230 – Mortising Jigs & Through Mortises

Video - October 6, 2014

*Note* – This video was excerpted from an episode of TWW Live.

There are lots of methods available for making mortises. One of the most versatile tools for mortising is the hand-held router. You can do a lot with the manufacturer’s edge guide but you can do even more if you know how to design and construct simple jigs or guides.

I usually make my guides from scrap pieces of plywood or MDF and I use them in conjunction with guide bushings. Because I never quite know what bit/bushing combination I’m going to use, it’s a good idea to have a full set of guide bushings on hand at all times. I recommend the Rockler Guide Bushing Kit.

The key to making these jigs is to know the distance between the edge of the router bit and the edge of the guide bushing. Let’s say you’re using a 1/4″ bit and a 3/8″ guide bushing. That means you’ll have 1/16″ on each side of the bit for a total of 1/8″ difference. So if you’re designing a jig to cut a particular dimension, you should make sure the channel in the jig is 1/8″ wider than your desired mortise width.

You can use jigs like this for standard mortises of just about any size, as well as more fancy joinery like through mortises (an example I show in the video). Essentially, the sky is the limit. Best of all, you can make these jigs in minutes on the fly while working on a project. As long as you know your dimensions, you can knock a simple jig out in mere minutes.

Be sure to let us know what kind of mortising jigs you’ve made in the past. We’d love to see examples!

Products Used

Guide Bushing Kit

Discussion

Zack October 10, 2014 8:06 am

Marc,

Do you account for centering the bit in the bushing? I have had mixed results from my guide bushings and jigs if I forget to check that the bit is centered in the bushing. Do you have a preferred method for this?

Thanks.

Reply
- Marc Spagnuolo October 10, 2014 8:46 am
  
  Probably depends on your router base and bushings but mine don’t really have any adjustability. So if something isn’t centered, there isn’t a whole lot I can do about it. Fortunately, the Festool stuff is pretty good so centering hasn’t been an issue for me.
  
  Reply
Dell Moore October 11, 2014 10:58 am

I beileve Zach may have a problem with the router base plate(?). Could it be off-center some, and it isn’t noticable until the smaller area of the bushing is surrounding the bit?

Just a thought. Zach, You might want to look at that also.

Dell

Reply
- Daniel A Deschenes October 19, 2016 12:20 pm
  
  You can bet it’s a problem with the base plate since the bushing’s center is based on the base plate. They sell base plate centering jigs. They look like little plastic cones.
  
  https://www.amazon.com/DEWALT-.....B004AJEUOY
  
  https://www.amazon.com/Bosch-R.....TQ1PT1ATND
  
  Reply
Jay October 14, 2014 6:00 am

One of my router base/guide sets came with an alignment tool to perfectly center the base with the guide installed. I haven’t measured it but the alignment tool fits with almost no gap in the 1/4″ guide. It works well and once I’ve aligned the base I can switch guide sizes and the bit remains centered in the guide within the tolerance of the guide OD, ID and center-line. I’ve never had a problem with it being noticeably out of alignment with any of the guides after the initial alignment.

Thanks, Jay

Reply
- Brent November 8, 2014 1:25 pm
  
  Yes, my bushing set came with the same alignment tool as well. Most router bases have some adjustability so they can be made perfectly centred around the collet. It’s an important first step in using bushings.
  
  Reply
Jeremy Crawford October 15, 2014 5:26 pm

Marc,
I am a little confused on how to determine the difference between the bit and bushing. If I have a ¾” bushing and ½” bit, is the difference ¼”? Also, can you use bushings with other types of bits besides straight bits, like v-groove, etc?

Reply
- Marc Spagnuolo October 16, 2014 6:45 am
  
  Your math is correct. But it’s a good idea to measure directly to double check. And yes, you can use any bit you like as long as it fits inside the bushing.
  
  Reply
  - Jeremy Crawford October 22, 2014 9:07 pm
    
    Would it be ¼” on either side of the bit or ⅛” on either side totaling ¼”?
    
    Reply
    - Michael Warner March 9, 2017 12:35 am
      
      1/8″ on either side totalling 1/4″
Tony October 25, 2014 8:21 am

Marc are you just using CA glue to hold the jig together? I’m about to do a facepalm, thinking about jigs i’ve left to setup over night using yellow glue. For some reason I just never think about using CA glue in the shop.

Reply
- Marc Spagnuolo October 25, 2014 10:54 am
  
  Yup. But I usually use yellow glue too. CA holds it together as the glue sets up. For jigs that might take a beating, it’s probably best to let them cure for a few hours. For re-usable jigs I think the yellow glue with an overnight dry time is perfectly fine.
  
  Reply
Dennis Rodrigues November 8, 2014 7:03 pm

Hi Marc – Love your videos. I’ve learned so much from you! Not to be picky but at about 2:30 you say “of course there’s a straight bit in there” but actually it looks like you have a upcut spiral bit. If someone tries to use a basic straight bit things get ugly.

Reply
- Marc Spagnuolo November 9, 2014 11:43 am
  
  Well a spiral bit is a type of straight bit, but i agree with what you’re saying with spiral vs traditional straight flutes.
  
  Reply
Clay Baldwin January 8, 2015 9:29 am

This is my first time visiting the new website. Great job, easy to find things and as always fantastic videos. Thanks

Reply
Randy January 24, 2015 6:34 pm

Marc can you recommend a good spiral bit that you like to use for your mortises?

Reply
- Marc Spagnuolo January 25, 2015 8:37 am
  
  I’ve been using Whiteside lately: http://www.amazon.com/gp/produ.....QQOWNYBXRD
  
  Reply
Michael Warner March 9, 2017 12:02 am

I don’t have space on my porch turned workshop for a miter saw and obviously I can’t really use my little baby table saw when i’m trying to cut say 2 feet off a 10′ board. I’ve been trying to find a good jig for crosscuts to use with my circular saw. I seem to either find jigs that are crazy trashy or so over-thought and use tools that I simply don’t have. The only tools I have are either hand tools or power tools. I’m just bored with having to set up a straight guide for literally every cut I need to make. Can either you make a video showing a nice simple jig or perhaps direct me to one you know of? I don’t mind setting up a guide for plywood, but when I’m making multiple cuts in lumber it becomes tedious to say the least.

BTW that is the quietest running router I have ever heard in my life. Barely makes a squeak compared to mine and mine’s just a trim router.

Reply
- Michael Warner March 9, 2017 12:33 am
  
  oh! I just had an idea for one I can build right into my work bench. Hopefully it works. I’d delete my previous post, but i don’t know how. Sorry to waste your time if you do read this. Thanks for another great video.
  
  Reply

230 – Mortising Jigs & Through Mortises

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