Straight or Spiral router bit?

[Scott Jungdahl]

What is the difference in cutting and why? Which is best for 3/4" dados.

[Prashun Patel]

Spirals are in general a little better at plunge cuts and resist tear out a little better. The up cut spirals excavate better but the Down cuts leave a cleaner top edge.

If you doing any edge work, the spirals will tear out a little less around grain direction transitions.

Shear cutting bits are kind of in between spirals and strict straight bits.

Compression bits are spirals on steroids. They simultaneously up and down cut which makes them very efficient and resistant to tear out.

The choice of which bit to use is in this spectrum is almost always (for me) dictated by economics and tolerance for having to be more careful about technique and depth and patience.

[Edward Weber]

3/4" spiral router bits are expensive ($56 last I checked) and not always necessary to achieve a good quality cut. What you're cutting the dado into might help determine if you need a spiral bit or not.

[Stan Calow]

I prefer a straight bit, especially if its a shallow cut.

[Tom M King]

In handling, the spiral bits can cut you a Lot easier than a straight bit.

[Richard Coers]

You have to buy a special straight flute bit if you want to plunge cut, but all spiral bits plunge cut.

[Mel Fulks]

When you need to move a lot of wood fast ,the single flute bits are best. Much faster than 2 flute bits.

[Bill Dufour]

For 1/2 or 1/4 I use solid carbide endmills. designed for aluminum if I can get them that way. About 1/2 the price of wood working versions since they sell so many more. I have quite a collection of used endmills for wood from the bay. Metal workers switch them out after 30-60 minutes of use.
Bill D

[Brian Holcombe]

For Dado’s I use a down shear mortising bit. I mark with a knife on cross grain cuts, or define the abutments with the tablesaw first.

[Brian Gumpper]

3/4" spiral router bits are expensive ($56 last I checked) and not always necessary to achieve a good quality cut. What you're cutting the dado into might help determine if you need a spiral bit or not.

That must be a high-speed steel version. The 3/4" carbide spirals are well over $100 and have never seen one with anything but a 3/4" shank.

[Brian Holcombe]

I have a 3/4” ball nose and it cost me $175

[Edward Weber]

Yes, the one I was talking about was a HSS bit, the carbide are up over $200

The brand I'm semi familiar with is Onsrud, they're sold at lots of places
(example)
https://www.burnstools.com/52-395-sc-3-4od-2-1-8cl-2fl-upcut-spiral