Dado Bits vs. Straight Bits

[scoutmgr]

Well, I think I have almost everything I need to begin a couple of projects that involve cabinet making and trimming. Table Saw (BT3100), Router (Bosch 1617), mounting kit for the router, Miter Saw (Bosch 3912), circular Saw (Makita ??), Jig Saw (Ryobi ??), etc.

The last thing I need is a set of router bits for some of the decorative edges, but most importantly for dado cuts. I'm very interested in either the Holbren 35-piece set or the Woodline 30-piece set from Amazon. BTW, do folks here have any preference?

The main reason for my post is that there are some bit sets been sold exlusively as "dado bit sets". I always thought that a straight bits are used to make dado cuts. Holbren's set for example, has a few striaght bits ... couldn't I just use those to cut dados? Am I missing something terribly obvious? What is a dado bit and how does it compare to a straight bit?

Holbren's:
1/4" Solid Carbide Double Fluted Streight (only bit with 1/4" shank)
1/4" Straight Plunge Double Fluted
3/8" Straight Plunge Double Fluted
1/2" Straight Plunge Double Fluted
3/4" Straight Plunge Double Fluted


Thanks for your help!

[MilDoc]

Sure, you can use straight bits for dados etc. IMHO "dado bits" are "chunky straight bits," ie, they are shorter than straight bits. Result - reduced vibration coupled with downshear cutting. They also tend to have shorter cutting edges. But, IMHO again, I really can't tell the difference, having used both!

If you are building with plywood, be aware that there are special plywood dado bits, since 3/4" plywood isn't.

In general, if you do a lot of router work, buy carbide tipped! If you need a router only occasionly, HSS bits work fine.

[leehljp]

For 1/2 inch and larger bits, I prefer the 1/2 inch shanks. One other thing to consider is that some dado sets are made for the industry standards of plywood thicknesses - if you are planning on making dados for plywood.

[Tom Hintz]

I like the specialized dado router bits because they are sized to cut grooves the right size for the goofy-sized plywood we get today. I know you can make two cuts with a smaller straight bit but it is not as accuarate as one pass with the correct bit size. I use them all the time and am very glad I have the set. I am perfectly capable of making bad cuts in other places!

[davidtu]

Are all dado sets STRICTLY setup for plywood widths or are there "normal" width dado sets (that are otherwise differentiated from regular straights as per ScoutMgr's comments)?

[Tom Hintz]

Some bit manufacturers, like Infinity, have specific sets designed for cutting grooves for the common plywood sizes today.

[LCHIEN]

straight vs dado

Are all dado sets STRICTLY setup for plywood widths or are there "normal" width dado sets (that are otherwise differentiated from regular straights as per ScoutMgr's comments)?

I think the difference is, straight refrers to the bit profile.
Dado refers to the cut. A dado is a Straight (e.g. in a line) groove, you cut it with a straight (refering to the edge of the bit profile) bit when using a router.

Most bits are called by their profile, But the exception is if they phelpo make a unique joint then they are named buy the joint they make. Sometimes they're in the catalog twice, once by the names joint and again by the profile.

You can cut a curved groove with a straight bit but it would not be a dado. Straight bit (referring to the profile) is the proper name for the bit.
Even if you are making dados with it, it's not only for dados. Straight bit dimensions, the primary number refers to the width of the groove it makes.

Now a plywood dado bit set, even though composed of straight bits, is probably called that because
1) the dimension refers to the "nominal" width of the plywood it was meant to work with rather than the actual straight bit size and
2) because they are generally used for dados for shelves and sheets pf wood beacuse that is what plywood is used for.
of the

[Holbren]

As others said, the dado bit is a straight bit sized for undersized plywood. Sometimes they work well and other times they can even be a little off, depends on where the ply comes from.

You can always get away with a regular straight bit but would have to use a smaller diameter bit and move the fence over for a second pass for a snug fit. My advice, buy the undersize dado set. I use the 15/32" bit all the time and has worked great for my imported ply.

Since I started selling Whiteside I noticed they have a 31/64" rather than a 15/32". I know in my case I don't want the extra 1/64". Maybe the imported ply is a little more undersized than domestic 1/2" ply, don't know.

