Halp To you engineers (and those who pretend on the internet),

Casper

Bobbert Cheapstein
Oct 6, 2009
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I have a mechanic's pit at my house in the garage that is roughly 3 feet wide and 8 feet long. It's cut in to the floor of the garage, so it's bare concrete. Right now, it's open and quite dangerous. It's also a waste of a perfectly good parking space.

I'd like to fabricate a metal grill that would be strong enough to stand on, and occasionally roll a car over to cover it for safety purposes. Any design ideas? Tips? Doesn't have to be fancy, but I would prefer it be fairly light so that one or two people could lift and move it.
 

gee

Blame It On The Gassa Nova
Sep 29, 2012
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Personally I'd make a few plates out of diamond plate steel, with rectangular steel stock welded to the bottom to provide reinforcement and 'index' the plate against the sides of the pit. Put them in a row to cover the pit.

Should be fairly lightweight (enough to pick up yourself), not too expensive, and not too hard to make if you've got a welder and not too expensive if you get someone else to weld it for you.

As for the thickness, amount/size of reinforcing, etc... I'm an electrical engineer, maybe there's a mech on here that can help with that.
 

Mr. Argumentor

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I would trust Gee's plan to hold the weight of a person, but you'd have to have pretty steady cross bracing to support the weight of a vehicle.

Only time I've seen a gap with grating made of sheet steel (as opposed to cast iron) it's not a lot wider than 8 inches or so. 3 feet is not something I would trust my skills with without getting actual engineering help with
 

Casper

Bobbert Cheapstein
Oct 6, 2009
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I would trust Gee's plan to hold the weight of a person, but you'd have to have pretty steady cross bracing to support the weight of a vehicle.

Only time I've seen a gap with grating made of sheet steel (as opposed to cast iron) it's not a lot wider than 8 inches or so. 3 feet is not something I would trust my skills with without getting actual engineering help with

Same. I thought I'd try the free internet advice first.

I was thinking of using steel angle around the edge of the pit. But again, I have no idea about load-bearing.
 

gee

Blame It On The Gassa Nova
Sep 29, 2012
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I would trust Gee's plan to hold the weight of a person, but you'd have to have pretty steady cross bracing to support the weight of a vehicle.

Only time I've seen a gap with grating made of sheet steel (as opposed to cast iron) it's not a lot wider than 8 inches or so. 3 feet is not something I would trust my skills with without getting actual engineering help with
I was sizing up my mechanic's drive-on lift earlier in the week, it's sheet of diamond plate metal on top of cast iron bars, about a foot apart and braced with sold cast iron bars every foot or so. I'd say the plate was 3/16" - 1/4" thick.

I'd do the same "ladder frame bracing" thing for this. The load would be held by the bracing, not the plate, and you'd have to select your bracing steel to handle the weight of a single car wheel + a bunch of derating.

There might be a book/manual you can find exactly for this which gives you "cookbook" calculations for a given braced length and type of steel. But I think this is definitely "get an engineer or specialized mechanic" territory.
 

Mr. Argumentor

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I was sizing up my mechanic's drive-on lift earlier in the week, it's sheet of diamond plate metal on top of cast iron bars, about a foot apart and braced with sold cast iron bars every foot or so. I'd say the plate was 3/16" - 1/4" thick.

I'd do the same "ladder frame bracing" thing for this. The load would be held by the bracing, not the plate, and you'd have to select your bracing steel to handle the weight of a single car wheel + a bunch of derating.

There might be a book/manual you can find exactly for this which gives you "cookbook" calculations for a given braced length and type of steel. But I think this is definitely "get an engineer or specialized mechanic" territory.
If you went with a ladder, I wonder if it would be better if you staggered the steps, or went completely across.

As in have a central "beam" every foot across the width, then add in the cross-support/steps.
 

gee

Blame It On The Gassa Nova
Sep 29, 2012
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If you went with a ladder, I wonder if it would be better if you staggered the steps, or went completely across.

As in have a central "beam" every foot across the width, then add in the cross-support/steps.
I'd say keep the beams solid from left to right edges. They'll carry the weight of the vehicle onto the edge bars, and from there onto the steel plate, and onto the floor. You wouldn't want to break these with welds and a parallel piece, especially in the center where the peak tension force is in the bar.

Bracing between adjacent bars in the ladder doesn't really provide any mechanical advantage.
 

Mr. Argumentor

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My concern is how you would actually get the bars across from one side to the other. If you drilled holes (or cut 'em out with a plasma welder) you'd be alright, but if you had to weld in each side it would weaken the shit out of it
 

CletusJones

CUCKGBLR
Oct 15, 2004
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Awesome that you have mechanic's pit. The wife and I have been talking about doing one when we build our garage.

Why cover it up? Just park a car over it and put up some cones.

What if you got a in-ground pool cover? Those snap into the ground and can easily support a few hundred pounds. You're not going to be able to drive on it but nobody will fall in and it won't move on you.
 

Amstel

The Hoarse Whisperer
Jul 12, 2009
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you're a whore, but in a good way. Kindof.
What if you got a in-ground pool cover? Those snap into the ground and can easily support a few hundred pounds. You're not going to be able to drive on it but nobody will fall in and it won't move on you.
this is a brilliant idea. If the cost can be significantly reduced, http://www.poolcenter.com/looploc.htm it's a great idea. not to mention, you can store all your christmas decorations in it!