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Old 02-27-2011, 10:37 PM   #1
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Default bed over sleeper

want to build a bed over sleeper and cab. want to make it as wide as cab and 6 to 8 feet forward. can i just build with 2" heavy tubing or will i need to add support braces?
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Old 02-28-2011, 06:43 PM   #2
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My bed over the sleeper isn't 6' long, more like maybe 4'? And there are no supports, it's all internal framing. Don't know what they used for the framing. I think if you go 6' that's pretty long, I'd use some heavy steel tubing and tons of it. I don't know how you could work support legs on the front of it.
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Old 02-28-2011, 11:37 PM   #3
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I've been scratching my head over the same issue in my plans. All of the factory jobs like Bob's have that tiny little 4' bunk which is only good for kids and to say you have a bunk to make it a legal RV. Good for what it is, but I'm with you, I'd like a big bunk up there to maximize what little floor space I have. My thing is I want to have some headroom cutout like on RumRunner so I don't have to crawl my big lazy a$$ into the cab through a little hole, and still have a small bunk going forward from there. I have never seen a conversion with a big bunk. The closest thing I can think of is a furniture mover:

Furniture Trucks For Sale

that one has a 9' attic, and one farther down has a 6' attic. I think that 8' idea looks way bigger than it sounds, plus the braces are fugly. I'm thinking I could get away with 5-6' done properly with PLENTY of tubing and diagonal bracing. The whole box is screwed if I get it a little wrong and it starts to sag later, though. But we're on the same page I think.

Dave
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Old 03-01-2011, 05:32 PM   #4
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Default Cantalever bunk

I see no reason why you can't make the bunk stick out 6' and cantalever over the cab. Yes, it would need to be engineered correctly with diagonal bracing but relatively speaking the taller you make it the stronger it gets. Something like 2" square steel tubing with 1/8" thick walls is massively strong if triangulated correctly.
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Old 03-04-2011, 07:43 PM   #5
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First, I'm not an engineer, fabricator, nor welder. But I've watched lots of things built, have asked lots of questions over the years, and try to use as much common sense as possible.

There are two types of loads: static and dynamic. If you were cantalevering the bed out beyond the box for a stationary truck. You'd have only the weight of the bed area to worry about. But since the truck will go down the road, possibly with people in the bed or with stuff stored up there, you need to be concerned about the dynamic loads ... up and down as well as lateral (right to left).

I don't think the problem is a single big bounce going down the road with two 300 pounds laying up against the front of the bed (maximum leverage), but the fatigue over time.

I presume that the top of bed box will level with the top of the mainbox. If so, start out with the top rail of the bed box extending back across the top of the upright studs of the box as far back as you can go (i.e. get long enough steel). That will distribute the loads back into the main box before the first weld or even without a weld (all the way to the back of the main box). This will reduce issues with fatigue on a weld in shear because the tube that weight is suspended from will sit on the studs.

I don't know if 2x2 tubing is big enough or not. If you can find it and afford it, consider 2x3 or 2x4 (longer part on the sides, not on the top and bottom; but you probably knew that already). I think 0.125 (1/8") should be enough. Consider talking to a local racer with a late model to find out what their chassis are made of. Many of them are 0.125, sometimes a little heavier.

As suggested above, put in a triangular tube. I think this should go from the top, front corner of the bed box to the lower, back corner (up against the main box). That should give you the best strength.

I recommend that you have a triangular bar on the top and bottom of the bed box, or an X. I would gusset all the corner on the bed box with 1/4" triangular plates and I would gusset all the joints between the long top plates and the studs and studs and the bottom plates. Also consider X'ing the roof from side to side a few times.

Like I said, not a welder, but everythign I've ever read or been told about welding and getting good strong joints is to make sure you chamfer then ends of the tubes to help ensure you get good penetration and good strong welds.

In the bed box, consider running in 110v and 12v to receptacles on either side and even the front if deep enough. Little reading lights would be nice too. Because hot air rises, consider a small fan or two and even windows. Who likes to hear a noise in the night and you can't even look outside.

I hope I've helped or at least given you somethings to think about. Good luck with the project and keep us posted.
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Old 03-04-2011, 11:27 PM   #6
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First, I'm not an engineer, fabricator, nor welder. But I've watched lots of things built, have asked lots of questions over the years, and try to use as much common sense as possible.

There are two types of loads: static and dynamic. If you were cantalevering the bed out beyond the box for a stationary truck, you'd have only the weight of the bed area to worry about. But since the truck will go down the road, possibly with people in the bed or with stuff stored up there, you need to be concerned about the dynamic loads ... up and down as well as lateral (right to left).

