The Dado Blade of the Router Bit World

The router table has always been particularly good for cutting a groove, particularly in smaller items (such as making boxes).  The orientation of the blade to the timber for one, the diameter of the blade (vs a tablesaw), the speed of the cutter, the accuracy in setup.

The one frustration I have found is having to accept the width of the groove is limited to the width of the cutter of the router bit, or having to take multiple passes.  Unlike a tablesaw, the concept of a dado blade is foreign to the router table.

Well until now that is. have available a really interesting router bit indeed from Amana Tool.  It is an EZ Dial Slot Cutter, and unlike a tablesaw dado blade stack, this router bit does not have shims, or even need to be taken apart and reassembled.

EZ Dial Router Bit

EZ Dial Router Bit

Looking at the anatomy of the router bit, from the top-down.  The top threaded section is the range of adjustment of the router bit, and there are two types available – a 1/8″ – 1/4″, and a 1/4″ – 1/2″.  Next is the locking nut – once the width of the slot is set.  The knurled knob is the adjustment for the router bit, and is then locked in position with the locking nut.

The blade is next – it is a four-flute router bit, but because of the adjustment, each side of the trench is cut with two of the flutes.  As the knurled adjustment knob is turned, two of the flutes move with the knob, and the other two remain fixed.

A bearing then sits under the flutes – useful when following curves, and other times a router fence is not in use.  Just below that is a section with two flats – this is useful if the locking nut is too tight – a spanner can be fit on this section so it can be undone without having to risk damage to the router chuck or shaft lock.

Finally, the shaft is a finely finished, accurate 1/2″ shaft.  (An inaccurate shaft is either difficult to fit the router collet if too large, or at risk of slipping if too small).

Variable slots

Variable slots

I was working with the 1/8-1/4″ router bit, but the concept is the same.  In the above image, the two opposite flutes move, the other two are fixed.  That dial-in adjustment is remarkably liberating.  Being able to set the width of the resulting slot to accurately match the material that will fit in it (whether that be another piece of timber, a sheet of glass etc), and also easy to add an accurate amount of clearance if required.

The quality of the router bit is obvious, as is the finish that is achieved.

55500-cNot only can the width of the slot be set, but it can be adjusted with the router bit fixed in the router. (So long as you intend to remove more material – too hard to put material back!) Rather than trying to work out the range to move the router up and down again, a test cut or two, a dial-in of width, and your accuracy and flexibility of the table is increased dramatically.

Once you experience the convenience of a shim-less, dial in width of slot for a router bit, you’ll be wishing a tablesaw dado blade was as easy, as infinitely adjustable, and as accurate.

Available from


Groove is in the Heart(wood)

The dado blade (or dado set) can be a particularly accurate tool when it is understood correctly.  With a combination of spacers and shims, a dado (or groove) of very precise width and depth can be cut in a single pass.  Unlike a router bit producing a groove, the size of the stock to fit that groove does not have to match the router bit, nor do you have to make multiple passes to get to the required width, or depth.

The tablesaw is also much more suitable for processing large amounts of stock, and long lengths.


Electroblu Dado Blade

The dado set I have been using recently is this one from Amana Tool (through  It is an 8″ dado set, with a 5/8″ bore.  The bore accurately matches the arbor of my tablesaw, so I don’t have to try to juggle washers for each blade and spacer, and means the blade set will produce a more accurate and flat-bottomed groove.  It has most recently also been upgraded to have the environmentally-friendly Electroblu coating, which help mitigate heat buildup during the cut (which has an adverse affect on accuracy – the more heat, the more the blade can warp.  This then results in more runout and therefore a change to the effective width of the cut.)

Click here to see the blade at  Don’t worry that the blade is not blue – the photo has not been updated yet to include their latest coating that is now standard on their blades.


Dado Stack Set

It is a particularly nice set, with four 1/8″ spacers and one 1/16″ spacer (or chippers), and a set of shims of various widths.  The outside blades (which must always be used for every cut) are dedicated left and right (as is normal for dado sets).  The blades are not ATB – they are either bevelled left, or right only (depending on which blade it is), with every 6th tooth being flat ground.  They each have two teeth missing – this allows a place for the chipper blade to rest, so that the carbide teeth can overlap without knocking into each other.  The flat ground teeth result in square corners at the bottom of the groove.  Many other dado sets leave a telltale triangle cutout, where the bevel cuts deeper than the chippers.


