Automatic Blast Gates for Your Dust Collection System, Part 2

TEXT BY ROBERT REED

PHOTO BY ROBERT REED

The electrical construction for the Automated Blast Gates introduced in the last issue consists of two parts: a junction/outlet box mounted on the machine and the internal wiring to connect that box to the machine. To start with, you will need a plastic single-gang electrical box of the type used for wall outlets in your home. Although any size will work, choose the one that is 2-1/4″ wide × 3-1/2″ long × 2-3/4″ deep. Remove any nails, “ears” and protrusions so that the box is clean.

     For the cover plate, any non-conductive material of adequate rigidity will work. I used two pieces of plastic laminate glued together. Machine the cover plate as shown in the drawing; drill holes as shown in the side of the electrical box as well.

     The wiring here is quite simple and straightforward (1, 2). The cover panel fuse holder is inserted into its hole and firmly nutted down. The indicator lamp, which lights up when a fuse has blown, snap-fits into its round hole, as does the NEMA outlet into the squarish hole.

     Pay close attention to the parts numbers when ordering your supplies and making up your boxes, as the 120VAC and 240VAC parts look almost identical; however, these parts have minor but important differences. In addition, one extra fuse/fuse holder is required in the 240VAC box. Since both sides of the line are hot on 240 VAC circuits, this is needed for any catastrophic failures that may occur on that side of the line. This fuse can be any generic brand rated for 2 amps/240V and would rarely blow out; normally, the cover panel fuse (with a much lower amp rating) would blow first. Mount this fuse holder in the approximate center of the box's rear wall.

     To make your connectons, you will need a small assortment of wire terminal female Quick Connectors (QC) in both 3/16″ and 1/4″ sizes. These are available at your local hardware store. There are also “Fork Adapters” available that convert a single male QC to two male QCs for situations where two wires connect to a single point. Or, you can attach two of those wires into the body of a single QC. These connectors can be crimped on or soldered on; your choice. Alternatively, the connectors could be completely eliminated and the wires soldered directly to the components’ terminals; again, your choice. If you opt for direct soldering, you will still want to use three QCs for the wires that will feed into the machine cabinet for easy box removal, should that become necessary.

PLANS AND PATTERNS

GATE-CONTROLLED SYSTEM

     The box is mounted on its side to the machine cabinet to keep it and its corresponding solenoid's cord/plug in a more compact and out-of-the-way position. Ideally, this would be in close proximity to its vacuum port and with the outlet looking directly at that port. This makes for a neat installation that has minimal cable exposure. Lay the empty box on the machine cabinet in the area you wish to mount it and make sure there are no obstructions on the other side of the cabinet wall. Scribe the three holes in the box onto the wall of the machine cabinet. For the large hole, drill a 1/2″ hole centered in the scribed circle, then install a rubber grommet in it.

     If you have adequate working room inside the cabinet, drill the two small mounting for a #8 screw clearance hole (#17 wire bit). Attach the box with two #8 × 1/2″ machine screws, flat and lock washers, and nut them tight. One of these screws could be used as a ground point for the incoming green wire. If used, make sure the area is clean and free of paint, then fasten the wire to it with a crimped ring terminal connection.

PHOTOS THIS SPREAD BY JOHN LAVINE

     If your access to the machine cabinet interior is limited, drill the mounting holes for a #8 screw tap hole (#29 wire bit). Attach the box with #8 × 1/2″ sheet metal screws and flat washers. These will be more difficult to screw down but can be managed with an ultra-stubby or right-angle screwdriver. I used a small screwdriver attachment on my ratchet wrench.

