What would you buy for your first spiral bit?

[Kesh Ikuma]

I am getting ready to invest on my first spiral bit (probably either a Freud or Whiteside 1/2"-shank). Looking at their options, I'm unsure what would be the most "future-proof" (or most useful) bit size/style would be. From past SMC threads, people are recommending spiral up cuts (others being compression bit, which seems to be a bit more $$$). But, I couldn't find much on the "best" bit dimension.

What would be your choice of the bit spec?

(a) double or triple flute
(b) diameter
(c) length

Currently I'm weighing between smallest (3/8" dia) triple flute and 1/2" dia longest double flute. But I'm wide open to other suggestions. Thanks for your input!

FYI, it is intended to be used with 2HP handheld router or 3HP router table.

[Andrew Joiner]

I bought a 3 piece set from Harbor Freight for $13. Great value. I cut a couple dozen mortises so far with fine results.

[david brum]

I think spiral bits are the cat's meow for cutting mortises and imagine that is most folks' main use. I'd buy the size that matches your most commonly used mortise size. For me, that would be 1/4" for cabinet doors and general work with 3/4" material. A good start is a 1/4" upcut, two flute bit, around 2 1/2" overall. By happy chance, that is also about the least expensive size.

One work of caution about buying a 1/4" cutter diameter with a 1/2" shank: You will be limited in the depth of your cut at the point where the cutter necks up to the shaft diameter. If you get a constant diameter bit, such as a 1/4" bit with 1/4" shaft, you can squeeze more depth out of the cut. Just sayin'.

[Jim Rimmer]

It's hard to tell you what size to buy. As David said, what do you think you will use the most. For me it was 1/2" up cut.

[Kesh Ikuma]

Thanks David & Jim,

I anticipate its main use will be to cut mortises but the first use probably will be to use it with circle jig... For mortises, I foresee myself using mostly 3/4" and 1-1/2" thick materials. I've read the rule of thumb for M&T is 1/2 the material thickness, so it sounds like 1/2" bit may get me in a trouble later.

I should have a 1/4" shank collet for my Bosch somewhere in my workshop... so perhaps I should consider getting a 1/4" shank bit, instead.

A smaller bit seems to have wider application (if I don't mind more work to cut out larger mortise with it). Does it have shorter life compared to a larger bit of a same make/quality?

[Mike Cutler]

Whiteside, 1/2" two flute spiral upcut with a 2" cutting length.
The "Rule of Thumb" for M&T joints as I know it is 3/3/5.
Tenon thickness is 1/3 the material thickness of the tenon member.
Tenon length is 2/3 the width of the mortised member.
Tenon width is no more than 5 times the tenon thickness, without a division.
Traditionally 4/4 material is done with a 3/8" M&T. It's simple easy and stong. Following the 3/3/5 rule it would be 1/4" thick, but that's kind of a wimpy tenon. These are rules of thumb though, and not etched in stone.

[Dan Hulbert]

As someone with more time than money, I'd suggest the smaller diameter bit. With multiple passes , you can always make the hole larger. Not so with large bit. 1/4" upcut on a 1/4" shank can do many things with multiple passes and patience.

[Stephen Cherry]

1/4 or 3/8 spiral upcut (3/8 takes a 3/8 collet) are pretty much universal bits. If I could only have 1, it would be 3/8. 3/8 is nice because you could drill out mortises, pattern route, etc. If you don't want to get a 3/8 collet, next up would be 1/4. (plus, it's cheaper!)

[Kesh Ikuma]

Whiteside, 1/2" two flute spiral upcut with a 2" cutting length.
The "Rule of Thumb" for M&T joints as I know it is 3/3/5.


Thanks for the RoT. I got mine off of a quick Google search, so it's nice to hear others' input.

So, it's looking more and more that I should aim for 1/4" bit for my 3/4" material.

[Kesh Ikuma]

As someone with more time than money

That's me, too :D

[Mike Heidrick]

Whiteside RU4700 from Brian at Holbren - sales at holbren dot com and get teh 10% woodnet discount. 1/2" shank 1/4" upcut spiral. Amazingly nice cut. I put miles on them with my CNC.

[glenn bradley]

I use 1/4" upcut spirals so much I automatically pick one up whenever a Whiteside, Freud, Amana, etc. show up at a good price. The cheap-o's aren't really worth bothering with. Just foul a nice piece of material and you'll think twice about saving a few dollars on something that isn't all that expensive ;-) I use them for cutting, flushing, mortising (mostly) dados and whatever.

I use a 3/8" most for dados as that is what my shop made dado jig is sized for. This allows me to do dados from 3/8" up through most any size you might do with a free hand router. My Mortise pal uses 1/4" through 1/2" spirals based on the size you're after. Whiteside makes an extra long 1/4" to allow for the jig thickness.

[Kesh Ikuma]

3/8 takes a 3/8 collet

I've seen those "non-standard"? collet sizes. How do you use these bits with odd shank sizes (5/16", 3/8", 5/8", and 3/4" are all available from Whiteside)? Are they intended for non-router use (CNC machine perhaps)?

[Kesh Ikuma]

Thank you all for your inputs!

As of now, I'm leaning towards:


Whiteside RU4700 from Brian at Holbren.

Once I get my feel for the bit and how I use it (and as a new kid on the block, woodworking in general :D) I'll slowly build up my collection to 3/8" and 1/2" as good sales pop up.

Now, with Holbren >$75 free-shipping deal, I need to start thinking about getting dado set along with it. I'm sure I will come back and ask that question later :)

[Mike Heidrick]

Whiteside 3/8 spiral upcut with 1/2" shank is RU4900. Can you tell I buy a LOT of bits from Brian :)

Brians shipping is cheap and FAST. You will be happy. The woodnet discount is 10%.

[Mike Heidrick]

I've seen those "non-standard"? collet sizes. How do you use these bits with odd shank sizes (5/16", 3/8", 5/8", and 3/4" are all available from Whiteside)? Are they intended for non-router use (CNC machine perhaps)?

You can buy other size collets for some routers from precise bits for different shank sizes. Or you use an adapter but some dont like the run out or weight they add.

My CNC uses a chinese elctrospindle instead of a router and I use ER20 collets. They make every fractional and metric size collet you could ever want.