Airbrush needles are important parts of the guns. If their bent you can not spray correctly, because the jet of paint and air mixture that the airbrush is disturbed. If their scratched you will get tip dry in no time and the airbrush does not spray nicely, because paint will flow into the minute cavities and build up from there since paint is made to adhere.
What happens beyond your capacity to see? I got a USB microscope today that allows me to see what is actually going on in the area of the needle's tip. Below you see a magnified capture of the needle of the Iwata Custom Micron SB I recently bought. I sprayed one A4 size portrait with it that contains 8 drops of Holbein Aeroflash paint:
|Iwata CM SB's needle after one portrait and 8 drops of paint|
I also captured the needle of my trusty old Iwata HP-BH after 8 years of abuse. I must add to this that I've began polishing this needle with Johnson Silver polish - a process not yet finalized (since it takes a lot of time I do the polishing in various stints). Before I began polishing the BH's needle looked like a moon landscape surface under the microscope. It still sprayed nicely, but the polishing seems to make a huge difference. Especially the tip dry reduced; I have to clean the needle tip between paint refills at a lower frequency:
|Iwata HP-BH's needle after 8 years of (ab)use|
Polishing around the needle's tip area is particularly difficult and time consuming, probably since the steel is to some extent flexible and therefore neutralizes some of the (cautious) pressure applied during polishing. I will explain the polishing in an other blog entry later. The minute differences in coarseness of the two needles' surfaces, makes a difference. The spraying of the CM SB is beyond compare - Iwata has made big steps in a few years and succeeded in improving the quality of its (already excellent) airbrushes even further.
As a comparison I also captured the needle of an Infinity that did not spray fabulously. Here is why:
|Harder & Steenbeck Infinity's bent needle|
The microscope image makes it clear why the Infinity was not behaving well. Air and paint molecules are taken for an abrupt D-tour while they prefer to travel in a straight line (the principle of inertia).
After repairing the needle the Infinity behaved noticeably better. Below is the image of the needle bent straight again (sort of). This was a quick fix by placing the needle tip under an angle against a hard surfave (a stack op paper) and rubbing over the tip with the back of my index nail while rotating the needle:
|Infinity's needle (somewhat) straightened again|
The needle cone surface of the Infinity is quite smooth actually, but it will roughen faster than the Iwata needles, because the material of the Iwata's needles is of a better quality - they are harder, more difficult to bend. The Infinity was rarely used I must add for the sake of completeness. The spraying result is less than that of the Iwatas.
Below is an image of the needle of the new generation Paasche V#1 (without the adjusting wheel directly in front of the trigger) that did not spray well, I regret to say. I was always a huge Paasche fan, but their new generation of airbrushes are in no way comparable with the excellent older generations. Today I only use Paasche's Turbo for very fine detail and controlled spattering. It is an older generation Turbo from the previous century, by the way.
|New generation Paasche V#1 polished needle|
The Paasche V#1 does not spray well. The needle blocked straight out of the box, because the siphon paint cup's stub was too long... After grinding off enough material to not obstruct the needle, the needle travel is still not smooth. And here's why:
|New Generation Paasche V#1 Airbrush Tip and Nozzle|
Although not clearly visible in the above image, because it is difficult to operate the microscope and hold the object below it simultaneously. The nozzle and rocker assembly (in which the needle is held and that is moved forward and backward by trigger action) are not in line; the needle is continuously stressed (slightly bent). If I wiggle the airbrush while looking down its internals from the tip, it is visible that the nozzle and rocker are not aligned properly. This is the result of inaccurate machining in the production plant.
I used a Bresser USB microscope that magnifies between 20 and 200 times and allows me to store images in my laptop. This way I can compare needle's surfaces from before and after polishing and to see in which areas polishing did not catch on.