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#193287 - 01/22/16 07:54 AM Backpack Design Questions
4evrplan Offline
member

Registered: 01/16/13
Posts: 640
Loc: Nacogdoches, TX, USA
I'm thinking about building a prototype backpack that's custom fit to me and will test out an idea or two, but I have a few questions about proper design that I hoped someone could answer.

1) How far below the waist should the pack hang?
2) Is my torso measurement (from waist to the prominent neck bone) the ideal exact distance between the top and bottom strap attachment points, or is there an allowance here or there for something I'm not thinking of?
3) Any tips for deriving a shoulder strap shape that fits my body best? My idea is to draw on myself with chalk and transfer that to fabric, but I'm not sure exactly where it should lie against me.

Thanks.

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#193288 - 01/22/16 09:21 AM Re: Backpack Design Questions [Re: 4evrplan]
Pika Offline
member

Registered: 12/08/05
Posts: 1733
Loc: Rural Southeast Arizona
I've made several packs with varying degrees of success. Perhaps my experience will be helpful. The packs I have made have been in the 2600 to 3400 cubic inch volume range. My weight goals have been 10 - 16 ounces. I have included an aluminum "hoop" stay as part of several packs. This adds both weight and comfort.
1). I generally have about 3-5 inches of pack below the bottom of the hip belt attachment. Much more than this and the pack can ride annoyingly on your upper butt. I also design this part of the pack to curve away from the hip belt.
2). My measured torso length is greater than the distance between the shoulder strap attachment point and the top of the hip belt. For me, the difference is 2-3 inches. The shoulder strap attachment needs to be low enough that the straps can curve up over your shoulder before dropping down your chest to the lower attachment. The exact placement of hip and shoulder strap attachments is best determined experimentally
3). I use a simple "J" shape shoulder strap similar to those used on the G4 pack. I think you can get the shape of the G4 straps online. Several things are important with the shoulder straps. First, the space between the straps where they attach to the pack at the top. If you are thick necked you need more distance. Second, the angle of the straps with the mid line of the pack is important. On my most recent pack the departure from vertical is about 3.5" in 12". The length of padding is important too. If the strap padding gets between your torso and your arm it can be irritating as you swing your arms. And, the width of the padding is a consideration. I prefer a narrower strap over some of the wider versions I have made. A wider strap can chafe against your neck and can rub against your arms when walking.

There are several pack patterns available with the designers ideas built in. I have made each of them and have not found any to my complete liking. You might, though, want to take a look at one or another to get some basic ideas. You can get the G4 pattern from Quest Outfitters, an alpine pack design from Rainshed in Corvallis, Oregon, or a RayWay pack kit from Ray Jardine. All have websites.

The pack I just finished is a 3000 cubic inch, 14 oz. version combining what I liked about each of these packs. I also incorporated an aluminum stay similar to that used in the Six Moons Design Starlite pack. Good luck with your planning.
_________________________
May I walk in beauty.

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#193289 - 01/22/16 10:23 AM Re: Backpack Design Questions [Re: Pika]
4evrplan Offline
member

Registered: 01/16/13
Posts: 640
Loc: Nacogdoches, TX, USA
I know craft foam is sometimes used for the strap padding. Is that what you use, and if so, what thickness?

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#193291 - 01/22/16 10:40 AM Re: Backpack Design Questions [Re: 4evrplan]
Pika Offline
member

Registered: 12/08/05
Posts: 1733
Loc: Rural Southeast Arizona
I use 3/8" thick closed cell poly foam. This is the same stuff that the blue Walmart sleeping pads are made of but 1/8" thinner and black. I get it from Quest Outfitters but I suspect that if I were to look around I could get it locally and cheaper.
_________________________
May I walk in beauty.

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#193293 - 01/22/16 11:05 AM Re: Backpack Design Questions [Re: Pika]
4evrplan Offline
member

Registered: 01/16/13
Posts: 640
Loc: Nacogdoches, TX, USA
That's good; I've got some scraps of WM pad foam I can use. I might sand it down to the preferred thickness (with a mask and goggles of course).

Also, where do you source the metal for your hoops? I'm going to try without one first, but I may need to add one afterwards if it's not enough support.

My idea for getting enough support without a stay is to roll an inflatable pad around the inside of the pack, load all the other stuff into the middle, and then partially inflate the pad until everything's nice and rigid.

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#193294 - 01/22/16 11:39 AM Re: Backpack Design Questions [Re: 4evrplan]
Pika Offline
member

Registered: 12/08/05
Posts: 1733
Loc: Rural Southeast Arizona
I use a pad pocket made of 1.8 oz rip stop in preference to the rolled pad. In my experience the rolled pad makes the pack ride somewhat like a beer keg with shoulder straps; not particularly comfortable IMO. My folded Thermarest Prolite 3, short, makes a good stiff "frame" if I go with the stay removed

It is better to plan for the stay while making the pack rather than trying to retrofit. I sew in sleeves for the stay and have a webbing pocket in which to seat the bottom ends. The pocket is sewn on to the hip belt reinforcement piece near where the hip belt attaches. All this is hard to do once the pack is assembled.

