Recently I was asked to build a project that required a nice looking , but inexpensive table top. I decided to put curved corners instead of the 90 deg tips as the table top needed to be moved around quite a bit and I thought it would be good to have the edges rounded to avoid injury.
There are probably several similar jigs out there to do this but I thought I'd build my own. This ible will show you how you can build one from scrap lying around in your shop (and living room) and get a very accurate curve. The key ingredient is using some old CDs
4 old compact disks (CDs) or other disks
5/8 inch dowel (1 inch long will suffice)
12 x 12 inch square 3/16 inch MDF board
Router with tracing bit
Bandsaw, you can use other types as well
Make sure you have a nice square piece of MDF OR at least 1 corner is 90 degrees, this will facilitate in aligning the corner jig to your work. More on this later but for now lets call this corner the "true corner"
Take the 5/8 inch dowel and gently force the CDs on to it. Make sure they are nicely aligned on the dowel. This step is used to make sure your final pack of 4 CDs is lined up nicely. Now take the CDs off and put some gorilla glue on each side and then gently forcing the CDs back on to the dowel. Like I mentioned, the dowel is just their as a guide to align the CDs. Make sure you don’t get glue on the dowel as it will be pulled out once the glue dries up. Take a bunch of clamps and make sure the CDs are nicely glued. With Gorilla glue, I've experienced that just a few drops does the job.
Mark a curve with a pencil on the true corner. Take your time as all your cuts are going to depend on this.
Take a bandsaw and rough cut the mdf leaving 1/8 inch or so outside the rounded edge.
After the glue is dried on the CDs, line up the 4 Cds to the curve on the MDF, glue the mdf to the CDs with Gorilla glue as well, clamp, and be patient for it to dry. I let it go for a few hours. Pull the dowel out and make sure that everything is still nicely lined up. Gorilla glue has a tendency to expand and spread while drying and so you do need the clamps.
Take your router with the tracing bit, bearing guide on top and clean the curved edge on the mdf. You are using the CDs as a guide here so make sure you know when to start and stop. If you cut too much, you'll land up with a little groove and make the jig useless. Take your time.
Measure twice, cut once.
Your jig is now complete. To use it, make sure you clamp down the jig to the work surface with the edges lined up correctly to get a good rounded corner. Make sure that when you cut the corner, you adjust the routed depth so that the bearing is lined up with MDF and CDs. In the pictures you can see that I cut a corner with this jig on 5/8 inch birch plywood. This was my first cut and apart from a little burn due to my router, it worked nicely. The other photo is after I edge laminated the corner.
TIP: you can use 3 Cds and thicker mdf but you'll need to figure out the right combination. Also just double tape the CDs on to the corner without the MDF would work but you will have to be careful you don’t dig in to the work.