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I'm planning to build a structure of about 1.2m x 1m x 0.5m (specifically it's a 1:6 doll house) in 12mm (half-inch) ply and don't want to use internal square-section to support the corners, because this will encroach into the interior space.

I'm considering using mitre lock joints but the information for this mitre lock bit states that it should only be used inverted. However, I don't have a router table, nor do I have space to keep one if I bought it. So I'd like to know if there is a technique for using this kind of mitre lock bit without a table, for example with some kind of jig.

I expect that a device like the WoodRat would be capable of doing this, but it takes up almost as much space as a roter table, so I'm somewhat reluctant to go that way.

Can mitre lock joints be made (in plywood) without a routing table? How?

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  • Wow, some of those pictures of the WoodRat in action... Looks like a good way to lose a finger.
    – FreeMan
    Aug 15, 2016 at 20:45
  • @FreeMan which picture(s) in particular? I didn't see anything that looked dangerous.
    – James Youngman
    Aug 16, 2016 at 5:50

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The reason the lock miter bit is restricted to the router table is mostly for safety - it is a large diameter bit, and it exerts a lot of force on whoever is holding the router, be it you or the table. In addition, using it handheld will increase the risk of misalignment of the cut, which is crucial for the lock miter to work.

I would suggest building a temporary router table - just take a piece of plywood, cut a hole (easiest with a hole-saw) for the router bit to poke out, and connect the router base plate using mounting screws (check your router's base plate to see which ones you need. You might even got some with the router). The fence can be any flat piece of wood that you can clamp while adjusting the lock miter (and you can even screw the fence in after the setup is good). The fence doesn't need to be aligned in any particular way, and it should just be flat enough around the router bit. Clamp the plywood to another table, lower the bit all the way, turn on the router and slowly raise it, so that the router bit will make a hole in the fence for itself.

Something similar to this (picture from Google Images search). Temporary router table example

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  • Thanks for the tips. I saw plenty of items on the web and YouTube about shop-built and sometimes temporary router tables. But I don't see how these contrive a router lift. Router lifts seem to be very expensive, and yet the ability to finely adjust the height of the cutter is an essential part of many routing operations. Could you expand a bit on this aspect? In case it matters, my router is a Makita RP0900X.
    – James Youngman
    Aug 9, 2016 at 13:22
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    @JamesYoungman I think it was assumed that you had an adjustable, fixed-based router rather than a plunge router, because you didn't specify. Does the RP0900X come with a fixed base?
    – Jason C
    Aug 9, 2016 at 13:36
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    Actually some plunge routers can also be used in a router table (some DeWalt's, for example). The particular Makita model has a depth lock, so you might be able to use it as a crude way to set the depth. I would prepare all of the boards you want to cut and then do a single run for all of them, so even if the setup process is long and tedius, you'll only need to do it once.
    – Eli Iser
    Aug 9, 2016 at 14:12
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    Just in case there is confusion on this point, a router lift is very nice for making precise alignment easier, but it can absolutely be done with a fixed base on the router table. There's just more fiddling to get it right. Which for the lock miter bit means you need plenty of scraps to test on. You'll be adjusting two variables: the height of the bit, and the placement of the fence. Both are crucial for the joint to come out right.
    – Katie Kilian
    Aug 9, 2016 at 14:30
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Unless you are using a high grade plywood, a miter lock bit is likely to produce a lot of tear-out. I've never seen one used in anything other than solid wood. And unless it's an exposed joint that you want to show off, it's more than you need for a solid join.

Consider using a dado and rabbet (a.k.a lock rabbet) joint instead. It's easy to make with a standard straight bit, and provides plenty of strength.

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    I've had good experience with lock miter on Baltic birch plywood.
    – Eli Iser
    Aug 10, 2016 at 4:41

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