I am planning a matched pair of solid panel alder music & tv cabinets, of different heights but each 98cm wide and 50cm deep, and want to make each with mitred case corners. I don’t feel confident in making dovetail mitres over the 5ocm depth. I could use e.g. a mitred spline or Domino joint but I have an unused 1-1/8″ lock miter bit that I thought I might try instead. I can find a number of videos etc. online but to my surprise nothing in FW since about 2000 – 2010 (not that I can find, anyway – see separate forum post on “Searching”). Is this because all has been said (basically: “chuck your lock miter bit”) or is it that a lock miter joint is not considered by the experts to be ‘fine woodworking’? I’d be grateful for advice on this – and, if advisable at all, on how best to adjust the bit and form the joint at the router table – before completing my final design.
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Replies
I can't find anything on FWW about setting up a lock mitre bit. As another forum post mentions, the search facility on the FWW website is next to useless, so its no surprise.
So, I'll recommend a webpage/article from another magazine:
https://www.popularwoodworking.com/techniques/lock-miter-drawers/
Hope it helps.
I've made a number of large cases using a lock mitre bit; also drawers. Once the set-up is done in the router table, the results can be very good, both in terms of very clean non-gappy corners but also strength.
When you do the set-up, it's beneficial to make and keep two pieces (for both the vertical and flat workpiece passes over the bit) as a set-up aid for future projects.
Thanks very much lat_axe, that's very useful and confirms what little I've found elsewhere.
On a point of detail: my cabinets will be backed up against a wall and will have front face frames so the corner joints will not be visible.
Been a long time since I used mine, but getting large panels across it will be challenging. Setup is trial and error to hit a point where a single pass on each board gives you a perfect fit. One side goes through face down and the other standing tall against the fence.
Since the cuts are deep end grain blowout is an issue, back up the stock on exit. I'd go with the domino.
Not fine woodworking? It's not cheating nor is it an inferior joint. If you can be patient and set up correctly, there's nothing wrong with it. It's just hard to run long edges past the bit steadily and consistently. That's why I've given up with three different bits, even using the matching set-up guides. The last time I thought it would be easier with a horizontal routing table, but decided not to make one.
Some feedback: I had no success despite several frustrating tries on test pieces then some more on a full blown test project (workshop router / router accessory cabinet using panels and parts regained from other pieces of furniture no longer in use). In the end I resigned to the inevitable, pared down the ruined ends on my table saw and went with a mitred domino joint - so my cabinet is a bit smaller than planned, but at least it's done. (As an aside, it was planned for dual use, with its top surface as an auxiliary extension surface for my mitre/chop saw, so I now just have to raise the whole thing about 40cm to make up for the loss in height).
Lock mitre joints are very good at detecting the inadequacies of both a poor router table and/or its set-up as well as the less-than-perfect technique of the operator. However, once those factors are improved and effectively eliminated, the lock-mitre provides an extremely neat and very glue-strong joint that's fast to make.
Any sag or bulge in the router table top or woggle i' the fence will cause problems. Failure to keep the workpiece travelling true past the bit as it cuts will cause problems.
There may also be the issue of workpieces that themselves are not dead flat and straight.
The answer to the first issue is to get or make a router table and fence that has very good precision - dead flat top with a straight fence, 90 degrees to the top and with micro-adjustment.
The answer to the second issue is likely good hold downs and other guides that ensure the workpiece travels true through the needed path over the cutter, with no chance of wobble, rise, tip or any other variation being introduced by the operator.
And well-made stock without any warps.
Personally I use a Veritas router table, sadly no longer available, which meets all the above criteria. I imagine that many modern router tables & fences are as good - and that many are not. Home-made router tables are also notoriously difficult to make with a top that'll stay dead flat and a fence-with-hold downs that's precise enough for the job.
I used the jig from this Fine Woodworking article with good results. Makes for a safer routing experience.
https://www.finewoodworking.com/membership/pdf/39041/011121054.pdf
For my purposes, I ask myself what is the purpose of adding anything to the simple miter joint. It is certainly not aesthetics as the interior of the joint can't be seen once it is assembled. Improved strength? Maybe. However, there have been tests (I can't cite or quote any without looking them up) that suggest minimal if any additional strength. So, for me, it is for the purpose of keeping the joints aligned during glue ups by keeping the joint from sliding around under the pressure of the clamps. For this, the lock miter joint, while functional, is just too much trouble. With a two minute setup on the table saw, I can cut a kerf in the miter face and insert a continuous or intermittent spline that serves my purpose.
Alignment is a big reason, and for long grain miters joint strength is not an issue.
For end grain miters or plywood miters adding flat & cross grain glue surface with biscuits or even better having a domino lever arm inside the joint improves survival odds.
A spline is great for alignment, but they're usually just a blade wide and can split right along with a miter if stressed.
Pete,
Hopefully this is not too late to help you, but Stumpy Nubs has a great video on setting up for accurate lock miter joints on the router table.
https://www.youtube.com/watch?v=L_rJhz9C3wk