Jig for using a Lock Miter bit on large pieces - Router Forums
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post #1 of 7 (permalink) Old 04-29-2018, 05:27 PM Thread Starter
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Default Jig for using a Lock Miter bit on large pieces

I'm building the second of two rifle boxes. The first one was made with mitered corners and keyed dovetails. Thought I'd give Lock Miters a try this time.
As most will know, a Lock Miter joint is cut on with one piece ran vertically across the bit, using the fence, and the mating piece is ran horizontally, flat on the table. The pieces for the rifle box ends are 12 x 6 x 5/8 and, the sides are 46 x 6 x 5/8. I was concerned about stability of the 12" high piece riding against the 2 1/2" high fence. And also, maintaining an accurate cut on the ends of the 46" long sides.

Here are a few pictures of how I've attempted to allay my concerns.

The first two show a fence with an added auxiliary fence for more height. That auxiliary fence came with the stock fence from Jointec. I rides in a T track on top of the stock fence and is secured in back with brackets and T bolts. Then another fence that slides on the auxiliary fence was added. That fence has a block at the back edge to help with stability as the work passes the bit. You can see that my paranoia also led me to clamp the work.
That yellow apparatus is/are four plastic feather boards from Harbor Freight. They are stuck together with fibered carped tape. Two 4" 1/4 20 T bolts secure whole thing to a T track milled into the cross table clamp. Also from Jointec. It was their method for mounting thinner feather boards, as the table doesn't have an embedded T track.

Jig for using a Lock Miter bit on large pieces-vertical-1-small.jpg

Jig for using a Lock Miter bit on large pieces-vertica-2-small.jpg

The next two pictures show two views of the "coping sled" supplied by Jointech. It is guided by the T track on the top of the fence. That's where their Auxiliary fence is mounted.
A 2' 2X3 was mounted to the coping device to provide stability for the long pieces. This is the first time I have wished for a T track in the table. A miter gauge would sure be handier.

Jig for using a Lock Miter bit on large pieces-horizontal-1-small.jpg

Jig for using a Lock Miter bit on large pieces-horizontal-2-small.jpg

First test flight tomorrow. I'll report my successes or, lack thereof, later.
Thanks for looking.
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post #2 of 7 (permalink) Old 04-29-2018, 08:17 PM
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Your setup looks pretty good to me, but what are you using to get the fence and bit positioned correctly? Do you have any kind of setup gauge? I have the Lock Miter Master gauges from Infinity Tool and they do a great job of getting the fence position and bit height correct. All you need to do is determine the exact center of the thickness of each board. The Lock Miter Master gauge then attaches with magnets to your bit and has a horizontal and a vertical line on it that you use to set the bit and fence positions so the center line of your boards line up with these marks. The resulting positions will be near perfect, requiring only a test cut pair to verify that they are correct.

Keeping the boards being cut horizontal is relatively easy, but more difficult for the vertical board. From what I can see in your pictures, I think you have a good setup. Feed the stock past the bit slowly and I think you will get acceptable results, but a pair of test pieces cut from the same stock before your final cuts should prove it.

Charley
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post #3 of 7 (permalink) Old 04-29-2018, 08:56 PM Thread Starter
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I'm with ya, Charlie. Got the Infinity set up gauges. The big 'un and the bitty one. Just ordered the "Baby" bit. And, I've made me a center finder. When I ran the stock for the box, I also ran some for trial runs. I hope, I ran enough.

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post #4 of 7 (permalink) Old 04-29-2018, 10:32 PM
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Your set-ups look good. If I might make a suggestion - I see that you don't have a back-up strip in either case to prevent some blow-out when the bit exits the part, might be an idea to add them. I like that idea of providing a mounting provision for the featherboards, I believe that Mike (@MT Stringer) posted details of a home-made version that he'd made.
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post #5 of 7 (permalink) Old 04-29-2018, 11:58 PM Thread Starter
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Quote:
Originally Posted by tomp913 View Post
Your set-ups look good. If I might make a suggestion - I see that you don't have a back-up strip in either case to prevent some blow-out when the bit exits the part, might be an idea to add them. I like that idea of providing a mounting provision for the featherboards, I believe that Mike (@MT Stringer) posted details of a home-made version that he'd made.
Hi again, Tom. Gotcha covered. Thanks, friend.
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post #6 of 7 (permalink) Old 04-30-2018, 01:20 AM
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Hey Gene,I have watched the video from Infinity Cutting Tools & it shows that you are doing every thing right & then some, using their lock miter bits,so you should expect a perfect result.All the best,Jamesjj

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post #7 of 7 (permalink) Old 05-02-2018, 02:05 PM Thread Starter
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After a few missteps, a change of glasses, and some YouTube instruction, I finally have cut a perfect lock miter joint.
The jigs worked great. My eyesight was the problem. With lock miters, precision is everything. After donning my magnifying headset, I found where I was off. Fixed that and it worked much better.
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