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A mask opens up a whole world of useful shapes
If you’ve ever wanted to venture beyond the world of squares and circles, consider incorporating elliptical shapes into your next design. Cutting an oval by hand can be complicated and usually involves a lot of sanding to smooth and smooth the curve. Fortunately there is an easier way.
Create the base
A mask made in-store is fairly easy to make with some scraps and a handful of mask hardware. To get started, you’ll need a 3/4 “piece of plywood that measures 18” squares. Install a router table with a 1/2 ″ straight tip and mill two grooves centered in the plywood. The grooves are affected at an angle of 90 °, so they look like a big “plus sign”. I made these initial steps with the straight tip a little less than the finished depth of 1/2 ″. Then swap the straight tip for a dovetail tip and set the cutting depth to 1/2 “full. Widen the central dovetail groove in several passes. The finished width of the dovetail channel is approximately one thumb in the widest part. The dovetail tip I used has a slope of 14 °, but the angle is not critical. As long as the dovetail tip has a cutting length of 9/16 “or more, it should work well.
Now create the dovetail sliders to fit the grooves. The stock used to make the sliders should be 9/16 ″ thick and extra long for safe milling. Make some of these strips and tear them off at various widths. I made three, with sizes ranging from 1 “to 11/8” wide. In this way, I can pass them through the whole dovetail at the same time. Once the sliders are beveled, test the fit in the plywood base. Choose the slider with the best fit and sand the angled edges until it moves easily in the channel.
With the sliders still extra long, mill grooves and holes to accept the T-bolts. A 1/2 “straight tip on the router table forms a shallow slot for the T-bolt head. Form two or three of these. shallow grooves along the white dovetail slider. Then head to the drill press and drill 5/16 “holes through the empty space centered in the shallow hollow.
Once all the milling operations of the dovetail sliders are completed, they can be cut to the final length. Dovetail sliders should be approximately 3 ″ long, with the T-bolt approximately centered. A touch of paste wax helps to create a sliding sliding action.
Create the swing arm
Now that the base and sliders are complete, let’s move on to building the swing arm component. The arm begins as a 27 “long x 4” wide rectangular gap. While it is tempting to get this component from a thick stock, I have found that a 3/8 “hardwood blank is sufficient. Start by routing a pair of slots on one end of the swing arm. These slots will allow further adjustment of the diameters. of the ellipse, without removing the dovetail sliders. This function is particularly useful for setting a final finishing step when cutting the elliptical shape. Next, bring the swing arm to the drill press and drill a series of 5 / 16 “in diameter with constant spacing. I spaced the holes 7/8 ″ from center to center. For a wider range of size possibilities, the holes can be positioned even closer together. The last hole on the swing arm will mount an optional handle with a 5/16 “T bolt. Route a 1/2 ″ slot x 7/8 ″ wide to receive the T bolt head (just as before with dovetail sliders). I proposed a handle from a spare router, which offers a comfortable and secure grip when using the mask. Finally, shape the swing arm as required for your router. I cut a concave shape on the end of the router swinging arm and I rounded the corners.
Base plate of simple router
My goal was to make a base plate that rests on the workpiece so that standard length router bits can be used. This simple step-down router base achieves this, with the router not being higher than normal. Start with a 1/4 ″ piece of plywood or MDF and trace the shape of your router. Transfer the positions of the mounting holes using the router base as a model. Now add the step-down block, which is a 9/16 ″ thick piece sized to fit your new base station. A 1/2 “MDF scrap would also work for the step-down block. Glue the descending block on the baseplate and sand the edges flush once the glue has set. Route and drill the step-down block for a pair of T-spots and you’re ready to assemble your new elliptical mask.
Assembly and use of the mask
Position the swing arm on the sliding T-bolts, setting the larger and smaller radius to the desired size. Install the washers and nuts first, then the star knobs to keep the swing arm in place. The 5/16 ″ nuts and star knobs work as lock nuts to hold the parts firmly together. Alternatively, lock nuts with integrated nylon inserts can be used. Connect the base plate to an immersion router and secure it to the swivel arm with a pair of 5/16 ″ x 11/2 ″ long T-bolts. Try the arc of movement to the rays you intend to use. It may be necessary to cut two sides of the base of the mask to allow the router to pass through.
A 1/4 ″ twist drill bit is the ideal choice for cutting the oval piece. Lower the 1/4 “bit at a time and make multiple passes to complete the cut. Make sure the piece is supported on a scrap of sheet items when completing the cut. Use this setting to perform a complete counterclockwise trimming pass. Make a fine adjustment for a slightly smaller ellipse. This will remove all the bit marks from the previous step.
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