Straight pattern vs. spiral pattern bits?

[Paul Arnold]

Which of the 2 is better for patterning from a table mounted router? Smoother cuts, better on tear-out, etc.?

Thanks,
Paul

[Scott Brihn]

I prefer a spiral flush trim bit. I use Whiteside #RFT5200.

[pat warner]

There's usually trade-offs.
End grain cuts, e.g., are generally cleaner with spirals. Spirals are more efficient cutters, hammer less, and require less power than a straight bit.

Notwithstanding, they are riskier than straight bits. They (spirals) can suck the material down on the router table or separate the stock from the templet unexpectedly (with poor fixturing). They will usually booger the top (or bottom) edge/corner of the stock, where a straight bit won't.

Straights are cheaper, easier to sharpen, cut well and are safer.
There is more to the story but for the short run I would not mess with spirals.
More at the 2 links.
1) No.12 (http://patwarner.com/faq.html) &
2) Straight bits. (http://patwarner.com/straight_bit_kit.html)

[Keith Outten]

Spiral bits are made in either upcut or downcut styles and each will preform differently depending on the setup. When using a router table an upcut spiral bit will help hold the material down to the table top. Downcut bits are generally best used in a CNC Router where the work and the router motor are both mechanically held.

There are also spiral bits that have both upcut and downcut spirals, these are used to provide almost perfect edges on the top and bottom of the wood and are also used in CNC Routers.

.

[Cliff Rohrabacher]

If you are one of those people who uses a router to do dados you'll find a down cut may leave you with cleaner edges. Especially in finicky woods like Oak Ply.

I'll use both a conventional 3/8" spiral end mill and a whiteside stagger tooth in my slot mortiser and both work great.

[Brian Gumpper]

FWIW, a pattern bit is usually the one with the shank mounted bearing and spirals are not offered in that style. The flush trim bits are available in both styles.