Incra Poisitioner - why set the scale to 0 for scoring pass when the bit protrudes?

When you’re doing half-blinds, the zero isn’t really zero = edge of board. It just means that zero = same distance from edge for each board. If you continue watching the video you’ll see where he finishes that board, and then clamps the other board to the crosscut fence. By going back to zero he ensures that he starts cutting the same width in on that board as he did on the first. It might look confusing, but it makes sense once you do it a couple of times. If you don’t have the big instruction book, it’s much easier to understand than the videos and you can keep it open right there on your router table and go step by step.

Edit: Another way of thinking about it is that you aren’t going to be measuring in 32nds or 16ths. With the LS Positioner you are going to be setting a zero point and then using the ruler to go 1A 2A 3A, 1B 2B 3B etc.

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I understand and buy into what you’re saying Joe. The instruction book says “You can use one of the 1/32” or metric scales as a reference so you’ll know how much you’ve widened the rabbet with each pass”. In the video there’s no mention of this. He just scores it and then makes a few passes to finish it without any mention of how he knew his target width was hit. I completely understand what you mean in your “edit” help, and I’m looking forward to that part of the process. Maybe I’m being dumb but I still don’t get how to measure the rabbet’s width without having a scale zeroed. Again, I understand what you mean by wanting consistency for all the boards and this arbitrary starting point is fine for consistency, but what about the end point?

Yes, he makes it a bit confusing. I suck at explaining, so bear with me.

In the first part you are making the tailboards. On a regular dovetail jig, the back of the tails is rounded. With the LS POsitioner, the backs are flat, you just rout out a rabbet. That is what he is doing with those first cuts, making that rabbet.

Here’s the fun part – it doesn’t have to be exact, just close to what the template says it should be. The template ruler that you slid into the long piece has a “guestimate”. For the one he’s doing in the video he says it is 7/32. He makes those multiple passes to sneak up to 7/32. But it doesn’t have to be perfect. You can be 6/32 or 8/32. And since you started with a light cut under 1/32, and set it to zero, and it locks every 1/32, you’re going to end up with 6, 7, or 8/32. And that is good enough for that step because:

When the tails are done you move on to the pin boards. They use a stop setup behind the bit that limits how deep you cut the sockets. You make the first series of cuts, and then do a test fit with the tail boards you already made, and then you adjust the stop so it makes the sockets just deep enough for the tails to sit in flush. (It should be a bit further in the video).
Hope that helps a bit.
Joe

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Oh that helps a lot Joe. Thanks!

I didn’t want to admit that I don’t even know why the rabbet is required in the first place but I guess honesty is best!

I’ll be working on this first thing in the morning, so I should have this all worked out tomorrow.

Thanks again and I’ll update you with the results.

Todd, you’re right. Honesty is always best.

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Joe, I wanted to update you. I was able to make my first set of half blind drawer boxes the other day and I must say that I thoroughly enjoyed the process with the Incra over the dovetail jig. What a difference!

Now I understand the beveled rabbet for half blinds and the described approach is perfectly adequate.

Do you have any insight over recommended stock WIDTH? With my dovetail jig it’s inch plus 1/4” for the larger bit and 1/2 inch plus 1/8” for the smaller bit.

I ask because I pretty much randomly chose a template that worked great for the first drawer size but was incompatible with the second size. I struggled for a good 15 minutes before settling on another pattern for that. I’d like to get a better understanding and approach for selecting templates. I haven’t seen any material on that selection process from Incra.

Thanks!

If you mean thickness, I don’t remember off the top of my head and its too cold to run out to the workshop and look at the book.
Width (like height or drawer) you use the full-scale templates in the book. Jut hold the end of one board up to each one until you find one that centers nicely and then note if you should start on an A or a B.
The A and B are interchangeable – you don’t have to use the A for the tails and the B for the sockets. If you make it one way (A for Tails, B for Pins) and don’t get half-pins on the end, then just do it the other way (B for Tails, A for Pins).

edited to say half-pins.

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Joe, I was actually talking about the width, not the thickness. I had three drawer heights to build. The first one was easy peasy, but the other two didn’t play as nicely because of the width. The template didn’t line up. For one I simply switched to another template. For the third I had to use the alternate side of a template. I have much to learn about that…

Let me jump in here with the way I did the half-blind DTs on a project I’m completing now. I designed and built a queen size platform bed with matching nightstand. The height of each of the four drawers in the bed is 9.5”. For a nightstand, I usually use three drawers with the largest at the bottom for visual weight. In this case, the drawer heights are 6.5”, 5.75” and 4.5” bottom to top. I used the same Incra template for all the drawers, aligning the center of the drawer height with a given pin on the template.

In the image below, the drawer on the right is what I used in the bed. I chose a template, DOV-K, to give me a full pattern top-to-bottom. The bottom of the three nightstand drawers also ends up with a full pattern because of the 3” repeat. For the other drawers, I simply re-centered the template using the Incra Centering Template, based on their widths.

-- Bill, Thomasville, GA