Is the bubble on my sight already correct out of the box?

Assume not. Mounting tolerances and riser geometry vary; the bubble is only true after you level it against a plumb reference on your bow.

Second axis vs third axis — which one do I actually need?

Second axis always: it makes the bubble honest on level ground. Third axis only matters for steep uphill and downhill shots, so flat-range target archers can skip it.

I don't have a bow press or jig — can I still set it?

Yes. A plumb line and a helper (or a vice with soft jaws) to hold the bow vertical is enough. Level the string to the plumb line, then adjust the housing until the bubble centres.

Second Axis

The second axis is the sight's level about the line of sight — whether the bubble reads true when the bow is held perfectly vertical on flat ground. Setting it means adjusting the sight housing so its bubble is centred when the riser is plumb, so that the archer's cant reads correctly every shot.

Details

Three axes describe a sight's alignment. The first axis is the pin bar's tilt in the plane of the riser (it should be parallel to the string). The second axis is the roll of the housing about the line of sight: it is what the bubble level actually measures, and if it is off, a bow that is truly vertical will show a canted bubble, and centring the bubble will cant the bow. The third axis matters only on inclined shots. Second axis is the one every sighted archer should set, regardless of terrain.

The setup is straightforward with a reference. Hang a plumb line or use a string level to establish true vertical, hold or clamp the bow so the riser (or the string) is plumb, and adjust the housing's second-axis screws until the bubble is centred. Bow presses and levelling jigs make this easier, but a plumb line and a steady hand are enough. Confirm by rotating the bow slightly each way: the bubble should move symmetrically.

Why it matters: a canted bow throws arrows sideways, and the error grows with distance. A cant of just two degrees moves a 60-yard arrow several inches. If the second axis is off, the archer levels the bubble faithfully every shot and still shoots a consistent left or right — and then chases it with windage, which only works at the distance it was set.

Any time the sight comes off the riser or the housing is re-mounted, re-check the second axis before the third. It is the foundation the third-axis setting and every sight mark sit on.

Related on BowSmith

Glossary

Printables

Common questions

Is the bubble on my sight already correct out of the box?: Assume not. Mounting tolerances and riser geometry vary; the bubble is only true after you level it against a plumb reference on your bow.
Second axis vs third axis — which one do I actually need?: Second axis always: it makes the bubble honest on level ground. Third axis only matters for steep uphill and downhill shots, so flat-range target archers can skip it.
I don't have a bow press or jig — can I still set it?: Yes. A plumb line and a helper (or a vice with soft jaws) to hold the bow vertical is enough. Level the string to the plumb line, then adjust the housing until the bubble centres.