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  Topic Name: Seatpack attempt - no sewing! on: January 19, 2015, 09:57:08 AM
unitdrop_forge


Location: Kalamazoo, MI
Posts: 15


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« on: January 19, 2015, 09:57:08 AM »

Materials:

Qty 1: 1/16" x 3/4" x 6' aluminum; $7.93
Qty 8: 7/16" x 3/16" rubber grommet; $1.27 ea; $7.62
Rope - you should always have rope
Drybag - you should always have drybags

Tools:
Lighter
Tin snips
drill and drill bits


Figure out how long you want the base rack and how wide.  I chose 6"  x 12".  Add 1" each side for the mount = 32" total length of aluminum to cut.

Make marks at 13" from each end.  Make a 90 degree bend at each mark so you now have a "U" shape.

Make a mark 3/4" from each end. Bend this part outward slightly such that when you pinch the two arms together it mates evenly (trial and error here).

Clamp the two mated parts together and drill a hole the size of your pinch bolt with an appropriate setback so it doesn't impinge on your seatpost.  Arbitrarily remove a semicircle on the top half of the pinched together pieces to allow the assembly to rotate upward when installed.

Install on your seatpost clamp.

Drill holes wherever it feels good.  Put the grommets in them.  Redo the rope routing as you see fit.  Add a toggle.  Or don't.  Or use regular accessory straps.

No, I don't know what this weighs.  My guess is: not enough to care

Yes, this is a lot like the Porcelain Rocket Mr. Fusion. 







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  Topic Name: Seatpack attempt - no sewing! Reply #1 on: January 19, 2015, 03:36:50 PM
roadpacker


Location: Baltimore, MD
Posts: 143


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« Reply #1 on: January 19, 2015, 03:36:50 PM »

This is cool! I think that stretchy bands and things sometimes have a proclivity to failing, though. Does the metal bracket move? You could use webbing straps, I bet, to cinch it down. The cam-style ones they have on revelate bags would be great.
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Best yet: 320 mi, 2 days, Baltimore-NJ-Baltimore, Sept '13
Goal: 330 in 36 hrs

3,000 mi from Baltimore, MD to Moab, UT. 40 days.

  Topic Name: Seatpack attempt - no sewing! Reply #2 on: January 19, 2015, 05:24:09 PM
unitdrop_forge


Location: Kalamazoo, MI
Posts: 15


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« Reply #2 on: January 19, 2015, 05:24:09 PM »

Thanks!  There's actually nothing stretchy.  I used rope throughout rather than shock cording.  This way the rope is in tension to support the weight of the load - which is why I don't need a webbing / camlock type strap.

The only movement of the rack is rotation up and down around the seatpost pinch bolt to accomodate different size loads.

Think of the aluminum like the hoop in one of those mesh laundry bags.  It gives the rope a structure to pull against and provides an anchoring point at the seatpost clamp.  Most everything else is in the rope itself.

I did try a webbing strap at first - that's why I have two larger holes near the rear.  It was functional, but I figured: 1) a 1/2" webbing strap is WAY overkill for the typical load in a seatbag.  The rope is 500lb test (assumes tension, doesn't apply when you go around things), and I have 6 vertical members taking up the load and 2) I always have rope with me. Easy fix if it does break.

Otherwise, I took it for an hour long shakedown ride loaded with mostly heavy packaged foods from the pantry.  Rode some 6" deep pock-marked footprint junk snow on 2.3" tires, a few curb hops, and surface transitions with no movement at all.  I actually forgot it was back there!  Still rock solid by the time I got back

In terms of longevity, yes, the porcelain rocket with a tubular CrMo stay will last forever as steel has more forgiving cyclical loading properties....but I doubt that I'm stressing it to that point of causing any stress or plastic deformation. Another, more robust option would be tube steel or tube aluminum.  Again, these felt like overkill to me.

and if I am fatiguing it to the point of failure, I still have 40" of aluminum left! Smiley
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  Topic Name: Seatpack attempt - no sewing! Reply #3 on: January 20, 2015, 09:30:38 PM
elitheknife


Posts: 60


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« Reply #3 on: January 20, 2015, 09:30:38 PM »

This is really great!  Way to DIY!  headbang

Scott
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  Topic Name: Seatpack attempt - no sewing! Reply #4 on: January 22, 2015, 04:47:41 AM
unitdrop_forge


Location: Kalamazoo, MI
Posts: 15


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« Reply #4 on: January 22, 2015, 04:47:41 AM »

I feel like I said Beetlejuice one too many times....


Improvements:  Rubber grommets are absolutely annoying.  They provide excellent friction, so the retention system has zero slip. However, that also means they want to follow the rope when tensioning.  Better would be metal tubular rivets or a plastic / metal grommet of that is tool-ed into the opening instead of pushed in by hand. 

Perhaps I'll try some of these...they're made for tarps, but should be fine for the thickness of metal involved:
http://www.harborfreight.com/103-piece-1-2-half-inch-grommet-installation-kit-30037.html

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  Topic Name: Seatpack attempt - no sewing! Reply #5 on: January 30, 2015, 10:32:39 AM
Stegerman


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« Reply #5 on: January 30, 2015, 10:32:39 AM »

Newbie, so be kind.

I know it's not technically DIY and so the answer to this might be "because I can", but why wouldn't you use a seatpost rack and tie it to the seat in a similar fashion? Just wondering.
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  Topic Name: Seatpack attempt - no sewing! Reply #6 on: February 01, 2015, 08:01:54 PM
unitdrop_forge


Location: Kalamazoo, MI
Posts: 15


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« Reply #6 on: February 01, 2015, 08:01:54 PM »

Good question! 

1) Weight, mainly.  This setup weighs about the same as the lightweight drybag it's holding in the photos.

2) I personally wouldn't use a seatpost clamp type if I had a carbon seatpost since I do not trust carbon with point loads.  Mine isn't carbon, but just throwing that out there as another scenario.

3) I find the clamp types to sway and wobble, which I dislike.  Tensioning to the seat would probably eliminate that, as you noted. 

4) But, yes, the biggest reason is "because I can"  icon_biggrin
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