Originally Posted by
Aaron Inami
Okay, first thing. CFM is not airspeed. CFM is "cubic feet per minute" which describe how much air is being moved from one place to another. The CFM on the 1-1/4" hose is never going to be as high as a 2-1/2" hose because of the actual volume/space inside the hose. If the turbine is advertised as 150 CFM, then the 2-1/2" hose may get you something like 120-130 CFM. A 1-1/4" hose will yield something like 30-40 CFM.
Airspeed is described as "velocity". The smaller 1-1/4" hose will likely have a bit less velocity than a 2-1/2" hose just because of the resistance of a smaller hose and all the internal hose ridges.
Once again, it depends on how much air you need to move. If I'm using a random orbit sander, I will use a smaller Festool 27/32 hose because it weighs less and is more flexible. The 27/32 hose is a 32mm diameter at the vac which then gradually tapers down to 27mm at the tool end. Even with this, I still need to turn down the suction on my extractor for best random orbit sander performance. A heavier/larger hose on a random orbit sander will tend to cause the sander to tilt back and it becomes harder to keep the sandpaper flat on the material.
If I'm using a router, I might use a 36/32 hose (starts at 36mm, then tapers down to 32mm at the end) or even a straight 36mm hose because I want as much air pull power as possible to draw the routed debris away. It depends on the router and the dust port connection. The full 36mm hose is larger, heavier and stiffer. Sometimes I want just a tiny bit more flexibility when handling the router and also how durable the dust port plastic is on the router. (and yes, I understand that routers sometimes have a smaller 1" or so inlet, but a bigger hose will have less resistance and the end result will still be better).
If I would be using a bandsaw or belt sander, you want as much air movement as possible, so a full 36mm or even a 50mm is recommended. These types of tools actually work better with traditional dust collectors and big 4" or larger hoses because you need massive air movement, but smaller bench top tools rarely have a port larger than 2-1/2" and are usually smaller than that.