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Self-Centering Mortising Base for the Router

comments (16) January 13th, 2012 in blogs

FineWoodworkingEditors Fine Woodworking Editors, 
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Rotate the router until each pin touches the workpiece for a perfectly centered cut.
This simple base, used with a plunge router, makes it easy to center a mortise on a leg or post. The base has two downward projecting pins at equal distances from the bit on opposite sides. The concept is elegantly simple: When you rotate the router so that the pins are touching the sides of the workpiece, the router bit is centered.

When building the base, it's crucial to locate the pins accurately. Do this after the base is attached to ther outer and a hole for the router bit has been plunged through. The distance between the pins should exceed the widest part your likely to use it for. With the locations marked, remove the base and drill the holes on a drill press. Finally, insert smooth dowels—not the kind with ridges—or metal pins into the holes.


Read the entire article for more clever router bases.
A better way to locate the holes is with a self-centering dowel jig, used in an unconventional way. With the base attached and the center hole plunged, chuck a 1/2-in. drill bit in your router (you won't be running the router with this, it's just a reference), then place the 1/2-in. bushing of the doweling jig over the bit. Align the 3/8-in. bushing hole so that it is either across or in line with the axis of the router handles, then position a straightedge against the jig and clamp the straightedge to the base. Drill throug the 3/8-in. bushing into the base. Then swing the dowel jig around to the opposite side, use the straightedge to align it, and drill the other hole. You can then enlarge the hole for the router bit to whatever you need.

In use, you may need to leave your workpieces a bit long in order to support the pins on when cutting mortises near the en of a leg or post.

Here's How it Works
 
click to enlarge		 First, plunge through a square base. Put a 1/2-in., plunge-cutting bit in the collet, and plunge down through the base.
 
click to enlarge		 An unlikely layout tool. With a 1/2-in. drill bit chucked in the router, use a doweling jig to locate and drill the pin holes directly opposite one another and equidistant from the bit.
 
click to enlarge		 Register the jig on a straight strip. Clamp the strip in place and align the jig with it before marking and drilling the first hole.
 
click to enlarge		 Rotate the jig. After drilling the first hole, spin the jig 180-degrees to locate the opposite hole.
 
click to enlarge		 Pins center the router. Add some glue, drive in two 3/8-in. dowels or metal pins, and the jig is done.
 
click to enlarge		 Rotate the router. When the pins touch the sides of the workpiece, the router bit is centered.


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posted in: blogs, router, Jigs, router jigs, mortising, self centering mortising jig
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Comments (16)

Bilk Bilk writes: LOL I guess I should have read ahead. Seems that was already mentioned :)
Posted: 1:51 pm on January 22nd

Bilk Bilk writes: I really like the simplicity of this method. I don't know if it was already mentioned above, but what would make this an even better design would be to use a clear Lexan base for it's strength, gliding properties and to provide visibility of the cut. Otherwise very nice idea.
Posted: 1:44 pm on January 22nd

glthornberry glthornberry writes: Half-inch clear Lexan would be a good alternate material for a base like this. It's very machinable and durable.
Posted: 9:23 pm on January 20th

nikejeff nikejeff writes: The idea is good. The suggestions for a clear base are spot on.
Thanks all!
Posted: 11:24 am on January 19th

jacobleefurniture jacobleefurniture writes: Seems it would be troublesome to keep pressure on the pins as you plunge the router deeper and deeper. Also looks like the plywood base blocks your view of the workpiece. How do you know where to stop the cut on the top and bottom of the mortise?
Posted: 7:48 pm on January 16th

Spilperson Spilperson writes: I like the idea, too, and have used other variations. I have run into one problem, though.

If you let the router body rotate even just a little while making the cut the bit will follow. It is pretty easy to mess up a piece that way.
Posted: 5:37 pm on January 16th

ColinScowen ColinScowen writes: Assuming you have a router with the european style mounting for guidebushes (such as the DW621) you can also do this with two small bearings, two spacers and two countersink head screws (with the same thread as the guide bush mounting screws). The screw head outer diameter should be larger than the bearing inner diameter.

I have used this for stopped dovetail grooves. I put two workpieces on the bench with a gap between their ends greater than the maximum diameter of the dovetail cutter, sandwhich them with two pieces of ply. Register everything on the bench, then pick the whole lot up, turn it over and clamp in your vice with some showing out the top. The bearings run against the ply. You can then move the cutter in to contact with one of the workpieces, make a mark, do the same for the other side. Take the router out, measure the depth you wish to rout, make an end mark. Then, put the router back in the jig, put the bearings in contact with the ply, start the router and make your cuts.

Colin.
Posted: 7:44 am on January 16th

we2lawsons we2lawsons writes: Really love this idea! I also like the post of epirnik (see above) about offsetting. This makes me wonder if you could put various thickness "sleeves" over one post to offset. Dang! Looks like I've got MORE experimenting to do.....
Posted: 11:24 am on January 15th

we2lawsons we2lawsons writes: Really love this idea! I also like the post of epirnik (see above) about offsetting. This makes me wonder if you could put various thickness "sleeves" over one post to offset. Dang! Looks like I've got MORE experimenting to do.....
Posted: 11:18 am on January 15th

guerrero10 guerrero10 writes: Muy ingenioso y facil de implementar. Gracias por el aporte.
Posted: 5:21 pm on January 14th

UTFan UTFan writes: Just need to remember to keep the pins up tight against the workpiece, otherwise, your mortise will not be true.
Posted: 10:25 am on January 14th

UTFan UTFan writes: Just need to remember to keep the pins up tight against the work piece to keep it centered. Otherwise, your mortise will not stay true.
Posted: 10:22 am on January 14th

Rocket1945 Rocket1945 writes: Hi. I did a bridal joint at the top of a rear chair leg with this method. Do use a clear material for he base and do leave the stock about three inches longer than needed to accommodate the distance between the pins and the bit. I just did a standard thru mortice then cut the top off to create the open joint.
Posted: 7:57 am on January 14th

bianchiwoodworks bianchiwoodworks writes: epirnik,
I just purchased a similar base from Rockler(on sale for 10 bucks!. I used a shim on one side of the routed piece to offset the bit. It worked great!
Posted: 5:47 am on January 14th

epirnik epirnik writes: LOVE this idea! Thanks TimR!!

I've also wanted to experiment with doing offset mortises by placing one of the pins closer to the bit. In theory, I think it should work - haven't tried it yet, though.

Thanks for the great idea.
Best,
Ed
Posted: 4:15 pm on January 13th

TimR TimR writes: I would suggest splurging a little and buying a clear material rather than plywood. That way you would have better visibility and could see where to start and stop the mortise. If you wanted to still use plywood I would open up the hole in the center where the bit passes through.
Posted: 2:23 pm on January 13th

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