I'm now convinced that the problem isn't air flow. It's design. The gantry has four 120mm hoses and an 80mm hose feeding into a single 225mm hose via a 5-way manifold. This means that at the point at which the manifold starts there is a cross sectional area of 39,740 mm2 whilst the hoses feeding it have a cross sectional area of 50,240mm2. Looks like the airflow is being strangled by poor design. I'm going to try putting three manual blast gates onto the manifold (one on each of the spindle heads) together with replacing that ridiculous 80mm hose by a 120mm. If I then run with three 120mm vents open I'll have 33,912mm2 cross section feeding 39,740mm2 which should considerably reduce the choking, although it may still be necessary to drill some air bleed holes in the manifold. Looking at other PTP machines, this looks like it could be a common problem - and unlike the big shops I can't afford to install a huge dust extractor to try to overcome the inefficiancies of design like this. I'm also considering replacing most of the flexible hoses which run along the sides of the gantry with smooth galvanised steel ductwork to reduce the drag created by the ripples in flexible hose. I'll post my results when I know how good (or bad) they are.
Scrit
__________________
Scrit
from the Sunny Pennines, England's Backbone |