Hey guys, I wanted to share my experience building my own pack frame. I partially wanted to save some money, but it also just seemed like a fun challenge. I initially thought about getting an aluminum pipe bender and doing it with aluminum, but I figured that would be a huge headache, so I went with PVC. The primary issue with heat gunning/bending pvc is that it kinks really easily, so I did some research online of different methods, and I came across some unique solutions that I use here -
First I gathered as many dimensions as I could of the frame. It seems like there’s a couple variations of the Karrimor brand out there, but I feel like the trapezoid style with the single top bar is the closest (from what I’ve seen). Juan posted a great photo of his frame with a load of dimensions, so that was my starting point. I also used Airborne troopers build as a reference for curves and placement of trays which was really helpful.
NOTE: I have the Trooperbay pack starter kit, and I believe some of the dimensions are off by a bit, specifically on the seed trays, but it’s what I have, so I fudged a couple measurements to work better with the trays that I have.
1/2” PVC piping (it says 1/2”, but the real diameter is 3/4”)
Sand (I used a bag of play sand)
An old pot
Wooden dowel slightly smaller than the interior of the PVC
First I drew out a template of the trapezoid shape (the bottom of the frame) that I could follow to bend the pipe to shape.
Next I marked the halfway point on the pipe, and the first two bends.
Then I masked off one end of the pipe and filled it to the brim with sand using the small funnel
Once the amount of sand had been measured out, I dumped it into a pot and put it on the stove on high heat for about 5 - 10 minutes. You basically just want it as hot as possible.
At this point I was ready to pour it back in the pipe and tape the other end off with masking tape. I made sure I had my thick gloves on and oven mitt close by, and also made sure I had the template all ready to go. Here’s a gif of how soft the pipe gets just a minute or so after pouring the sand in and taping it off.
Now I was able to lay the pipe on the template and slowly bend it to match the form I had drawn out. I used a heat gun a little bit for the corners, but I’m not sure it was even necessary. The hot sand acted as more than just the heating element, it also prevented the pipe from kinking and collapsing in on itself.
I waited for the PVC to cool to hold the shape, then used a heat gun to bend the 45 degree angles, using the floor and wall to prop it up while it cooled.
The next thing I needed to do was to give the long vertical pipes a subtle bend backwards. I sketched out what I felt like the curve should be, and then re-heated the sand for one side at a time. The sand is much more effective for soft subtle curves than a heat gun. (I also used a bojangles setup to prop everything up for a while to cool)
I repeated the process on the other side...
And also used the heated sand technique to bend the crossbar with a gentle curve. I cut it a couple inches longer than I’d need.
To attach the crossbar, I cut it down to the distance between the crossbars plus about an inch. Then I wrapped a piece of PVC with sandpaper to sand down the ends of the crossbar so it would fit nicely in place.
To attach the crossbar, I decided to use a couple wooden plugs (I made by whittling down the shape from a dowel) with pilot holes drilled in them that can be screwed in from the outside.
Then I hammered them into the ends of the crossbar to be flush with the shallowest point.
After drilling pilot holes in the frame, I screwed into the crossbar wood plugs to fasten it in place.
Once that was in place, I cut the ends off the frame to about 3” above the crossbar, and voila!
After a coat of paint and some old backpack straps, I’ll have a Karrimor-esque frame for about $10.
I hope that this might help some people build their own affordable pack frame!