This week there came a need to rout an oval that matched a smaller oval, and we needed to make the new pattern 1-1/4″ wider all around. A new design could have been made, but that’s a lot of extra work to layout, cut and shape. And getting the oval as an exact match would be difficult at best.
In the past (especially when working on goose-neck molding layout), I’ve made a wooden circle with a center hole just sized to allow a pencil to pass through to accurately draw around a pattern, providing a perfect over-sized pattern. As we discussed this technique, Dave (friend and fellow woodworker) suggested we bypass the pencil and use a router bit instead. Great idea.
To make it happen, you need to size the needed bushing. To add 1-1/4″ when using a 1/4″ spiral-upcut router bit, you need a 2-9/16″ outside diameter bushing – you cannot find that in the router accessories department of any store. So step one is to make a plywood disc to that size. If you do the layout work with a compass, you get the size and you mark the center of your disc, which is a good thing. Cut the rough shape at your band saw then smooth the edges using a disc sander. (You could set up a band saw jig to make the disc, but that’s way to involved when a single disc is needed.)
With the wooden disc in hand, drill a hole in its center that is perfectly sized for a standard bushing you have in the shop; in this case, we used a 3/4″-outside diameter bushing. Make sure you accurately center the hole in the disc – that’s where the prick from the compass leg comes into play. When you’ve drilled the hole, the disc should fit snug on your bushing. Load the over-sized guide bushing into your favorite router and your set to work.
With this arrangement, the bushing offsets the router as the cut is made. A good practice is to step your way through these cuts, making several passes while dropping the cutting depth with each step. The photo below shows the first light pass, which also confirmed the offset cut.
Router bushings are a great asset to have in the shop. In most available kits, the largest outside diameter is 51/64″. You can find odd bushings sized as large as 1-3/16″, but if you need something larger, turn to plywood and make the bushing in your shop.
Build Something Great!