Irwin Marples 8" Dado Blade Set Review

Make quick work of dados and grooves with Irwin's premium quality dado blade set.

Irwin Marples 8" Dado Blade Set

Irwin Marples 8" Dado Blade Set



If you cut a lot of dados and grooves, then a dado blade set is an excellent table saw accessory to consider. With a bit of experience under your belt, you're likely to find that a dado set is just as convenient, and perhaps quicker and easier to use, than a router set-up. You can also use it to cut tenons, tongue and grooves, box joints, rabbets, and half-laps.

Basically, there are two types of dado blades – adjustable dado blades (also called wobble or dial adjustable dado blades), and stacked dados. Stacked dado blades are the most popular among furniture and cabinet makers – they're easy to set up and use, and the best ones cut dados with clean, crisp edges, and flat bottoms.


Task Wobble

Adjustable Dado Blades

If you want precise dados and grooves, then skip these blades; otherwise they're fine for general purpose cutting. They're called 'wobble' blades for  good reason — they have a tendency to vibrate quite a bit in use, and they're notorious for chipping-out the sides of dados. They're also more likely to leave a concave, rather than flat dado bottom. This is because of their design - a single blade housed on a beveled hub, where each tooth cuts a different arc in the stock as the blade rotates.


Unless you cut dados by the dozen day in and out, a good quality dado set will last years. The Dimar set I purchased over a decade ago, and have had re-sharpened twice, still has years of useful life ahead of it.
 
Irwin introduced a new line of twelve 'Marples' saw blades earler this year, which includes the Irwin Marples 8" Dado Blade Set. The set consists of two matching outer blades, three chippers, three spacers, and four shims.

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Everything fits together nicely in a durable plastic case, which makes it convenient to store the set or transport it to a worksite, and more importantly, protects the teeth from damage.

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The Irwin dado set is manufactured in Italy and has all the features you would expect from a premium blade. The plates are laser cut, precision tensioned, and then covered in a heat-resistant, non-scratch, non-stick coating. While there is some debate about the effectiveness of blade coatings, I find they make blades easier to clean. The blades and chippers in this set also have an anti-kickback design that limits the bite of each tooth, helping to reduce overfeeding. 

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The teeth are made of C4 micro-grain carbide, and precision-ground for a very smooth finish. Irwin uses a Tri-Foil material to bond the teeth to the plate. It consists of a layer of copper sandwiched between two layers of a brazing material made of a copper/zinc alloy. The way the teeth are cemented to the plate is important, as they need to be cushioned from the severe stresses they undergo in use.

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A dado set comes with two outside blades, a right hand blade, which sits up against the arbor flange, and a left hand blade, which mounts against the arbor nut and washer. On most dado blades you'll find either 12 or 24 teeth per blade. In theory, perhaps, more teeth will provide a smoother cut. However, I've used both formats and don't see much of a difference. While the teeth on the outside blades do remove stock, their primary function is to score the stock and define the square edges of the dado.

These Irwin blades have 12 teeth per blade, beveled 20 degrees – to the left on the left hand blade and in the opposite direction on the right hand blade. The teeth aren't huge – 3/16" wide with a 5/32" long re-sharpenable face – but large enough that they can be re-sharpened a number of times, depending of course, on blade usage.

The chippers, which are stacked between the outer blades, hog out the bulk of material. Each blade has two flat-top teeth, 9/32" wide and 3/16" long, which ensure a flat bottom dado. As with the outer blades, the chippers have a -12 degree hook angle – you'll often seen a negative hook angle on miter saw blades. The general concensus is that a negative hook will cut less aggressively, but more cleanly.

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The set comes with three 1/8" spacers and four shims (.02", .012", .008", and .004") that you insert against the chippers to further adjust the width of cut. You'll be able to cut dados from 1/4" to 7/8" wide, a common width range for most dado sets. The shims in the photo below look like burnt toast, but they're perfectly flat.

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Irwin provides an indespensible guide that lists the combination of chippers, spacers and shims you'll need for 22 different widths. This should cover just about any dado size you're likely to cut. But, you can always purchase an extra set of shims to fine-tune a dado width. The guide, by the way, is printed on cardboard rather than more durable plastic. You might want to photocopy it in case the original becomes damaged or lost.

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I tested this dado set by cutting three sizes of dados in Alder (a fairly soft wood), red oak, veneer core plyywood, and MDF. I followed the set up listed on the guide when installing the blades, spacers and shims. For all three dado sizes the resulting dados were spot on. As you can see in the photo below, the set-up for a 9/16" dado was....exactly 9/16".

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I was very pleased with the quality of the cuts. The sides of dados were crisp and clean, and the bottoms were virtually dead flat. Cutting with the grain, either in hard or soft woods, and in MDF, resulted in the cleanest cuts.

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Dados cut across the grain were almost as good as those cut with the grain. If you look very closely you'll see a miniscule amount of tear out. Hardly worth mentioning.

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Cuts made on plywood, while not as good as cuts made in solid wood and MDF, were nonetheless very acceptable. There was a slight fuzziness along the top of the dado cut, but this was easily removed with a light pass of 220-grit sandpaper. 

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If you've not used a dado set before, installing the blades is straightforward. You want to keep the teeth on the blades and chippers staggered so they don't hit each other. Staggering also prevents sawdust from becoming wedged between the teeth. I orient the chippers so that their teeth align with the gullets in the outer blades.

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If the dado width you intend to cut calls for spacers or shims it's a good idea to spread them evenly between the blades and chippers rather than stacking them all together, otherwise you might end up with a paper thin sliver of material left in the dado.
 
As you would when making most saw cuts, take shallow cuts rather than trying to hog out all the waste at once. I generally take off about 1/4" of material or less on each pass. And because your making a wider cut than with a standard saw blade, you want to reduce your feed rate somewhat. 
 
If you follow the guide you'll likely find, as I did, that you'll end up with perfectly sized dados. Still, it's a good idea to make a test cut, particularly if you're working with expensive wood.

I'm very pleased with the results that I got with the Irwin Marples Dado set. With a suggested retail price of $210 it's very competitively priced - a tad less than the popular Freud SD508, about $70 less than a CMT set, and about $100 less than Freud's SD608 Dial-A-Width (which uses a dial hub rather than spacers and shims to adjust the dado width).

irwin_dado

KEY FEATURES:

  •  8" 12-tooth (outer blades)
  •  ATB (main blade), flat top (chippers)
  •  C4 micro-grain carbide
  •  Tri-foil brazing
  •  Laser-cut plate
  •  Heat-resistant non-stick coating
  •  Precision tensioned
  •  20° top bevel
  •  15° top clearance bevel
  •  -12° hook
  •  3/16" thick length (main blade), 9/32" (chippers)
  •  Cuts dados from 1/4" to 7/8" wide
  •  Includes: (2) outside blades, (2) chippers, (3) 1/8" spacers, (7) shims (0.1 to 0.5mm or .004” to .02”)
 
Brand:Irwin
Model #: 1811865
Retail Price: $210
Made In:Italy
Where to Buy:Retail Locator
May 2013

Author: 
Carl Duguay
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