deep mortises with a plunge router

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Forum topic by brianP posted 02-24-2011 06:07 AM 11691 views 0 times favorited 10 replies Add to Favorites Watch
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20 posts in 2975 days

02-24-2011 06:07 AM

Topic tags/keywords: mortise plunge router

I usually make mortises for table legs and door stiles by drilling out most of the waste with a brad point drill bit and then using a mortise chisel to take out the rest. But I sometimes have difficulty getting the sides clean. So for my current project I thought I’d use a plunge router and an MDF jig. But my 1/4” wide mortises need to be around 1.25- 1.5” deep, so to accommodate for the 1/2” of MDF for the template I would need a bit that has a cutting depth of 1.75 -2 ”. But I can’t find a 1/4” bit with a depth of cut greater than 1”.

What does everyone else do?

-- --Brian, Brooklyn, New York

10 replies so far

View Loren's profile


10477 posts in 3850 days

#1 posted 02-24-2011 06:28 AM

I think single flute high speed steel bits are available in longer lengths.

1/4” carbide bits are fragile when flexed so that’s why they aren’t made longer.

That said, I’d go to 3/8”. Longer bits are available in that size.

You can also get an extender for your collet.

I usually make templates out of 1/4” masonite. It’s tough and thin
enough you don’t lose too much cutting depth.

View Bernie's profile


422 posts in 3039 days

#2 posted 02-24-2011 06:32 AM

I’m sure there are other ways, but I have a drill centering jig and I drill out the bulk of my mortise joints and finish them with a wide chisel (or as wide or long as your joint is. After drilling dead center with my jig, I take my very sharp chisel and lay the flat side along the edges of my drill holes. I then stand it up-right and tap it with my mallet to finish the cut. This works great for me. If I make a very minor error, it gets covered by the tenon piece, but my joints are generally snug and my work is fine for me and great for 99.9% of the observers. Of course my jig opens up to a 1.5 inch width, so this method is only for the narrow surface of boards. My last project was a cherry hosier step stool and my mortise cuts had to be on the face side of my boards. I cut a jig from hard board the same width as my boards, drilled a center hole and used it for centering the holes on my project. This methods works great for me… thanks for posting this question. Like you, I’m all ears for a better method!

-- Bernie: It never gets hot or cold in New Hampshire, just seasonal!

View richgreer's profile


4541 posts in 3276 days

#3 posted 02-24-2011 04:41 PM

Why are you using 1/2 MDF for the template. There is thinner material that will work fine.

Also – You could build what I call an external jig. You put the router directly on the stock but you are guided by frame around the outside of the router. I usually get by with a guide on one side only but I always attach stops for each end. Take it easy and only bite off a little with each pass. Go in the direction where the bit is pulling you into the guide.

-- Rich, Cedar Rapids, IA - I'm a woodworker. I don't create beauty, I reveal it.

View brianP's profile


20 posts in 2975 days

#4 posted 02-24-2011 08:16 PM

I guess I was going to use 1/2” MDF because there is a piece of it sitting at eye level on my rack. Hadn’t thought of using thinner, though clearly that would be better. That’ll teach me to think outside the (scrap) box! Thanks everyone.

-- --Brian, Brooklyn, New York

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4541 posts in 3276 days

#5 posted 02-25-2011 02:55 AM

You can’t push this idea too far, but you will find that you do not have to set the bit real deep in the collet. IMO, you can get by with only inserting the bit 3/4”.

-- Rich, Cedar Rapids, IA - I'm a woodworker. I don't create beauty, I reveal it.

View DLCW's profile


530 posts in 2856 days

#6 posted 02-25-2011 03:11 AM

Look into CNC bits. They come in some pretty long lengths and can be used in a hand held router. I’ve done this with some projects in the past. Just make sure you guide the router and not the other way around. Take shallow cuts on each pass – no more then 3/8” in soft wood and 1/4” in hardwood. This will give you clean cuts and enables you to keep control of the router.

-- Don, Diamond Lake Custom Woodworks - - "If you make something idiot proof, all they do is make a better idiot"

View cabs4less's profile


235 posts in 2964 days

#7 posted 02-25-2011 03:48 AM

well if your using a bushing/bit combo you need 1/2” template stock or cut your bushing down in lenght but i would just use a regular bit in go as deep as i colud then grab a 3/16” drill bit and drill to the final depth and using the side walls of the existing mortise as a guide chisel the rest of the way.

-- As Best I Can

View McKinneyMike's profile


80 posts in 2863 days

#8 posted 02-25-2011 01:38 PM

I used a 4 1/4” long double fluted spiral bit to cut 2” deep mortises with my router recently when I built my reloading benches. These were 1/2” shank and 1/2 diameter bits though as my mortises were 3/4” wide. Flex is the big issue with thinner bits of course. I would drill out the majority of the mortise and then slowly route with a bushing and incrementing no more than 1/4” at a time to minimize any chance of the bit deflecting during the routing. Go slow and be deliberate. You will be fine.

-- McKinney Hardwood Lumber --Specializing in exotic and figured hardwood lumber -McKinney, TX

View Domer's profile


252 posts in 3568 days

#9 posted 02-25-2011 04:58 PM

Why do you need to have a 1/4” mortise 1 1/2” deep. Is it a through tenon? It seems to be pretty deep.


View swayze's profile


97 posts in 3290 days

#10 posted 02-26-2011 08:41 AM

I believe you can get a whiteside spiral upcut bit in either a 3” or 3 1/2” overall length.

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