Extraction Rate Maths (I'm Confused)

[billw]

OK so I know there's a difference between HPLV and LPHV extraction, the former for hand tools and the latter for larger stuff.

However, I've done some rudimentary maths and I can't figure out why, for my current set of machinery, I can't use an HPLV on all of them. I have probably made some hopelessly dumb assumption along the way and being an accountant I'm terrible at maths. So, can you spot where I'm going wrong?

Assumptions - for each machine I take a width and depth. This should give me the amount of material taken off for each mm of material that passes through.

Next, I look at feed rates. The only machine that has a fixed rate is the thicknesser, all the rest are manually fed so I can control the throughput rate. I've made assumptions for those.

So what I end up with is basically the volume of material requiring extraction per second. The vacuum unit is rated at 52 l/sec. Thing is, my results suggest that the tracksaw is by far and away the most intensive requirement (12,600 mm3/sec of material based on kerf of 3mm, thickness of material 18mm, and feed rate of 14m/min) so a board takes approx 10 seconds end to end if I'm being careful.

This means that for every litre of air, there's 241mm3 of waste to extract.

The other results are: -
Thicknesser (max 1mm each pass, max width 300mm, 7m/min) 67mm3
Planer (max 1mm each pass, max width 150mm, 5m/min) 24mm3
Bandsaw (Kerf 1.5mm (way OTT?) max depth 100mm, 1.5m/min at that thickness, quicker if thinner) 96mm3
Router (arbitrary really, 19mm groove of 3mm depth, 4m/min) 73mm3

So now I'm wondering how on earth the vacuum can cope with the handtool tracksaw but can't do the fixed tool planer, which churns out a tenth of the waste?

 

[Mrs C]

I think you might be over thinking this - if you use a vacuum on your thicknesser you will very quickly fill the bag, and possibly clog the thinner hose with the coarser shavings. Possible the size of the shaving that is relevant (dust compared to coarse shavings)

 

[pe2dave]

Maths wise, is the error in not thinking of Litres per second?
Measures are in air, what we're concerned with is 'chips' / dust?
As @Mrs C says, Huge volume of wood with p/t, lesser (dust?) with a sander?

 

[Jameshow]

The router wont the cut as much as the thicknesser. Nor do the saws by a long margin.

In my limited experience it the PT that you really need hvlp on the rest are ok on hplv

Cheers James

 

[pe2dave]

Has anyone tried a decent cyclone with a hvlp extractor? Should deal with the volume
if the bin is up to it?

 

[Jacob]

Through my PT a deep cut on a wide board of say sycamore the shavings can be stiff and long enough to block the 4" pipe to my Axminster ADE 2200 extractor. The outlet on the PT is 5" dia so I guess I should be using 5"pipe. And a bigger extractor?

 

[mr rusty]

The problem is that there are two aspects of vacuum - the actual vacuum pressure and the flow volume, and you get the maximum of one with the minimum of the other, so for example, the maximum suction a vacuum can deliver is when there is zero flow (think hand over the pipe), and the maximum flow is when there is zero pressure, so as the back pressure increases (i.e. the "work" to move the product - and the longer the hose, the more product in the hose, the higher the weight in the hose and the higher the work needed to shift it), the flow diminishes. If you look at Vac specs, you will find the maximum vacuum for a 1kW machine and a 15kW machine are not that much different, but the flow rates will be. The bigger machine has the ability to maintain a good flow rate against a high back pressure.

Then there is the airspeed and the density and size of the particle. A feather may weigh exactly the same as a (large) grain of sand, but you need a much higher air speed to lift a grain of sand than you do a feather! Air speed is a factor of the input power of the machine and the hose diameter. In fact, on a big vacuum (say 15kW) if you put too small a hose on it, the heat generated because of the high air speed and frictional back pressure, will cause the machine to overheat.

Moral of the story - you can play around with the ratio of vacuum/flow by changing the hose diameter, but at the end of the day there is no substitute for input power if you want more "work" done.

 

[billw]

OK so that all makes sense, I'm still wondering whether the amount of chips/dust coming off the planer and thicknesser (they're separate) would be too much for the vacuum to handle. I suppose I'd better test them.

As @Jacob says " Through my PT a deep cut on a wide board" what's deep and what's wide to you? In comparison to the numbers I've given? Neither of mine recommend taking any more than 1mm off for hardwood, in reality I generally used the planer at under that just to be on the safe side and the thicknesser hasn't seen much action yet.

 

[Fitzroy]

I think your maths is off for the thicknesser and others 1 x 300 x 7000 / 60 = 35000mm3/s. The other thing is as stated thicknesser shavings are bulky and more likely to get caught up and accumulate.

F.

 

[PAC1]

For effective dust extraction the issue is how much air needs to pass along the duct to effectively move the shavings and dust and keep it airborne until it reaches you filters. In other words you need a flow of air to keep a shaving in the air otherwise gravity does its thing. You are measuring the volume of shavings which is interesting on one level but only a very small part of the story. The biggest factor is the airflow. If you look at Bill Pentz website he states how much airflow you need for each machine. When sizing dust extraction the factors are. (1) how much air does the woodworking machine need, (2) the size of the fan (3) the diameter of the duct, (4) the length of the duct, (5) the material used for the duct, (6) bends, branches etc, (7) leakage, (8) real world performance of the fan, (9) the air speed (10) Performance of the filters.
Optimising all of these to achieve efficient dust extraction that does not leave the workshop full of the superfine deadly particles takes some thinking about. Thankfully Bill has done most of that thinking and all you have to do is learn what matters for your set up and apply his teaching.

