May 9, 2012 at 5:23 pm #1289727
I am a newbie here and I am attempting to make my first backpack. I literally stumbled upon this website after I started drawing up the backpack. I have already made a prototype of the frame 1/4" x 7.5" x 18" HDPE and epoxied 1/8" x 3/4" x 18" aluminum stays and 1/8" closed cell foam. I measured myself according to different custom pack websites, and the frame maybe an inch short. Now I am going to start with the prototype fabric (probably cheap nylon from walmart) for pattern work.
I have already ordered my fabric materials: VX-21, 500D coated Corurda nylon ripstop, 1.3 oz silnylon, 4 mm neoprene ~1/8" , and 1/8" closed cell foam. I still need to find a good mesh fabric for the anterior side of the pack. I am trying to make a sturdy, yet lightweight pack. The sample of 0.74 oz cuben I received did not feel strong enough.
I have also ordered 3/4" polyester webbing for lid closure, hip-belt adjustment, and compression straps. The high use straps such as the hip-belt and lid closure straps will use aluminum buckles, and all others will be plastic ( I have had several buckles break in the past on my commercial packs vaude, osprey, and black diamond). The aluminum has been anodized, and will also be lacquered. The hip-belt will use two buckles, one at the top of the hip-belt and one at the bottom of the hip-belt.
According to my calculations my with an approximate volume of 5200ci I will use at a very minimum without reinforcements the following dimensions for different compartments for my pack:
Main Chamber 4000ci
r= 7.5in (center of pack to lateral side) d=15in
v= 4062ci So a length of 47.1in and width of 23in will give the approximate volume of 4062ci without the added length for seams.
Sleeping Bag Pocket 1000ci
v= 923ci So a width of 7in and length of 43.96in wrapped around will give a height of 6in and a volume of 923ci.
Lid Pocket 400ci
r= 7 to 0in
v= 340ci for the volume of a paraboloid.
Does this sound right? The calculations for the lid are a bit different because I used vector calculus to estimate the hight from a a given tapered radius and estimated volume then tweaked it.
I would like some input about some of my ideas. I am not trying to go super lightweight because I want this backpack to last.
Thanks!May 9, 2012 at 6:22 pm #1876032
You might get more specific feedback if you posted pictures of your prototype frame and sketches of your design ideas. I use the free 3D modeling program Google SketchUp for MYOG design–if you're not already a SU user you could get up to speed in a few days–very useful visualization tool, and will do accurate area and volume calcs.
5200 ci/85 liters is kind of a monster pack by the standards of this site–even at that, your description of the frame seems a bit (oddly) overbuilt, esp. the 1/4" HDPE (what does that weigh?). If you're set on that thickness for the framesheet, you might consider extensive lightening holes.
Conventional wisdom is doing MYOG frameless pack for light loads is pretty forgiving–things don't have to be perfect to work okay. Big load haulers are a lot trickier, for fit, structure, construction, etc.
Out of curiosity, what do you estimate for total weight? And how are you using the 1.3 oz silnylon?May 9, 2012 at 8:04 pm #1876080
David thanks for the info…
I must have missed that typo, the HDPE sheet is 1/16" thick, and has been designed to follow my spine from the lowest lumbar vertebra to just above my shoulder blades. Just below the scapulae (plural) its width is designed to fit between then becomes wider to create a y at shoulder height. Think of a modified Arclight frame from Dana Design, and you will be close to the overall idea. I will create my own dual density padding from the closed cell foam and neoprene. Estimated pack weight is optimistically 4lbs, but will hopefully be closer to 3lbs depending how much I shave off the frame.
I have an excel sheet that says about 2lbs 2oz with extra fabric for the seams, zippers, buckles, compressions straps, webbing, reinforcements, frame (including aluminum stays and HDPE sheet epoxied), and sewn weight. That is not including padding, shoulder straps, and a couple plastic ladder locks and heat shrink for certain polyester strap coverings. The predicted weight off the top of my head with the extra items added in is about 3lbs 5oz +/- 5oz leaning more towards the plus for the tolerance limits.
Disclaimer- I am not trying to be rude or confrontational, just blunt.
