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| Lock Mitre Router Bit Setup Guide |
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| Written by Charley | |
| Wednesday, 28 August 2002 | |
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I'm using the CMT baby lock mitre router bit, which can handle a maximum 19mm and minimum 9.5mm thickness timber. It's for use in a router table and it produces strong mitre joints. It can be a pain to set up so I've made a step-by-step guide.  (click photo to enlarge) As one of the pieces to be joined has to be run through the router table vertical against the fence, I decided to add a new fence front. My normal one is too small to support big pieces. I added a length of plywood about 200mm high.. As I said before, it can be tricky to set up. In the Axminster catalogue (CMT section) it says to set the bit to the center of the timber. The first time I set the router bit up by following these instructions and ran a sample, the joint didn't fit. You have to be lucky or have a very good eye to set this bit up correctly the first time. So to set the bit up it's a trial and error process. However, if you follow the these steps you'll be able to produce perfect joints and it only takes about 5 minutes to set up.  (click photo to enlarge) The first thing to do is to take two scrap pieces of wood the same thickness as the pieces you want to join. And on one of them mark a center line. Then you need to adjust the router bit height. You can see in the photo to your right -> that the arrow is pointing to a small lip, that lip is the center of the bit and that's what you've got to line up the center line on the wood with.  (click photo to enlarge) Now you have to set the fence as shown in the photo on the right ->
When setting the bit height and the fence you are trying to get it spot on center but as I said this is hard to do, so just try and get it as close as you can for now.  (click photo to enlarge) On your two test pieces mark one "A" and the other "B".  (click photo to enlarge) As you can see in the photo (right ->) I have installed a feather board and have added a fence to my mitre gauge for better support when running small pieces through.. It is also important to turn the router speed down to 16000rpm.  (click photo to enlarge) We're going to start to get the height of the router bit set correctly first, so run both pieces 'A' and 'B' through flat on the table with 'A' facing up and 'B' facing down.  (click photo to enlarge) Lay the two pieces on a flat surface to check the fit, as you can see 'B' is too low, so I need to raise the router bit. Cut off the first attempts from each board with a hand saw or mitre saw, raise or lower the router bit and run the pieces through again. It took me three try's to get the router bit height right.  (click photo to enlarge) With the router bit height set up it's time to set the fence depth up correctly. This time the pieces need to be run through the router against the fence. I have moved the feather board so it will keep the wood against the fence and I'm using a push block. You run 'A' facing the fence and 'B' facing outwards. When I ran the pieces through, 'B' was just a tiny bit high so I brought the fence towards me just half the distance of the error. Making sure you cut off the last attempts, run the pieces through again and check the fit, this time it was perfect.  (click photo to enlarge) With the router bit set up correctly I can now run the final pieces through. One piece is run flat on the router table with the face facing up and the other piece is run against the fence with the face facing outwards.  (click photo to enlarge) Well there you have it. A perfect, strong and square mitre joint. Its defently worth 5 mins to set it up.  (click photo to enlarge) |
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