The Best Idea is WORK CAREFULLY! Do not get glue anywhere except near the edges of the lens.
Glues for the Objective (front) Lens
The objective lens is held in place initially by the middle tube, so take care not to use a runny type of glue which might run down the inside of the outer tube and glue it to the middle tube.
Four spots of glue 90degrees apart around the perimeter of the lens are sufficient.
The best type of glues here are pastes which do not run. NoMoreNails appears to be the best choice.
Prestik works fine too, especially where you might want to use the lens elsewhere at a later time.
One of the Pratley epoxy glues such as Quickset Glue or Putty will make a strong permanent bond.
Donít forget the range of silicone sealants, for instance the one that goes around the edge of a bath.
For a very fast bonding time, nothing beats the Glue Gun, but take great care to only bring the glue gun closer when you have the lens fitted into tube and are holding them at an angle them such that the glue can drop down only onto the join.
Glues for the Eyepiece (back) Lens
The eyepiece lens must be fastened dead-centre in the middle of the cardboard disk. A runny glue might work, because it cannot end up gluing pieces together that you do not want to be glued together. However, work with care.
Again, the best type of glues for the eyepiece are pastes. NoMoreNails is ideal.
Prestik will do the job in the short term.
As with the objective lens, the Pratley epoxy glues and silicone sealants can also be used.
Glues for the Stop and Baffle Rings
Here the glue sticks such as Pritt are easy to use. For a longer lasting bond, use a runny type of office glue which will soak into both surfaces.