I got the aluminum from a metals supplier in Tucson. I don't recall the alloy number but it is used in aircraft. It needs to be bendable but still stiff. I used 1/4" diameter rod. The piece I use for the stay weighs a bit under 4 oz. If I can remember, I'll look up the alloy number but if someone else reading this has the info, don't be shy about posting it.
_________________________
May I walk in beauty.

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#193295 - 01/22/16 11:52 AM Re: Backpack Design Questions [Re: Pika]
bluefish Offline
member

Registered: 06/05/13
Posts: 677
2024-t4 aluminum rod. You can buy it online.
_________________________
Charlie

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#193296 - 01/22/16 12:08 PM Re: Backpack Design Questions [Re: Pika]
4evrplan Offline
member

Registered: 01/16/13
Posts: 640
Loc: Nacogdoches, TX, USA
Originally Posted By Pika
I sew in sleeves for the stay and have a webbing pocket in which to seat the bottom ends. The pocket is sewn on to the hip belt reinforcement piece near where the hip belt attaches.

So, the horizontal part of the stay is at the top, right, like an upside-down U? And this sleeve is on the inside or the outside of the pad pocket (closer to your back or farther)? Any chance you could share pictures?

Thank you for all the help, BTW.

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#193297 - 01/22/16 12:51 PM Re: Backpack Design Questions [Re: 4evrplan]
Pika Offline
member

Registered: 12/08/05
Posts: 1733
Loc: Rural Southeast Arizona
Yes, the stay fits in as an upside-down U. I use Velcro tabs on a lightweight flap to cover the upper, cross-bar, end and to hold it in place. The sleeves are 2" wide by about 20" long strips of coated rip stop that are folded into a tube and sewn into the seam that joins the side panel to the back panel (closest to your back). The stay is placed on the piece nearest your back and the pad sort of fits between the side rails.

Pictures of the stay installation would be tough since it is almost all inside the pad pocket. I'd be happy to share photos of what I can photograph including the upper part of the stay assembly. PM me your email address and I'll dig out my camera.
_________________________
May I walk in beauty.

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#193298 - 01/22/16 12:59 PM Re: Backpack Design Questions [Re: Pika]
4evrplan Offline
member

Registered: 01/16/13
Posts: 640
Loc: Nacogdoches, TX, USA
It says you're over your message limit. That's okay, though; I think I've got it. smile

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#193471 - 02/04/16 12:43 PM Are Load Lifters Necessary? [Re: 4evrplan]
4evrplan Offline
member

Registered: 01/16/13
Posts: 640
Loc: Nacogdoches, TX, USA
New question: I'm having trouble wrapping my mind around just what exactly load-lifters even do. Are they even necessary with a properly fitting pack?

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#193473 - 02/04/16 01:37 PM Re: Are Load Lifters Necessary? [Re: 4evrplan]
aimless Online   content
Moderator

Registered: 02/05/03
Posts: 2852
Loc: Portland, OR
Hint: they won't lift your load off your legs, but they ought to lift the load off (the top of) your shoulders.

They are an adjunct to your hip belt, which ought to be transferring all your pack weight to your hips. Ideally, your shoulder straps are only stabilizing your pack from falling backwards, and they will only press against the front of your torso and shoulders, not heavily down on your shoulders.

Necessary? It all depends! grin

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#193476 - 02/04/16 01:54 PM Re: Are Load Lifters Necessary? [Re: 4evrplan]
OregonMouse Offline
member

Registered: 02/03/06
Posts: 6389
Loc: Gateway to Columbia Gorge
If, like me, you have pressure-sensitive shoulders, load lifters are absolutely essential to take the weight off the tops of your shoulders. Properly posititioned, they do transfer additional weight to the hip belt. Whether this is necessary for you depends on your personal body configuration.

Go try on a bunch of different packs--with weight--to find out what load lifters do, if anything, for you.
_________________________
May your trails be crooked, winding, lonesome, dangerous, leading to the most amazing view--E. Abbey

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#193479 - 02/04/16 02:18 PM Re: Are Load Lifters Necessary? [Re: OregonMouse]
4evrplan Offline
member

Registered: 01/16/13
Posts: 640
Loc: Nacogdoches, TX, USA
After reading up on it some more, I think I've got it. If anything, perhaps with properly fitted load-lifters, the part of the shoulder strap that goes over the top would be unnecessary. It seems like, in an ideally fitted pack at least, the shoulder straps only real utility is holding the pack up long enough to get the waist buckle clipped and the load lifters adjusted.

