In cutting any material effectively, a critical aspect is the speed the cutting edge, usually referenced in SFM -- Surface Feet per Minute.? Very roughly speaking, woodworking requires around 5,000 SFM.? For rotating tools, this means proper RPM is related to tool diameter.? A 3/4" router bit needs ~25,000 rpm; a 4" shaper bit needs ~5,000 rpm.? ?So even high shaper speed of 10,000 rpm is way too slow for small bits.? A 3/8" router bit at 10k rpm is hitting less than 1,000 SFM.?
As you'll remember from high school physics or just know from intuitive experience, the energy (force, momentum) of a rotating mass is proportional to the speed and amount of mass (weight), but it's not a linear proportionality.? Driving your car through a given curve at 60 mph has a lot more than twice the energy of going 30 mph.
A 4" shaper bit that weighs several pounds moving at 7,500 rpm has ~20 times the energy of a 1/2" bit running at 30,000 rpm.? ?These are forces that are basically impossible to "manhandle".
An accident with a 1/2" bit in a router table might take the tip of your finger off.? A shaper accident might take several fingers or your entire hand in an instant.
Basically, a shaper should be used with a power feeder.
The only reason to buy a combo is being very tight on space.? If you have enough space, buy a saw and J/P and no shaper.? ?Someday if you find you really have a use for a shaper, buy one then.
Mark
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