When using any CNC router, a method to collect the copious amount of chips generated in converting sheets of plywood into amazing projects is essential for a clean shop. Sadly, all that remained of the dust boot, on my new to me CNC router, was the mounting bracket. I decided to build a replacement that reuses the original bracket as this would allow vertical adjustment of the brush. What follows is the construction process for the new dust boot that fits 4" flexible duct.

Step 1: Materials and Tools

Materials

12x12x1/2" ABS sheet (McMaster-Carr part 8586K191)
3ft of 3" conveyor brush, 5/16x5/16" steel back, 0.014" bristle (McMaster-Carr part 74405T15)
Caulking to hold brush in slot (used 100% silicone not in photo)
3/4x6" aluminum round rod (length determined by desired range of height adjustment)
1/4x2" drill rod
(12) 5/16 x 5/16" rare earth cylinder magnets
1/4-20 1" button head fastener (hex key for fastener)
ABS glue

Tools

CNC mill or router
1/8" end mill with 1/2" depth of cut
Metal lathe (used to prep the ends of the 3/4" aluminum rod, could probably do this by hand)
Drill press (drill bit slightly larger than screw head)
Narrow wood chisel and or pocket knife
Angle grinder with cut-off wheel (for cutting the drill rod and notching brush)
Saw to cut 3/4" aluminum rod to length (if not using parting tool on lathe)
1/4-20 tap and #7 drill bit
Side cutter

Step 2: Cut ABS Parts

Look at the provided drawing to get an idea of the part dimensions and the best way to cut them on the machine you have. The provided DXF files contain the two parts in the drawing and should be used with your CAM software. Attach the ABS sheet to a waste board and cut out both top and bottom pieces using a 1/8" 2-flute end mill with a 1/2" minimum depth of cut. I used tabs to hold all the pieces together while cutting.

Step 3: Separate Parts and Drill Counterbore

The parts now need to be separated and the retention tabs removed. A small side cutter can be used to cut the tabs from the backside. The remaining portion of the tabs can be cut smooth using a wood chisel or other narrow blade. Next drill a counterbore on the backside of the top plate (see drawing in previous step) to fit the 1/4-20 button head fastener.

Step 4: Turn Mounting Rod and Cut Alignment Pins

Locate the 3/4" aluminum rod and chuck it in the lathe. Face the end of the rod and use a center drill to create a starting point for the drill bit. Using a #7 drill bit, drill a hole in the center of the rod to achieve a 3/4" tapped depth. Finish the hole with a 1/4-20 tap. Cut the bar to the desired length (about 6" for my application). A hacksaw was used for the cut because I'm using a chucker lathe with insufficient reach on the parting tool. Finally turn the part over and face the other end.

Two 1/4" diameter alignment pins should be cut to 1" lengths from the drill rod. An angle grinder with a cut-off wheel was used for this task. These pins will support the bottom plate when shear loaded and keep it from colliding with the cutter and spindle.

Step 5: Press in Magnets and Alignment Pins

Mark one end of the magnet stack in order to keep track of the poles. Press the magnets into the 0.31" holes with the marked pole only facing in on one plate and only facing out on the other. This will allow the two smooth sides of the plates to be attracted together. I was able to start the magnets in the holes by hand and finished using a rod smaller than the magnet's diameter to push them to the bottom of the holes. Finally press the alignment pins into the 0.248" diameter holes on the bottom plate. The pins should face the side without the magnets and be flush on the side with the magnets. An arbor press was used for this task but I was able to adjust the pins by simply pressing them against a hard surface.

Step 6: Glue and Assemble Top Plate

Fit test the 3/4" mounting rod in the smaller rings and adjust if needed. Insert the 1/4-20 fastener into the counterbored hole and then apply glue to the smaller rings making a stack around the end of the fastener. Now quickly slide the mounting rod into the ring stack and use the fastener with hex key to pull the rod snug against the bottom plate. Glue together the large diameter rings on the 3.5" hole in the top plate. Look at the inside of the stack to align the rings and top plate hole.

Step 7: Cut and Install Brush

This is the step I had the most difficulty with. The initial plan was to bend the entire length of brush to fit into the slot on the bottom plate. I quickly realized the difficulty of this approach. The brush would twist outward when bending the steel back making it impossible to fit in the slot and producing an undesirable bristle angle. After much frustration a workable approach was discovered.

This should be done with a continuous length of brush but I did not have a usable continuous length after my first failed attempt. Measure the length of straight sections and curved sections. Mark on the steel brush back where the straight and curved sections will go after bending. Measure out 1/2" increments on the curved sections. Using the angle grinder with cut-off wheel, notch the inside of the curve only leaving the outside portion of the brush back intact at the 1/2" increments. Then cut the the entire brush to length. These cuts should be made quickly as too much time cutting will excessively melt the bristles (some melting and bristle loss in the cut is expected). Bend and test fit the brush strip and make adjustments as needed.

Glue the brush in place using silicone caulking. Apply caulking to the bottom of the brush slot and between the cuts in the curved portions. Push the brush into place and apply a bead of caulking to the inside and outside edge of the bristles. A flat headed screwdriver can be used to push the brush into place.

At this point my project was complete. You more than likely do not have the same mounting bracket I had on my router but a similar bracket can be quickly fabricated to meet your needs. The location of the mounting rod should be adjusted to fit your bracket location and machine layout.