Thread: Sherwood DC1750 dust extractor from Timbecon

Pros
It has the impeller close to the filter housing and already has a 6" inlet of no modification needed to run with 6" ducting.

The claim of 1750 CFM is fanciful. A 6" duct at the sort of pressure that fan can generate (it will be less than called) cannot be more than 1250 cfm and in practice will be less than 1000cfm
Still quite good for a 2HP fan.

Is it worth it - you could purchase a generic 3HP DC for around $400 and convert it yourself (as per the generic 2HP DC sticky in this forum) and put the extra into a PF or ducting and connectors.
6" ducting, flexy and gates will cost more than 4"

Whatever one you but I would recommend long runs of ducting or too many junctions

There has been some discussion on this machine in a few posts in the Dust section of the forum, so perhaps do a search.

I think there was a view by some that you could buy the cheaper version and do the Sticky Modification a lot cheaper.

If you are not inclined to do your own modification, I think it is probably a good option. It has a 6in inlet and the direct connection to the housing that is recommended.

I think the real value would be in the "improved impellor" if that is genuine. The cheaper Sherwood unit lists a 300mm impellor, but this one is silent on size, just better engineered.

Bob would advise that you should doubt the claimed CFM figures, but that applies to all.

Regards

Bauldy

Sorry, typed my response earlier, but forgot to hit "enter". Subsequently Bob covered the same ground, but with much greater knowledge and authority!

Bauldy

I'd be interested to know if you get it. I've been eyeballing it for a while, but with the 1200 pleated filter on top and replacing all my 4" pipe with 6".

I've a generic 2hp with PF, but I don't fancy doing the surgery from the sticky as mentioned. My thoughts are to replace the generic unit with this one and sell the "old" one.

Thanks for all reply, I am setting up a small shop at home I will use the extractor on one machine a time (T/S, Planer & Thicknesser) if I buy this one can I run 6" flax hose from dust extractor to machine say 3 meters than use a reducer 6" to 4" to connect to machine
Bob Please advise

Originally Posted by Mehrdad

Thanks for all reply, I am setting up a small shop at home I will use the extractor on one machine a time (T/S, Planer & Thicknesser) if I buy this one can I run 6" flax hose from dust extractor to machine say 3 meters than use a reducer 6" to 4" to connect to machine
Bob Please advise

Unfortunately that is not a solution.
As soon as a 4" connection is used anywhere in the system (including using a machine with a 4" port) this throttles the flow meaning you won't pick up anywhere near as much fine dust from its source.


The 6" ducting has to go all the way to the machine AND the port in the machine has to be opened up to a full 6" opening, AND sufficient air flow has to be available into the cabinet from the shed at a pint on the cabinet somewhere opposite the machine dust port. Unfortunately this may mean getting out the angle grinder and cutting holes in machine cabinets.

The most difficult things to deal with are planer/thicknesser combos as this really involves a complete rebuild of the dust extraction hood.

If you don't want to or can't do that to your machines then you might as well just purchase the lowest cost 2HP and run 4" flex (cheaper than 6") to the machine.

You could of course do as you suggest in the short term and slowly modify your machines later but you will have major dust problems inside the shed until the machines are modified.

More importantly, if you are worried about fine dust, it sounds like you will be moving the DC to each machine this leaving the DC inside your shed?
If this is the case then 4 to 6" is irrelevant because DCs (even new ones) leak and you will eventually fill the air in your shed with fine dust.
The DC must be enclosed in an airtight chamber and vented outside the shed, or better still located outside the shed.
Thus all DC leaks are outside the shed

Originally Posted by BobL

Unfortunately that is not a solution.
As soon as a 4" connection is used anywhere in the system (including using a machine with a 4" port) this throttles the flow meaning you won't pick up anywhere near as much fine dust from its source.

Bob, I've heard this said many times but I haven't actually seen any evidence to suggest that an extremely short section (eg. 10cm) of 4" pipe in a 6" network will significantly reduce flow. Looking at Bill Pentz's spreadsheet for static pressure drop, or the Cincinnati fans guidance on static pressure losses in ducting, suggest that a short section of 4" pipe does not add significantly to the total static pressure drop in a 6" network. Running 6" all the way up to a machine and only reduce to 4" at the last few cm would have to be MUCH better than simply running 4" hose all the way and not that much worse than running full 6". Is this just a rule of thumb / approximation that has been used so often it has become a hard rule? Air is easily compressible so it's not like a valve in a water pipe.

