Abusing a Dado Blade Set for Box/Finger Joints? - Woodworking Talk - Woodworkers Forum
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post #1 of 21 Old 02-18-2018, 05:00 PM Thread Starter
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Abusing a Dado Blade Set for Box/Finger Joints?

There is an active thread about the correct joint for boxes. I recommended a box joint (finger joint), but it got me thinking. Here is the original thread:

http://www.woodworkingtalk.com/f2/joint-194449/

My first box joint was made with a Forrest Woodworker II blade. The problem with using the Woodworker II blade for box joints is that the blade makes alternate top bevel (ATB) cuts, which leave a V-shaped groove at the top of the "slots." (You could sand or file them, but that's a lot of work. Better to use a blade with a flat bevel on top.)

I have a Freud SD208 "professional" dado set. The Freud dado set cuts flat on top, of course. That is what it is designed to do. The narrowest dado cut that it can make is 1/4 inch, which is twice as wide as the regular Woodworker II blade. It would be nice to have a narrow-ish flat bevel blade for box joints.

Here are my questions:

1. What bad thing happens if I use only one of the two outer blades alone? Freud specifically says not to do that in their instructions. Why would they say that? Is it lawyers? ... or ... Is there a real, genuine safety reason to avoid using only one of the two outer dado blades by itself?

2. If you were to use only one of the two Freud blades (see question #1, above), which one would you choose? The inner blade (the blade that normally goes closest to the motor)? The outer blade (the blade that normally goes closest to the arbor nut)? Does it matter?

3. Can you safely reverse the order of the two outer blades to get a wider box cut without involving chippers, shims, etc.?

4. What is the difference between my two SD208 outer blades, and the two blades that come with Freud's SBOX8 box joint cutting set, if any? Can I use my dado blades the same way that I would use the SBOX8 box joint blades?

P.S. Yes, I know that the outer dado blades leave a tiny "score" along the edges, to help prevent chipout.

Last edited by Tool Agnostic; 02-18-2018 at 05:17 PM.
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post #2 of 21 Old 02-18-2018, 06:27 PM
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Dado stacks dont cut perfectly flat bottoms. Not the outside ones, at least. Look at the teeth, every other one will be beveled, just all in the same direction. You might try getting a ripping blade, those are usually flat teeth

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post #3 of 21 Old 02-18-2018, 06:39 PM
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I found a Freud FTG - but it's 10" x 24 tooth - might demonstrate way too much tear out on a cross cut unless you back up every joint.

I also have a 10 x 30 tooth triple ground - oddly it does not do a perfectly square corner tho.
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post #4 of 21 Old 02-18-2018, 07:09 PM Thread Starter
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Quote:
Originally Posted by epicfail48 View Post
Dado stacks dont cut perfectly flat bottoms. Not the outside ones, at least. Look at the teeth, every other one will be beveled, just all in the same direction. You might try getting a ripping blade, those are usually flat teeth
Yes. I could buy a blade with flat teeth, but I would prefer to use the blades I already have, if they will work.

I did look at the teeth on the outer blades before I posted. You're right - they alternate between bevelled and flat. One blade is beveled left, then flat; the other blade is beveled right, then flat.

I would like to try out a single dado blade to see what kind of cut it makes. My guess is that it will be mostly flat, with a tiny edge groove where the bevel sticks up to reduce tearout.

The question is:

Is it safe to run only one outside dado blade by itself? Why does Freud tell you not to do it?
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post #5 of 21 Old 02-18-2018, 07:14 PM
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there is no danger .....

You can use just one blade, BUT each blade has an orientation based on the bevel direction or offset of the teeth. There are two ways to orient the blades ... bevel sides in or bevel side out. In this link the "graphics" indicates which way to face the blades. You get a 1/4" wide groove one way and a 3/8" wide groove the other way. There's no danger in using just one blade, but it will serve no purpose for making box joints.
http://www.freudtools.com/admin/manuals/SBox-8.pdf

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post #6 of 21 Old 02-18-2018, 08:01 PM Thread Starter
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Quote:
Originally Posted by woodnthings View Post
You can use just one blade, BUT each blade has an orientation based on the bevel direction or offset of the teeth. There are two ways to orient the blades ... bevel sides in or bevel side out. In this link the "graphics" indicates which way to face the blades. You get a 1/4" wide groove one way and a 3/8" wide groove the other way. There's no danger in using just one blade, but it will serve no purpose for making box joints.
http://www.freudtools.com/admin/manuals/SBox-8.pdf
The instructions (for the box joint set) in the link above say the same thing as the instructions for the dado set, "Always use both blades." but they don't say why.

