cutthroat style frame with speedrails? - Mountain Buzz
 



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Old 05-20-2017   #1
 
Flagstaff, Arizona
Join Date: Apr 2015
Posts: 13
cutthroat style frame with speedrails?

Anyone tried this before? Trying to make a narrow cataraft frame out of an old raft frame for a Chama trip in June. Trip is during the week so lower water is likely. It'll go on 16' Jag tubes once I have the bottom half sorted out and connected.

Length is right at 7' for the section I have together now. The bottom rectangle is going to be a bit shorter than the upper because that's how long the tubes I have are. Thinking something like 10" of drop between sections. Probably going to drill/bolt all the critical corners to keep it from self-destructing on me. Depending on how much flat tube length I have left I might make a trailer frame to go with it to hold some rocket boxes/beer.

Could be a stupid idea, but the frame wasn't being used and I'd rather have more space for junk than I can get away with on a ducky.
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Old 05-21-2017   #2
 
Willi..., Willimina, OR
Paddling Since: 68
Join Date: Jan 2007
Posts: 482
add a couple of yokes

I'd add a couple of yokes as well or make your own from tees. I find 9.25" on center vertically is a good dimension for a 24" cat tubes; allows ammo boxes to rest on handles and bottom cross members. Allowing pipe to sit around unused is an economic crime.
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Old 05-21-2017   #3
 
SLC, Utah
Paddling Since: 1983
Join Date: May 2011
Posts: 148
I made a very similar frame 2 year ago to make 3 JPW packcat tubes into a tiny Cutthroat-like 1 person oar boat. It works, but the first problem was that the set screws that fix the speedrail fittings weren't strong enough to hold the frame together (resulting in an impaled tube on day 1 of a MFS trip..). I wound up drilling all the frame tubes and replacing the set screws with thru-bolts. The frame works now but there is a bit of wobble to it as the holes in the tubing elongate. Looking back at the time and $ I spent on this project, I wish I had just started with NRS tubing and fittings or welded it. At least now I have the dimensions I (actually my wife) want and the next one will probably work pretty well.
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Old 05-21-2017   #4
 
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Denver, Colorado
Paddling Since: 2002
Join Date: Feb 2012
Posts: 859
Yeah, don't run a frame on set screws...SMH
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Old 05-21-2017   #5
 
Flagstaff, Arizona
Join Date: Apr 2015
Posts: 13
This frame was originally all set screws aside from the corners and made it through a GC trip just fine other than a couple cracks. The self-tapping set screws seem to help a bunch, but tightening them to the point they really bite into the tubing deforms the bracket. Going to do the same thing here, just need a few more t's and corners. Considering using wire lock pins instead of bolts since bolts are a pita.
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Old 05-22-2017   #6
 
Willi..., Willimina, OR
Paddling Since: 68
Join Date: Jan 2007
Posts: 482
setscrews walking so pin the fitting

Buying a pricey frame from the big box raft frame retailer will not get you a quality frame. Setscrew fittings will work just fine when accompanied by a quick release pin. Yokes are better when welded; struts are a good work-around. Use good alloy 6061-T6 in lieu of the 6063 T6, T4 and T0 for a 40%, 100% and 350% increase in strength respectively.
Many of the fabricators use 6063 because it strains plastic without grain separation. This make nice bends and swage joints which are pretty but dysfunctional. This characteristic of being plastic causes the pipe to strain under the force of the setscrew. The 6063 pipe deforms and the setscrews loosen. Tightening the setscrew additionally in the plastic range only make the problem worse. Properly constructed, a setscrew tee w/pin will accommodate 500# of thrust in any direction. Said setscrew tee will outperform a ubolt tee 3:1 and the older version circa 1990 1.5:1
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