Inner edge of outside blade

An interesting feature of the outside blades is a raised section on the inside, effectively increasing the thickness of the blade, and when not using any chippers or shims means the two outer blades can rest against each other, again without the carbide teeth impacting.


Chipper Blades

This particular dado set has only 2 tooth chipper blades.  This may seem a disadvantage (the general principle is the more teeth a blade has, the finer the cut), but the chipper blades don’t impact the side of the cut, where smoothness really counts.  Chippers only remove the material in the middle of the groove, so they only touch the bottom of the cut, and with a combination of the quality of the carbide, the angle of the grind and these chippers leave a very smooth finish.  The other really important aspect is the chipper blades have to be exactly the same diameter as each other, and the outside blades.  This leaves a flat-bottomed groove.  If one is over (or under) sized, it leaves a step in the groove base.


Dado Stack

As you stack the dado set, you stagger the individual blades so that the carbide teeth have no chance of pressing on each other.  Other than risking damage to the teeth, if they are pressing on each other, they will distort the effective width of the dado stack.  When using shims, you need to space them out between each of the blades used.  It is a good idea to put the thinnest ones nearest the arbor washer & nut.  That way it is easier to change the finest shims to fine tune the effective width of the stack.  When measuring the width of the blade stack, you cannot simply add up all the width of the components.  The amount of runout of the two outside blades (in particular) (and to a lesser degree, the runout of the chippers) needs to be added to the final width, as does the runout of the tablesaw itself.

This can be determined by trial and error.  Set up the stack for a certain width of cut (adding together the kerf of the outside blades, the chippers and spacers used).  Perform a cut, and measure the result.  This will give the actual width of the cut, and the difference between the two is the runout of the stack and tablesaw combined.


Zero Clearance

Despite the fact I have a 10″ tablesaw, an 8″ dado blade set is more than enough.  There are a number of reasons for this: Unlike a normal blade, the dado set is only ever for cutting a groove (and more often than not, no more than 1″ deep).  There is therefore no need to incur the extra expense of a larger blade.  A dado set is already much heavier than a single blade, and can really push the limits of the saw motor just to get it up to speed, let alone maintain that speed during a cut.  A larger blade has significantly more bulk and mass, and can exceed your saw’s capacity to spin it up.  The benefit of this set, is those 2 tooth chippers have a lot less bulk than other chippers, so this also helps deal with the overall bulk of a dado set.  The other thing is that a dado blade really does not need anywhere near the depth of cut of a standard blade.  It is for cutting grooves, not cutting workpieces in twain.

As far as how this blade performs, it is excellent – but you’ll have to see the associated video (which I am working on) to see the result.  Needless to say, I had a precisely cut dado that absolutely matched the board I was inserting, so the friction fit was beautifully tight.

To get that precision, I took the typically supplied notes on the various combinations of blades, chippers and shims to achieve a standard set of widths, and threw them out the window.  Instead, I came up with a comprehensive set of every single combination possible, in order of increasing width, so I can exactly choose what combination to start with to match the board I am inserting into the resulting groove.  Instead of having about 24 combinations that were provided, my list is just over 3000 combinations.  And because I have it in Excel, it is easy for me to add in the runout of the blades and tablesaw to end up with even more precision.

Out of interest, I have attached the full list below (and below the smapshot of part of the table)


Snapshot of a few rows of the table

Dado Set Combination pdf

The Dado set by Amana Tool, from is a worthy version, and well worth considering when looking for a dado set for your workshop.  When the video comes out, you will see just how precise a dado set can be!

The Secret Language of Saw Blades

Ever gone to purchase a sawblade and wondered just what all the codes are engraved on the side (or printed on the packaging)?

There are a surprising number of variables that are possible with saw blades, so many versions that can be considered.  Some are irrelevant when choosing between one blade and another – they distinguish between a blade suitable for wood vs plastic (for example).  Some blades do cross over – the Flai Mustang for example, which will have variables that suit both materials.

For example: ATB D250, K3.0 B30, Z40, H10


ATB = alternating top bevel – this blade has its teeth set so it is like a chisel, with one tooth cutting to the left, and the next to the right of the kerf.

You could have 4+1 (4 ATB teeth, plus one FT (flat tooth) as a raker tooth, flattening the bottom of the cut).  An ATB blade leaves a V groove in the bottom of a partial-depth cut, and the 4+1 is a way to resolve this, leaving a flat-bottomed kerf.

