Mark (TheCraftsmansPath.com) on March 17th, 2008

I get a lot of questions via e-mail on things I’ve posted about here. I usually just reply to the e-mail directly but, I thought that it might be instructional to post some of these questions and my responses because there may be others out there with similar questions who could benefit from the dialog.

I recently received a question from Jeff in North Carolina regarding the Mortising & Loose Tenon jig that I previously posted about. Actually, I’ve received a number of questions regarding this post so, I thought that this might benefit a number of you out there. Jeff and I actually had a couple of e-mail exchanges on this. Below is a transcription:

I’m pretty new to woodworking and enjoyed your article on loose tenon joinery. I’m going to give it a try and will soon purchase the DeWalt 518PK Router Combo kit.

Do you have dimensional plans for the router mortise jig? A rough idea will do since I can adapt it to scale. Material construction
appears to be maple and MDF. Correct? I’d appreciate any other tips that you can offer for constructing and using the jig (i.e., do’s and dont’s).

I don’t have a router table so I envision some problems cutting and shaping the tenon stock (1/4″-3/8″ thick). I may try my hand using a low angle block plane on a test piece. Any other suggestions?

Many thanks for your help.

-Jeff

Here was my reply:

The jig I made was adapted from one found in Bill Hylton’s book Router Magic. It is fairly simple to build. Mine was made from scrap MDF and Poplar, but really any stable wood or sheet good would suffice. My jig is about 14″ wide x 8″ high x 5″ deep. It originally built mine from available scraps but, if I built it today I would make it higher than 8″. This is because after clamping the stock into the jig, sometimes there is not a lot of material left available to clamp into my bench vise. Other than that, the only thing I would double check is the depth based on whatever edge guide you are using. Depending on how much adjustment you have on the edge guide, you may need to adjust that dimension to give yourself enough extension to cut mortises.

When you use the jig, you want to be moving the router so that the rotation of the bit tends to draw the edge guide fence against the jig. Do this by standing in front of jig and moving the router from right to left. Also, when mortising, I usually take small bites, no more than 1/8″ to 1/4″ deep at a time, using a spiral upcut bit. It helps if you have a vacuum attachment for the router to clear the chips but if not, just stop after the mortise (or when it gets too filled with chips) and vacuum them out.

As far as the tenon stock, it is nice if you have rounded the corners of the tenon stock to match the mortises. However, there are other ways of dealing with it if you do not have a router table. One way would be to use square tenon stock of the correct thickness and just square the ends of your mortises with a chisel to match. Another option would be to just chamfer the corners of your tenon stock with a block plane until it fits. Most of the strength of the joint comes from the long grain glue surface provided on the sides of the tenon stock so, if it is a bit short in height because of the chamfers, that’s OK. Just be sure that you align things a bit more carefully when assembling the joint because you will not have the benefit of the tenon height to help there.

Jeff made some progress on the jig and wrote back with a couple of other questions:

Thanks for the advice. I’ve just about finished making the jig. I ended up using particleboard because my local Lowe’s doesn’t stock MDF. The 5″ depth works out fine for my DeWalt 318 plunge router and its accompanying edge guide. There is plenty of back to front adjustment to accommodate thicker stock if necessary; I’ll probably be in the 3/4″-2″ range most of the time.

I’ve just finished constructing my own version of the “New-Fangled Workbench” and I’m playing with the configuration to secure the jig in its clamping system to allow cutting a mortise in the vertical position (stile?). The vertically adjustable planing bench is a nice feature for supporting the bottom end of the workpiece. However, I’ve gotten pretty good at simply cutting a classic tenon on the table saw and using a shoulder plane for fine tuning so I may go that route.

You noted moving the router from right to left in order to draw the edge guide fence against the jig. This seems counter to router practice where the clockwise rotating bit is moved from left to right. Is your suggestion based on a peculiar characteristic of the spiral up-cutting bit?

Thanks for your help.

-Jeff

Here was my reply:

Glad to hear that you are progressing on the jig. I think the particle board will be fine as long as it is flat. You may want to coat it with a light coat of finish to keep it from picking up moisture and swelling over time.

With respect to the router feed direction, I am going by memory here without trying a piece in the jig, but I think that what I stated is correct. It is different from a typical edge router operation (like you described), because of the edge guide. You should try this for yourself, but I think you will find that if you feed right to left that will pull the edge guide in toward the jig. When you go left to right, the edge guide will pull away from the jig and you will have a typical climb-cut scenario (because there is no bearing on the router bit stopping this). One other thing that I sometimes do when using the jig is to plunge both ends of the mortise straight down to the final depth first and then route between them R to L until I’ve completed the mortise.. For deeper mortises, this ensures that the ends of the mortise remain vertical.

Doing tenons on the table saw is also something that I do after making mortises with this jig (look at the Queen Anne Side Table on the blog for an example). This is fine. You get the benefits of a clean, precise mortise with the router jig and then a tenon that you can fine tune on the table saw and/or with the shoulder plane.

Hopefully, this kind of question and answer is beneficial to others out there. Please let me know what you think. You can either leave a comment using the comments link at the end of the post or send me an email at thecraftsmanspath@gmail.com.

Tags: , ,

One Response to “Q & A: Mortising jig and loose tenons”

  1. Not really a question but a comment, I am glad I found your site and the explanation of how to make a Maloof style joint. Frankly I am tired of the Maloof style, the same as Krenov, A&C, G&G, etc. As furniture designers I feel we must take the next step, not keep rehashing the same old designs. Nevertheless some technques are useful, the Maloof style joint for chair I feel is very elegant and something I plan to use in a chair I am designing that looks nothing like a Maloof chair.

    Thanks again for posting your instruction set, while I had an idea on how to do it, your post made it a lot clearer.

Leave a Reply