Okay, why does Freud say, "Always use both blades"? That's true for the Freud SBOX8 miter joint set and the Freud SD208 dado set that I have.

As long as there is no danger to use one blade, I don't mind giving it a try to see what the top of the kerf looks like. I just want to be sure it is safe. I still don't know why Freud warns you not to do it.
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post #7 of 21 Old 02-18-2018, 08:10 PM
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it's fake news...kinda

All that will happen is your saw kerf will have "ears" facing left or right, if I remember my Freud box blades correctly.
Like these:



Infinity blades are flat top, with no bevels:

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #8 of 21 Old 02-18-2018, 08:54 PM
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For future reference, the Forrest Woodworker II is also available in a special grind with 8 flat teeth that leaves a flat bottom groove. They are harder to find, but when you find it the cost will be the same as the standard Woodworker II.


In woodworking there is always more then one way to accomplish something.
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post #9 of 21 Old 02-18-2018, 11:28 PM
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You can use just one blade, but not one blade and a chipper.

The two outside blades that come with most stacked dado sets have beveled teeth alternating with flat topped teeth. The beveled teeth cut the shoulder of the dado. The chipper is designed to cut only the bottom of the dado not the shoulder, don't think I would want to trust a 1/16" thick strip of steel flying around anywhere near to me.

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post #10 of 21 Old 02-19-2018, 07:08 AM
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I did this exact thing with the box I just built. Only problem was that it didn't make as clean of a cut as I would have liked...but I'm guessing it was due to a dull blade rather than the type of blade.
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post #11 of 21 Old 02-24-2018, 11:42 AM Thread Starter
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I used Freud's contact form on their website, and I sent them the same four questions that I wrote in my original post above:
Quote:
Originally Posted by Tool Agnostic View Post
[...] Here are my questions:

1. What bad thing happens if I use only one of the two outer blades alone? Freud specifically says not to do that in their instructions. Why would they say that? Is it lawyers? ... or ... Is there a real, genuine safety reason to avoid using only one of the two outer dado blades by itself?

2. If you were to use only one of the two Freud blades (see question #1, above), which one would you choose? The inner blade (the blade that normally goes closest to the motor)? The outer blade (the blade that normally goes closest to the arbor nut)? Does it matter?

3. Can you safely reverse the order of the two outer blades to get a wider box cut without involving chippers, shims, etc.?

4. What is the difference between my two SD208 outer blades, and the two blades that come with Freud's SBOX8 box joint cutting set, if any? Can I use my dado blades the same way that I would use the SBOX8 box joint blades?
Here is Freud's response:
Quote:
Originally Posted by Freud Tools
It would be dangerous to use either outside blade alone or in the reverse orientation, they must be used as a pair in the correct order. Additionally if you could use one you would not like the results. It would make a very unattractive joint. If you want a wider joint than then you should use shims, spacers, or chippers to get the width you want. I would however strongly recommend the SBox8 for box joints and here is why. The SD208 is designed to cut in a wide range of applications both with the grain and against the grain. The reason it does this so well is the way it is ground with a slightly higher bevel tooth that cleanly severs the cross grain of the wood. The bad thing is it leave a small cut in the corners of the groove. While on dadoes that is not a problem it is in box joints unless what you are making is more utilitarian or will not be seen much as in a drawer box. The SBox8 will produce a clean square cut. Also the tooth geometry is designed to give you the cleanest cut in the end grain of the wood. Box Joints are never cut across the grain because they would have no strength.
The response came from "Jim" at Freud. I wish he had explained why it would be dangerous to try a single blade, just to see what the kerf pattern looks like.

I get that a box joint may not look good enough for my interests. The kerf pattern might be "weird."

-> Can someone please explain why using a single dado blade to make a non-through cut on the table saw would be dangerous?

