This may be misguided; wobble-dado blades are sharpened at the factory in a manner that will be a bad match for either extreme (wide or narrow) of the width setting. There IS likely a setting at which the wobble-blade cuts a flat bottom.
For my (Sears Craftsman 720.3261) blade, the instruction sheet indicates that width is 3/4" (0.750 inches).
DJ Delorie wrote in news: snipped-for-privacy@delorie.com:
Wish my dad had had that advice. He was consistant - always bought the least expensive tool. I threw them all out after he passed on (actually, saved a set of screwdrivers and a hammer, just in case my Mom ever needs to hang a picture or tighten a loose knob).
John
It will be less pronounced but it will NOT be a flat bottom dado.
The only time a wobble blade will cut a flat bottom is if the kerf is, let's say, 1/8" and you have it set for a 1/8" dado. In other words NO WOBBLE and the blade tip remains perfectly perpendicular to the workpiece.
Just think about the path that wobbling blade takes for a minute or so and visualize it sweeping back and forth like a pendulum.
Wobblies are handy for removing large amounts of wood quickly and for dadoes where it doesn't matter if the bottom is curved, as in door panel inserts or drawer bottoms.
My dad's philosophy, common I've always thought among many who grew up in during the depression. Always suspected that had my folks won a $100 million lottery, Dad would have gone to his grave with $99,990,000 unspent. And, he would have begrudged my mother for foolishly spending the other $10k. I'll always buy the best tool/toy I can afford but, alas, it's more often than not like pulling teeth.
Dave in SoTex
Regardless of how a wobble blade is sharpened at the factory or where ever, if it wobbles/cuts wider than the width of the teeth on the blade, it will not produce a flat bottom.
The only setting that the wobble blade will create a flat bottom is when it is adjusted to not wobble at all.
Actually, the wider the cut the more extreme the cup in the bottom of the cut.
Sears/Craftaman power tools say a lot of things to sell their product. Remember the 6.5 hp shop vacs?
Not true. The sharpening of a wobble blade is NOT RIGHT ANGLE at all the tooth faces. That analysis holds only for straight-blade sharpened blades used with wobble washers, not for wobble-dado assemblies. Standard blades are sharpened in the zero-wobble-angle state, of course.
That depends on the manufacturer's wobble-setting when the blade was put into the tooth-grinder. For my blade, flat cuts occur at 3/4".
Think of it this way: to cut a flat bottom dado with a 24T blade tilted at 10 degrees, the leftmost edge has to be cut by tooth #1 whose crest is 80 degrees to the left sawblade face, and 100 degrees to the right blade face. The rightmost edge has to be cut by tooth #13 whose crest is 100 degrees from the left face, 80 degrees to the right blade face. And the middle of the cut is made by tooth #6 which is 90/90 degrees, regular square-cut, but at a slightly smaller distance from the axis of the blade rotation. Dado blade teeth for wobble-dado assemblies are sharpened exactly as required to make a flat-bottom cut, but ONLY AT ONE SETTING.
I think you have read some hocus pocus info promoting wobble blades.
But to be clear, I am not talking about a smooth bottom, I am talking about a bottom that is the same measurement in the middle of the cut as the outer edges of the cut.
In order for a wobble blade to not cut a round bottom, when adjusted to wobble, the blade would have to elongate where the outer cutting teeth come in contact with the outside of the cut and shorten where they come in contact with the center of the cut. The wider the blade setting, the longer the part of the blade with the teeth cutting the outer sections of the dado will have to be. If the wobble blade was manufactured to be non adjustable it could be made to cut a flat bottom but it would not be perfectly round. The outer teeth would be farther from the center of the blade than the teeth in the center of the cut.
Think of a ladder standing straight up in the air. It stands 10' up in the air. Now lean the ladder over 12", how high up in the air is it now. This is how a wobble blade works the farther away the teeth are from dead center the shallower they cut. Those teeth that are still located near the center of the blade will cut deeper.
OK, I'll step back and retract the hocus pocus comment. ;~) I can see how a wobble blade can produce a flat bottom but only at one particular width setting. It does in one way as I indicated have properties that the cutting surface of the outer teeth are farther from the center of the blade as those that are closer to the center.
But with that in mind, is a blade that only cuts one width well worth having? While a 3/4" setting seems like a common size to cut, in the real world it only works well for cutting dado's to receive 4/4 S4S lumber and possibly MDF but not for receiving the common 3/4" piece of plywood.
Bottom line is: no one who has ever gone from a wobbler to stacked dado blades ever even thought of going back.
Heck even when I had a wobbler, I switched to a regular rip blade on my table saw to cut cove molding because if left me with less sanding to do.
Precisely: I've read the instruction sheet that came with my own blade; I find no copy online, but this article has the basic info, too (see Figure 1d especially)
My dadoes are usually rough straight from the saw, and sandpaper and a knife or chisel always come out for step #2. I don't mind doing some cleanup by hand.
The original poster was making tongues (tenons); a fixed setting would work for him.
My stacked dado set is steel, the wobbler is carbide; maybe I'll use the wobbler again someday.
But, I have stacked dado blades, and would usually use those instead.
'Bout damned time! LOL
That is why I got a stack up blade set - in metric. Plywood is mostly if not all metric. The stack up does imperial as well. My very old wobble is in the case - for the job just made for it.
Martin
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.