5-cut method misconception

***The below is referring to the 5-cut method of squaring a table saw sled fence to 90 degrees.
Unless I am mistaken, it is a misconception to think that the 5-cut method squares your table saw blade to the sled fence. What it really does is squ are your fence to 90 degrees of the direction of travel (miter track). If the blade was angled by a small amount the process would still align the fe nce 90 degrees to the direction of sled travel.
If the table saw blade were a cutting laser projecting 90 degrees to the ta ble, the 5-cut method would still work. Because this is true, the thought that the 5-cut method squares your fence 90 degrees to a blade can not be t rue.
Am I missing something? I know it's picky but it makes me cringe when peop le make that claim.
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On 10/2/2013 8:25 AM, snipped-for-privacy@garagewoodworks.com wrote:

What it really does is square your fence to 90 degrees of the direction of travel (miter track). If the blade
was angled by a small amount the process would still align the fence 90 degrees to the direction of sled travel.

Because this is true, the thought that the 5-cut method squares your fence 90 degrees to a blade can not be true.

I have always questioned the 5-cut process. If the blade were not parallel to the fence. the blade would cut a wider kerf.
Once the angle between the blade and fence became large enough I suspect there would be problem.
Has any body tried to measure the parallelism by measuring the width of the teeth on the blade, to the width of the kerf?
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On Wednesday, October 2, 2013 8:35:37 AM UTC-4, keith snipped-for-privacy@sbcglobal.net wrote:

I assume you mean perpendicular and not parallel.

Exactly. Analogous to a fatter or skinnier cutting laser. The process does NOT consider the squareness of the blade to the sled fence. Only that the process involves cutting.

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** Should have read:
It only matters that the process involves cutting.
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On 10/2/2013 9:10 AM, snipped-for-privacy@garagewoodworks.com wrote:

Basic geometry:
Parallel lines never meet. ||
Perpendicular lines met at a 90 degree angle _|
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On 10/2/2013 7:35 AM, Keith Nuttle wrote: ...

That would also add any runout in the blade/spindle to the indication of misalignment.
--


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On 10/2/2013 7:25 AM, snipped-for-privacy@garagewoodworks.com wrote:

Your thoughts are mostly correct. With the assumption that the saw is set up precisely to begin with, the 5 cut works for squaring the miter fence to the blade "ONLY" if the blade is parallel to the miter guide slot to begin with. It does this by squaring the miter fence to the direction of travel, therefore the blade is square to the miter fence also.
If you blade is parallel to the miter slot to start with it works, if not it does not.
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On 10/2/2013 9:10 AM, Leon wrote:

You are supposed to square the blade to the miter slot first.
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On 10/2/2013 1:02 PM, Just Wondering wrote:

Yes you are but some don't realize this.
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For most people, words are simply a way of *relating* to ideas, not *defining* them. As long as the right idea is communicated, communication has happened successfully.
Perhaps they mean "[...] the cut made by your blade by moving the sled along the miter slot" but abbreviate it to "[...] the blade" because everyone's blade is true enough that it doesn't matter?
Also, to true the blade to the cut it makes, I cross-cut some hardwood and inspect the teeth marks in the wood, to make sure I have as deep marks from both "front teeth cutting down" and "back teeth cutting up". Just an FYI aside :-)
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On Wednesday, October 2, 2013 11:31:30 AM UTC-4, DJ Delorie wrote:

I only wish that were true. There is a common misconception that is quite wide spread (in my encounters w/ folks discussing alignment) that the 5-cut method aligns the fence with the blade to 90 degrees.
A common criticism that I receive from folks when I discuss using a dial in dicator and a square to align a sled fence to 90 (see link below for an exa mple in the comments) is that the 5-cut method is superior BECAUSE it align s the fence to the blade while the dial indicator only aligns the fence to the miter track. While their logic is flawed as discussed in my original p ost, it is also flawed in other ways as well. Assuming they are correct, t hey would still need to have a blade aligned with the miter track regardles s.
See here:
http://www.youtube.com/watch?v=YTlpY_chcio

Alignment method is at 5:30. See first comment.

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On 10/2/2013 10:41 AM, snipped-for-privacy@garagewoodworks.com wrote:

I see two things that can introduce error.
1. If you square is not square.
2. And what ever threw your fence out between squaring it and locking it in place.
Food for thought for your next sled, In-Line Industries makes a cross cut sled called the Dubby. I have been using both a left and right hand for 14+ years with great results.
FWIW Rockler has attempted to copy the design but falls short.
I think if one was spartan enough he could duplicate the Dubby and save a couple hundred dollars.
The Dubby sled fence adjusts a lot like your fence did for squaring purposes. The Dubby fences adjusts so that you can have an infinite number of miter angles. The Dubby also has a fixed back stop with an adjustment screw to square and insure the fence returns square after cutting an angle.
Additionally the Dubby sled is extremely accurate at setting angles, it has a stainless steel angle gauge that runs along the edge of the sled to align with the front of the fence. The fence moves an average of 1/4" between each degree marker so setting the fence to a specific degree mark is going to get you dead close to perfect with out effort.
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On 10/2/2013 3:21 PM, Leon wrote:

to zero it out after making a dead on square cut and getting the stop set.
--
Jeff

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On 10/2/2013 10:31 AM, DJ Delorie wrote:

If you see tooth marks on the front and back of the cut you need a better blade. Tooth marks on a crosscut is something I DO NOT tolerate I barely tolerate them on a rip. ;~)
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Normally true, except I use a magnifier to see them. Which just makes them more accurate as a means of squaring ;-)
I suppose you could keep a cheap blade around just to square the blade to the table! :-)
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On 10/2/2013 4:51 PM, DJ Delorie wrote:

I doubt you would see tooth marks with a magnifier, except perhaps a microscope, with the cuts I am getting when cross cutting. ;~)

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You are correct but even if the blade is out of square a bit or perfectly square at some position but has runout so it is not square at other positions, it just cuts a wider kerf but results in a square cut so you end up in the same place.
I think typically people would first align the top to the blade (you usually move the top, not the blade\trunnion) using some prescribed method (usually a dial indicator). Then the 5 cut can give you a quick way to line up fences\accesories.
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