"deployable" braces for horizontal tray supporting a 50lb object

[donovandigital]

Apologies in advance if I get some terms wrong or am less than clear, I come from electronics-land .

I am designing a workbench for myself using 8020 extrusions (

https://www.8020.net/)

and one of my requirements is that I integrate a 50 lb object, dimensions approximately 60"x15"x5", such that it can be stowed away into the body of the bench when not in use. The simplest solution I have been able to come up with is a pair vertical legs with casters supporting a platform below the bench surface. The back of the platform will rest on low-friction plastic "bearings" (

https://8020.net/freetextsearch/search/result/?keyword=motion)

inside the workbench. so it can be "closed" by sliding backwards into the body of the bench (similar to a pc keyboard tray). My concern is that when the platform is fully deployed (all the way out of the bench) it will be insufficiently supported to hold the weight of the object.

I recall seeing somewhere (I cannot remember where) a system that used 45 degree angle braces that deployed when the tray was fully opened, and lay parallel to the horizontal members when closed. Could someone point me to technical drawings, photos, or descriptions?

Many thanks in advance

Joe

 

[MikeHalloran]

Four of those bearings mounted at front/top and corresponding positions halfway back could support a pair of 80/20 horizontal members that would slide through them, allowing a supported shelf to extend a little less than half the bench depth forward of the front.

It's a damn expensive way to make a sliding drawer to hold a mere 50 lbs.
Take a look at full extension drawer slides mounted to the inside surfaces of the legs.



Mike Halloran
Pembroke Pines, FL, USA

 

[donovandigital]

Thanks so much for the advice.

First off, if by half the bench depth you mean 7.5 (15/2), that's insufficient; I need to come out _at least_ 3/4 of the way, preferably the whole way.

Second, I'm afraid I'm unclear about what you mean by "inside surfaces of the legs".

Thanks again

Joe

 

[MikeHalloran]

Let's start again; make a drawing of what you want.

I was assuming a bench depth of 30", in which case sliding 80/20 members would let you move the shelf from flush with the front to extended maybe 12"
... which, assuming that's not enough travel, is what brings up drawer slides. Just go to the home store and look at what's available, and how they attach to the drawer and to the supporting structure.

While you're there, look at the Simpson Strong-Tie Workbench Kit; that and a bit of pressure treated lumber will net you a nice workbench for way less than what just a few 80/20 bits will cost you.



Mike Halloran
Pembroke Pines, FL, USA

 

[donovandigital]

Here is a rough drawing

http://ctrlv.in/774100

The side view shows the tray "deployed"; each separate line represents 2 parallel pieces of 8020. The top rectangle in both views is the "drawer".

The kit you recommended looks quite good; if I wasn't forced to build this in my bedroom I would use it. As it stands, I am forced to use 8020 for mostly cosmetic reasons. If I can somehow avoid those $50-a-pop linear guides, that would be super awesome.

And, yes, I have seen drawer slides, and have a number to spare. Are you saying that they will support 50lb, or that they sell any that do?

 

[hendersdc]

There are many cheap drawer slides that are rated for more than 50 lbs. Full extension is also available, meaning that they will extend a distance equal to their starting length. Here are some on McMaster.

 

[1gibson]

Chop up an old filing cabinet. File drawers (when full) are heavy.

 

[SwinnyGG]

I will second (or third.. or fourth) the use of drawer slides for this application. 50 lb plus another 10lb of drawer frame is a very light load, comparatively. McMaster (and anyone else who sells drawer slides) will have sets rated for 500lb a pair, if you ever needed to build a drawer that big.

80/20 is expensive enough that using a quality drawer slide is going to be, at worst, a wash compared to the additional 80/20 you would need to buy for legs and braces.

 

[donovandigital]

Guys

Thanks so much for the hints, tbh I should have thought of this myself case I worked as a fileclerk in an office briefly. But then I guess thats why you're mechanical engineers and I'm an electrical guy

 

[kjoiner]

Hello,

Check out Accuride. They make a wide variety of slides for everything from kitchen cabinets to rack mount electronic equipment. Also, do you have any concerns with tipping of the bench when that 50lb load is deployed?

Kyle

 

[donovandigital]

@kjoiner

Thanks for cluing me in to Accuride, I should know them because I work with a lot of rackmount stuff. Re tipping over, probably not. But, just in case, what is the calculation?

Thanks again

Joe

 

[kjoiner]

Hi Joe,

You'll need to know the CG of the bench and where the support feet are located. Find the CG of the depth of the bench by itself using a convenient datum point - the back of the bench is probably good. Then take your 50lb weight and re-run the calculation with the weight hanging out in front of the bench. Use the same datum point to calculate the new CG. If the CG is near or out past of the front leveling feet, you've got a problem with the bench wanting to tip over.

I can add more detail on the calculation if necessary, but it's basically a weighted average of the moment loads of the bench and the 50 weight x their locations from the datum over the entire weight.

Kyle