Dado Duel

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This article is from Issue 1 of Woodcraft Magazine.

We put the “head” in “head-to-head” with our stack-up of three dado sets. Find out which one is best for your needs in the areas of accuracy, smooth cutting and ease of use.

IT’S THE MOST BASIC MACHINED JOINT in woodworking – a simple groove that houses the edge of another workpiece. Yet the dado can cause heartache for hobbyists and pros alike. Torn edges (especially in veneered stock), an uneven bottom and problems matching the thickness of standard plywood sheets are just some of the challenges involved. 

Three relatively new dado sets – Forrest’s Dado King, Amana’s 658040 and DeWalt’s DW7670 – seek to address these issues. Wishing to discover what each has to offer, we put them through their paces for a week in a standard shop setting, where they were pitched against a variety of materials. There is a wide price variance among the three, so they are clearly targeted to different budgets, skill levels and needs. All three sets were set up for a 5/8" arbor, although Forrest offers custom boring to suit different saws’ arbor diameters. 

We tested all three dado sets in quartersawn white oak, plain sawn red oak, Spanish cedar, aspen, melamine-coated MDF (medium density fiberboard), red oak veneered plywood and Baltic birch multi-ply.

Forrest Dado King

With six chippers, two 24-tooth outside blades, and a full quota of shims, Forrest Manufacturing Company’s 8" Dado King mills grooves (with the grain) and dadoes (across the grain) from 1/8" to 29/32" wide. In all of our tests, this set delivered perfectly flat-bottomed grooves in every material. Equipped with C-4 carbide tips, the Dado King promises long intervals between sharpening, even when its primary use is on dense fiberboards and other hard composites. Each of the two trim saws – the circular outside blades – has 24 carbide tips. But where both the Forrest Dado King and the DeWalt DW7670 excel is that each of their chippers is equipped with four carbide tips instead of the traditional two. This means that fresh cutters are offered to the material twice as often, which is a large part of the reason that the Dado King delivers such a clean groove. 

Forrest makes the Dado King set with negative hook on all of its teeth, including chippers. This is a huge advantage when cutting dadoes, as the angle of a tooth with negative hook emerging through the back side of the cut can dramatically reduce tearout. In our shop tests, this was quite evident, especially in the more fibrous species such as aspen and Spanish cedar.

There was very little we didn’t like about this dado set. It’s designed for demanding woodworkers and it lives up to its marketing. The Blade Runner plastic tote that houses the set is a bit chintzy – the guys in the shop said they would have preferred a sealed case similar to the ones the other manufacturers provided – but it’s not really an issue as dust can’t hurt the tools, and the tote protects the cutters from collision with each other. 

All of the Dado King sets come with Forrest’s new magnetic shims. Akin to a very thin version of those floppy refrigerator magnets, these shims allow fine adjustment of a groove width, so that you can match any slight variances in plywood thicknesses. The holes for the arbor were quite large; this meant that the shims weren’t always centered on the arbor and we wondered if that affected the balance of the dado head. It sure didn’t seem to. There was no evidence of vibration.

Street price on the Forrest Dado King is $299, although we came across specials online which listed it for as little as $249. For a serious amateur or a professional shop, this is a hard-working dado set that creates as close to a perfect groove or dado as we’ve seen. It’s a little pricey up front, but fewer sharpenings and reliable performance certainly justify the investment.

Forrest Manufacturing Company: (866) 398-9336

Amana 658040       

With a street price of $189, the Amana Tool 658040 Premium 8" carbide-tipped stacking dado set bridges the gap between hobbyist and professional budgets. While the set will cut grooves and dadoes from 1/8" to 13/16" wide, the company points out that wider cuts can be made with additional chippers. That would, of course, depend on the length of your saw’s arbor, but it’s an interesting concept, especially for production shops or any application requiring parallel or very wide dadoes.

The standard Amana 8" dado set consists of two outside saw blades and four inside chippers. Most interesting here is the fact that this set has 46 teeth on its two outside blades, more than either of the other two heads we tested, and fewer tips on the chippers (two apiece). Results with the Amana set were a very close approximation of the Forrest tests. The bottom of the trench was perhaps not quite as smooth, but it was still very acceptable. 

Thanks to those 46 teeth, the edges of every single dado cut with the Amana were extremely crisp. The outside blades feature hollow-ground plates for proper clearance (the tips of the assembled cutterhead can’t touch), and they have an alternate top-bevel grind, with every sixth tooth being a flat grind. Amana’s 8" diameter sets have a negative 5-degree hook angle on the outside blades which is designed to minimize tearout. We performed all tests without a scrap backup, and the engineers were vindicated: There was no visible tearout as the cutterhead exited each workpiece.

The four two-wing chippers in this set include one 1/4", one 1/16" and two 1/8". The hinged case is sturdy enough to protect the set during a fall from a shelf, and it’s sealed against sawdust. 

A 14-piece set of shims is included for fine adjustments. They are color-coded for thicknesses ranging from .002" to .02". Four of the shims are paper, while the remaining ten are plastic. We weren’t thrilled with the thinner ones – they were flimsy and a little cumbersome to use – but this isn’t a serious drawback, as most dado cuts don’t require shims. 

All things considered, the 658040 is a superior tool that will meet or exceed most expectations.

Amana Tool: (800) 445-0077

DeWalt DW7670

The least expensive of our three sets, the new DeWalt 8" dado head is listed by several retailers at just $149. Like the Forrest set, the outside blades on the DW7670 each have 24 carbide teeth. The blades are heavy-gauge steel, with a very solid feel, and they are laser-cut for accuracy. The six carbide-tipped chippers each sport four teeth (again, like the Forrest), and every chipper is very visibly etched with its thickness –

four at 1/8", and one each of 1/16" and 3/32" thickness. This makes choosing the right one a very simple task. 

One of the most pleasing aspects of this set was that the shims were all high-quality steel and rather large in diameter (3-1/8"), so they were easy to handle. All 12 of them had their thicknesses stamped on one face – .005", .010" and .020".

With its economical pricing, this set is perhaps aimed at the less-frequent user – for the shop of a serious hobbyist rather than for daily use in a professional cabinet shop. It delivered a satisfactory cut in most materials, although there was a small amount of tearout on the exit side of each test board. 

Our lead cabinetmaker suggested that results would be more than acceptable if a scrap backup had been used, which would be the case in most actual shop situations. The bottom of the trough in composite materials was quite smooth; there was very slight roughness in some of the hardwood stock, but nothing that would affect a joint in a negative manner.

The maximum cutting width of this set is 29/32", and it comes in a very sturdy, hinged plastic case.

DeWalt Industrial Tool Co.: (800) 433-9258

The Forrest Dado King includes six chippers, each with four carbide tips.
The Amana 658040 includes four two-winged chippers with the largest carbide teeth in our comparison.

The DeWalt DW7670 includes six chippers with carbide teeth and convenient thickness measurements.

More is better: 

Due to their four-toothed chipper blades, the bottoms of the grooves cut with the Forrest and DeWalt blade sets are cleaner and smoother. Because fibrous woods like Spanish cedar (bottom photo) tend to have a lot of tearout, all three blade sets were tested to check side-by-side results.

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