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====== Laminar flow hood

The plans presented below have required many hours of work, and some expensive trials and errors. If you find they were useful for you, a financial contribution, regardless of the amount, would be greatly appreciated.

Please note that like all the unreferenced information on this wiki, this content is only available under the terms of the license Creative Commons BY-NC-SA 3.0. Make good use of it.

Prototype 1 & 2

The first prototype met the expectations, but several details deserved to be improved. The plans, drawings and the budget of the second version are available below.

Prototype 1

Improvements

Structure & aesthetics:

  • The fan replaces the legs and reduces the total height.
  • The pre-filters are placed facing the air entry of the fan.
  • The pre-filters are more accessible for cleaning.
  • The mounting depth of the pre-filters is doubled.
  • The cover of the pre-filters and the lamp cover are removed.
  • The depth of the air chamber is reduced.
  • The internal shelves are made of glass.
  • The structure requires less wood (lighter, more compact, less expensive).

Electronic Components:

  • Lighting with a prefabricated LED strip. More uniform, requires less wiring.
  • Transformer 12V 3A, instead of 12V 1A.
  • Grouped switches with a more intuitive utilization.
  • The magetic stirrers use two magnets rather than one (magnetic fields stronger).
  • The stirrers engines are replaced by 200rpm 12V 0.5A DC motors. They are stronger (can shake 2.8 L), and no longer need dimmer.

Instructions

Materials and assembly

Plywood

Choose select quality plywood. On one side, the holes left by the nodes are filled and wood is sanded. For the interior of the hood body, especially in the work area, cleaning will be easier. This prevents the accumulation of particles in the cracks.

Primer & Paint

Before cutting, paint both sides of the plywood. First clean the dust with a damp cloth, and when the wood is dry, apply a primer. A primer before the first coat of paint provides better grip and faster drying, preventing it from entering the wood.

Then give two to three coats of white epoxy paint. Although rather toxic, it is durable and easy to clean. Use gloves to protect your skin and apply the paint in a well ventilated area. Use a grease to clean your skin if necessary. Between layers, wrap the paint brush and the roller into plastic wrap and store them in a cool place.

Centrifugal fan (“squirrel cage”)

The chosen model is the most powerful of Fasco in this category. If you choose another fan, make sure that its strength allows enough airflow despite the strong resistance exerted by the static pressure of the HEPA filter. You will probably have to do weld a custom bracket1).

Assembly

  • When possible, plan a 1/8“ space between each parts to compensate for the width of the saw cut.
  • (optional) Pre-assemble all pieces with a air nailer.
  • To avoid cracking of the plywood, pre-drill the screw holes with a bit of a smaller diameter.
  • Seal well all the internal parts of the hood by drawing a silicone seal. The junction between the two parts (filter and engine), and the periphery of the prefilters are sealed with packing tape, much easier to remove than silicone. Each pre-filter is individually sealed to the support.

Tools needed

  • Painting set (tarp, tray, roller, paint brush)
  • Circular saw
  • Jigsaw
  • Drill & bits (3/32 ”, 5/8“, 1 ½ ”)
  • Caulking gun
  • Glue gun
  • Soldering iron
  • Measuring tape, screwdriver, locking pliers (4), square, pencil
  • (optional) Pliers, wire stripper, hot air gun, crimping tool, air nailer

Magnetic stirrers

Commercial magnetic stirrers are large, expensive, and often stronger than necessary. To stir one to two liters, you can build one simply by sticking two hard drive magnets2) on a coupler mounted on a DC motor. The result, very compact, is easy to integrate directly below the work area.

  • Start by picking up the magnets from an old hard drive. You will probably need a special screwdriver (torx). Each magnet is mounted on a metal plate. To recover it, bend the plate in the opposite direction to the magnet.
  • Join two magnets together, then preheat the magnets and the coupler (with a hot air gun or a bain-marie…). Meanwhile, preheat a hot glue gun.
  • Put some glue on the coupler and attach it to the magnets, well centered. Leave to dry.
  • Place the assembly on a motor, then secure the coupler by tightening the screw against the shaft.
  • Solder the wires to the poles of the motor, as shown in the wiring diagram.
  • Drill SF (as shown below).
  • Align SF, DF and SFa with the holes, screw the pieces together and drill them (as shown) to place the engines.
  • Place a piece of styrofoam between the magnets and DF (temporarily) and make sure that there is a space left between the top of the magnet and the surface of SF. Then fill that space with another piece of styrofoam.
  • Stick the magnets to the surface with some tape, turn the screwed sheets (SF + DF + SFa) upside down, pull the wires out between the two SFa, and secure the engines with hot glue.
  • Turn over the sheets, remove the tape and the styrofoam, and complete the wiring.