-> Can someone please explain why reversing the order of the two main dado blades on the arbor to make a similar cut would be dangerous?
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post #12 of 21 Old 02-24-2018, 03:00 PM
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Quote:
Originally Posted by Tool Agnostic View Post

-> Can someone please explain why using a single dado blade to make a non-through cut on the table saw would be dangerous?
Because then they wouldn't get to sell you their fancy new ultra 1/8" box joint blade. Probably legal speak too, all the testing has only been done that one specific way so any other forms of use are automatically dangerous. As has been pointed out, there's not really any difference between a dado chipper blade and any other blade

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post #13 of 21 Old 02-24-2018, 07:39 PM
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the outside blades are different from ordinary saw blades

Read this article and see if you don't agree that there is a right side and a left side outside blade because they have left and right facing bevels on their respective outside faces. They are marked to orient them on the right or left side respectively.
Read the "What you get" paragraph:
http://www.table-saw-guide.com/dado-saw-blades.html

Setting up the stack:
https://youtu.be/EZAa2-bimmQ?t=140

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

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post #14 of 21 Old 02-25-2018, 09:39 AM Thread Starter
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Quote:
Originally Posted by woodnthings View Post
Read this article and see if you don't agree that there is a right side and a left side outside blade because they have left and right facing bevels on their respective outside faces. They are marked to orient them on the right or left side respectively.
Read the "What you get" paragraph:
http://www.table-saw-guide.com/dado-saw-blades.html

Setting up the stack:
https://youtu.be/EZAa2-bimmQ?t=140
I read the article and watched the video. To be honest, they did not teach me anything I didn't know already.

The open questions are: Why does Freud say that it is dangerous to using one dado blade only? and Why does Freud say that it is dangerous to reverse the order of the two dado blades on the arbor?

I like @epicfail48's guess the best:
Freud probably didn't test those configurations. Since Freud didn't test those configurations, they must warn customers that it could be dangerous to avoid any potential liability.
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post #15 of 21 Old 02-25-2018, 10:05 AM
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Why it is dangerous ......

Quote:
Originally Posted by Tool Agnostic View Post
I read the article and watched the video. To be honest, they did not teach me anything I didn't know already.

The open questions are: Why does Freud say that it is dangerous to using one dado blade only? and Why does Freud say that it is dangerous to reverse the order of the two dado blades on the arbor?

I like @epicfail48's guess the best:
Freud probably didn't test those configurations. Since Freud didn't test those configurations, they must warn customers that it could be dangerous to avoid any potential liability.
The manufacturer must put all the warnings possible in their instructions for all sorts of potential liability issues. Why would it be dangerous to use just one blade? ..... for the reason I suggested. The blades have different outfacing bevel teeth, one blade to the right, one to the left. To cut with a single blade with outfacing bevels "might" have a tendency to favor that side in feeding and throw the work sideways to the "no bevel" side. This could result in a kickback, hence the danger. Best to contact Freud if this issue really stumps you.

OR if you are brave enough, just mount up one blade, set the fence and see what happens.... Don't say I "advised" you to do this, it was a suggestion made in jest. I'm sure you have other blades to use if you need to make a single width kerf.

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #16 of 21 Old 02-26-2018, 09:49 AM Thread Starter
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Quote:
Originally Posted by woodnthings View Post
The manufacturer must put all the warnings possible in their instructions for all sorts of potential liability issues. Why would it be dangerous to use just one blade? ..... for the reason I suggested. The blades have different outfacing bevel teeth, one blade to the right, one to the left. To cut with a single blade with outfacing bevels "might" have a tendency to favor that side in feeding and throw the work sideways to the "no bevel" side. This could result in a kickback, hence the danger. Best to contact Freud if this issue really stumps you.

OR if you are brave enough, just mount up one blade, set the fence and see what happens.... Don't say I "advised" you to do this, it was a suggestion made in jest. I'm sure you have other blades to use if you need to make a single width kerf.
I did contact Freud, and posted their reply above. I had already planned to risk my life and perform that dangerous single blade test. I chose not to announce it. I ran the tests yesterday, and learned a few things:

* As we know, the carbide blade tips overlap each other in a two-blade dado pack, which is the minimum recommended use of the Freud SD208 dado set. The overlap occurs between the two blades. One function of the overlap is to allow a proper cut even if a shim is between the blades.

* Observe that the carbide tips on inner blade (closest to the motor) stick out sideways from the blade plate (body), toward the arbor nut. The carbide tips on the outer blade stick out toward the motor.

* If you try to mount the outer blade on the inner part of the arbor, closest to the motor, the carbide tips will stick out toward the motor and the blade will not turn because of interference between parts in the saw itself and those protruding carbide tips. This means that you cannot make cuts with the outer blade only or with the inner and outer blades reversed in position.

