I've finally run out of the plano-convex lenses I bought last year from Surplus Shed. These were great as they had a 50mm or so focal length which resulted in a short IR focus tube. I've ordered some more lenses but these have a FL of 100mm, therefore I needed to re-design the focus tube of my tag guns.
I changed the tube design to be in two parts. One holding the LED mount, endcaps and focus screw. A second tube is designed to slide over the first, but also it can be lengthened/shortened or given a larger diameter to suit the lens being used.
I forced the two parts together in my carpenters vice.
The ridges produced by the RepRap process interlock providing a fantastic strong joint. No glue is needed, I'm not going to get these two apart in a hurry.
Here is a complete IR tube kit. These are now available at Tagbits: