On my most recent project, the American Chippendale Mirrors discussed in my last post, I was forced to choose between using a table mounted router or a shaper. Specifically, was how to shape the picture frame molding which was complicated by the use of tiger maple hardwood.

Tiger maple is notorious for tear out whether hand planing, jointing. thickness planing or shaping. I have described in this blog numerous times how I thickness plane the final 1/8” to 1/16” of tiger maple using my Performax Pro 22-44 for just this reason.

CMT 855.902.11 Traditional 1/2” Shank Router Bit The bit used to shape the molding in this project was a CMT 855.902.11 Traditional 1/2” shank bit. Its overall cutting length is 1 5/8” and its overall diameter is 1 1/16”, rather small for even considering a shaper.

The primary decision making criteria between using a router and shaper is the bit diameter. Bit RPM being equal, large diameter bits have a higher tangential velocity compared to small diameter bits. Large diameter bits remove more material requiring more horse power. This is where routers and shapers differentiate themselves (portability is another but not applicable when comparing table mounted routers to shapers).

Routers generally spin at higher RPM, typically 10,000 to 21,000 RPM and range from fractional horsepower to 3 1/2 horsepower. Hence they are useful mostly for small diameter bits. Shapers generally have two or three speeds to select from, usually 8,000 and 10,000 RPM and start at 2 horsepower and range to in excess of 5 horsepower. Hence applicable to large diameter bits.

RPM are directly comparable, but not all horses are equal; a 3 1/4 HP router is not equal to a 3 HP shaper, the latter being much more powerful. I should also mention that shapers tend to be much more hazardous than routers, so special attention to safety is required.

Molding Picture Frames On The Shaper This all being true one would normally mount this bit in a table mounted router and shape away. I started that way and quickly realized I needed to consider the shaper. Even though I was using a 3 1/4 HP variable speed router with speeds selectable from 10,000 to 21,000 RPM I couldn’t achieve a tear out free finish, no matter how many light passes I made. I put the same bit in my shaper and selected 10,000 RPM and discovered I could make tear out free finishes if I cut the molding in five light passes and proceeded slowly and smoothly on each pass. I can’t explain this rationally but I can demonstrate it quite clearly. If someone has a technical explanation I would certainly like to hear it.

This is not the first time I discovered this about tiger maple. In fact, on almost every project requiring tiger maple molding I end up on the shaper. I always try to avoid the shaper because of the long setup time required, but in the end I succumb. So this time I committed to design a fence for my shaper that will allow fast setups, flexibility, and safety. Designing such a fence may take a while but will pay large dividends in the end.