I doubt you'll get much tear out cutting with the grain and it looks like a good part of the groove is already in place. Use a downcut spiral bit and you'll reduce the tear out possibilities even more.
You'll be cutting with both sides of the bit, assuming you're using a 1/8" bit to cut the 1/8" channel. So one side will be climb cutting and the other will be conventional cutting; make sure your guide is on the correct side for the direction you'll move the router or it will try to walk away from the guide. Do a test on scrap if you're not sure.
David
You'll be cutting with both sides of the bit, assuming you're using a 1/8" bit to cut the 1/8" channel. So one side will be climb cutting and the other will be conventional cutting; make sure your guide is on the correct side for the direction you'll move the router or it will try to walk away from the guide. Do a test on scrap if you're not sure.
David