While a decent pair of calipers would work, a drop indicator would be the ideal tool for the job. It will be able to measure the movements of the Z-axis very accurately. Just make sure to move it in small increments, as this indicator only has a 10mm range. You’ll also want some form of a stand for it to hold it steady.
Have you run an test of your X-Y accuracy? I’m worried that your plywood thickness is different than what I had in my design, so your spindle is off-center relative to the ring. That could have an effect on your machine’s accuracy. We can always adjust the new spindle clamps to center up the router.
Out of curiousity, those of you out there that have made plywood clamps, how well have they held up? It sounds like the hose clamp method that @theHipNerd mentioned might be a better route to go for the wooden clamps.
Either way, I can print you a set of the spindle clamps this weekend if you want. I’ll want to print them so that they are the correct offset to align your spindle as I mentioned above. PM me and we can work out the details.
Ouch, that’s a bad oversight on my part. I like your idea further down in this thread to notch the acrylic. I will make that change to the main model when I have a spare moment. I modeled the Rigid router in the Fusion model, so it shouldn’t be too hard to use that geometry to place and size the notch.
Yes, the chains should always be parallel to the work surface. Is your ring currently above the CoG of the sled?