Maintenance

Cleaning

Before each use, the internal surfaces of the work area should be cleaned with 70% isopropyl alcohol. The “floor” must be particularly clean. Pre-filters are cleaned with a vacuum cleaner, if needed.

Lubrication

The motor should be oiled once a year with a suitable lubricant. With a screwdriver, remove the cap in the center of the fan and apply a few drops of sewing machine oil.

Plans cuts

Each plan represent a sheet of plywood 4 'x 8' x 3/4 “.

The hood is assembled in two modules. The gray cuts are for the engine part, while those in green are for the filter part.

                    

Overview of cuts

Filter (F)

u Description Code Inches Centimeters
2 Sides CF 18 ¾ x 38 47.625 x 96.52
1 Top PF 24 x 38 60.96 x 96.52
1 Bottom DF 20 x 25 ½ 50.8 x 64.77
1 Rear AF 18 x 24 45.72 x 60.96
1 Stirrer SF 23 x 24 58.42 x 60.96
2 Stirrer-a SFa 2 x 25 ½ 5.08 x 64.77
4 Stirrer-b SFb 1 x 5 2.54 x 12.7

Motor (M)

u Description Code Inches Centimeters
2 Front/Rear AM 24 x 27 60.96 x 68.58
2 Top/Bottom DM 18 x 25 ½ 45.72 x 64.77
2 Sides CM 18 x 27 45.72 x 68.58
4 Side-a CMa 2 x 9 ¾ 5.08 x 24.765
4 Side-b CMb 2 x 23 ½ 5.08 x 59.69
2 Side-c CMc 3 ¼ x 7 ¼ 8.255 x 18.415
2 Side-d CMd 3 ¼ x 23 ½ 8.255 x 59.69

Assembly diagrams

Wiring diagram

The LED strip and the motors are connected in parallel, as shown. A switch can turn off the AC/DC transformer, and five secondary switches provide independant use for the lighting and each magnetic stirrers. A connector is used to facilitate the disassembly of the hood into two parts, in the event that it should be moved. Since only one thread links all the negative poles, it must bear the intensity of all modules simultaneously (2.6 A). To avoid overheating, the wire must have a minimum quality of 16 AWG (3.7 A). It was hard to find a generic connector with both the right amount of pins and a sufficient wire gauge, so in this case 16 AWG wires were manually soldered to a connector3). The end of each wire has been insulated with an heat-shrink tubing to avoid short-circuit.

The three-position switch allow fan speed selection. It may be replaced by a two-position switch, set to the highest speed.

Budget

Most parts are easily found in hardware stores. The electronics come from Ebay Canada, the HEPA filter from Fungi Perfecti and the 6-pin connector from Sparkfun.

Structure u $/u $ Surfaces u $/u $
Fan (Fasco™ A1200 + bracket) 1 450 450 Front doors 2 ? ?
HEPA Filter (18”x24“x6”) 1 175 175 Glass work area (24”x23“x¼”) 1 30 30
Pre-filters (9 ¾”x19 ¾“) 2 7 14 Glass shelves (4 ½”x12“x1/8”) 2 7 14
3-positions switch (115V, 15A) 1 6 6 Glass Shelf Clip4) 4 6 24
Power cord (115V, 15A) 1 10 10 68
AC plug (115V, 15A)5) 1 5 5 Electronic u $/u $
Plywood (quality select, 4'x8'x¾”) 2 40 80 Switching Power Supply6) (115V AC, 12V DC, 3A7)) 1 11 11
Primer & epoxy paint (for 128ft²) 1 50 50 Dual Switch Wall (115V, 15A)8) 1 7 7
Handles 6 18 108 LED Strip (50cm, 30 LED, 12V, 0.6A, waterproof)9) 1 3 3
Latches 3 12 36 6-Pin Chassis Connector10) 1 11 11
Screws ½”, ¾”, 1”, et 1 ½” 4 4.5 18 4 Gang Button Wall Switch11) 1 7 7
Silicon 1 6 6 Motors (12V, 0.5A, 200RPM, 3mm shaft)12) 4 8 32
Tuck™ tape 1 6 6 Shaft Coupler (3mm)13) 4 6 24
Paint brush, roller, tray & sleeve 1 9 9 Wire (16AWG, 2 pin, red & black) 1 ? 4
973 99

Total: 1140

     


Note: Most of the pictures of the electronic components shown in the budget section come from Ebay Canada.


1)
2)
3) Image from Sparkfun.com
4)
5)
6)
7) Amperage for all the modules shown (motors 4*0.5A + LED 0.6A = 2.6A)
8)
9)
10) Image from Sparkfun.com
11)
12)
13)