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#193494 - 02/05/16 11:23 AM Re: Backpack Design Questions [Re: 4evrplan]
4evrplan Offline
member

Registered: 01/16/13
Posts: 640
Loc: Nacogdoches, TX, USA
I've more or less cemented all the major design features in my mind, and I've ordered all the hardware, webbing, and shock cord. I was really pleased with how inexpensive it all was. I'll be using free 'fabric' (feed bags - it is a prototype after all). The foam I'm using for padding was left over from another project, so it's essentially free. I'll also be using a nice piece of birch plywood that a friend is going to give me for $3 as a frame sheet. With all that and the thread it'll take, I estimate this project will cost about $13 and some time.

Here's a few details about the design, though it's still somewhat fluid.
* I'll be using a full wrap-around style hip belt with generous foam and 1 1/2" webbing. It'll slide into a sleeve on the main body of the pack, so it'll be removable. If everything works out, I'll strongly consider adding pockets to the hip-belt.
* The shoulder straps (SS) and load-lifters (LL) will be the McHale style where the LL and SS adjustments are independent.
* I'm considering steaming and shaping the plywood frame sheet into a more natural curve, but I'm not sure. I've never tried to re-shape plywood, and even if it worked, it might not be worth it, especially with a wrap-around hip belt holding it off of my back anyway. I will probably also drill holes in it to lighten it up.
* The main body of the pack will essentially just be a minimally modified feed bag, but I will rip the bottom seam and add a better shaped bottom so it's not flattened out like an envelope.
* The top closure will be the dry-bag style where it just folds down a few time or more and then the two side clips buckle to each other. Or, would that be, "the two side buckles clip to each other"?
* Even though It'll have a frame sheet, I'll still put my pad in it to take up extra volume and stiffen it up. Hopefully, this way, I won't need compression straps. If this doesn't work, I'll add compression straps by hand down the road, or I'll just know I need them on my 'forever-pack'.
* The feed bag material is very water-resistant, if not water-proof. I might seal the seams.
* I'll also do the more or less now-standard large exterior pocket to hold wet or quickly-needed items and two side pockets for beverages, all with shock cord at the top. I'll also punch drain holes in the bottoms of the pockets.

Can you tell I'm getting excited?

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#193518 - 02/06/16 01:08 PM I've Got Should Straps! [Re: 4evrplan]
4evrplan Offline
member

Registered: 01/16/13
Posts: 640
Loc: Nacogdoches, TX, USA


Thanks to Rodney Liwanag for making his LAB pack plans available online. These straps are heavily based on his.


Edited by 4evrplan (02/06/16 01:10 PM)

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#193519 - 02/06/16 02:07 PM Re: I've Got Should Straps! [Re: 4evrplan]
OregonMouse Offline
member

Registered: 02/03/06
Posts: 6389
Loc: Gateway to Columbia Gorge
It will be interesting to see how your final pack works out and how well it works! With photos, hopefully?
_________________________
May your trails be crooked, winding, lonesome, dangerous, leading to the most amazing view--E. Abbey

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#193530 - 02/08/16 10:16 AM Re: Backpack Design Questions [Re: 4evrplan]
finallyME Offline
member

Registered: 09/24/07
Posts: 2710
Loc: Utah
I was going to tell you to go read McHale's site about load lifters.....Looks like you already did that. Looking forward to your final product.

One thing that McHale talks about and that I have found out, is that the more the load is transferred to the middle of the hip belt (think just below both arm pits) instead of riding on your but, the better it rides and the less tight the belt needs to be.

Also, for sealing the feed bags, look at the tape used to seal tyvek at home depot. It will probably stick better than a lot of other options.


Edited by finallyME (02/08/16 10:21 AM)
_________________________
I've taken a vow of poverty. To annoy me, send money.

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#193535 - 02/08/16 11:47 AM Re: Backpack Design Questions [Re: finallyME]
4evrplan Offline
member

Registered: 01/16/13
Posts: 640
Loc: Nacogdoches, TX, USA
Thanks for the tips, FME. I was thinking about using this stuff to seal the seams, but tyvek tape would be a lot easier and look better.

And speaking of hip belts. I've pretty much finished the base part of the hip belt, meaning I made the padded part, but I haven't attached the webbing or buckle. I hope to post a picture before too long. But, I'm not really happy with it. I think it's too short. It would probably work for me, but I'm really thin. If anyone ever wants to borrow it, it probably wouldn't be long enough to cushion their hips. I also don't think I made it wide enough, especially since it doubles as a lumbar pad. I'm going to re-do it.

I also had to re-make the shoulder straps. The ones in the picture are the second and, hopefully, final version. The first version was based on the G4 "J" straps, but I made they WAY too big. Here's hoping making everything twice won't be a continuing pattern.

