SSYTC069 Dado FUBAR

Episode 108 DadoStop!

Had a look at the blade(s) after the fact, and found out where the significant cascading sound comes from when the brake activates.  12 separate tungsten carbide teeth ripped loose of the blade.  Most presumably are due to the spacer blades not being in direct contact with the aluminium brake, so were able to move when the blade was (rapidly) decelerating, and knocked the teeth off as they slid past.

It is a good effort, stopping that much spinning steel on a dime!

Episode 92a Enter the Dado

Episode 92A Enter the Dado

A short (approx 5 min) version of the dado video, on the Amana Tool Dado from Toolstoday.com

Episode 92 Amana Tool Dado Blade

Episode 92 Amana Tool Dado Blade

Click here to see the blade at Toolstoday.com  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 Spreadsheet

Dado Excel Spreadsheet

I have had a few queries about the original Excel spreadsheet that I created to generate my precise dado table (the one with 3000 or so combinations).

I have attached it, but here is the disclaimer:  it is nowhere as neat as Excel spreadsheets can be, but this was the easiest way I could make it to deal with the number of combinations.  Someone familiar with the latest versions of Excel would be able to do a much better job, but I haven’t used it since the XLSX format came out, so there have been a lot of changes since the last time I did use it.

Column A: All combinations must include the combination of the two outside blades, so this column is always “1”
Column B: The number of 1/8″ chipper blades used in the stack. The set I had provided 4
Column C: Whether or not the 1/16″ chipper blade is included.
Column D – G: The number and size of the various shims included in the stack.

Column H: This is the theoretical width. Add to this the additional width that is created by the runout of the saw and blades. This is easily achieved by setting up a basic stack, with the theoretical thickness from the spreadsheet. Make a dado cut, and measure the actual width. The difference is caused by the combination of runout from the various blades, and the saw.

Column I: This is the runout. At this stage I only have calculated the runout for one setup. If you wanted to be even more exact, you could calculate the runout for each blade the same way, and amend column I accordingly.

Column J: This is the money column – the final size of the stack that is built.

Column K – Q: These are the calculating columns – leave these alone.

Columns R – X: Input each of the widths of the various blades and shims.

As I said: it is not the most eloquent spreadsheet. But it works, for me at least!

Dado Excel Spreadsheet

Click here to see the dado blade at Toolstoday.com

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.

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Electroblu Dado Blade

The dado set I have been using recently is this one from Amana Tool (through Toolstoday.com)  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 Toolstoday.com  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.

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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.

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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.

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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.

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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.

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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)

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Snapshot of a few rows of the table

Dado Set Combination pdf

The Dado set by Amana Tool, from Toolstoday.com 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!

Way of the Dado

The dado blade – taking a standard sawblade, and deconstructing it into its various elements.  Then taking one of the fundamental variables of a saw blade and making it variable, making it controllable.

Normally, we accept (and suffer) the kerf (the width of cut) of a sawblade.  When you cut a piece of timber, the kerf is wasted timber – it is turned to dust and sucked away.  The thinner the kerf, the less material is wasted, and the less power the saw requires to drive the blade.  But then, the thinner the teeth (more susceptible to damage, and less resharpening opportunity), and the more flexibility of the blade.  It seems the most popular kerf is 3.2mm.

However, there are times when you want to have width to the cut.  If cutting a long slot (a dado, slot or trench depending on your country’s definition), then doing this on the tablesaw is a lot faster, and puts a lot less load on the machine than trying to do it with a router bit.  So the dado blade is one where the alternating top bevel is now on different blades (a left and a right one), and the chipper teeth are on chipper blades that sit between the two outside ones.  By adding additional chipper blades, the kerf of the assembly can be increased, and then finetuned with thin shims.  This obviously cannot be done with router bits, so now the dado blade has two advantages over completing the same job with a router bit.

A router bit can plunge and cut a stopped dado, a dado blade cannot, and there are other instances when using a dado blade is not the method of choice.

