I could have sworn that I posted a chart previously about my findings, but I'm posting again today because though it's been more than a year since my last post, I have recently (as in yesterday) worked out a process for, and been able to measure spray pattern shape.
The process is pretty simple, and involves spraying white paint through a peice of black window screen in a frame. The idea being that ~80% of the paint and air will flow through the screen but the screen fabric will pick up the shape of the flow.
I did also pick up the 0.6mm needle, nozzle and cap for the H&S series, so I have that data for flow and pattern as well.
In response to the comments on my findings with the 0.5mm Iwata... I've since replaced the 0.35mm needle set entirely, and re-confirmed that I have the correct 0.5mm needle, as well as nozzle and cap (both of which yes, is different).
I've updated my publicly editable spreadsheet with data that I captured here: https://docs.google.com/spreadsheets/d/1c-4cmwrlagSfVg84IWSIO9MQPuh_ESpdP_6nSO7ZNiU/edit?usp=sharing, which now includes corrected 0.35mm HP-CS data (new needle set rather than the old, damaged one), and H&S Infinity 0.2, 0.4 and 0.6 needle sets.
For easy visibility here, the results for flow are, in order from lowest to highest:
- 50 s - Iwata HP-CS 0.5mm needle set (~0.04ml / s)
- 55.3 s - Harder & Steenbeck 0.2mm needle set (~0.04ml / s)
- 42 s - Iwata HP-CS 0.35mm needle set (~0.05ml / s)
- 34 s - Paasche Talon 0.38mm needle set (~0.06ml / s)
- 19.2 s - Harder & Steenbeck 0.4mm needle set (~0.10ml / s)
- 7.8 s - Harder & Steenbeck 0.6mm needle set (~0.26ml / s)
- 6 s - Paasche Talon 0.66mm needle set (~0.33ml / s)
The chart below with a line of best fit shows a pretty clear exponential trend, which I'd sort of expect.
The really new data for the spray pattern size is in the linked spreadsheet on a different tab. Again, for easy visibility, the results are:
- Iwata HP-CS 0.5mm needle set - 15mm diameter
- Iwata HP-CS 0.35mm needle set - 17mm diameter
- Harder & Steenbeck 0.2mm needle set - 19mm diameter
- Harder & Steenbeck 0.4mm needle set - 26mm diameter
- Harder & Steenbeck 0.6mm needle set - 26mm diameter
Since I still had the old, trumpetted 0.35 needle set for the HP-CS, I tested this as well and found it to have a slightly bigger spray pattern at 18mm diameter.
So the takeaways here aren't that the Iwata HP-CS is a bad airbrush... we all know that it isn't, but it does flow significantly less paint and has a much smaller spray pattern than any of the Harder & Steenbeck needle sets I tested. I haven't tested the H&S 0.15mm needle set yet, but I am really tempted now!
Also interesting is that the 0.6mm H&S needle set has much more flow but the same size spray pattern. In use I've found that you can spray larger areas by simply spraying from further back.
This data also does explain the issues that I was having with the Iwata HP-CS for auto modelling painting large areas. The spray rate is slow and the pattern narrow making it difficult to achieve wide overlapping strokes. It seems to me that the HP-CS needle sets are more applicable to fine modelling work, or to achieving very fine lines for artistry. The H&S airbrushes (which all use the same needle sets) offer a greater range of use cases with their needles - I expect the 0.15mm needle set to perform somewhat similar to the HP-CS.
One explanation for the low flow rate of the 0.5 HP-CS needle set becomes clear when you include data from the spray pattern dimensions. Flow rate and spray pattern size appear to be a combination of needle diameter and needle taper. I've not studied the taper of the 0.5mm needle, but if the taper is slow, the actual opening at max trigger can still be very small, limiting flow.
As an end user, I'd totally expect that a larger nozzle set from the same manufacturer would result in more flow, which is why I believe flow rate and spray pattern should be standardized measurements offered with airbrushes and nozzle sets.