 

[Sideways]

The cutter block of a planer is say 12" wide and protected by a loose fitting extraction hood. You need a strong wind (high airspeed) to be able to pick up and carry big heavy chips and you need that over a large area to extract the chips from the entire width of the cutter block. You then allow for extra air leaking all around the loose fitting hoods used on these machines and you end up with a big air volume requirement as well as a minimum airspeed.
A high pressure low volume extractor just can't move enough air even though it can achieve higher air speeds in a small pipe.
Compare the sizes of the hoses. Vacuum cleaner about 30mm inside diameter if you are lucky.
HVLP 100mm to 150mm depending
Amount of air moved depends on airspeed x cross sectional area of the hose.
Area relates to square of the diameter (pi × D squared/ 4
Just do the ratios : 100mm : 30mm = 3 ish diameters, 3x3 = 9 the area
So even a small planer with only a 100mm outlet needs about 3x3 = 9 vacuum cleaners worth of airflow to clear the chips.
It's not quite that bad - you might get away with 8 vacuum cleaner motors worth

 

[Chris Hawkins]

I can only quote my own experience. I use a shopvac for hand held tools (domino, sander, router etc). I use a HPLV (55L 1100W - about £100) for thicknesser, jointer, table saw and router table. I have a 6m 100mm hose which I switch from machine to machine - it's a pain but takes a few seconds. It all works just perfectly. I have no problem with jams and chip clearance capacity. I've learnt that reusing the paper filter bags too many times is not good for suction power. Yes, capacity is limited, but so is space in my workshop. I've considered - many times - switching to a LPHV system or even a 2000W HPLV device, but for me there's no point.

 

[billw]

Well I've tried it with the bandsaw, it's certainly doing the job. Love the fact I can hook the tool up to the vacuum so when the tool comes on, so does the vacuum. Makes life a breeze.

 

[Jameshow]

On the subject of dust collection anyone know how to capture the dust from my biscuit jointer?

My Freud one spits it out all over the place!!

Cheers James

 

[Sideways]

Has anyone tried a decent cyclone with a hvlp extractor? Should deal with the volume
if the bin is up to it?

There's a pretty big pressure drop across a cyclone. Like 25% plus of your available suction. Cyclones are great for separating the big shavings but on an HVLP extractor, you don't have a lot of pressure drop to play with and with a cyclone in as well, you have to be really dilligent about keeping pipe runs smooth, short and full bore all the way to the machine.
This is based on the experience and copious time wasted rectifying a poor installation of a big Axminster trade extractor with a 3HP motor, built in cyclone and an automated cleaner for the cartridge filter. I couldn't believe how poorly the system worked given the enormous volume of air that the fan was moving when the ducts were disconnnected and the bins uncoupled.
That machine had an 8" inlet and a factory standard adaptor to 2x 5" ports. That's more than 20% of the flow choked before you even reach the ducting ! Add 4 inch ducting, 90 degree bends and T pieces and the incompetent installation turned a £2.5k machine into an expensive chocolate teapot.

 

[Jameshow]

Why would you put a cyclone on a hvlp extractor leaves you with two bags to empty??

On a vacuum with a small volume container yes but a hvlp will have a large drum / bag??

Cheers James

 

[MikeK]

Why would you put a cyclone on a hvlp extractor leaves you with two bags to empty??

On a vacuum with a small volume container yes but a hvlp will have a large drum / bag??

Cheers James

I have an Oneida Ultimate Dust Deputy cyclone on my Festool CT-36. After using it for about a year, I've emptied the cyclone bin about five or six times, but the CT-36 bag is still empty. There might be some very fine dust in it, but I can't see any.

Before I bought the CT-36 and Oneida cyclone, I used a generic cyclone, attached to a metal bin, that I bought from an Amazon vendor for use with my Kärcher shop vacuum. I had similar results with the Kärcher, but didn't use a bag in it. The only time I found dust or chips in the Kärcher is when I didn't empty the metal bin when it was full.

 

[Jameshow]

Is the ct 36 hvlp? Looks like lvhp??

Cheers James

 

[MikeK]

Is the ct 36 hvlp? Looks like lvhp??

Cheers James

Yes, you are correct, it is a LVHP. I misread your post.

However, to answer your post correctly, I hope, I do have a 3HP HVLP dust extraction system that uses an Oneida Super Dust Deputy cyclone fitted between the blower and the 35-gallon dust bin. The output of the blower goes to a plywood plenum with a pair of Wynn Environmental 35B222NANO filters, each with a Wynn 18FP30 catch pan attached to the bottom. This gives me about 480 square feet of MERV15 filter.

In a traditional extraction system, such as the Axminster AC82E, the filter canister or bag is above the simple separator and the collection bag is below the separator. Everything passes through the blower impeller before it reaches the separator and drops into the bag or is blown up into the filter. Installing a cyclone separator between the blower and the machine separates the majority of the dust and chips before the air stream reaches the impeller. This also reduces the amount of material that falls into the collection bag or tries to pass through the filter back into the room. The cyclone does reduce the airflow through the system, but this can be compensated for by sizing the blower and ducting accordingly.

In my system, the catch pans take the place of the bag and makes it easy to clean out the filters when necessary. Except where the seal on the dust bin fails or the dust bin fills, the filters and catch pan are clean. When the seal fails or the bin is full, the filters fill quickly with dust and chips that should have gone into the bin. This creates a mess to clean up, since this stuff also passes through the blower and requires a full teardown to access the impeller and the inside surface of the filters.

 

[Jester129]

Dear benefactor MikeK (you did remember to put me into your will, didn't you?), I guess you remember to empty your bins regularly then!