Marco's Cyclone (aka The Nordic Sucker)

I have always been bored about having my little shop permanently dusted from occasional use of power tools (usually sanding or sawing). In summer it is usually viable to move outdoors the table saw (!) but if it's raining or snowing it's just a mess.
It was autumn 2003 and my renovation project was complete. I was left with a wood dust collector that had been great to pump building dust outdoors but was a poor performer with its original filter bag (see Dust management for do-it-yourself building). It simply let all the fine dust through, namely the most dangerous one for my lungs.
After reading a lot on the internet, expecially Bill Pentz pages (which I kindly recommend) I understood that even a better (read pricey) bag wouldn't have helped. I decided to modify my basic dust collector by adding a cyclone at its intake and a cartridge filter at its exhaust. The cyclone would capture all solid particles and coarse dust, the impeller would pump only almost-clean air and the cartridge filter would retain the finest dust.
I don't have my shop in a two-car garage, with several woodworking tools scattered all around: my shop is only some 12 m². Two meters of flexible suction hose were enough for me and I was confident that my 550 W dust collector was up to the task.

Components

Components for the Nordic Sucker where selected keeping the price/performance ratio as the primary target. Everything could have been better but it would have costed much more. Yet the filter used is probably the best choice available.

The cartridge filter

The cartridge filter is made by PlymoVent AB (Sweden) and has got the following characteristics:

Size:	325 x 755 mm / 12.8" x 29.7"
Frame:	Galvanized steel
Filter medium:	Polyester 100%
Filter area	15 m² / 161 sqf
Filter class:	BIA U, S, G, C / > 95% efficiency
Air permeability:	130 l/m²
Can be gently washed in water

This beauty's list price was over 250 euros, but I was able to get an obsolete version of it for only 60 euros. It is closed at one side and has got a gasket at the other one. There is a grid mask on the inside but, as I wanted to protect it from accidental punches, I added a second one on the outside, with a raster of about 8 x 8 mm.

The motor, the impeller and their assembly

I purchased the cheapest dust collector available here in Finland (on the left) from a well known German chain-store. The beast is Made in Germany and costed a little less than 300 euros.
It has got the following characteristics:

Power consumption:	550 W
Power to the output:	370 W
Rotation speed	2800 rpm
Air flow:	1000 m³/h
Static pressure:	1.6 kN/m²

I discarded the two bags and the cart structure, keeping only the motor, the impeller and their moulded enclosure assembly. I opened the enclosure and carefully sealed the small leasks around its perimeter. I did that by applying a thin layer of elastic sealant adesive (Sikaflex), letting it cure and, only then, screwing the enclosure closed. This way I practically created a flexible gasket while the enclosure could still be reopened if needed.

The cyclone

I built the cyclone by myself using galvanized iron sheet 0.7 mm thick. I had already built a smaller one with rivets and the result, although functional, hadn't been so cute: this time I wanted something better looking. Thanks to Bill Pentz and his instructions, after some practicing on scrap sheet, I managed to (soft) solder together the whole cyclone. See my soldering hints at the end of this page.
The cyclone is composed by a 280 mm cylinder with a lateral inlet. There is a so-called "evolution" changing the 100 mm circular joint shape into a rectangular 140 x 70 mm inlet, which is entering tangentially the cylinder. The inlet extends inside the cylinder to create a "neutral vane" and reduce the turbulence created. On the bottom of the cyclinder there is a funnel, terminating with a 100 mm slip joint. Both slip joints are built by sawing off the bottoms of two end plugs and soldering them to the rest of the cyclone. The result is very robust and clamps for the flexible hose can be tightened with no mercy.
A 140 mm cylinder enters the bigger one from the top, through a plywood cap. On the cyclone top, the cylinder section is reduced to 125 mm in order to work as an outlet to be joined with commonly available HVAC antistatic plastic pipe.

An Excel spreadsheet for building the funnel can be found here.
An Excel spreadsheet for the inlet cutout can be found here.

The collector bin

The collector bin is made from an old Shell bearing grease barrel, sized about 30 l. The bin features its original quick-lock sealing band. I opened a hole in the bin closing cover and sealed there a 100 mm flange. The bin is connected to the cyclone with a length of flexible hose. For emptying, it is easy to open the band, lift the cover and take the bin away.

Pipes and hoses

The blue pipe I used is 125 mm sized PVC HVAC pipe, antistatic (black) on the inside. I thought 125 mm would be a suitable compromise between 100 mm (sensible pressure drop) and 160 mm sized (too big). For about the same price of spiral galvanized pipe, it offers lower losses and easier assembly.
Flexible hose is just the usual 100 mm type (actually 103 mm, to be exact). 100 mm slip joints normally used for spiral pipe are viable to connect sections of this hose too.

