How to install the drag chain?
Un power the machine and move the laser gantry slowly into the position to the hole in the side panel (or a light armature and remove the light) to get access to the side gantry Allen screws (qty:2) that holds the gantry end cap.
Remove the two screws and install the plastic end cap plate that came with the reward. This fit only in one position and screw it into its position. Shorten the drag chain by splitting it into two halves (30 cm) and move one end cap from the drag chain to the other half. Install the L shaped end plate on the laser head.
Install the drag chain between the L shape end plate and end gantry plate with the 4 supplied M3 bolts and nuts.
Route gently your electrical wire or air assist hose through the drag chain depending on which air assist method you use (pc fan or aquarium air pump).
How to install the ZnSe Lense and care for it?
Unscrew the lens cap but not the whole lens holder. Both unscrew in the same direction so take care not to unscrew both otherwise you need to realign the laser head.
Take the existing lens out and insert the new one with the concave (curved) side up facing yourself and the flat side down facing the laser working area. You can check proper installation by a simple rule. If you can see yourself mirrored in the lens surface than it’s correct. Hold the lens by its sides and never don’t touch bottom or top surfaces.
All laser lenses have a coating which can be damaged or even rubbed off when you rub too hard. Clean them by dragging a paper tissue drenched in isotope alcohol solution and not touching the lens (for each top and bottom; follow the same procedure).
The lens has a diameter of 12 mm. The laser beam itself is about 0.15 mm. Some machines have larger lenses install which does not matter. Make sure the lens sits nice in its seat. If the seat is not standard and larger than 12mm than install an o ring to center the lens. Most common K40s do have a standard 12 mm lens seat.
You can (optionally) add a cone shaped pinhole appliance too to protect the lens further from getting dirty but it’s not necessary. These can be 3d printed and found on thingiverse, for example: https://www.thingiverse.com/thing:2421971