Other options include HATB (or HiATB), where the teeth are even more angled which is good for melamine, and timbers prone to tearout, TCG (triple chip grind, also known as triple cut, FT (Flat Top), HG (hollow ground)


D stands for diameter – size of the blade in mm.  A 250 blade (or to be exact, a D254) blade is 10″


This is the kerf of the blade, measuring across the teeth.  This does not mean the blade will actually cut a 3.0mm wide kerf however. Blades have runout (just how flat is the blade, and during use just how flat it remains as the temperature of the blade changes).  Saws (tablesaws or circular saws) also have runout, and it is a combination of both that will dictate exactly how wide a kerf you will get.  If you want to know it exactly each time, you have to measure it whenever you change blades.  The next time you mount the same blade, it could be different depending on at what point of rotation that the saw is vs the blade.  It is much easier just to do a test cut and remeasure if it is that important.  This concept is greatly (and deliberately exasperated) for a wobble dado blade, which is designed with a large amount of runout which can be dialed in, creating a dado (or wide trench).


This is the size of the bore – the hole through the middle of the blade.  Depending on your saw you can either get a blade that specifically matches your saw, or one that is larger and get some saw blade bushes (or reducers) to match both the blade and you particular saw.  They are not as convenient (but are still easy to use), and they allow you to purchase blades that are suited to your needs without necessarily being made for the size bore you require.  Of course, if the hole is smaller than your arbor, you have a problem! Getting back to dado blades for a sec, when using stacked dados, I would strongly recommend getting one where the bore is correct for your saw – there are enough things to juggle without also having to try and manage a bunch of bushes as well.


Z stands for the number of teeth.  A ripping blade can have around at little as 24 teeth, a crosscut blade as many as 100.


H is the hook angle (or rake angle). Large hook angles are an aggressive blade, particularly for ripping soft timbers.  Small, zero or even slightly negative for crosscutting hard timbers.


These are just some of the variables and codes that can be written (engraved) onto the blade.  They may not all be listed, and some blades may list a whole bunch more.  If you know these at least, you are well on your way of being able to distinguish between one blade and the next.


Some other variables include top clearance angle, top bevel angle, gullet size, gullet plug, expansion joints, noise reduction slots, max operation RPM, carbide type, base blade material, blade coating, body thickness and so on.  We’ll stick with the most common concerns at this stage!


Float like a butterfly

I asked Muhammad Ali recently what is favourite activity is, and the answer wasn’t a surprise. “I box”

So I trundled off to the Apple Store to see what their latest product was, and again the answer was “iBox” (with the iBox2 due out about 9 months later).

Next it was over to Professional Woodworkers Supplies to find out what their latest woodworking product was.  Can you guess the answer? i-Box from Incra.

Seems to be a bit of a trend happening here!

Given we are all pretty familiar with Ali’s boxing, and not everyone is an Apple fan, let’s stick with the third product and have a closer look at that.

Incra are renowned for creating items that bring incredible precision to woodworking.  And the iBox is no exception.  Unlike the other box jigs, the iBox has a completely variable finger size to exactly match the size of the cutter (whether that is a router bit or a dado blade).  It also has a microadjustment capability but my first use of it seemed to also cause the two sides to no longer be aligned.  The best option I found from a bit of trial and error was to get the width of the finger right in the first place!

Incra i-Box

The jig has good protection for the operator – both the block guards (red) so the operator is not exposed to the blade, particularly after the cut, as well as the perspex shield which discourages contact with the blade, and stops chips being flung up from the rear of the blade.

For all the safety items, what really sets this jig apart is the variable finger.

View from above

The finger is first zeroed off the blade during the initial set up.  If you have a left-tilting saw, you won’t have to redo this calibration even when changing blade or using a different dado width.

Using a test block, cut an initial slot then use this slot to accurately set the finger width by turning the adjustment knob.

Adjustment knob

Not only does this set the width of the finger, but the mechanism also moves the finger the same exact distance from the blade that the finger is wide.

Width set of a smallish dado blade stack

Underneath the jig

From underneath you can see the adjustable finger (not a lot of the mechanism itself).

Narrow finger setup

I also tried the jig with a single blade rather than a dado stack – worked very well with a basic blade, as well as with the large variable kerf achievable with a dado.

Fingers cut with a dado blade

The result looks pretty good to me, and very easy to set up and create.

Fingers cut with dado, and fingers cut with a single blade

It is a very effective jig – looking forward to seeing what else it can do (such as variable central finger width).

Available from Professional Woodworkers Supplies. Unless you want to try the Apple store 😉

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