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

2 Responses

  1. […] Way of the Dado (stusshed.wordpress.com) […]

  2. […] = ''; } Jasper 200J Model 200 Circle Cutting Jig for Plunge RouterWay of the DadoWay of the Dado var topsy_style = 'big'; var topsy_nick = ''; var […]

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