Is this tool deflection?

I’m still working through the process of calibrating and fine tuning my machine (3 years and counting lol).

I have noticed that when cutting squares or rectangles one corner is always deformed. I think what is happening is that when the tool is plunging for the next pass it deflects slightly causing that little bump. Pictures below:

Machine deflection for sure.

During plunge, the initial contact point is «true to design» but once the bit starts to carve its subjected to sideway force causing the deviation from true path.

I would agree with your assessment. Even with an aftermarket Z axis, plunging can go off course. I have two other commercial machines that do it too. I slow my feed down and use sharp bits. When possible, I start in the interior waste and move out to the perimeter of the shape I’m cutting out. I suspect that better quality router bits with different grinds on the bottom would impact this too.

https://www.rockler.com/identifying-router-bits-plunge-fix-base-router

I’d also imagine that router slop, bit shanks bending, as well as Z axis play and direction of feed, all impact this kind of thing.

This is using all the default feeds and speeds in Easel and cutting the calibration pattern, there is not much control over path strategy. Generally I’m using a 1/8 straight cut bit in MDF, though the result is the same if using a more standard 1/4 two flute. Maybe the router is deflecting rather than the tool.

Put a pencil in the router collet and a paper on the wasteboard, router power OFF and lower it so it touch the paper.

Apply a sideway force in each direction (X/Y +-) and tug on the Z-assembly.

Even modest sideloads can cause deflection, Easel rates are not a «deflection free» suggestion.