I also believe there is a point when gear can become too light, and that point is when it does not perform its duty to fully protect from the elements. That's just the eagle scout in me (1/100)… I know this is supposed to be a 'superlight' site, but in my experience, Murphy's law takes precedence.
Thanks for the interest I will post pictures as soon as possible,
P.S. I have a lot of funny stories of people not being prepared.May 9, 2012 at 8:11 pm #1876085
The silnylon will be for interior pockets.May 9, 2012 at 9:51 pm #1876108
Ahh–1/16" makes a lot more sense, esp. given how clearly it seems you've thought through your design.
>"I also believe there is a point when gear can become too light, and that point is when it does not perform its duty to fully protect from the elements."
I expect just about everyone here would agree with that. Quite a few Eagle scouts here, too, including (IIRC) the Backpacking Light publisher. It's been a few years since I stumbled on this site–these days, I'm at least as well-prepared carrying a base weight around 7-8# as I ever was carrying a fully loaded Dana designed K2 Shortbed. I'm also hiking longer, further, and in more challenging terrain.
Regardless, there's a wealth of knowledge here, esp. among the MYOG folks, and I've benefited tremendously from it. 3# and change sounds pretty respectable for the size pack you're planning–I really look forward to following your progress, even though your project is quite different from those I've done or have in the works.
Keep posting, and welcome to BPL.May 11, 2012 at 8:24 am #1876635
@socal-nomadLocale: North San Diego county
You stated you want a very strong pack.
I was reading over your plans for the pack.I have one question have you stress tested the aluminum rods epoxied on to the HDPE frame sheet to see if they pop off the HDPE frame sheet. Also stress test in heat above 80 degrees to see if the epoxy softens and the rods pop off.
Personally I would use a 1" to 1 3/4" nylon pocket to put the rods in,Go to a your local shoe repair have them sew through the frame sheet the nylon rod pockets
You also listed 3/4" polyester webbing this is the worst webbing you could use true polyester webbing can resist UV rays and is used through outdoor water sports equipment. Most polyester webbing is not tightly woven in less they make a new tight weave I don't know about.
Your better off using nylon flat weave that has tight weave is very strong used through out backpacking and climbing industry.
I hope this help you build a stronger pack.
TerryMay 11, 2012 at 9:07 am #1876645
@cameronLocale: Idaho Falls
Mike welcome to BPL! I have made a few packs of my own and I'm currenlty working on an internal frame pack project so I have some idea what you're doing.
I think making a prototype with cheap materials is a very, very good idea. Its easy to make a small mistake that can make a pack unusuable. For example I have a pack right now with shoulder straps that are just a bit too close together at the top. That little error (probably .5 inches) puts enough pressure on my neck that I'll probably never use the pack as it currently is.
Here is one idea you might consider. Take a look at the "sandwitch" style dry bag haulers like the ULA Epic pack. The advantage of something like that is its a bit easier to put together and easier to modify if you're not happy with the finished product.May 11, 2012 at 9:22 am #1876647
@powell1njLocale: North Carolina
Sounds like a cool project. I'd be interested to hear about more specifics about the HDPE framesheet. Where did you get the material? Also, where did you get the aluminum tubing? I'm having a hard time sourcing the thin aluminum tubing that so many people use for frames. Any info. would be appreciated.
Good luck on your pack.May 11, 2012 at 9:39 am #1876653
+1 what Terry says re: epoxy. Generally, not much sticks to PE, including epoxy. Aluminum can also be tricky to bond to, but maybe the anodizing helps with that. If HDPE and alum. have different thermal expansion rates, that will cause trouble as well. FWIW, I've used System 3 epoxies in the past–there's a wealth of general epoxy info on their site.
I like Terry's idea with the nylon pockets a lot–simple, and makes the stays removable for those times only the framesheet is needed. You could also rivet the alum to the HDPE (peened over aircraft rivets would leave smooth heads on both sides, unlike pop rivets). Or drill a line of holes in the alum and sew directly to the HDPE, using something like a Speedy Stitcher sewing awl (have to dress the holes in the alum, so it doesn't cut the stitching).
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