I made a pair of extra long, collapsible trekking poles about a year ago. It was actually pretty dang easy.
I sourced my carbon fiber tubing from eBay. Search for “3k wrap” carbon fiber tube. You don’t want the extruded stuff, it’s not as strong. I used 14mm OD/12mm ID and 12mm OD/10mm ID tube for the main sections, plus some 10mm/6mm at the bottom to join to the pole tip. For fixed length, either 14mm or 12mm OD should be fine for the main pole. They’re commonly sold in 100 cm lengths, so you’ll need three full sticks to get two 125 cm poles (duh).
I sourced pole tips from Black Diamond, and sanded down one end of the 10/6 tube to a taper that fit the pole tip reasonably well and stuck out a few inches. I then used a small amount of quick-set, 2 part epoxy to adhere the pole tip the 10/6 section. I glued the other end into my 12/10 lower section.
I used Gossamer Gear grips. I’ve grown quite fond of them. Not true cork of course, but they’re holding up well. Just a dab of epoxy to keep them in place atop the 14/12, which probably wasn’t necessary actually, and will make replacing them much more of a chore. Alas.
Not relevant for OP, but eventually I sourced Speed Locks from Leki. IF you already have a set of Leki poles, and you ask their customer service nicely, they’ll send you a pair of spare Speed Locks for free. :) The nice thing about Leki locks (as opposed to Black Diamond) is that you don’t have to notch the 14 mm tube, which would weaken it significantly in that area. The clamping part is built into the lock. Cool. It was a tight enough fit on the 14/12 that I didn’t bother to epoxy them. I tried the BD Flick Locks first, but they cracked at the end of the notch almost immediately. Not catastrophic failure, but not reassuring at all, especially if you use your poles as shelter support. If you’re going to make adjustable poles, I think it’s worth the extra hassle to source Leki Speed Locks.
I didn’t add straps to mine, but doing so should be pretty straightforward. I’d make a plug for the top of the pole that could accept some grosgrain webbing, then glue that in. Maybe add a clip or buckle so that the majority of the strap could be replaced/removed easily.
My poles extend to just under 60″ and weigh 4.9 oz each.
Here’s a pic of the finished product before I swapped out the BD locks:
