Quote Originally Posted by decent_espresso View Post
Each hole in our portafilter baskets can have an error of +/-.05mm. Over the many holes in a basket, the average error mostly cancels out (some ever so slightly larger, some ever so slightly smaller).

However, if a basket only has 1 hole, and we want to calibrate against it, we're looking for 4x better tolerance. This is quite hard to achieve, which is why calibrated orifices are expensive
http://www.theleeco.com/products/pre...s/restrictors/ and made by very few companies. The best ones, that we use, are made for the US military, for jet fuel injection systems.

As to measuring "the actual hole size" with a microscope, I don't know of any practical way to do that. Every basket would have a different labelled hole size, it wouldn't be repeatable, and even this assumes that the hole is perfectly circular, which at these dimensions, isn't usually the case. Here's a photo example I took of a competitor's basket some time ago.

cheap_holes.jpg
It is actually a pretty easy calculation given that you know: Pixel size of the microscope camera, total magnification (objective×lens(if any)×cam mount), also take into account if the software acquisition does binning (grouping of pixels, to reduce noise, pretty common on microscopes).
Plenty of image analysis softwares will be able to do that. When you know the actual hole size it should be an easy calculation, and definitely cheaper than going with calibrated flow restrictors. Only trouble I can think of will be artifacts on the image because of illumination on a smooth metal surface, but seems like you can already get a pretty nice image that should be usable.
Shoot me a PM if you want to know more, I don't want to be spamming this thread with random information!