[Bob Adams]

I would have thought the whole point of the guide rail adapter was so you could put the track right on the mark and go. But it's obviously dependant on the size of the bit so I guess you have to fine tune the rods position each use carefully making sure the bit doesn't cut into the splinter guard or worse, the track.

I am not familiar with the Makita system, so I am assuming that it is similar to Festool. When I started this project I made an exact width dado jig: 139 - Exact-Width Dado Jig - The Wood Whisperer, but I was cutting dados in full size sheets of ply and the jig flexed during the cut and ruined the piece. Instead of wasting time to build another jig, I went with the rail system and it worked out nicely.

This is how I set up for exact width dado/rabbet cuts using the rail system. Ply is rarely a standard thickness, even within the same batch of ply so I never use the undersized ply bits. I always use a caliper to measure the thickness and go from there. In this project the ply varied from 18.92 to 19mm, so I set up for 19mm dados. I used a 1/2" down spiral bit for the cuts. I set up the router to the rail so that the router edge was touching the rail edge. I measured from the edge of the rail to the inside edge of my bit. This was 3" so I cut a 3" wide piece of mdf to use as a setup jig for all of my cuts. This jig let me set up the rail for repeatable cuts. With the rail clamped I make the first cut. Then I used a 6mm domino (1/2" + 6mm=close enough), as a spacer to set router for the 2nd cut. Because it's 4 in the morning and I need more coffee, I know this is clear as mud, so here are some pictures.

 

[Bob Adams]

@Bob Adams

Do you clamp the track to the part being cut, or do you find that the strips on the bottom of the track keep it from slipping while you're cutting?

I use the EZSmart version which has stops in the Y-direction so you can cut the dado in two passes without moving anything other than the carriage between the stops - but I do clamp the track so it doesn't move.

https://www.youtube.com/watch?v=su88uvZN_Ac

That is slick! I have been using the Festool track for about 5 years, I tried 1 time without clamps. Never again!