     Next, locate the power connection points on your machine. Exercise extreme caution when doing this electrical work. YOU ARE DEALING WITH LETHAL VOLTAGES—ALWAYS UNPLUG THE POWER FIRST! Most motors will have a junction box mounted directly on the frame, and many of these boxes will have knockouts for cable entry. If available, this is the easiest tie point. Remove the cover and locate the two wires running into the motor's housing. These will probably be tied to the incoming cable with wire nuts or something similar. Remove one of the knockouts, add a cable clamp to that hole, pass your cable through, and tighten the clamp. Strip the cable back to give you several inches of wire; strip off 5/8″ of insulation from their ends. Now simply tie your wires from the outboard junction/plug box to these points, using larger wire nuts as necessary. The ground lead can also be tied here using one of the hold-down screws in the area. Clean the area where that bolt/screw seats and make sure it is free of paint. Crimp a ring terminal on the ground lead, slip it over the fastener and tighten securely.

     No motor box? Then follow the motor leads up to the first point that they are landed, usually the machine's front-mounted power switch. The landing point will probably be a screw terminal on a terminal block. Connect your wires at that point; again, there should be a suitable grounding point in that area. Double-check that you have connected to the motor side of that switch and not the line side; otherwise, the solenoid would energize the moment the machine was plugged into its power outlet.

     In built-up machines (such as a router table) you probably won't want to tear those motors apart to gain wiring access. The good news is that any router table worth its salt will certainly have a front-mounted switch box, and the router motor will be connected to this switch with the router's switch left in the “on” position. The access is easy here.

     Once you have located the machine's connection points and have a “plan of action” in place, you should be able to hook up any machine in your shop with no difficulty. However, you may be thinking at this point—why even make up this machine-mounted box? Why not just wire the solenoid cable directly and eliminate the box completely? There are three good reasons for this box:

• Easy connect/disconnect of the gate/ vacuum hose system
• Proper fusing, which is imperative for safe operation
• Easy access to the fuse and a visual indicator when it's blown.

     Let me mention a few more things. If the machine's motor is moveable (such as a tablesaw), be sure to allow enough cable slack to accommodate this movement. Also, if you want to dress the cable (routing and anchoring), nylon ties or adhesive pads with nylon ties are available at most home centers.

     Once your box is located and mounted to the machine, you can complete your wiring between box and solenoid. For the solenoid connections, I purchased a cheap 25′ extension cord ($3-$4). After cutting the plug end to the proper length needed (which averaged 8′ in our case), the free end was stripped back and two 1/4″ QC connectors were added to the two power leads. The green ground lead received an appropriate ring terminal. Connect the power leads to the solenoid and ground the green wire to one of the solenoid mounting screws. Add a 1/2″ cable clamp on the operator board to secure this cable at the board. Run the cable along an out-of-the-way side of the vacuum hose drop and secure it every foot or so with thin strips of duct tape or velcro fasteners. I really like the shop-variety extension cords for this use as they are cheap, have the molded plug and a durable outer jacket to enhance safety. Also, the box-to-machine cable was cut from the leftover piece.

     Let me mention again that when doing the electrical assembly it is important not to confuse 120VAC and 240 VAC units. I was a bit hesitant when choosing the same solenoid cable plug configuration for both 120VAC and 240VAC units. 240 VAC plugs and sockets are available to make a positive difference between them, but their price is extraordinary and also would require a larger machine-mounted junction box. Since both plugs are the same and the completed units look identical, a very positive identification for the units is necessary. Starting with the operator board, boldly label it for its intended voltage. Then clearly label the boxes and associated plugs for the same. Hopefully, this will prevent you from cross-connecting components of different voltage. In the future we plan to color-code the boxes and plugs for their voltage ratings.

DON'T QUIT JUST YET

     If you build these blast gates and you haven't already built my “Dust Collector Auto-Start” [see Woodwork #91, February 2005], then I have one more addition for this system. That is: an easy way to add “dust collector auto-start” to these blast gates. The system is based on my blast gate article from Woodwork #98, April 2006. See the sidebar on the next page for a fuller explanation.

     Now if you go the “full route” of this article, the whole system will be automated. Nothing else to do but push the start button on your machine…sweet!

Robert Reed is an amateur woodworker with a background in electronics engineering; he lives in Roaming Shores, Ohio.