hand plane that a lot of folks so, fair is fair :).

The 5-cut relates the blade directly to the sled whereas the video assumes perfect alignment of blade and miter slots. While we all strive for that perfect alignment, aligning the fence to the miter slot path ignores the blade, and this could lead to some sub-optimal results despite a good dial indicator reading. The fence ends up wonderfully perpendicular to the slots. As long as the blade is true, you're good.

When chasing things in the hundredths of an inch, any introduction of an additional metric (the dial indicator to square to fence) can multiply your error or your attempt to correct same. My saw, is of course, perfect so, either method would work for me :D:D:D.

The fun and interesting parts about this forum are the many different methods and opinions. I am always learning something here.

[johnny means]

The last angle cut will show show the cumulative error off the first four. That's howyhe test works.

[Art Mann]

Althought I'm pretty new to woodworking, I like the method shown in this video better than the 5 cut moethod to square the fence.


http://www.youtube.com/watch?v=tZM1OBcC6ok

That is a clever method. However, it presumes that the person doing the calibration has a dial indicator at his disposal and that he has a square of known accuracy. There is also the problem of geometry. You really need a square that is 2 or 3 feet long because in the video, the person only measured the squareness of the last 6 inches or so of the fence. The fence itself is just presumed to be perfectly straight. That is really a leap of faith unless you have a calibrated machined straight edge to verify (you really need that anyway). If you already have a 2 or 3 foot square that is dead accurate, you don't need his method. You can just use the square aligned to the kerf on the sled to make adjustments. The five cut method does not require that you have a large high accuracy square or a dial indicator. It does require that you have a set of calipers (~ $10 at Harbor Freight). Also, the five cut method amplifies the error by a factor of 4 so as to reveal smaller errors. I like to use a test piece of 18" square because it increases the measurable compared to a 6 or 12 inch piece.

[Floyd Mah]

Is there any chance that your piece of wood isn't completely flat? The described method presumes that all the angles lie in the same plane.

[Bob Coleman]

This is probably your culprit. In reality, every corner should be out of square by a quarter of the error you measured on the 5th offcut. You've not actually squared anything, just measured that error. The first four cuts serve to make the side against the fence on the first cut non-parallel to the side against the fence on the fifth cut.

Other possible culprits: runout (as mentioned below), work not held firmly or held with a shear force so it slips mid-cut.

You can check how parallel the table is with a feeler gauge, a thin stick, whatever. Just compare the gap at the front of the slider to the gap once you've slid it all the way to the end of its travel or crosscut two sticks, one at each end and measure their length (although not being familiar with that type of saw, I may be wildly off base here).

[Rick Christopherson]

The problem is that the 1 --> 2 angle is not exactly square but the rest of them (2 --> 3, 3 --> 4, 4 --> 1) are. How can both these statements be true? None of them are square, but the error for any single cut is so small that you can't accurately measure it. That is the whole purpose of the process--it takes that really small error and amplifies it 4-times to make it within your ability to measure it.

Here is a picture of what the 4-cut method really does. (By the way, it shouldn't be called a 5-cut method because you already have your answer on the 4th cut, and all subsequent cuts after that are just redundant and will give the same result. The 5th cut (actually the 0-cut) was simply ensuring that you started with a board that had at least 1 straight edge, and that is actually a jointer operation.)

263893

Your first cut will be 1-times the error of the saw, but if you started with a board that was not square to begin with, this error could be that error too. But don't worry about starting with a square board. That gets eliminated, and you could start with any shape board as long as it has 1 straight edge to go against the fence for the first cut.

Each successive cut adds one more copy of the saw's error, so it will be 1x, 2x, 3x, and finally 4x the actual error. But as I said above, after the 4th cut, all subsequent cuts after that will remain at 4x the saw's error. So even your 100th cut will still have only a 4x error.

Here is a link to the 2-page PDF excerpt from the Festool Kapex manual I wrote. It fully explains how the 4-cut method works, and even includes a built-in calculator in case you want to know what the error-angle is. You wouldn't need the error-angle to adjust the saw, but it gives you a better idea whether you should adjust the saw or not.

http://www.waterfront-woods.com/festool/4-cut_pages.pdf

[Kev Coleman]

here is a link to an excellent video from William NG that explains the 5 cut method in great detail and also a great way of squaring up your sled.

http://wnwoodworkingschool.com/5-cuts-to-a-perfect-cross-cut-sled/

[Larry Fox]

The last angle cut will show show the cumulative error off the first four. That's howyhe test works.

Duh - this is it. I have not squared it, I have simply gotten it to the point where I can't measure the deviation from square on the other three sides and it is showing up on the 1 --> 2 side as that is where the 5th cut is made and is 4x the error.

Thanks everyone for the input - I was not thinking clearly.

[Von Bickley]

I have quit worrying about "Super Accuracy"..... If I make a cut on a board or piece of plywood, I will hold it up to my tri-square or framing square, and if I don't see light, it's close enough for me.

[Art Mann]

I'm with you Von. I think we can get too anal about accuracy. On the other hand, when I use my crosscut sled, I know the cut is good without ever picking up a square because I took the time to make it dead accurate and very stable in the first place. By the way, I have several framing squares but only one that is accurate enough for furniture work. I was surprised at how difficult it is to buy a framing square at a big box store that is actually square. I have compared several new ones right there in the store and they are not the same.