Building the Nordic Sucker

I mounted the impeller-motor-enclosure assembly on a thick plywood board, making a 280 mm opening for what originally was the filter bag flange and a second opening big enough to have the motor pass through. Note that the enclosure got turned upside down compared to its original working position.
I closed the old filter bag opening with a bottom cap made with a chipboard disk and a plywood disk glued together. On the disk edge I applyed a soft gasket I built using neoprene cellular rubber (cut from a bigger mat and glued as a ring). I applied a second, square cap on the enclosure top opening, where the dust bag was connected. The upper cap is pressed agains the opening by four threaded rods, nuts and washers. Another home-made neoprene gasket is used for a perfect sealing.

The cartridge filter is placed on the top of the upper cap. A plywood ring screwed on the top of the cap helps to center and keep in place the filter, which is pressed against the cap using a long threaded rod running from the top of the filter to the middle of the cap. The cap middle is reinforced by a thick block of metal (not visible in the pictures). The filter is sealed using its neoprene gasket and an extra one I built and glued on the inside perimeter of the centering ring. It helps to keep the heavy filter stright up.
Note that each upper cap fixing threaded rod uses four nuts and four washers. I am not just compressing the whole thing as a sandwich, risking to break the impeller enclosure. The same arrangement is used for the filter central rod in order to apply only a limited pressure on the gaskets and still being able to tighten up all nuts as needed.

The cyclone passes through the plywood base board and is connected to the underlying trash bin by some 10 cm of flexible hose. The cyclone is supported by a plywood ring and four threaded rods. Its air exhaust (on the top) is routed to the impeller enclosure intake using PVC pipes and a 125/100 mm reducer. The joint is made using flexible hose, in an attempt to isolate the cyclone structure from the impeller vibrations and avoid fatigue opening of the soldered joints.

Bottom cap

Using the Nordic Sucker

Using the Nordic Sucker is really easy. Just make sure you don't constrict too much the inlet (e.g. using 35 mm tubing for your electric tools). If needed, leave some leaks to avoid strangling the impeller and the motor. On a regular basis use compressed air to clean the filter by blowing from the outside radially, left to right, up and down, all around it. Avoid a too high pressure or you'll break it! Allow some time for the fine dust to fall down inside the filter. Then open carefully the bottom cap and collect all the fine dust. Clean well the seal and lock back in place. That's it. Ah, of course you might like to empty the trash bin when almost full, otherwise you'll get solid particles pumped up to the filter, which is really not so nice.

About soft soldering

In my experience, difficulties with soft soldering of sheet iron go as follows:

50% of the effort goes in finding the right materials. I recommend 50/50 tin-lead alloy, with no rosin core, in spools of 3 mm thick wire. Avoid alloys containing any Sb (antimony) or Cu (copper), or with more than 50 % of Pb (lead). Tin-lead bars for car repair are too cumbersome to use and rosine is simply inadeguate for galvanized sheet. The flux I have used is a non-acid "syrup" containg alloy powder, meant for car repair. Avoid the "old way" with concentrated hydrochloric acid, use instead fluxes containig zinc chloride.
Brush the joint overlapping surfaces with a tiny layer of flux, close the joint (I used holes at regular intervals of about 3 cm and screws) and solder together, adding solder alloy from the spool as needed to fill the joint. When the metal has cooled, remove the screws and fill the holes with solder.
20% of the effort can be put in finding the right tools. I used a butane-propane torch, with a carefully selected nozzle. Use a nozzle with a diameter of about 10 mm, suitable for temperatures around 500-600 °C. Buy also a length of tubing so that you can leave the gas can on the table and move much more easily the flame as you need. Avoid the standard solution of a 2 cm nozzle fixed to the gas can!
To close the holes I use a 500 W soldering iron with a huge chisel tip. I clean the hole with a drill bit and brush some flux in it. With a backer board on the other side of the hole, I apply as much solder as required to fill the hole. Using the torch for this could result in partial reopening of the joint, although I believe it can be done.
10% of your time will go into learning how to recognize the right soldering temperature. At about 450 °C the galvanizing layer will melt, changing from matt to glossy. At that temperature the sheet will also deformate badly. You must not reach that point! The 50/50 alloy is solid at 360 °C and liquid at 420 °C. You will be able to solder properly by staying inside that temperature range. The flux will first boil, then smoke and turn white. Rising more the temperature, the alloy powder contained in the flux will melt and turn glossy. Now you can apply more solder from the spool, trying to keep the temperature about stable.
The remaining 20% of the effort is just manual skill. Practice first on some scrap sheet. Learn how to move the flame, how to secure the joints, how much solder is required to fill them without having runs all over. Spend enough time on one joint (4 - 5 cm at a time) to allow the solder to spread uniformly but do not stay there for too long: the flux is not going to do its job for many minutes.

WARNING AND DISCLAIMER: Remember to operate in a well ventilated place: flux fumes are dangerous for your healt. Soldering iron, gas torch and solder drops can cause severe burns. Note that a 500 W soldering iron can have its dip still very hot even 30 minutes after being turned off. And you can blow up your place if there is a gas leak. I am not responsible for any injuries, damages or losses you experience by following my instructions.

Comments? Please, send me mail

Cyclone links

Bill Pentz Cyclone pages
Oneida
Steve Cater's Cyclone
Dustvent Inc.

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