Dom take a vacuum cleaner and make a hole 1/3 the area of the hose and put it over the end of the hose. Try sucking things with it. Does it still work the same as when there is no restriction? It is actually worse with a dust collector because they don't suck as hard as a vacuum cleaner can. A 6" diameter pipe dropping to 4", even for an inch, can't draw much better than a 4" all the way, maybe worse because of the turbulence.

It's like trying to snorkel wit a straw.

Originally Posted by QC Inspector

Dom take a vacuum cleaner and make a hole 1/3 the area of the hose and put it over the end of the hose. Try sucking things with it. Does it still work the same as when there is no restriction? It is actually worse with a dust collector because they don't suck as hard as a vacuum cleaner can. A 6" diameter pipe dropping to 4", even for an inch, can't draw much better than a 4" all the way, maybe worse because of the turbulence.

It's like trying to snorkel wit a straw.

I have to say I can't agree with you on this, though I may be wrong. I would need to see an argument based on logic/engineering to be convinced.

Hi DomAU.

I'm with Bob on this one. Regardless of the length of 4" pipe run, the killer is the 6" to 4" reducer. You are right that air is more compressible than water but the fans that most of us use are not compressors so the air in our systems behaves more like an incompressible fluid.

By way of an example, I've just shot out to the shed and taken a few measurements on my cyclone which is powered by a 2HP fan (yes, I know it's underpowered). In its standard operational mode with about 2m of 6" pic duct and 3m of 6" flex, I measured about 3" of static pressure. Plotting this on the fan curve I produced a while ago using a hot wire anemometer gives about 600 cfm of air flow.

When I added a 6" to 4" reducer to the end of the flex, the SP increased to about 4" which equates to about 450 cfm on the fan curve.

There's a good reason why you've heard this many times before - because it's true !

Best regards to everyone on Anzac Day. Tim.

Originally Posted by DomAU

Bob, I've heard this said many times but I haven't actually seen any evidence to suggest that an extremely short section (eg. 10cm) of 4" pipe in a 6" network will significantly reduce flow. Looking at Bill Pentz's spreadsheet for static pressure drop, or the Cincinnati fans guidance on static pressure losses in ducting, suggest that a short section of 4" pipe does not add significantly to the total static pressure drop in a 6" network. Running 6" all the way up to a machine and only reduce to 4" at the last few cm would have to be MUCH better than simply running 4" hose all the way and not that much worse than running full 6"..

QCI has pretty much nailed it

I agree there will be an improvement but this will only be significant when the flow is non or low turbulent, such as in very large aircon ducting which is what a lot of the fan charts are designed for.

In DC systems much higher air speeds (>4000 fpm) are required to keep sawdust suspended and at these speeds the flow is well and truly turbulent so improvements are unfortunately not "Much better"
In the case of a DC system where long ducting is used there is a small improvement purely because the frictional losses of the 4" relatives to 6" duct will be reduced but the turbulence effectively dominates the flow so gains due to frictional effects are small.

The problem is not just the pipe diameter but added turbulence induced at transition and the end of the duct, where a naked 4" duct opening has much greater turbulence than a naked 6"
This effect can be reduced through the use of gradual (10x ducting diameter) transitions and/or reverse bell mouth hoods on the inside the cabinet.
When I first came across all this 30+ years ago I could not believe it either and ended up doing dozens of measurements on this and I consistently got the same results.
The best flow ever measured between and 6 and a 4" pipe was was using a 5x duct diameter transition where I measured ~465 CFM.
Only when the air speed dropped into the non turbulent flow zone could I see the air speeds approaching inverse cross sectional ratios.

Air is easily compressible so it's not like a valve in a water pipe

Thats correct but to transfer 3x the volume of air (that's what 6" ducting carries relative to 4" ducting at DC pressures)
- either the absolute pressure of that air has to be increased by 3x, and that's just not going to happen at DC pressures and such a pressure difference could not be maintained across a 6/4" transition anyway.
- or the air speed has to increase by a factor 3 which means much greater wall resistance, and around 9 to 27x greater turbulence and that just knocks the stuffing out of the flow.

