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Old 02-26-2013, 03:32 PM
Dustin B Dustin B is offline
 
Join Date: Aug 2009
Location: Saskatoon, Saskatchewan, Canada
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Default Shelf Engineering Help

Not really HT related but I think this will be a good place to get some help in making sure I choose the right material for the tracks and get bearings/bolts rated appropriately to support the forces this thing could end up exerting when fully extended (and what overlap I should leave at full extension). I don't know enough about steel or where to look right now to get the values to do the math (not 100% sure I can do the math necessary either), so I'm hoping someone here can point me in the right direction and make sure I get the math right.

So here's the rough plan.

DropBox gallery with 3 images and the first rough SketchUp model

The cupboard space is roughly 7' deep and 40" wide and in my kitchen/dinning room. In the current model the shelf extends just over 60" and has about 18" of overlap when fully extended. Will have a door that closes on the opening. Want adjustable shelving for the first 16" that you don't have to pull the shelf out for at all. Then I'll setup some more shelving behind that shelf that you'll get access to from the side as you pull the shelf out. Shelf at the front will be used to store pantry type items. Behind it will be small appliances and more pantry type items.
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Old 02-26-2013, 04:23 PM
bumpnstump bumpnstump is offline
 
Join Date: Mar 2011
Location: Austin, Tx.
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Quote:
Originally Posted by Dustin B View Post
Not really HT related but I think this will be a good place to get some help in making sure I choose the right material for the tracks and get bearings/bolts rated appropriately to support the forces this thing could end up exerting when fully extended (and what overlap I should leave at full extension). I don't know enough about steel or where to look right now to get the values to do the math (not 100% sure I can do the math necessary either), so I'm hoping someone here can point me in the right direction and make sure I get the math right.

So here's the rough plan.

DropBox gallery with 3 images and the first rough SketchUp model

The cupboard space is roughly 7' deep and 40" wide and in my kitchen/dinning room. In the current model the shelf extends just over 60" and has about 18" of overlap when fully extended. Will have a door that closes on the opening. Want adjustable shelving for the first 16" that you don't have to pull the shelf out for at all. Then I'll setup some more shelving behind that shelf that you'll get access to from the side as you pull the shelf out. Shelf at the front will be used to store pantry type items. Behind it will be small appliances and more pantry type items.
When I'm needing to 'step outside the bounds of normal reality', like you are wanting to do with this project, I start thinking about what kind of solutions exist that I normally don't use, and, where can I find them.
You might want to consider these guys (or others like them):
-http://www.gsfslides.com/
-http://www.pbclinear.com/
-http://www.igus.com/default.asp?c=us&L=en

Call them up, talk to a tech, send them your problem, they will design a solution.
I've done this with Igus before, and they've 'pulled rabbits out of a hat' for me.
Worth the phone call.

For more options, Google something like 'telescoping rails', and see what comes up.
Let us know what you find.
Rick
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Old 02-26-2013, 04:43 PM
Dustin B Dustin B is offline
 
Join Date: Aug 2009
Location: Saskatoon, Saskatchewan, Canada
Posts: 88
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The design is based off a truck box slide my uncle installed in his trailer. I got to take a closer look at it and was amazed at how simple it actually was. It was rated to 1500lbs spread over the area of a shelf that could fit inside a short bed pick up truck. It extended roughly 5 feet out and had less than 18" of overlap. He also paid $1200 for it.

I have access to someone who can weld and the rest is wood working I can handle myself. I'm just hoping to build the same thing, but beefier and cheaper.
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Old 02-26-2013, 09:50 PM
Dustin B Dustin B is offline
 
Join Date: Aug 2009
Location: Saskatoon, Saskatchewan, Canada
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So little more reading. Lets say I had 400 lbs at the end and 400lbs at 40" and 400lbs at 20". That should work out to about 2700lbs pulling up on the rear bearings and 3900lbs pushing down on the front bearings. Still no idea on whether the channel could take 1350lbs pulling up on it at the point of contact of a single bearing. Or if the angle steel that's 2.5"x1.25" and 1/8" thick would bend or not with a 1950lbs force at the point of the front bearing.

I think putting multiple bearings at each contact point would likely be a good idea. Hope that much weight will provide a decent safety margin on what will actually end up on the shelf.
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