Mar 22, 2007 at 7:46 pm #1222492
I was toying with the idea of lightweighting an old Kelty External Frame Backpack.
The frame has two large 1" dia 30" lengthwise aluminum (1/16" wall thickness) tubes and a grand total of 6 transverse aluminum tubes about 22" long in diameters of 3/4" (2 of these), 5/8" 3 of these and a top extension of also 5/8".
This frame is way overbuilt, as surely has been noted for years.
I calculate the base aluminum structure to weigh 2.75 pounds out of the total 4.7 pound backpack.
Two of the 5/8" cross tubes can almost certainly be eliminated for a savings of 0.488 pounds.
If the remaining tubes were to be scaled down in size, 1" becomes 3/4", 3/4" becomes 5/8", and 5/8" becomes 1/2", then there would be a slimming down weight savings of 0.409 pounds.
So, elimination of excess cross tubes and slimming down of all remaining tube diameters in an aluminum structure gives 0.897 pounds of weight reduction.
I am winging it on weight reductions in hip belts and shoulder straps, but feel redesign using lighter weight materials and designs could save 0.7 pounds there.
The cloth bag could be fabricated from lighter weight fabrics with as much as a 30% reduction in the roughly 2 pounds of bag weight for another 0.67 pounds lost.
So, with no resorting to radical new design concepts for an external frame backpack, the weight of a 4.7 pound external frame backpack could drop to about 2.3 pounds.
I always liked the air circulation and coolness of the external frame pack. I haven't sampled any recent internally framed packs that attempt to create an airflow path between the pack and the back.
This year, I may just try tinkering with this idea.
I feel sure that others have been down this road long ago. Ideas like this are bound to occur to lots of people.
I have been away from backpacking for over 20 years – the family bit, you know – and am trying to catch up.
My reason for posting is to hopefully tap into the experience of others who have already thought of this and likely have done this.
Reinventing is fun, but bootstrapping on the experience of others is fun too, and rewarding often.Mar 22, 2007 at 9:02 pm #1383250
@jeffcadorinLocale: paper beats rock
what about making the frame so you can take it apart…..use it for structure in a shelter? chair? etc????Mar 23, 2007 at 10:28 am #1383313
The idea of disassembling the frame is interesting. But my mind currently isn't able to bend that way yet.
The extra weight of the removable fasteners is one factor, and the second is I hate squeaky sounds of equipment.
There used to be packs on non-welded frames, and they sometimes were said to squeak when hiking.
But thanks for the thought and maybe I can limber up my mind and really think about it.
JimMar 24, 2007 at 3:10 pm #1383413
@emptymanLocale: the other, big Ontario
Hey, I think I must have a similar Kelty external frame pack. I think it is called the 'scout' model.
Please let me know if you tinker with this, as I would obviously love to be an accomplice.
I was wondering about this before, but honestly, I don't think that I am skilled enough to do anything but harm to this bomb proof pack that has got me through a lot already.
email me directly, if you would like, : robruthmcrae at hotmail.comMar 25, 2007 at 5:28 am #1383450
I removed the "top extension bar" because it weighed about 5 ounces and replaced it with a carry strap of 3/4 nylon connected by a plastic side clasp buckle.
I changed out the hip belt from the really old one with hardened thick ensolite and heavy steel buckles – new one had light plastic buckle and lighter padding.
Replaced the hard ensolite in the shoulder pads with lighter weight blue foam. Will replace the entire set of shoulder pads with Thru-Hiker shoulder pads which eliminate heavy metal fasteners as well.
Eliminated one of the unneeded cross bars (the middle one) so it "only" has 4 cross bars in the Kelty frame.
I am looking for aluminum tubing 1/2 dia x 1/16 wall x 36 long to lighten up the "hold-open" and replace a 10.6 Oz hold-open with a 4 or 5 Ounce hollow one.
If I can find that, the 3000 cu in Kelty external frame backpack will weigh almost exactly what the Osprey Atmos 50 weighs.
That Osprey Atmos 50 pack has a funny internal aluminum frame and mesh panel that puts the frame back away from your back for ventilation. But there is no good place to tie on tents or externally stored sleeping bags or mattresses.
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