Lock Miter Tips and Tricks

[J0hn]

I have found once you understand where the center of a Lock Miter Bit is, it is pretty easy to setup.  You do need a proper tool to measure - I use a Wixey WR200 Digital Height Gauge which comes in handy for other things

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I should mention there are two parts to setting up a lock miter bit

Set the height of the bit
So with my Bosch 84508M Lock Miter Bit, I know that the center is .177" below the top edge of the top cutter.  I want the center of the cutter to be centered on the workpiece, so I measure the thickness of the board I am using and divide by two.  .75" / 2 = .375".  So I take the .375" and add it to the .177" and I know that I need to set the top edge of the top cutter to .552" above the router table.

To test - run two boards flat (horizontal) through the bit, flip one over and mate them together.  The top surfaces should be flat and level.  If not, fine tune your height adjustment.

Set the fence
Once the bit height is set, place one of the boards against the fence (vertically) and with a straight edge, adjust the fence so that the bit is almost touching the straight edge.  You want a sharp point, but if the fence is set too far forward, you will get a flat spot on your edge, and if it is too far back, you will be cutting off material which will shorten the length of the piece you are working on
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Lastly is technique.  You need to make sure the boards are properly held down or pressed firmly up against the fence.

Edited to Add another example:
Here is a couple pieces of 3/4" MDO.  The actual thickness is a little shy of 3/4"  (.722)

So I take half of my thickness of the board (.361") and add it to half of my router bit measurement (.177") and get .538" which is how high the top edge of the top cutter gets set above the router table and then I use the same board with a straight edge to set the fence position as noted above.  Didn't even have to run any test cuts - looks right on after the first run
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[antss]

The infinity jig Tom showed is much faster and simpler to use.  Being cheaper isn't a drawback either.

Of course it's not versatile like the gauge.

 

[J0hn]

I have looked at the Infinity Jigs  (I love buying new tools) but declined for a couple of reasons

Fine Wood working wrote a brief review and noted "You still need test cuts to dial in the setup to perfection, but Infinity’s jig gets you closer from the start."http://www.finewoodworking.com/2014/10/01/lock-miter-jigs

I like repeatability.  I plane my own wood to 3/4" and I already know exactly how high to set the router bit for that thickness of wood and exactly where to set my Incra wonder fence/positioner.

Also, reading through some of the reviews on the Infinity web site, it appears the jigs work best with Ininity's lock miter bits - I have a Bosch bit which I am very happy with.  I also read that the jig doesn't really precisely fit the router bit - one user reported there is up to 2mm in play.  Lastly I prefer digital indicators with numbers versus matching up lines (old eyes)

To each his own, if something works for you, that is all that counts

 

[tjbnwi]

I have looked at the Infinity Jigs  (I love buying new tools) but declined for a couple of reasons

Fine Wood working wrote a brief review and noted "You still need test cuts to dial in the setup to perfection, but Infinity’s jig gets you closer from the start."http://www.finewoodworking.com/2014/10/01/lock-miter-jigs

I like repeatability.  I plane my own wood to 3/4" and I already know exactly how high to set the router bit for that thickness of wood and exactly where to set my Incra wonder fence/positioner.

Also, reading through some of the reviews on the Infinity web site, it appears the jigs work best with Ininity's lock miter bits - I have a Bosch bit which I am very happy with.  I also read that the jig doesn't really precisely fit the router bit - one user reported there is up to 2mm in play.  Lastly I prefer digital indicators with numbers versus matching up lines (old eyes)

To each his own, if something works for you, that is all that counts

I've never made a test cut. Set the bit and go.

In the video I posted there is no opportunity for a test cut. I had to set up the router for the fence and rail using 23/32nd plywood. Then had to set up the bit in CMS using 3/4" solid material, I split the center line and first tick mark on the jig to make up for the difference. You have trust your set up.

The jig works with both the lock miter bits I have, a Rockler and an Infinity.

Yes there is "play" in the jig, you place the jig on the bit, slide it up to the edge of the cutter. It does move about 2 mm by design.

I do own the Wixey you mention, I will give your set up method a try also.

Tom