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truck bedslide

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i had been wishing for a bedslide for my pickup truck pretty much ever since i put the contractor cap on. my old boss offered me one but it was too far out of my pay grade at the time, and he wasnt offering since he bought me the $3200 contractor cap.
fast forward a 5 years. current boss decided i needed one. did some research, was appalled at the price of them. $1599 installed. for some hot rolled angle iron, some cheap bearings and a slab of plywood. thats really all they are.
so, i decided, heck, i can build that. so i started planning it out. and when i say plan, i was planning all the cool drawers and shelves i can put in my truck to add permanent organization.
i also decided i wanted a full extension slide instead of the 3/4 the factory ones are. i want full extension because my plan is to place a shelf and parts cases in a rack at the back of the slide.

i studied some full extension drawer slides and came up with a plan. i am currently building a small prototype, when i stumbled onto a potentially crucial design flaw....

so, i ask the collective to unite! .... i need some help, please...

so, this is a small 5" chunk of the slide im planning. i have some bearings and a bunch of iron.
the idea, from left to right.
the left side will be fastened to the truck bed by some means TBD.
the right side will have a bearing setup much the same as the middle extension slide, only, it will be held very securely, straight and true by the slides frame, cross members, and plywood.
the middle extension portion will be pretty much free flowing. it will have no support from either side. so, to stop it from wanting to just cripple over i have the big bearing as the main weight bearing point, and the small bearing on the bottom to keep the center slide upright. the bar stock acts as a slot for the bearing to ride in.

this brings me to my issue. there is about .080" of total space between the OD of the bearing and the rolling planes. this allows the bearing to switch contact surfaces (top or bottom) depending on the extension of the slide at any given moment. whether its full in, and all bearings are contacting on the bottom. or full out and half of the bearings are contacting the top and half on the bottom as the weight is moved forward of the center of gravity.
when the bearing contact point is on top, the bearing is riding the bar stock in the direction of travel.
when the bearing contact is on the bottom, the bearing is spinning against the direction of travel on the bar stock, it will be grinding across it spinning in the wrong direction. this is going to create a huge amount of drag, and eventually gall beyond repair. and grease isnt likely to help. i chose bar stock because i figured as the bearing is turning, i guesstimated 1/3 of the total force on the bearing will be side load. the radius of the bearing and the round stock would make for smooth engagement over anything square.... still wont help when its turning the wrong way.

so, im going to spend the next 45 minutes staring at this trying to get out of my corner, and in the mean time, im gonna drink a beer and really hope for some good advice. 

Why not use a standard "C" channel and buy bearing rollers made to run in the tracks.  OR, make you own rollers and mold polyurethane on the wheels for a smoother ride?

think of this as if i was on the space shuttle, its Apollo 13 and i only have a bag of "THIS" to work with...

i had thought about specialized bearings, or a linear slide, etc, but they wouldnt have been nearly cost effective.

what im currently pondering is another small bearing on top, similar fashion as the bottom, only "pulling" the weight instead of pushing. my concern is getting too complicated with angle and flat bar. welding is not nearly a precision process. and absolutely every conceivable place of wholesale, supply, hardware, etc, are all closed this weekend. but i have the whole weekend to build this... and argued with the wife over having the whole weekend to work on it.


Yeah, get the duck tape out, you going to need it. ;D ;D ;D

ok. heres what ive come up with. a very rough and dirty version, anyways... the bearing over-arm will be a single assembly that will be bolted onto the main rail thats bolted to the truck. ill have 3 or 4 of them spread across the length or spread out in specific positions based on the need. i can eliminate the round bar inside the C channel and use it on top to capture the bearing. the over-arm is adjustable to control the angle of the center extension slide. i will also probably eliminate the round bar on the second bearing race as well as im not 100% sure its necessary. the last bearing to the right will be held on by a 3x4 angle iron that the bedslide platform is affixed to, with cross members and necessary support. since it will be fairly rigid, it may not need anything to keep the bearing inside the race. the whole bolted down/welded together assembly should keep it aligned. ill just need to make sure its installed aligned. i could add some poly style plastic as skid pads... but im less concerned with those steps as i was this one...
now i have to go make dinner, and itll allow me to sleep on this and think some more.

but in any event. the goal overall was to make the whole system easy to build. as it stands, i can drill all of the necessary holes and countersinks before the angle is welded into the C channel. 


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