upcut or downcut spiral bit for mortises?

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Forum topic by UncleBen posted 10-17-2007 10:35 PM 2993 views 0 times favorited 10 replies Add to Favorites Watch
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37 posts in 4960 days

10-17-2007 10:35 PM

The title pretty much asks it all, but let me add that I will be using my new Freud 3 1/4 hp plunge router, at only $120 ($100 off, no edge guide). If interested, see this LINK

Anyway, the post is not about the router, but it’s a good deal that some of you might be interested in.
I have heard that an upcut bit will clear chips better, but will have more tearout, and a downcut bit will not clear chips as well, but will have less tearout. How does one decide?
Thanks for the input.

10 replies so far

View Mark Mazzo's profile

Mark Mazzo

352 posts in 4921 days

#1 posted 10-17-2007 11:01 PM


For mortises I use an upcut spiral bit. because the mortise is typically covered by another piece and any damage to the mortise edge is not seen. That said, I can’t say that I have ever experienced any tearout. Downcut sprial bits are more useful for things like inlay or marquetry where you require a pristine edge.

I have a post on my blog that describes a jig that I use for router cut mortises and loose tenon joinery.

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

View Bob #2's profile

Bob #2

3810 posts in 5030 days

#2 posted 10-17-2007 11:03 PM

Mortises are usually covered by the tenon piece of the joint so tear out is not a signifcant factor.
Truthfully, I have not seen much difference vs up and down cut bits in the small sizes we use in woodworking.
i.e. under 3/8” generally.

p.s. I did some butterfliy inlays a while back and did not notice a huge difference between either style at 1/8 and 1/4” bit size.


-- A mind, like a home, is furnished by its owner

View UncleBen's profile


37 posts in 4960 days

#3 posted 10-17-2007 11:33 PM

Okay, well I’ll just go with an upcut bit.

View niki's profile


426 posts in 5088 days

#4 posted 10-18-2007 12:48 AM

I’m using just a simple straight bit and did not have any problems

You can see the mortise jig here

The test of the jig, here

The router lift, here

And some table construction, here


View UncleBen's profile


37 posts in 4960 days

#5 posted 10-18-2007 04:11 PM

Thanks Niki

View SPalm's profile


5338 posts in 4890 days

#6 posted 10-18-2007 04:17 PM

You seem to have already chosen, but I agree that upcut will work best for mortises. Actually all three styles will work, but the upcut will clear chips better, and seems to plunge better. Where I see some difference in tearout is on ply, with that thin top sheet. They are usually solid carbide, so handle them with care. With that size of router, make sure to go with 1/2 inch shanks. The difference in a larger shank is amazing.


-- -- I'm no rocket surgeon

View UncleBen's profile


37 posts in 4960 days

#7 posted 10-18-2007 04:22 PM

Thank you Steve. I had decided on a downcut bit since I thought that was what was supposed to be used, but then I heard otherwise. I also was going to get a 1/4” shank since the bit size I need is 1/4”, but I guess I’ll have to rethink that too. It is a large router and is around 11 pounds, so I’m a little worried about breaking the bit. How would HSS do in comparison?

View Bob #2's profile

Bob #2

3810 posts in 5030 days

#8 posted 10-18-2007 05:31 PM

I wanted to add that my experience suggests that only 1/2” blades come on 1/2’ shanks.
Maybe some one could chime in here and tell me where to get 1/4, 3/8” on 1/2” shafts?
I have not seen them in solid carbide – spirals around here.

For what it’s worth, this where I am getting my carbide spirals currently.


-- A mind, like a home, is furnished by its owner

View Douglas Bordner's profile

Douglas Bordner

4073 posts in 5072 days

#9 posted 10-19-2007 06:19 PM

Whiteside makes good spirals.

-- "Bordnerizing" perfectly good lumber for over two decades.

View Alin Dobra's profile

Alin Dobra

351 posts in 4896 days

#10 posted 10-20-2007 05:13 AM

Down cut clears better the bottom (important for inlays but irrelevant for mortices) and up cut clears better the shavings (desirable). Thus is clearly an up cut bit. As Niki mentioned though, you can easily cut them with a regular bit (much cheaper since you do not need all that carbide).


-- -- Alin Dobra, Gainesville, Florida

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