New Back Pack - MYOG -03/02/2006

I am working on a new backpack. I am using some of the ideas from the new Mountain Hardwear Exodus series frame. I thought about buying the pack with my REI discount plus a small dividend but the frame alone weighs so much (3 pounds 8+oz). I decided to see if I could make something like it but much lighter. I am about finished with a cardboard mockup. I can use Titanium for the "frame sheet" sort of thing at about 7oz or maybe Carbon Fiber sheet at about 1/3 that weight and Carbon Fiber Tubes to replace what ever they use. I have to call or email about the Carbon Fiber sheet.

The pack bag will be made out of Cuben and will not weigh much.

I will post some pictures when it starts to look like a pack.

Questions:
why no frameless pack?

what happened to the external frame pack idea?

Whatever, I cant wait to see this project, an 8-9oz pack with a titanium frame.Amazing


Reply:
Q -1. why no frameless pack?
A -1. I don't like a frameless pack if I expect to carry more than a few pounds or if I am on a long hike. I also don't like anything that complety lays against my back. For a hike of a day or two it is OK, for more than that I want some ventilation. Remember I am old.

Q -2. what happened to the external frame pack idea?
A -2. This frame will be a sort of hybrid if it works like I hope. Have you had a chance to look at one of the Exodus Packs in person? The Exodus are made in two parts, the stand alone frame and the pack bag. I lot of really good ideas but heavy.

Q -3. Whatever, I cant wait to see this project, an 8-9oz pack with a titanium frame.Amazing
A -3. I have a Titanium/Carbon Fiber Frame (9oz-) that my Cuben Pack (2.10oz) and my G6 (3.4oz) attach to.

If it works out the frame should be over-kill up to say 15 pounds but very good up to 30 + pounds. This is really where I am going with the idea and the hoped for light weight. Think Summit pack or winter pack where you need more pack volumn.


This is what the two frames used for the Exodus pack series look like with the pack bags removed.







Questions:
I think a good system would be a carbon framesheet, and carbon exo frame like on the pure air zone system. and an evozate foam with holes wrapped in mesh on the top and bottom like the pure air.

sorry Bill, I know you like that mountain hardwear frame, but I have not seen it, so I am spitting out some other ideas.

Reply:
I have looked and relooked at most of the packs you are talking about. They all have things in there favor. You really need to get your hands on this pack and take the bag off and look it over, play with it, take it apart etc. I like some parts and other parts are just OK.

The design I end up with for my new pack will be what I think is the best of several different brands blended with a few of my own ideas. Some of my ideas need parts I am not sure yet how I will make or where I can get them. What ever I end up with the frame part needs to be as light as possible with a weight limit in the 1 to 1.5 pound range or less. The pack bag is a given to be one of the Cuben products.

Comment:
Bill,
I've done a lot of work with carbon fiber and glass in canoe building and other projects. It is practical to make a carbon fiber frame sheet starting from scratch. Trouble is, you will spend more than $75. And if this is your first attempt at working with composites, you may waste time and material. I wouldn't recommend it unless you are already familiar with the processes and are ready to spend the bucks to experiment with different layups. I cannot do more than ballpark what would work.

Carbon cloth usually costs about $30 per yard for 36-40 inch widths. But you might consider using a mix of carbon and S-glass - a treated glass that has improved adhesion to epoxy or a Kevlar/carbon mix. More flexible than the glass mix, but even stronger and almost as light as the graphite alone. Both are lots cheaper and perform better than carbon alone. Not as rigid, but less likely to fail catastrophically. Much of the weight is in the resin anyway.

I would use a thin form core - 1/4 to 1/8 inch. It will double the strength. You will still probably need to mold in some structural shapes (like channels) for rigidity.

Here is where I would start: Two layers of 100% carbon cloth ($30) - one on each side of Rohacel foam 1/8" (about $15) Any hobby epoxy such as West System, Eager or System Three (I prefer either of the latter two. You will need one quart of each epoxy component - total 2 quarts. Cost ranges widely - from $35 to $60 for both quarts. I would not consider using polyester resin.

I would mold several test tabs right onto the framesheet and stress them to failure one at a time, adding more material (additional layers) as needed and where needed. When the sheet reached the target strength, I would then cut off any remaining tabs.

Eager Plastics, the Composite Store, John R. Sweet and West Marine are good sources. If you shop around, you can get enough epoxy for about $40. You will need other supplies such as gloves, epoxy measuring pumps ($15), auto repair squeegees.
Vick.


Comment:
In the "New back pack -MYOG" thread Bill Fornshell says that he can either use titanium or carbon fibre at about 1/3 the weight. He was talking specifically about a framesheet.

Anyone out there with experience of laminating carbon fibre/epoxy (canoe builders perhaps?) care to comment on this? Is this sort of fabrication generally a better bet for weight than titanium? Is there a rule of thumb that says "you can do it x% lighter in carbon fibre/epoxy?

David - in the "New back pack -MYOG" thread Bill Fornshell says that he can either use titanium or carbon fibre at about 1/3 the weight. He was talking specifically about a framesheet.

Anyone out there with experience of laminating carbon fibre/epoxy (canoe builders perhaps?) care to comment on this? Is this sort of fabrication generally a better bet for weight than titanium? Is there a rule of thumb that says "you can do it x% lighter in carbon fibre/epoxy?

David

Reply:
I need to buy a piece 14" by 20" for what I want. It is 0.015" thick and 2.465oz. The Titanium is 0.016" thick. The weight of each seems to come out at or near -Ti 0.049oz per sq inch, Carbon Fiber 0.00882oz per sq inch. I need about 140 sq inches for the frame.

The price of the Carbon Fiber and the Titanium is almost the same. $75 and change.

This is the web site I am looking at for my Carbon Fiber Sheet.
http://www.robotcombat.com/marketplace_carbonfiber_cust.html