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Which router bit to use for mortising???

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Blog entry by David Drummond posted 03-28-2011 06:26 AM 12693 reads 0 times favorited 5 comments Add to Favorites Watch

What do you use for plunge cutting mortises with a router; an up or down cut spiral router bit? I want to say a down cut but it seems counter intuitive as it will push all of the waste into the hole but on second hand it would eliminate tear out. What do you use?

-- "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did do... Explore, Dream, Discover” Mark Twain



5 comments so far

View jsheaney's profile

jsheaney

141 posts in 3456 days


#1 posted 03-28-2011 07:35 AM

Normally, you don’t need to care about tear out with a mortise. It won’t be visible. It’s only with a through mortise that you have to be concerned and then only on the show side. Since you’re going all the way through, you don’t need to be concerned about pushing chips into the mortise; they will be falling out the bottom. I always stay away from the ends of the mortise, though, and finish up with a chisel. You have to do that anyway, if you want square mortises.

-- Disappointment is an empty box full of expectation.

View pintodeluxe's profile

pintodeluxe

4859 posts in 2281 days


#2 posted 03-28-2011 07:43 AM

I agree, use an up cut or straight bit for mortises. The shoulder of the tenon board will cover it anyway. Upcut bits help clear the chips from the mortise as well. I still don’t think I will ever go back to routing mortises though. I just prefer a hollow chisel mortiser. Especially when you consider a solid carbide spiral bit is half the cost of a good used mortiser.
Cheers and best of luck!

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

View ratchet's profile

ratchet

1389 posts in 3255 days


#3 posted 03-28-2011 02:33 PM

Upcut bit is the way to go. As mentioned, it clears the chips out. Tearout is not really a concern. Althought nice, an all carbide bit really isn ‘t necessary. The slicing action of a mortising bit is different (and far more gentle) from the chipping action of a regular router bit, the HSS ones I’ve used work nicely. Besides, how many feet of mortises are you planing to do? For most of use its far shorter than other types of routing.
I took a look at hollow chisel mortisers recently and have neither the $ or space in my shop for a good one.

View David Drummond's profile

David Drummond

97 posts in 2133 days


#4 posted 03-28-2011 03:49 PM

I am mortising rails on a crib for slats so there are a total of 72 visible mortises so tearout is a concern for this project. I am also building a rocking chair that will have exposed visible mortises. Thanks for the input!

-- "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did do... Explore, Dream, Discover” Mark Twain

View David Drummond's profile

David Drummond

97 posts in 2133 days


#5 posted 03-28-2011 05:45 PM

I think I have decided to use a downcut… here is some info found on the internet in regards to my inquiry for those of you who are interested. Thanks for the feedback though, I will most likely be using an upcut for any hidden mortise and tenon joints. I should have been more specific as well in my original posting.

The downward slicing action of a down cut bit leaves a very clean, crisp edge around the hole or groove it cuts. While chips still are evacuated from the hole, a down cut bit is far less efficient in this respect than is an up cut design.

This chip ejection deficiency of down cut bits is minimized by the relatively shallow cuts they most commonly are used to make. Down cut spiral bits are a good choice for cutting dados or shallow grooves, especially when the edges will be visible when the project is assembled.

Down cut bits require a slightly slower feed rate. This reduced pace allows the bit a little more time to throw chips out and for them to be re cut into smaller pieces that eventually are thrown from the hole or slot.

Making shallow cuts to achieve the full depth needed is always important, but especially so with a down cut bit. The combination of a deep cut and a build up of chips can cause the bit to over heat and even break.

For most woodworkers, the down cut type of spiral bit is most useful, particularly for those using a router to cut dados, rabbets and visible slots. Some woodworkers like cutting mortises with a router, table mounted or hand-held. For them, the up cut bit will be most efficient.

The ideal situation is to have both types of spiral bits in the drawer, in the size or sizes you most often use. The quest for more tools certainly does not end with spiral router bits.

-- "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did do... Explore, Dream, Discover” Mark Twain

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