Hi Birch
When it comes to using the jig saw in the RIP mode the blade is the key,,,you can find blades that are made just for that... they are a bit thicker and wider than the norm..
The blade will rip wood just like cutting hot butter...

and will cut true...but don't turn well..
Bosch makes many kinds

and you can find them at HD,Lowes,ACE,etc.
http://www.toolup.com/productinfo.as...bosch%20T101BR
Bj
