Up Spiral Bit or Down Spiral Bit?

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Forum topic by Nicholas Dillon posted 08-20-2009 07:43 PM 4143 views 0 times favorited 4 replies Add to Favorites Watch
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Nicholas Dillon

33 posts in 3225 days

08-20-2009 07:43 PM

Soon i will be starting a garden bench project that requires some mortise and tennon joints. I could do them by hand but I have a lot to do. I do not have a plunge router.

I want to use my router table and need to know whether I need to use a down or up spiral bit when lowering the wood down onto the router bit. Thanks

-- My workshop is a 8 x 8 shed! No Joke!

4 replies so far

View PurpLev's profile


8535 posts in 3642 days

#1 posted 08-20-2009 08:03 PM

up to pull the shavings UP from the mortise towards the router (and since it’s upside doen, it means = down to the floor)

-- ㊍ When in doubt - There is no doubt - Go the safer route.

View teenagewoodworker's profile


2727 posts in 3761 days

#2 posted 08-20-2009 08:06 PM

upcut…. both for handheld and router table… not gonna make it any more confusing than that

View DaleM's profile


958 posts in 3377 days

#3 posted 08-20-2009 08:47 PM

Okay, I know this is the exact opposite of what everyone just said, but I use the down spiral bit for mortises, to get the clean edge as noted above. Some of the shavings do tend to build up in the hole sometime, but no worse than a straight bit, at least in my experience. Of course, if you weren’t using a table, just the router, you would need the up spiral or your mortise would really fill up with shavings. Either one gives a cleaner cut than any straight bit I’ve tried.

-- Dale Manning, Carthage, NY

View Mark Mazzo's profile

Mark Mazzo

352 posts in 3906 days

#4 posted 08-20-2009 08:53 PM

For the reasons stated, use an upcut bit for mortises to eject the chips more efficiently when the mortise is being cut.

The only time you need to use a doowncut bit is if you need a very cleanly cut opening such as on a through mortise or when inlaying one piece into another.

On the standard mortise, the mortise is covered by the piece with the tenon so using the upcut bit trades off the efficiency of chip ejection and ease of cutting for possible tearout at the surface (which still almost will never happen with an upcut bit)

-- Mark, Webster New York, Visit my website at

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