The first time most people look at a kinematic mount the “What did I get myself into?!” thought is experienced. I am going to try to help with that as understanding the mount is crucial to being able to align your laser.
So why 3 screws?
It is simple really, 3 points are needed to make a plane, you also need 3 legs or supports to balance something. If the mount had 4 screws it would introduce an unnecessary element and one that would complicate the alignment geometry.
So how does this work?
The mount can be adjusted to redirect the beam very precisely but you will need to understand the different adjustment types to be able to control it. I have named the screws A, B and C in clockwise rotation. Also, for the examples, a full turn of the screws was used in both directions. After each movement the position was returned back to the center.
There are 4 types of movement that apply to the K40 Laser mount.
1. Independent screw movement.
The first and the most common adjustment uses only one of the screws. This causes the mount to pivot on the other two screws and the beam to move on a diagonal, up/down or left/right depending on the screw used.
Simple right? I know it’s still unclear at this point but I have separated every movement so you will be able to see the effect of every single one.
Because A causes the mount to pivot on the 2 diagonal screws(B&C) this moves the beam in a diagonal manner.
Because B causes the mount to pivot on the 2 screws(A&C) that are parallel to the beam plane/bed, this moves the beam up or down.
Because C causes the mount to pivot on the 2 screws(A&B) that are perpendicular to the beam plane/bed, this moves the beam left or right.
2. Two screw combo.
Moving the two screws at the same time causes the beam to move up or down, left or right or on a diagonal, depending on the screw combination. If you are thinking right now that this is the same as moving only one screw you are correct to a degree. The movement of the mount is similar but not identical. The difference comes from the the fact the mirror is not centered to the mount so the angle change caused by a full rotation on screw that is closer to the mirror is different than one that his further.
The examples will help better visualize the differences.
As you can see the direction is identical to moving just C but the position is slightly off but still in a relatively straight line.
The general direction is still up/down like when moving just B but there is a slight clockwise twist. I tested it multiple times with similar results. I suspect this has to do with the position of the mirror on the mount and the general construction of the mount.
Again, the general diagonal direction is similar but there is a slight counter clock wise twist in respect to just turning screw A.
3. Moving all screws at the same time.
This does not change the angle of the beam but shifts it left to right. It is commonly used to move the spot closer to the middle of the mirror after the initial alignment has been achieved.
4. Moving the whole mount.
The whole mount can be moved in case you go through the alignment and reach a point where the range of motion provided by the screws is insufficient. Moving it left to right will shift the beam target spot right to left. The mount can also be moved up by adding spacers and using longer screws. There is no easy way to move the mount down. If you find the mount needs to go lower you will need to modify the bracket or move the tube and other mounts up.
I hope this helps.