[Roy Wall]

here is a link to an excellent video from William NG that explains the 5 cut method in great detail and also a great way of squaring up your sled.

http://wnwoodworkingschool.com/5-cuts-to-a-perfect-cross-cut-sled/

Larry - this William Ng Video is superb! But it does take some tinkering to get it dead square..... not as easy as William Ng makes it.....he has serious skills!!

Shoot me a PM and let's catch up......long time been off the grid!!

[Phil Thien]

I'm with you Von. I think we can get too anal about accuracy. On the other hand, when I use my crosscut sled, I know the cut is good without ever picking up a square because I took the time to make it dead accurate and very stable in the first place. By the way, I have several framing squares but only one that is accurate enough for furniture work. I was surprised at how difficult it is to buy a framing square at a big box store that is actually square. I have compared several new ones right there in the store and they are not the same.

Add me to that list.

I've got good squares (including a trusted framing square for larger cuts). If they say the piece is square, that is good enough for anything I'm making.

[Larry Fox]

I seem to have it sorted out. Fiddled with it again today and was able to get it to just about 0 deviation on a 23x23" piece. This should be close enough for anything I will be doing. Others have mentioned squares - I recently bought 2 16"x12"-ish metal machinest squares and they come in VERY handy. Can't see any light at all on any of the corners. Thanks again for the time to look and respond.

[Metod Alif]

OK, it is not about 5 cuts. I cross-cut a straight piece of stock (parallel edges a must). Flip one piece and butt it to the other. If I get a straight alignment, I am good enough. I saw this idea mentioned in several places, it made sense, and I started using it.
Best wishes,
Metod

[Ole Anderson]

First problem I ran into with my track saw was making a good 90 degree crosscut on a piece that had already been ripped. Neither my carpenter or drywall square met the flip test. So I took a piece of 1/2" ply, prefinished one side, and cut it square on my sled, (which was previously shimmed to cut within a thousandth over 12" using the five cut method) added a fence and I had a sturdy guide I could square my track to. Went prefinished side down so I would slide easily on the unfinished ply. As stated, by measuring each end of the offcut on the fifth cut, you know your error on one cut is one fourth the difference.

[john bateman]

I have quit worrying about "Super Accuracy"..... If I make a cut on a board or piece of plywood, I will hold it up to my tri-square or framing square, and if I don't see light, it's close enough for me.

Try making a 6 sided box sometime, with all edges of all sides being beveled at 45 degrees so that no plywood edge shows. You will appreciate having dead-on crosscutting capability. http://diyspeakercabinets.com/images/002l.jpg

[Phil Thien]

Try making a 6 sided box sometime, with all edges of all sides being beveled at 45 degrees so that no plywood edge shows. You will appreciate having dead-on crosscutting capability. http://diyspeakercabinets.com/images/002l.jpg

I have made six sided boxes to conceal plywood edges.

First, let me say, I don't think your picture shows one, does it? That loudspeaker has four beveled corners, and front and back are fitted into a groove. And the rolled front profile makes me think it is vinyl-wrap (probably cut via a CNC-controlled beam saw), although hard to tell by the picture.

Let me point-out some possible issues w/ the 5-cut method:

First, in order for the five cut method to work well, there can be no (none, notta) slop between the sled's runners, and the miter slots on the table. Otherwise, you'll end-up chasing your tail (you may achieve a perfectly parallel cutoff on your final cut one instance, but the next instance you may get a cutoff w/ convergent lines). In this case. 001" of slop in those runners can throw the entire process off.

Second, the amount of movement required (of the fence) to get to these minute adjustments people are trying to achieve are not easy, especially when we're working w/ hardwood, plywood, and MDF.

Third, in order for this to work, your fence must be (and remain) dead-nuts flat. Otherwise you will get different results, depending on the side of your test piece.

Fourth, any error the user introduced by not placing the test piece perfectly against the flat, on just one cut, tosses off the results.

Fifth, blades (especially thin kerf) can deflect during the cut. And they don't always deflect the same direction. Differences in material thickness, and blade tilt, can effect the deflection of the blade.

Sixth, many saws, due to their trunion design, may introduce geometry problems when you tilt the blade. This can be adjusted-out on many cabinets saws by shimming the table to the cabinet, but not many people do this.

I use a plastic triangle to check my cuts. I was making some wrapped-up subwoofer boxes yesterday, and they wrapped-up perfectly (this is sort of a five-cut method, if you think about it).

To get there, I did have to make an adjustment or two to my fence after tilting my blade to 45-degrees. I made a couple of test cuts while adjusting my fence, and was able to dial it in perfectly.

I find that, for me, this results in far more precise output from my saw.

[john bateman]

more info
I have made six sided boxes to conceal plywood edges.

First, let me say, I don't think your picture shows one, does it? That loudspeaker has four beveled corners, and front and back are fitted into a groove. And the rolled front profile makes me think it is vinyl-wrap (probably cut via a CNC-controlled beam saw), although hard to tell by the picture.

Actually that is walnut veneered mdf which I cut on my tablesaw. The front has a solid piece in order to put a round profile on it. But the other 5 sides are all beveled. It doesn't take much misalignment to get a box where none of the corners will come together tightly. And the box plus the baffle board must be very square or the joinery will look quite poor...maybe .01" out of square looks terrible. But my earlier post was in response to the guy who just holds a framing square against the cut and moves on. http://diyspeakercabinets.com/images/650l.jpg

[Chris Fournier]

Your point is well taken John, sometimes perfect is "good enough". I've made similar items and there really isn't room for error is there. Very nice work!