How to measure the nozzle diameter?
On a Creality CR-10 Max, there is a bag of unidentified spares, which include three unmarked nozzles.
There is a needle that is exactly 0.4 mm in diameter, which needle fits exactly inside one of nozzles. It also fits loosely in the largest nozzle, which diameter looks like it's really close to 0.8 mm on my digital caliper. The smallest one has only room for the tip of the needle, and the digital caliper reads 0.34 mm on the tip of the needle when pushed from the inside of the nozzle.
I assume the sizes are: 0.8 mm, 0.4 mm and 0.3 mm.
Can you tell me how to measure the diameter with better accuracy?
You don't really need to measure the diameter with any degree of accuracy since it is irrelevant for printing. The diameter of the extruded plastic is controlled by changing the flow rate of the extruder v.s. the movement speed of the print head. The exact nozzle diameter does not factor into it in any way. It only loosely determines what extrusion diameters are feasible (e.g. you can't extrude a 1mm line with a 0.2mm nozzle and you can't extrude a .4mm line with a 1.2mm nozzle).
Tiny addition on Tom's: it's *generally* irrelevant, but the nozzle diameter is used to set up the *basic* extrusion width in general. Sure, you could *try* to force 1.2 mm extrusion through a 0.2 mm nozzle but possibly get extreme under extrusion and clogging. Try to get them fitting.
Interesting. I will read on the subject and come back later. How important is it to match the nozzle size in the slicer with the installed nozzle ? Can you give me an example of a problematic mismatch ?
@alecail It does not matter for the slicer. The nozzle diameter is not used when slicing at all. Slicers only ask for the nozzle diameter so they can suggest values for the other settings (e.g. for extrusion width). If you get it right within +- 0.1 there should be no problems.
I have found that normal measuring devices are not particularly helpful with accurately measuring nozzle diameters. But you're already off to a great start.
What is helpful is to take them somewhere that has a wide assortment of drill bits, and find which two adjacent sizes will and will not fit in the (clean) nozzle; then convert the diameters to mm (if needed), and your nozzle is larger than the small bit, but smaller than the large bit. From that, you should be able to narrow it down to a standard dimension.
How about the physical size of the nozzle verses layer height? Does it work to tell a 0.2 nozzle it is 0.4 mm and have a 0.3 mm layer height?
The correct tool for measuring a hole usually is a Bore Gauge, but that doesn't work for super small holes like nozzles and generally needs holes at least 5 mm in diameter. For those small holes, there's a different tool:
These are Thread Measuring Wires of known diameter. While generally used to find out the depth of thread you are dealing with in a threaded (or if your thread is correct depth), they are also useful for measuring small bores. In this capacity, You'll use them as follows: The diameter of a hole can accompany any smaller diameter, but never a larger diameter wire, so a clean nozzle of 0.4 mm should accompany a 0.3 and o.35 easy but not a 0.45. A 0.4 might or might not fit, depending on how accurate the hole is. You'll need a very fine set of thread gauges though, and wires, pins, and needles of known diameter are a suitable replacement for this.