But when you want one, they can really do the job quickly, easily, and repeatably.  So long as they are a good quality set.  So far, the dado sets I have used have been a disappointment when it came to testing them, so rather than run through all the potential variables if this set (the CMT 230.524.08 8″ 5/8 bore to suit my specific saw, from Carbatec) can cut a decent trench, it will be the winner – all the others I have tested so far have been rejected.

Here I have assembled a 16mm dado stack, mounted in my tablesaw and already plunged up through a wider insert that I made for my tablesaw from MDF.  The maximum size dado the set can create is 25.4mm (1″), but this is wider than my particular tablesaw can cope with.

The blades are 1/8″ each (and you must use both for all setups) so the minimum dado width is 1/4″  If you use all the chippers and the shims, you get the maximum dado size of 1″.

The chipper blades are 1x 1/16″, 1x 3/32″ and 4x 1/8″

The shims are 2x 0.020″, 2x 0.012″, 2x 0.008″ and 2x 0.004″

I also chose the 5/8″ bore version to match my current setup.  Most of my other blades have a 30mm bore (from memory) and then use an insert to get them to match my saw.  But if I was to try that here, I would be juggling one for each outside blade, then one for each chipper.  Too much stuffing around just to future-proof a dado set.  And I’m not planning on upgrading my tablesaw any time soon (not unless a SawStop Pro or Powermatic  falls into my lap!!!)

My tablesaw is 10″, but I’ve chosen to have an 8″ dado set.  That might seem strange – why not get a dado set that matches the capacity of the saw?

This is actually a very common practice.  A normal blade is only 3mm wide, and if it takes a significant proportion of the saw’s power on the most testing of cuts, what would it mean if you tried to spin up a dado set that could weigh 5 – 8 times as much, and then push that thickness through a block of timber?

So a smaller diameter blade is significantly less weight to spin, and even the splitters are weight-reduced with portions selectively removed to decrease the power required to drive them.  Even so, this set is no-compromise.  The splitters are 4 tooth on a full disk.  Some dado sets have very limited splitters, more like a airplane prop than a blade.  Not sure which I’d prefer, not sure I care (other than 4 teeth are better than 2)

The biggest reason for going for a lower diameter blade?  You don’t need bigger!  This is for dados, not for sawing timber in twain.  And creating a zero-clearance insert is much easier and safer when the blade can be wound down into the table far enough that it fully clears the bottom of the insert.

Not the best photo, but you can clearly see the outside blades have a combination of bevel tooth and chipper, and the chippers in the middle only have chipper teeth.  Also, you can see that the width of the chipper teeth is not important – it is the thickness of the body that determines the full stack width.  So the wider teeth make for overlap, to ensure they fully clear out the slot.

Setup for the dado cut.  The fence is locked down and the timber held against it with the latest featherboard from MagSwitch (the reversible featherboard on the universal base).  The guard and splitter are removed – cannot be used with a dado, or partial depth cut.  A zero-clearance insert is in place (shop made) and the blade set for the depth of slot required.

Setting the dado height, you have to be careful NOT to measure to the height of the bevel teeth – they do cut deeper than the depth of the slot as you will see in the next photo.  You measure to the top of the chipper teeth.

But the final truth is simple: can it cut a decent slot with a flat bottom or not?

Yes, it can.

You can see how the bevel teeth cut a bit deeper at the edges – not ideal (although pretty normal for dado sets).  It ensures there is a sharp, sliced corner rather than a rougher chipped one.  That’s not a bad thing – only matters at all if you are going to see the end of the slot at all (and you can see it is pretty minor even so)

This slot took no time at all – it really demonstrated to me just how useful a dado set is if you have a fair few slots to cut – blows routing them completely out of the water.

So the bottom line.  This CMT dado set is a win (as is the storage case personally – industrial, tough, and functional).

The CMT 230.524.08 8″dado set, from Carbatec.  This has a 5/8″ bore.  For the 30mm version, it is the 230.524.08M

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