So what to do? I'm finally getting around to building the first section of cleat wall in my shop, which means I'm looking at a lot of bevel ripping. Now mind you, extreme precision is not required for simple wall cleats! But I like to use utility projects such as this to improve my skills and processes, so that I'm ready when a real need arises.
After noodling the problem around for a while, I decided that finish-machining the bevels at the router table could be a good solution. Both to save material (expensive Baltic Birch plywood) and to reduce the amount of material that I'd have to remove at the router table, I decided to first straight-rip workpieces wide enough to make two cleats, with allowance for kerf width and a little waste material. Then rough bevel-rip the workpiece into the two separate cleats. Finally, as I didn't want sharp edges on the cleats in any case, I straight-ripped the sharp edges off of the cleats, taking the wider face of the cleat to final width. I chose a finish-machined width for the edge flat of 1/8", giving a good surface to guide on the router-table fence.
Next question: what router bit to use? I already had a 45 degree bevel bit that came in a cheap set of 1/2" shank Chinese router bits, but it wasn't large enough to cut this bevel on 18 mm plywood. I settled on a $50 Whiteside 2306 chamfer bit from Amazon, that's just large enough to put a full 45 degree bevel on 3/4" material. They make a larger one that can handle 1" material, but it costs $100, and would be overkill for my immediate needs. I also found some cheaper bits, but I know from frustrating personal experience that the edge profiles on cheap bits are often inaccurate.
Here's a pic of the Whiteside bit:
- Whiteside 2306_.jpg (31.37 KiB) Viewed 5317 times
The Amazon review below is what really sold me on this bit:
I've been making miters using a table saw for years. I've used shooting boards to cleanup miters and even with all the prep and painstaking care, I still ended (at times) with ill-fitting miters. Enter the Whiteside large 45-degree miter bit capable of cutting perfect miters in 3/4-inch material. With this bit and square lumber one can make true 45-degree cuts that provide for a gap-less fit.
For the average hobbyist wood worker, these bits can help you achieve a good miter. For the experienced wood worker, this bit will help reduce production time. However, using these bits requires careful consideration on type of wood and bit speed. This bit is massive (maybe not as massive as some profiling bits but heavy none-the-less) and requires router speeds in the neighborhood of 12 to 16 thousand RPM to achieve a smooth finish. Also one must use a template with this bit to cut miters unless one cuts in the vertical rather than horizontal position. I use 1/4-inch MDF to make templates and this gives me a crisp edge needed. One final note, sneak up on the final cut taking only about 0.01 to 0.005 off on the final cut to prevent burnt edges that might not accept glue.
I hope that this helps others considering this bit as a way to improve miters.
So how did it work out for me? With a 2" cutting diameter, this is a pretty large bit, so I had to remove the insert from my router plate. The photo below shows the setup on my stand-alone Shopsmith OPR, and a test cleat that I've already finish-machined. It would be hard to beat the finish on that bevel.
- Setup.JPG (305.13 KiB) Viewed 5317 times
And finally, how accurate is the 45 degree angle? Well, here's an end-view of a mating pair of cleats after finish-machining. The angle is not absolutely perfect, but with a worst-case edge gap of about 0.004", I calculate that the bevel angles are within about 0.1 degrees of nominal. And that may well be due to the perpendicularity of my router in the table -- I've never tried to tweak it for that much precision.
- Results.JPG (370.98 KiB) Viewed 5317 times
So all in all, I'd call this process a great success. Hopefully it will help some other Shopsmith users that struggle to make accurate bevel cuts.
