Assumptions:
- 0.1mm spot size - no idea if this is achievable with that laser. One issue is that I won't be varying the focus over the surface of the build plate, so the distance from the galvanometer to the build plate will have to be long enough that the deflection angle is small enough for the difference in distance to be fairly small across the plate.
- I'm assuming a square spot. It makes the math simpler.
- Resin critical irradiance of 45 mJ/cm^2. This is based on the spec for MakerJuice SF resin. There are other resins with much lower critical irradiance (eg MakerJuice G+ 10-15 mJ/cm^2). I've tried to contact other resin manufacturers for a detailed specification but no results yet.
A spot size of 1e-4 m and a laser power of 0.5 W gives irradiance rate of 5e+7 W/m^2. (P / d^2)
That gives a dwell time on each point of 1.35e-13 s and therefore spot travel rate of 7.41e+8 m/s (approaching the speed of light...)
The galvo can do 30kpps (the headline says 20kpps but if it's only travelling 8 degrees then it can do 30kpps). Suppose each point means travelling 0.01m (10cm) then that's a spot travel rate of 300m/s.
That gives an actual spot dwell time of 3.33e-7 s and an actual irradiance of 16.7 J/m^2 operating at full power.
So to get my 6.75e-6 J/m^2 irradiance, I'd have to operate the laser at less than 1 millionth of its rated power. No doubt it could be operated at somewhat higher power than this with acceptable results, but I'm guessing that putting 1,000,000 times the recommended irradiance into the resin is going to cause problems.
Have I made a stupid math error here? Or is the idea of using a half-watt laser and an off-the-shelf galvo for SLA wildly unrealistic?
[1] http://www.ebay.co.uk/itm/405nm500mW-Sq ... Swl9BWMG6f
[2] http://www.ebay.co.uk/itm/20Kpps-HightS ... SwzgRWynrk