All the problems I encountered came up regardless whether I was using fresh or old silicone. However, the silicone I was using was never older than 2 days. Inside the syringe, the silicone seems to be sealed off enough to prevent almost any curing. The silicone inside the tube, especially at the nozzle on the other hand, cures faster. I recommend replacing the tube when you are using silicone that is not fresh in order to lower the pressure difference between the syringe and the tube.
The part’s size
Apart from demanding more time and material, a bigger print can also have an influence on the print quality. This is especially true for prints with complex geometries. The more complex a layer is the more inconsistent the motion of the nozzle will be. Characteristic for the silicone is its ‘inertia’, which means it lags behind the nozzles motion and takes a little time to be actually deposited to the point where it sticks to the layer. Especially if the flow rate is low, a complex geometry will not be realized if the nozzle changes its motion direction fast and frequent.
If the print’s size is increased, which means the geometry is scaled up by a certain factor, these directional changes became less frequent and slower. This gives the silicone more time to be deposited and form the desired geometry and thus increases the print’s quality.
Steps per mm of the motor
Using the FELIX printer and Repetier-Host, this setting can be adjusted live, during the print. An increased value will increase the revolutions of the motor shaft per time and this increases the flow rate. However, in all prints in which I used a higher value (increase from 1200 to 5000) I could not detect a significant influence. After I increased this value for the flow rate in print 13 it showed no beneficial effect. In any case, the effect of pausing the print and extruding material until the flow rate increases visibly is much more effective.
This is a companion discussion topic for the original entry at http://www.structur3d.io/blog/2015/8/24/technical-details-of-printing-with-off-the-shelf-silicone