[cabinetman]

I've stayed away from buying "sets" because there's always bits that are included that never get used. The price of the set most likely includes the bits that don't get used. So, I buy what I need. For the names of the bits, to dado, a mortising bit can also be used. It's a straight faced cutter that cuts a flat bottom. Differences in bit design may be in length of the cutting face, shank diameter and length, and shape of the gullet. Personally, I stay away from HSS and solid carbide bits. I've found the solid carbide bits are very brittle. I prefer the carbide tipped.



"I'M NEVER WRONG - BUT I'M NOT ALWAYS RIGHT"

[scoutmgr]

OK, Thanks for the helpful hints. I sounds like in reality, it shouldn't matter what the bit is named, if I want to cut dados, all I need is a bit that would allow me to cut a straight groove that fits that thickness I'm looking for.

Having said that I also understand that for plywood, 3/4" is generally smaller than 3/4" ... so it's possible that the "dado" bits are made for this undersized thickness ... and that would certainly be something to look for.

Consequently, I also measured that thickness of some of the "cabinet-grade" plywood at Depot and Lowes ... and it appears that the 3/4" plywood is actually 3/4" and not some undersized thickness ... so in this case, it seems like that regular 3/4" that comes as part of any popular set (i.e. Holbren) should allow me to cut 3/4" grooves. A "dado" bit made for undersized plywood would be too small for this application, unless I run it more than once.

There is only one way to find out ...

Thanks!

[LCHIEN]

OK, Thanks for the helpful hints. I sounds like in reality, it shouldn't matter what the bit is named, if I want to cut dados, all I need is a bit that would allow me to cut a straight groove that fits that thickness I'm looking for.

Having said that I also understand that for plywood, 3/4" is generally smaller than 3/4" ... so it's possible that the "dado" bits are made for this undersized thickness ... and that would certainly be something to look for.

Consequently, I also measured that thickness of some of the "cabinet-grade" plywood at Depot and Lowes ... and it appears that the 3/4" plywood is actually 3/4" and not some undersized thickness ... so in this case, it seems like that regular 3/4" that comes as part of any popular set (i.e. Holbren) should allow me to cut 3/4" grooves. A "dado" bit made for undersized plywood would be too small for this application, unless I run it more than once.

There is only one way to find out ...

Thanks!

the thickness of plywood is generally considered to be 1/32 under the nominal dimension. So 3/4 plywood bits are usually 3/4 minus 1/32 or 23/32".

But in actuality 3/4" plywood can vary as there don't seem to be any real standards and probably there are tolerance ranges. I'm guessing Because plywood is made up of maybe 5-or 6 laminations the real control of thickness is the laminations and if each one was +/-.003 ( a reasonable manufacturing tolerance for slicing the layers) then you could could potentially have a +/-0.018" in the finished product with most of them centering around nominal and a few near the limits (what statisticians call a Gaussian or a bell curve distribution). So if they shot for 23/32" (46/64") and had a +/- .018" tolerance, the actual plywood would be between about 45/64" to 47/64".

In this case the plywood bit may or may not fit perfectly and you might very well measure 3/4" if you have a ruler with 1/32 markings.

When you thought you measured 3/4" did you use a pocket ruler,
a tape measure with a hook on the end, or a pair of calipers? The difference is the first does not hard reference either end (Makes you eyeball both the zero point and the reading), the second only references the first end (makes you eyeball the reading) and the third uses hard references for both ends of the reading. If you used the first method you could easily have mistaken 46/64 or 47/64ths for 3/4".

Since the thickness does have some leeway, a plywood dado bit set (or more accurately a straigh bit set with nominal plywood dimensions) is not always a perfect answer.

I might also change the subject back to straight bits, there are a number of types of striaght bits, differentiated in their cutting edges and their bottom characteristics. This is by no means complete, but these choices do exist:

Types of straight bits:
Plain - just cutting edges on the sides, meant to enter from the side of the wood
Plunge bits with flat radial cutting edge on the bottom, meant to enter from the side or plunge in
Plunge bits with conical pointed (or round) end meant to make a V-grooved (or round) bottom when plunging or entering from the side
Straight shear bit (cutting edge does not go straight up and down but at a slight angle)
Solid Carbide spiral upcut
Solid Carbide down cut
Solid carbide combination up and down cut