I’ve spoken recently about dado blades, and the results are going to start appearing soon, but I haven’t actually mentioned what a dado blade is. Seems a bit strange defining it, but there again a few years ago I wasn’t sure what a dado blade actually looked like (I knew a bit of their function from all the US woodwork shows, and their project plans often referred to them).
I went into one shop – a Tool Centre as it happened (since closed down), and asked in there. What I was shown and was explained to be a dado blade I now know to be a coving blade – a completely different animal, so there are at least a few out there who don’t know what one is, and thus the point of the story.
Now don’t get me wrong – I’d love one of these blades for the tablesaw, but they are designed for coving, not for trenching!
The most common form of dado blade is called a stacked dado. This consists of two primary blades, one left, one right (and these are not interchangeable), and a number of chipping blades. There are normally shims included for finetuning the width of the kerf that the dado set is creating. You choose which combination of chipping blades and shims to create the width of slot (dado, trench, whatever your term).
As you can see in this example here, we have the two outside blades (orange CMT in this case), with black chipping blades in the middle, designed to clean out and flatten the bottom of the trench. The outside blades are typically around a 24 tooth blade (8″ diameter blade), with between a 2 and 8 tooth chipping blade, depending on the brand. Given that the ones I am trialing range from a 2 tooth chipping set, a 4 tooth chipping set, an 8 tooth chipping set, and a 9 tooth chipping set. It will be interesting to see how the results (and cost) range between the sets.
The other sort of dado blade is one that you can ‘dial in’ the width you require, and it is a “wobble” dado. This is a blade that literally wobbles to produce a wider dado than the blade would normally achieve. With my recent blade review throwing up results that showed that even a little amount of runout in the blade had a drastic impact on the resulting quality of the cut, it sounds a stupid idea to deliberately cause that to occur. Not only that, but do you really want a blade that isn’t properly balanced running at high speed in your tablesaw?
One of the things you need to do when using a dado set, is to have a table insert that can cope with such a wide ‘blade’.
There are commercial inserts available, but it is a simple job indeed to make your own. I haven’t documented here how I made the actual insert to right shape and size to fit the tablesaw (will cover that another time), but in a nutshell, I took the original insert, copied it with a bearinged router bit, then used that to create a number of blank inserts ready to be cut from below with the dado set to create a zero-clearance insert.
The inserts are made from MDF, and I have cut a couple of finger holes with a forstner bit so the inset is easily removed and replaced.
The dado set is already mounted, and is wound down below the table. I then bring the tablesaw fence across so it covers one edge, and assists in holding down the insert as the slot gets cut.
This is a very thin dado setup, with the two outside blades, and a single chipping blade. As you can see I have already wound the blade up through the insert cutting the slot, and have set up here to conduct the first dado slot test.