When using a router on a trammel cut — whether it’s an oval or circle — Woodworker's Journal field editor Chris Marshall says he always takes the extra time to make the cut with two router bits. “This old cabinetmaker’s trick usually makes the difference between a clean cut or a splintery one,” Chris says.
Start your first cut with a 5/8"-diameter straight bit wrenched into your plunge router and cut clean through the stock (in this case, cherry veneer plywood). Then, replace it with a 3/4"-diameter bit and repeat the cut. The larger bit will provide a clean final cut, since it’s removing much less material than the first bit.