* The only tests I could run were with the normal two-blade dado stack and a cut with the inner blade only. Freud has stated that running the inner blade only is dangerous. In the interest of science, I ran the test anyway. I will post photos of the test setup in this post, and photos of the results in the next post. Here are my photos of the test setup:

* Two Blade Setup 1: This is a normal two blade dado stack in the saw.
* Two Blade Setup 2: This photo shows the angled bevels and flat rakers in the two blade dado stack. Observe how the bevels alternate. (If I had to do it again, I would pay better attention to the bevels and rakers, so that they alternate, instead of bevel, bevel, raker, raker as shown in the photo.) Also note how the carbide tips on the outer (right) blade protrude toward the left. They stick out far enough to bump into the saw parts to the left of the blade, preventing the outer blade from turning at all if mounted alone or in a "reversed stack."

* One Blade Setup 1: This is the inner blade alone. WARNING: Freud says that this is dangerous!!
* One Blade Setup 2: You can see the alternating bevel and raker carbide tips on this inner blade alone. The bevels point in only one direction.
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post #17 of 21 Old 02-26-2018, 10:34 AM Thread Starter
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On behalf of the members of Woodworking Talk and in the interests of furthering scientific knowledge, and despite the incredible, death-defying danger, I ran the single blade test. IMPORTANT: Freud has issued warnings that it is dangerous to make cuts with a single dado blade.

RESULTS:

Here are the results of my tests on a piece of scrap wood. See the photos:

* Dado Grooves Side: You can see the "bat ears" that come from the bevels. The wider cut on the right was made with the standard two-blade dado stack, the narrower cut on the left was made with the inner dado blade alone (WARNING: Dangerous!!). You can see the single "bat ear" on the left side of the cut.
* Dado Grooves Top: A top view of the two dado grooves.
* Two Blade Dado Closeup: A closeup of the two blade dado groove.
* Single Dado Closeup: A closeup of the single blade cut.

Freud warns uses that running a single blade from a dado set is dangerous. I observed the following as I mounted the single dado blade on my table saw, in anticipation of this dangerous cut:

* The chirping birds in the yard all went completely silent.
* The dog hid under the couch.

Interestingly, the dado groove is not a perfect 1/4 inch. It is close, but not exact. The groove width varies slightly from measurement to measurement. I used cheap SPF wood for the scrap; it tears out easily - the grain is, well, grainy.

Here are my best measurements for groove width:

Two Blades:
6.0 mm = 0.236 inches

One Blade:
5.2 mm = 0.204 inches

CONCLUSIONS:

* The cuts worked as expected. The dado blade(s) left "bat ear" scores on the bottom edges of the grooves. You can see them in the closeup photos.
* The "outer" dado blade's carbide tips protrude far enough that they touch some of the saw's parts on the "inner" side, which prevents the blade from rotating in my Bosch REAXX table saw. At least for my table saw, you cannot use the "outer" dado blade alone, or the dado set in a reverse arrangement. (I wonder whether Freud's SBOX8 box joint blade set will rotate on my saw when configured in the wider reversed blade order, which is an approved configuration.)
* I survived the dangerous cut with a single dado blade, without injury. I felt that there was no apparent danger, despite the warning from Freud.
* I cannot recommend that you use a single inner dado blade in this dangerous configuration. Speaking only for myself, I would use the blade in this configuration for my own production work if I found a use for it.

* I observed that wild and domestic animals cower in fear whenever I install a single dado blade in the table saw.

* Further testing is required. I need to make real box joints to see for myself how the "bat ears" will affect the look of the box joints. I assume it will be very much better than the Forrest Woodworker II blade, which has an alternating top bevel (ATB) grind. The question is whether it is satisfactory enough for my skill level and needs. I will post the results of my box joint tests here in this thread, but don't wait for it. It will take some time before I can get around to it.
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post #18 of 21 Old 02-26-2018, 10:42 AM
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As I suggested and suspected ....

QUOTING:

* Observe that the carbide tips on inner blade (closest to the motor) stick out sideways from the blade plate (body), toward the arbor nut. The carbide tips on the outer blade stick out toward the motor.

In the case on your particular saw... make, model unknown.... you would have a physical interference issue with "part of the saw", hence the danger warning from Freud. On my saws, older Craftsman , I don't have that issue.
I am still curious as to the feeding issue, whether it will favor the non-bevel side and move away from the fence, BUT I don't care enough to try it myself as I won't be using a single dado blade for any projects in my shop. Kudos to you for risking your life and scaring the wild animals back into hybernation.

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #19 of 21 Old 02-26-2018, 11:14 AM Thread Starter
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Quote:
Originally Posted by woodnthings View Post
QUOTING:

* Observe that the carbide tips on inner blade (closest to the motor) stick out sideways from the blade plate (body), toward the arbor nut. The carbide tips on the outer blade stick out toward the motor.

