Offset/crossover Frame design thoughts? - Mountain Buzz
 



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Old 06-18-2013   #1
 
Yukon, Alabama
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Offset/crossover Frame design thoughts?

Making a frame for an 18 foot raft. Trying to incorporate a double rail frame centered over the tubes while having both side rails in contact with raft. I have only seen "one" cat frame built with crossover offset design that I believe used welded fittings (not sure). The idea is that this design would put the the side rail pipes flat on the raft tubes and the all the cross bay pipes run the full width of the frame and are secured on "top" of the side rails with offset/cross over fittings. I have absolutely no experience doing this and do not know if the design is structurally sound and/or what other issues besides slightly raising the height of the cross over bars would be - but I am suspect since I have not seen this design used before. I certainly am not recommending this design - just asking for thoughts on the idea. Many thanks.

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Old 06-18-2013   #2
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my cat frame has two side rails that make contact with each tube, but the cross bars only contact the inner rail, there are bars on either end that are shaped to the tube that are welded in place. most of my cross bars are welded, but I have a couple NRS cross bars that are clamped in place so they can be moved depending on if i'm using a dry box/cooler for a seat, or a high back seat mounted on a cross bar. Why would you want the cross bars to span the entire width (go to the outer side rail) if whatever you put in the bay would be restricted to the width of the inner rail? You just thinking it'll make the frame stronger?
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Old 06-18-2013   #3
 
Yukon, Alabama
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Many thanks for your time and reply.

I need the frame to be modular for flying and I'm doing it with fittings. I'll be using 1 1/4 inch pipe that is available locally. The cross bars would be adjustable. Beside strength, I'm hoping the cross bars being attached on top of both side rails will help better evenly distribute weight to both side rails which would be centered on the tube. I'm also hoping that having the cross bars on top of the side rail tubes will allow the side rails to fit very flush with the tubes. The additional weight and fittings required to expand the three bay cross bars the full width is about 6 pounds. Wild goose type fittings allow for an even distribution of weight for centered double rail and also allow for a flush fit - but I can't find any.

I know there are a huge variety of ways to make frames, but am most interested to hear from anyone who has tried this offset/cross over design or may knows something about the structural integrity I need to think about.
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Old 06-18-2013   #4
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your question and explanation of need got me thinking... sorry I don't have an answer. but you make some good points. I hope you find what you need, and I'll be sure to follow. I'm now interested as well.
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Old 06-19-2013   #5
 
Walterville, Oregon
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Originally Posted by Yukon77 View Post
The idea is that this design would put the the side rail pipes flat on the raft tubes and the all the cross bay pipes run the full width of the frame and are secured on "top" of the side rails with offset/cross over fittings.
Is this what you are talking about? Your frame would be bomber. The drawbacks are a little more weight and the crossbars can interfere with lashing stuff to the side rails.
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Old 06-19-2013   #6
 
Yukon, Alabama
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Wadeinthewater - Well - yes - in that there is a cross bar on top of the side rails

I'm looking for a light weight option for removable double rail platform material. I see you are using the poly grating. I've read about it but haven't actually seen it. Is it very heavy - and how do you like it? Where did you get it? Many thanks.
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Old 06-20-2013   #7
 
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Just a thought- I have tried several times to reinvent the wheel too, but found, that with materials and parts available, the standard frame designs are the standard for a reason. are you planning huge water adventures with heavy loads that need additional strength over current expedition type designs?

Strength aside (if it is actually stronger than a DRE designed double rail) you certainly can use the 90* offset elbows to attache a second side rail higher or lower than the existing frame, and allow your cross bars to span the entire length of the frame (like a single rail with a bolt on second rail underneath) but you loose the nice ability to cradle buckets etc, on your double rail (if underneath), and the ease of mounting a side board- two big reasons they do the double rails like they do.
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Old 06-20-2013   #8
 
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I see you are using the poly grating. I've read about it but haven't actually seen it. Is it very heavy - and how do you like it? Where did you get it? Many thanks.
It is called polymax, available at tek supply online. Awesome stuff, not too heavy, cuts like butter, but does need a bit more support than wood.
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Old 06-20-2013   #9
 
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Originally Posted by Yukon77 View Post
I see you are using the poly grating. Is it very heavy - and how do you like it? Where did you get it? Many thanks.
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Originally Posted by lhowemt View Post
It is called polymax, available at tek supply online. Awesome stuff, not too heavy, cuts like butter, but does need a bit more support than wood.
Polymax. More expensive than it should be, but I couldn't find an alternative. It spans side rails without additional support. At first I used zip ties to secure it, but since my frame doesn't break down I changed to pop rivets. I also use it as walkways on my smaller frame and as a floor with 20 inch spans on the cargo module for my smaller cat.
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Old 06-20-2013   #10
 
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Polymax. More expensive than it should be, but I couldn't find an alternative.
And watch the shipping cost. Up to a certain # of sheets it gets cheaper per sheet, then there is a jump where it is more expensive again. I always order one or two spares, I keep finding uses for it.
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