Hi Tom,

I purchased one of those dustbin types with the motor on top over a year ago (R2D2 style), but wouldn't recommend it. Although cheap (£100), it is quite noisy and gets quite hot, being a universal type motor. Much better are those shown by FatFreddie in post#2, which use induction type motors (quieter), have a good collection capacity, and run cool. My dad has something similar and it's a nice unit.
I found this unit, which is quite cheap:
http://www.powertooldirect.co.uk/woo...0-p-90590.html

Can I also suggest you try and run the 4" hose all the way to the cutting area, rather than throttle it down.

Even using the type shown above, with the filter bags on top, there will be fine particles released and would suggest you locate this near the door. MDF is nasty.

If the router machine you cut with blows cooling air down onto the workpiece, this often blows the fine dust out of the collector foot before the vac can suck it up. Even with brushes/flaps. The blowing out action spreads quickly, but the sucking up action is quite local to the pipe, so often looses out. I'm talking here about the really fine stuff that you might not see. You might be able to arrange it so that the machine exit air is ducted away, rather than down into the collector foot.

Another option is to arrange the dust collector foot so that it is at a fixed (but adjustable) height, independant of the Z axis moving up and down. Even between cuts, and when cuts are just starting/finishing you will have 100% coverage. Only works for low clamps and flattish workpieces.

Finally, when money allows, those ceiling mounted filters on a timer are another additional option e.g.:
http://www.powertooldirect.co.uk/cha...e-p-90270.html

Sorry I'm going on a bit, but dust is a slow killer in my view.