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#193541 - 02/08/16 05:28 PM Re: Backpack Design Questions [Re: 4evrplan]
finallyME Offline
member

Registered: 09/24/07
Posts: 2710
Loc: Utah
If you are using a feed bag for the pack, they are made from polyethylene. Silicon won't stick that great to it. Tyvek is a polyethylene, so the tyvek tape will stick better since it is made for that purpose.
_________________________
I've taken a vow of poverty. To annoy me, send money.

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#193584 - 02/10/16 10:13 AM First Version of the Hip Belt (Failed). [Re: 4evrplan]
4evrplan Offline
member

Registered: 01/16/13
Posts: 640
Loc: Nacogdoches, TX, USA

Here's the first hip belt I made, which I don't like. The foam in it is only 26" long (the hem makes it slightly longer), which would probably work for me, but not many other people. More importantly, it's shy of 3" wide, which I don't think will be supportive enough, especially in the lumbar region. I'm still working on it, but the next version will taper from 2.25" at the ends all the way up to 4" in the lumbar region (plus hems). This widest part will be 8" long before it starts to taper.

I've got another quick question for people who have made a pack before. Do you prefer to sew the webbing directly to the padded part of your hip belt or to have it run through loops (like the belt loops on a pair of pants)?

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#193585 - 02/10/16 10:21 AM Re: Backpack Design Questions [Re: finallyME]
4evrplan Offline
member

Registered: 01/16/13
Posts: 640
Loc: Nacogdoches, TX, USA
Originally Posted By finallyME
One thing that McHale talks about and that I have found out, is that the more the load is transferred to the middle of the hip belt (think just below both arm pits) instead of riding on your but, the better it rides and the less tight the belt needs to be.

Interesting. That got me brainstorming ways to transfer the load better to the sides, including some that resemble the "wing thing" idea. One idea that I think might work is to back the hip belt with something rigid in the vertical direction and flexible in the horizontal. Corrugated plastic (from political campaign signs) would fit the bill. I'd simply orient it with the channels running vertically and pre-crease every one so it'd be nice and flexible around my hips. Do you think it would be worth the weight?

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#193586 - 02/10/16 10:50 AM Re: First Version of the Hip Belt (Failed). [Re: 4evrplan]
Pika Offline
member

Registered: 12/08/05
Posts: 1733
Loc: Rural Southeast Arizona
I sew the webbing directly to the fabric of the hip belt (or shoulder straps). I sew the webbing to one of the fabric pieces with bar tacks and a perimeter stitching. I then sew the two fabric pieces together with the right sides in and then roll the fabric over the foam bringing the right sides to the outside. Then, I will stitch through the fabric and foam in several places to bind the assembly into a unit. This last step is important, I think, because otherwise the fabric will shift on the foam and the webbing can wind up riding you where you least want it. BTW, I'm making all of this sound easier than it is.
_________________________
May I walk in beauty.

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#193587 - 02/10/16 10:54 AM Re: Backpack Design Questions [Re: 4evrplan]
finallyME Offline
member

Registered: 09/24/07
Posts: 2710
Loc: Utah
Originally Posted By 4evrplan
Originally Posted By finallyME
One thing that McHale talks about and that I have found out, is that the more the load is transferred to the middle of the hip belt (think just below both arm pits) instead of riding on your but, the better it rides and the less tight the belt needs to be.

Interesting. That got me brainstorming ways to transfer the load better to the sides, including some that resemble the "wing thing" idea. One idea that I think might work is to back the hip belt with something rigid in the vertical direction and flexible in the horizontal. Corrugated plastic (from political campaign signs) would fit the bill. I'd simply orient it with the channels running vertically and pre-crease every one so it'd be nice and flexible around my hips. Do you think it would be worth the weight?


I don't think that would be as comfortable as you think. You want your belt to contour on your hips. I have been kicking around different wing ideas. I think the weight is worth it, while at the same time trying to minimize the weight increase as much as possible.

As far as sewing on the straping, my first one, I sewed through the padding. I had to do this by hand and used really heavy thread. It worked just fine. My second attempt, I used a heavier fabric and sewed directly to the outer fabric and then used spray adhesive to attach it to the foam, and then sewed a border and an inner fabric to the whole thing. I think it just matters what you are attaching the pack to. If the pack is attached to the webbing, then the padding itself isn't holding the weight, it is just padding the webbing.
_________________________
I've taken a vow of poverty. To annoy me, send money.

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#193588 - 02/10/16 11:06 AM Re: Backpack Design Questions [Re: finallyME]
4evrplan Offline
member

Registered: 01/16/13
Posts: 640
Loc: Nacogdoches, TX, USA
Originally Posted By finallyME
I don't think that would be as comfortable as you think.

Even with 3/8" of foam between me and the plastic?

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