Thanks a lot good info coming, I have not much room in my shop plus I might change house buy end of next year that's why I wouldn't bother to make a nice pipe line around
my Table saw and 8" jointer are close to each other and my thicknesser is on mobile bench all of this are in my car port 3.5 X 7M the rest of my gear are in next room 2.5 X 7 meters which I will spend more time in there
so do you guys think I can do this for next 18 to 20 months one flaxy hose between these 3 machine and 1 shop vac connected to dust deputy for my mitre saw and festool dust collector to router table

Originally Posted by Mehrdad

Thanks a lot good info coming, I have not much room in my shop plus I might change house buy end of next year that's why I wouldn't bother to make a nice pipe line around
my Table saw and 8" jointer are close to each other and my thicknesser is on mobile bench all of this are in my car port 3.5 X 7M the rest of my gear are in next room 2.5 X 7 meters which I will spend more time in there
so do you guys think I can do this for next 18 to 20 months one flaxy hose between these 3 machine and 1 shop vac connected to dust deputy for my mitre saw and festool dust collector to router table

I can appreciate the situation and you can only do what you can.
Just keeping the floor clear of chips has some value.
Overall risk is related to exposure so if you are not in the workshop making dust that often the risk is reduced accordingly.
Watch for tell tales signs of leaks on the DC - especially around the bag clamps and attend to these ASAP
Consider wearing a face mask for dusty jobs

Originally Posted by BobL

QCI has pretty much nailed it

I agree there will be an improvement but this will only be significant when the flow is non or low turbulent, such as in very large aircon ducting which is what a lot of the fan charts are designed for.

In DC systems much higher air speeds (>4000 fpm) are required to keep sawdust suspended and at these speeds the flow is well and truly turbulent so improvements are unfortunately not "Much better"
In the case of a DC system where long ducting is used there is a small improvement purely because the frictional losses of the 4" relatives to 6" duct will be reduced but the turbulence effectively dominates the flow so gains due to frictional effects are small.

The problem is not just the pipe diameter but added turbulence induced at transition and the end of the duct, where a naked 4" duct opening has much greater turbulence than a naked 6"
This effect can be reduced through the use of gradual (10x ducting diameter) transitions and/or reverse bell mouth hoods on the inside the cabinet.
When I first came across all this 30+ years ago I could not believe it either and ended up doing dozens of measurements on this and I consistently got the same results.
The best flow ever measured between and 6 and a 4" pipe was was using a 5x duct diameter transition where I measured ~465 CFM.
Only when the air speed dropped into the non turbulent flow zone could I see the air speeds approaching inverse cross sectional ratios.


Thats correct but to transfer 3x the volume of air (that's what 6" ducting carries relative to 4" ducting at DC pressures)
- either the absolute pressure of that air has to be increased by 3x, and that's just not going to happen at DC pressures and such a pressure difference could not be maintained across a 6/4" transition anyway.
- or the air speed has to increase by a factor 3 which means much greater wall resistance, and around 9 to 27x greater turbulence and that just knocks the stuffing out of the flow.

Thanks for the response. I guess I don't have the practical experience so cannot comment too much on "real world" application. However, based theoretical engineering principles that I have seen I don't see how running a 6" duct run that is terminated in a 4" port is not going to be far better than a straight 4" run, particularly if there are some elbows and flex used along the way. The static pressure losses will be far greater in a 4" run before you even get to the entry/end and so you will simply be making bad far worse. As a real-world example I just went out and turned on my Clearvue. With both the 6" main port to my tablesaw, along with the 4" overhead port open (with no actual hose connected to the guard, just the y-transition open) the motor was pulling 16.8 Amps. With only the 4" port open the motor was still pulling 15.67 Amps; and I can assure you that 4" port was pulling far more than 450 CFM! It damned near pulled my arm off and was howling like a banshee. This compares with a very similar motor amp draw when my 3 x 4" band saw ports are all open but with a longer run to these ducts. I still think a short (eg. less than 20 cm) piece of 4" ducting anywhere in the system will not be anywhere near as bad as a straight 4" all the way; which is what people seem to be suggesting.