I see some members are starting to open up their cabinet ports which is good to see.
The biggest restriction to air flow by DCs is the use of too narrow a ducting - remember a 100 mm duct can at most only carry about 40% of what has been deemed necessary to catch and transport fine sawdust.
It's also not much use using 150 mm ducting but then to have the collection port at the DC end restricted to 100 mm - the use of the bigger ducting has to be all the way to the filters/bags/cyclone.
After this has been been attended to the next major restrictions to flow are usually the dust ports on machines.
Many so called 100 mm dust ports are only ~90 mm and some are even smaller with metal grids that further block the flow.
If you intend to use the existing machine port, start by removing any grilles
Use of multiple small ports can generate sufficient flow but remember that it takes THREE 100mm ports to equal the flow through a single 150 mm and more than 12, 50 mm ports to equal the flow of a single 150 mm port.
Most dust collection ports on machines are poorly thought out both in structure and location.
Step 1: Dust port location
Step one would be to determine if the current location is appropriate or has it been located for some other unrelated purpose i.e. ease of construction.
It may even be better to close off the existing dust port and open up a completely new one
The dust port should be located as close as possible to the dust source and (as much as possible) opposite to any air intake(s) (e.g. a throat plate on a cabinet saw).
Remember this is not "opposite the source" but " opposite the air intake to the cabinet"
This is likely to entail some sort of trade off between the inlet and outlet as they may not be aligned.
Step 2: Air Inlets
would be to look at where and how much air is able to enter cabinets to pick up and carry away the sawdust.
If little or no air can get into a cabinet then no matter how hard the DC sucks it cannot remove the sawdust efficiently.
Some example of this is using a extra narrow gap throat plate and the restricted air into lower cabinets of band saws.
So be prepared to enlarge other intakes or generate additional air intakes.
The sum of all air intakes should be at least twice the cross sectional area of the cabinet dust port.
If any of the intakes are less than 10 mm in any dimension then only count half their area as contributing to air intakes
Don't count any intakes less than about 3 mm in any dimension e.g. Small holes drilled in throat plates do bugger all for fine dust collection so don't count these at all.
Step 3: dust port construction
The most common form of dust port construction is design #3 - the sudden transition means it is restrictive to air flow and there are much better designs.
If you have the length and are able to make tapered ports like #2 then this is more efficient than #3
If you don't have the space then design #1, using a bell mouth exit is as efficient as #2.
These ports can be easily turned up out of MDF sandwiches or thick pieces of melamine
Remember in both cases 1 & 2 you will need to make the hole in the cabinet significantly larger than the ducting size.
In the case of #1, if 150 mm ducting is used the hole will need to be at least 225 mm in diameter.
In the case of the flared port like #2, 225 mm would be the smallest diameter to consider, 250 mm or bigger would be better.
Whatever you do, avoid using #4 as this generates the greatest turbulence and hence the greatest resistance to flow.
If anyone has any other report design then I would be happy to comment on it.
The biggest restriction to air flow by DCs is the use of too narrow a ducting - remember a 100 mm duct can at most only carry about 40% of what has been deemed necessary to catch and transport fine sawdust.
It's also not much use using 150 mm ducting but then to have the collection port at the DC end restricted to 100 mm - the use of the bigger ducting has to be all the way to the filters/bags/cyclone.
After this has been been attended to the next major restrictions to flow are usually the dust ports on machines.
Many so called 100 mm dust ports are only ~90 mm and some are even smaller with metal grids that further block the flow.
If you intend to use the existing machine port, start by removing any grilles
Use of multiple small ports can generate sufficient flow but remember that it takes THREE 100mm ports to equal the flow through a single 150 mm and more than 12, 50 mm ports to equal the flow of a single 150 mm port.
Most dust collection ports on machines are poorly thought out both in structure and location.
Step 1: Dust port location
Step one would be to determine if the current location is appropriate or has it been located for some other unrelated purpose i.e. ease of construction.
It may even be better to close off the existing dust port and open up a completely new one
The dust port should be located as close as possible to the dust source and (as much as possible) opposite to any air intake(s) (e.g. a throat plate on a cabinet saw).
Remember this is not "opposite the source" but " opposite the air intake to the cabinet"
This is likely to entail some sort of trade off between the inlet and outlet as they may not be aligned.
Step 2: Air Inlets
would be to look at where and how much air is able to enter cabinets to pick up and carry away the sawdust.
If little or no air can get into a cabinet then no matter how hard the DC sucks it cannot remove the sawdust efficiently.
Some example of this is using a extra narrow gap throat plate and the restricted air into lower cabinets of band saws.
So be prepared to enlarge other intakes or generate additional air intakes.
The sum of all air intakes should be at least twice the cross sectional area of the cabinet dust port.
If any of the intakes are less than 10 mm in any dimension then only count half their area as contributing to air intakes
Don't count any intakes less than about 3 mm in any dimension e.g. Small holes drilled in throat plates do bugger all for fine dust collection so don't count these at all.
Step 3: dust port construction
The most common form of dust port construction is design #3 - the sudden transition means it is restrictive to air flow and there are much better designs.
If you have the length and are able to make tapered ports like #2 then this is more efficient than #3
If you don't have the space then design #1, using a bell mouth exit is as efficient as #2.
These ports can be easily turned up out of MDF sandwiches or thick pieces of melamine
Remember in both cases 1 & 2 you will need to make the hole in the cabinet significantly larger than the ducting size.
In the case of #1, if 150 mm ducting is used the hole will need to be at least 225 mm in diameter.
In the case of the flared port like #2, 225 mm would be the smallest diameter to consider, 250 mm or bigger would be better.
Whatever you do, avoid using #4 as this generates the greatest turbulence and hence the greatest resistance to flow.
If anyone has any other report design then I would be happy to comment on it.
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