The blue wool is the input of rotational energy.
Green wool is the input for bone meal.

Make sure to deal with redstone repeating for dispensers.

There are three controllable settings.
The block with stone button is to force start cutting just in case.
The block with the lever, stops the machine completely even during its track.
And the third is the pulse extender, you can set the time of whatever source of rotational energy it should be.
If its too slow you can change the time to fit a slower rotational energy source you had.
If its too fast you can decrease the time for faster rate of wood.

To start, make sure when your source of rotational force is feeding into the system but does not start.
If it does, reset the machine and counter clockwise your rotational force source.

Then feed in spruce saplings into the top chest.
And have a skeleton farm to get bonemeal