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New member with questions on LS positioning fence and double, double dovetails

939 Views 7 Replies 5 Participants Last post by  Alphonse53
Hoping to find some answers to questions on using the Incra LS positioning router fence system and using it to make double, double dovetail cuts.

My first attempt with the LS super fence positioner was a simple box joint assemble which went pretty smoothly. Next I was able to perform the through dovetail and half dovetail using pine so I decided to try doing the double, double dovetail and that's when I ran into issues.

When cutting the tails and pin boards everything went well as was still using the soft pine for pins and tails however I used Walnut for offset color. As I cut the offset Walnut and came to the end cut were the fence is retracted I knew I was in trouble as the wood was entering the spinning blade in the wrong direction (one is suppose to move wood left to right on router table correct, in other words into the cutting blade, but at this extension its going as if its left to right. So how does one do it without getting wood thrown or torn apart?

I tried approaching the cut with minimal cut in, like 1mm but even at this little amount I had the bit grab the wood and throw the wood across the table or tear big chunks out of it. So how does one approach this?

One thought I had was if the board is perfectly centered could one just rotate the walnut and make both cuts as inner cuts to avoid this issue? The pattern is symmetrical correct? But how does one handle an uneven double tail pattern then? Can anyone shed any insight into this for me please. Incra makes it look so easy
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There are several pages describing the process of getting the board perfectly centered on the bit. The centering test cuts need to be in scrap stock the same exact width as the real project wood.

it’s been awhile, but once you get the bit perfectly centered you start cutting on the edge and move the fence, cutting the piece from edge to edge on each subsequent pass. You don’t actually start in the center. If there is any error in the centering it will show up on edge of board where it can be sanded, not in the middle of the board from turning it around and cutting from both directions.
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Did you pre-cut the long dovetail face cuts in the walnut with a straight bit first? This will minimize the amount of material the dovetail bit is removing and make it less prone to overheating and tear-out. On the table (router inverted) you should be cutting right to left.
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I started all over from hand planing wood down to specific thickness, etc. Made sure length, etc all the same and found an excellent video I used to produce the double, double dovetail. Turned out much better. Realized I was making some major errors in the process. Feel rather dumb now :).
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I've done some double dovetails, French dovetails for drawer fronts, wooden drawer slides etc in addition to blind and through dovetails. I love the Incra positioner and table, and once I get back into woodworking I plan to add the adjustable fence (forget what exactly it's called). After having this system I honestly can't imagine doing any sort of detailed or repeatable router cuts without one. I have the Incra table saw fence on my PM66 as well.
Don't have one, but want to say welcome. Sounds like you're serious about woodworking.
Thanks. I'm just a hobbyist and love to tinker. Probably a better description is that I am, as my wife says, OCD Man! I managed to find good deals on both the router and later the table saw positioner systems used, then bought an Incra table top and built the cabinet around it. My PM66 cab saw is an auction find that I put new arbor bearings, drive belts and a rattle can paint job on.
Snorthener has a worthwhile point in using a straight bit first on through tails. I'm also wondering if the difference in material strength might be a factor. Perry McDaniel at Taylor in Dallas wrote the book on Incra, and might be available if all else fails.
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