I don't think the problem is a single big bounce going down the road with two 300 pounders laying up against the front of the bed (maximum leverage), but the fatigue over time.

I presume that the top of the bed box will level with the top of the mainbox. If so, start out with the top rail of the bed box extending back across the top of the upright studs of the box as far back as you can go (i.e. get long steel tubing). That will distribute the loads back into the main box before the first weld or even without a weld (all the way to the back of the main box). This will reduce issues with fatigue on a weld in shear because the tube that weight is suspended from will sit on the studs.

I don't know if 2x2 tubing is big enough or not. If you can find it and afford it, consider 2x3 or 2x4 (longer part on the sides, not on the top and bottom; but you probably knew that already). I think 0.125 (1/8") should be enough. Consider talking to a local racer with a late model to find out what their chassis are made of. Many of them are 0.125, sometimes a little heavier.

As suggested above, put in a triangular tube. I think this should go from the top, front corner of the bed box to the lower, back corner (up against the main box); I think the engineering logic to to squeeze the cross piece, not stretch it. That should give you the best strength.

I recommend that you have a triangular bar on the top and bottom of the bed box, or an X. I would gusset all the corners on the bed box with 1/4" triangular plates and I would gusset all the joints between the long top plates and the studs and studs and the bottom plates. Also consider X'ing the roof from side to side a few times.

Like I said, not a welder, but everything I've ever read or been told about welding and getting good strong joints is to make sure you chamfer the ends of the tubes to help ensure you get good penetration and good strong welds.

Finally, consider putting in some inspection access holes so that you can look at the critical welds; like where the bottom of the bed box attaches to the big box and the front stud of the bed box and the top plate.

In the bed box, consider running in 110v and 12v to receptacles on either side and even the front if deep enough. Little reading lights would be nice too. Because hot air rises, consider a small fan or two and even windows. Who likes to hear a noise in the night and you can't even look outside.

I hope I've helped or at least given you somethings to think about. Good luck with the project and keep us posted.
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Started looking for 379 Peterbilt TC, 24' to 30' box, bumper pull--but ended up w/1999 Liberty Coach conversion of 45' Prevost XLV bus. 1,000sf heated/AC'd race shop w/dump station, 50amp shore pwr where bus parks, 3 NASCAR/ARCA race cars & 26' Bravo trailer.
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Old 03-05-2011, 06:56 PM   #7
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What #90 GTSC mostly sounds right. Minor point of clarification, the top longeron will be in tension (Not shear) and so would the point where it meets the main box. Having the top longeron be all one piece would be nice, but I think properly made welds with reinforcing plates should be at least as strong as the base metal.

The bottom longeron will be in compression which means you need to support the point where it meets with the main box. A diagonal brace from the floor of the main box to the point where the bottom longeron meets the box should do nicely. That would carry forward with a diagonal from the bottom longeron where it meets the main box to the top front corner of the entire structure. That would put both of those diagonal members in compression as #90GTSC suggests.

#90GTSC did get me thinking though. You should not plan to carry a lot of weight up there. I am less concerned about the structure, static or dynamic, than I am with overloading your front axel. You could compensate slightly by putting heavy stuff behind your rear axel, but the lever arm to the rear axel is long so the benefit not so great.

Good luck.
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Old 03-07-2011, 11:19 AM   #8
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Hey Bob!

I know you have a factory United unit- any chance you could do me a big favor and give me the interior dimensions (depth and height) of the sleeper over your cab? I've been snooping in a few of those type trucks, but did not have a tape measure with me. I know they have just an adequate amount of headroom and depth to function as a bunk. My scheme would be to have a deeper bunk so I can have a walk in cutout into the cab maybe 18", and still have a usable bunk forward of that. Using a factory job like yours a reference would help me with figuring if my idea is feasible. I know pony express does a cutout just like I want into the roof of the truck like I want to do, but they use a regular depth on the sleeper and a wedge shaped drop in board to fill it in to convert to a bunk, and some funky custom made cushions to piece together the mattress. I'd rather just make everything permanent and use a regular mattress.

Thanks! Dave

here is a link to the pony express brochure showing their walk in:

http://www.hgrstrailer.com/pdf/pony_.../toterhome.pdf
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Old 03-09-2011, 07:05 AM   #9
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My rig is in my shop, about 30 minutes from home. I hope to get there sometime in the next couple days so I'll make some measurements then.
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Old 03-09-2011, 11:11 AM   #10
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no particular hurry, I am far from firing up the welder!

Dave
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