that is a heavy router to hang upside down. You need a much stronger, stiffer plate

 

The inserts are molded and the tops are not machined so they all develop that dip when they cure. You will either have to build them up with some kind of material that will bond to the plastic and machine down or build jigs that will span the insert and carry the material across.
All manufacturers inserts have the same problem. its cheaper to manufacture.

 

That's a Woodpecker plate, anodized blue.

Every so often, Woodpeckers does limited runs of aluminum insert ring sets, which should also fit the Kreg version. You can check with Woodpeckers on if/when they're doing them again via woodpeck.com. Bring money…

I have sets of aluminum and plastic rings, and use them both successfully.

As Bruce pointed out, you need to reference off the plate, not the ring. Other router plates I've owned also had irregularities in the rings, and it's important to develop a technique where you're not pushing right over the bit. Similar to machine jointing, you want to push on the table and fence, and let the cutter work.

 

The plate was included with the router so I assumed it would work fine. As I said, the plate is still flat . The problem is I'm trying to cut half blind dovetails with an Incra fence. The technique requires cutting the parts on end which means I can't reference off of the table. Without a flat insert ring it's not possible to make a good joint. My solution was to just order an Incra router table which includes a 3/8" aluminum plate with laser cut steel inserts that are perfectly flat. They also have leveling screws for both the plate and the insert rings.

 

I think metal inserts are the way to go. I use an aluminum Bench Dog plate and inserts, and they stay flat.

Good luck with the new setup.

 

I have an older jessem lift with newish (1 year) plastic inserts like that. Mine are perfectly flat and have been since I bought them, so not all plastic inserts are bowed. They can flex slightly if you try to overtighten them, but that should be fairly obvious when it is happening. Hopefully your new plate/inserts work out.

I've also got an incra. When you run the boards through on end are you using the fence that slides along the incra? If so you can pull the fence back, put the board in front and referenced on the flat table, and clamp it to the fence. Make the cut, back off, reposition and reclamp and make the next cut. (I think in one of the videos for the ls positioner that is what the demonstrator does.)

 

@JustJoe

The first step in cutting pins for a half blind dovetail with the Incra system requires making a relief cut on the back side of the pins. That cut is made with the board on end and the inside face against the router fence. That relief cut is where I had problems. I was using 4 inch wide boards to make a small box and at one point in the cut, nearly the entire width of the board is supported by the insert ring (the rings are 3-3/4" OD). The resulting cut was curved to match the dip in the insert ring. This creates a joint that is tight in the middle, but has gaps at each end.

 

...as an aside, how do you like the Triton? my High School (12 years ago) had an Incra jig ultra and i made the boxes in the project book. as I'm trying to get back into woodworking and just now getting to the point where i have enough tools to make cool things, I'm thinking about the Triton because of the above table adjustment. (like everyone) I just inherited an incra jig original from '91 with the aluminum fence and templates and will start with that but need a better router. Our use will be pretty close, so i would like to hear what you think. (if you have a review on the router already posted, please direct me and forgive a noob.)

 

I believe several other reviews have been posted for the router, but my early impression is that it's great. The above table adjustment works very well, and I've also found that the dust collection is pretty good. I was originally going to get a Dust Bucket type of enclosure for the router, but I'm getting reasonably good dust collection with the built in port. I bought a cheap sump pump hose from Home Depot and cut a chunk off to create a pigtail for easy hook up. The hose is only $11 and fits very tight in the port for the Triton. I used some of the rest of the hose to create pigtails for a couple other tools with similar size ports. Eventually I'll buy the CleanSweep lock rings from Incra which should make the dust collection even better.

Once I have more time to use the router I'll post a real review, but for now I'm very happy with it.