Many years back, some number of companies produced a special blade that could cut dados with just a single blade. The invention was really pretty cool, but simple. The single blade would have to rotate a bit on it's axis which would mean that it could plough out a trough of wood, depending on how far the blade was turned. When it was not turned I would carve out a slot approximately 1/8 inch wide, but when it was turned fully it could make a dado cut that was well in excess of 3/4 inch. These blades were called wobble wheels and were quite common at one time. I am not sure if they are still made and I have not been able to find a source for them in recent years.
Like all things that change, the wobble wheel has all but gone away, replace instead by the stack dado set which consists of a couple of outer cutting blades and sandwiched between them are something called chippers, and together they are used to dado cuts of varying widths, depending on how many chippers are installed.
I used a wobble wheel for many years and always found to make decent cuts, my only real complaint was it often took a lot of time getting the width the perfect size. Over the years I have heard (but never actually tested) from many people, that wobble wheels, because of their design create somewhat coved bottoms on the dado cuts. Based on how the blade works, it's pretty easy to assume this would of course be the case, but how much of a cove does it make and does it really make any difference? That's what I set out to see ...
Of course the first thing to select is a material to cut and I finally settle on MDF. I felt that even a good quality plywood might not show up the cut as well and thought that either nice hardwood or and MDF material would work best, I settled on and MDF that was just slightly over 3/4 inch.
I set the wobble wheel to just over the 3/4 inch mark and set it up in the table saw. Since I did not have a zero clearance insert, I had made one and now needed to cut the insert before making the first cut.
The first dado test cut ... Well, the first cut proved to be a bit narrow for my insert piece, so turn the saw off, take out the wobble wheel, re-set it and ... back into the saw, tight the nut, re-set the insert and try again.
As you can see from the video, even working in small increments, it was very tedious getting the blade width correct ... and it reminded me why I didn't like using the wobble wheel blade.
After several attempts, and even one where I was too large and had to make the slot slightly narrower, I finally had the width down to a nice snug fit, and ran the final board through the saw.
When I put the insert into the dado, you can barely see that there might be a hint of a curve, certainly nothing outstanding, and really, only barely visible when you look at it at the ends of the board. This may not be suitable for some people, but for others it would be just fine. It really depends on what you are making and what tolerances you are wanting to work with.
Had the gaps been something like 1/32 of an inch, I would have grave concern, not for one dado cut, but for multiples, for example, if you were making kitchen cabinets that were 4 drawers long, a 1/32 inch dado gap would be a 1/6th inch error each drawer and combined would work out to a 1/4 inch error, which could be quite a lot if you were trying to fit it between a couple of walls, or, even worse what if you had ordered a custom granite top and found out that it was 1/4 inch too long or too short, now you are into some serious money.
My test showed that the curve with the wobble wheel was not anywhere close to being out that much as you can see in the picture, yes, you could argue there is a small curvature, and it may not be a perfect bottom of a dado, but in many cases this would be acceptable.
If you already have a stack dado set then you already have an excellent working blade set. If you have nothing for cutting dados, and you would like to be able to do this from time to time, perhaps for the cost of purchasing a used one somewhere, it might be a good investment, even with the fiddling around to get the width set correctly ... I leave that to you to decide ...
Late Breaking News ... apparently Wobble Wheel Dado Blades ARE still available to purchase new at Rockler, Grizzly and others, for those who are interested in these blades.
Copyright Colin Knecht