In the case on your particular saw... make, model unknown.... you would have a physical interference issue with "part of the saw", hence the danger warning from Freud. On my saws, older Craftsman , I don't have that issue.
I am still curious as to the feeding issue, whether it will favor the non-bevel side and move away from the fence, BUT I don't care enough to try it myself as I won't be using a single dado blade for any projects in my shop. Kudos to you for risking your life and scaring the wild animals back into hybernation.
It is a Bosch REAXX jobsite table saw.

I would accept your explanation, except that the inner blade won't interfere with the saw, and obviously won't interfere with any table saw that supports this dado set (Freud SD208) at all. I doubt that Freud bothers to distinguish between the two blades when Freud writes the warnings.

I wonder whether the interference on my Bosch REAXX table saw is a real problem for Freud's SBOX8 two blade box joint set when it is configured in the reversed, wider configuration. I suspect that the carbide tips on the "outer" blade would interfere in the same way. I will never know, unless I feel a strong need to buy a box joint blade set, and I might buy one from a different manufacturer anyway.

I used the miter gauge and pushed the thin piece over the dado blades like a crosscut. I did not notice anything unusual about how it fed, but it was a thin piece of scrap. For a box joint, that is how I would cut it, with a box joint jig clamped to the miter gauge.

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post #20 of 21 Old 06-09-2019, 04:50 PM
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Looks like you got the desired .236" kerf

Quote:
Originally Posted by Tool Agnostic View Post
On behalf of the members of Woodworking Talk and in the interests of furthering scientific knowledge, and despite the incredible, death-defying danger, I ran the single blade test. IMPORTANT: Freud has issued warnings that it is dangerous to make cuts with a single dado blade.

RESULTS:

Here are the results of my tests on a piece of scrap wood. See the photos:

* Dado Grooves Side: You can see the "bat ears" that come from the bevels. The wider cut on the right was made with the standard two-blade dado stack, the narrower cut on the left was made with the inner dado blade alone (WARNING: Dangerous!!). You can see the single "bat ear" on the left side of the cut.
* Dado Grooves Top: A top view of the two dado grooves.
* Two Blade Dado Closeup: A closeup of the two blade dado groove.
* Single Dado Closeup: A closeup of the single blade cut.

Freud warns uses that running a single blade from a dado set is dangerous. I observed the following as I mounted the single dado blade on my table saw, in anticipation of this dangerous cut:

* The chirping birds in the yard all went completely silent.
* The dog hid under the couch.

Interestingly, the dado groove is not a perfect 1/4 inch. It is close, but not exact. The groove width varies slightly from measurement to measurement. I used cheap SPF wood for the scrap; it tears out easily - the grain is, well, grainy.

Here are my best measurements for groove width:

Two Blades:
6.0 mm = 0.236 inches

One Blade:
5.2 mm = 0.204 inches

CONCLUSIONS:

* The cuts worked as expected. The dado blade(s) left "bat ear" scores on the bottom edges of the grooves. You can see them in the closeup photos.
* The "outer" dado blade's carbide tips protrude far enough that they touch some of the saw's parts on the "inner" side, which prevents the blade from rotating in my Bosch REAXX table saw. At least for my table saw, you cannot use the "outer" dado blade alone, or the dado set in a reverse arrangement. (I wonder whether Freud's SBOX8 box joint blade set will rotate on my saw when configured in the wider reversed blade order, which is an approved configuration.)
* I survived the dangerous cut with a single dado blade, without injury. I felt that there was no apparent danger, despite the warning from Freud.
* I cannot recommend that you use a single inner dado blade in this dangerous configuration. Speaking only for myself, I would use the blade in this configuration for my own production work if I found a use for it.

* I observed that wild and domestic animals cower in fear whenever I install a single dado blade in the table saw.

* Further testing is required. I need to make real box joints to see for myself how the "bat ears" will affect the look of the box joints. I assume it will be very much better than the Forrest Woodworker II blade, which has an alternating top bevel (ATB) grind. The question is whether it is satisfactory enough for my skill level and needs. I will post the results of my box joint tests here in this thread, but don't wait for it. It will take some time before I can get around to it.
Quote Post 17 above:

* Two Blade Setup 1: This is a normal two blade dado stack in the saw.



The thread started by RickKr was in search of that .236" dimension:
https://www.woodworkingtalk.com/f2/f...9/#post2058385

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

Last edited by woodnthings; 06-09-2019 at 04:59 PM.
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