Calculating screw lengths needed for shelf load

srichards

srichards

Suspended / Banned
Messages
10,968
Name
Suz
Edit My Images
Yes
I have a projector shelf. It's got 2 supports like those hanging basket thingies. 2 screws each side. It seems fairly sturdy but the projector on it is a petite 3.5 kg and the likely replacement is going to be more like 8.

If I stuck 10kg of bricks and it doesn't move or fall off overnight, it is that a fair test that it would be ok? Would that weaken it if it were marginal though?

I'm struggling to find the right information. The diy websites claim their titchy angle brackets are good for 18 kg each so I assumed these bigger ones would be more than ok but a friend of mine that is more diy savvy reckons not.

I don't know how long the screws are into the wall. Standard wall plug length so probably 30 mm.

I was thinking of just adding a third support with much longer screws to spread the load as the shelf is in the right location so I don't want the faff of re drilling the other 4 holes.

I also wondered whether a large meat hook on the ceiling and some chains might be an alternative to take the weight if the shelving is a bit iffy . . .

Any idea what I need if you assume a 10kg load on an mdf shelf with 2 metal angle brackets?
 
Would go for 40mm screws min and if you want to test put 18kg of bricks on overnight. Alsoit depends on the construction of the wall.
 
Last edited:
How heavy is the projector?

Edit - must learn to read..

What projector are you going to get? I don't even think the huge Epson at work (size of an atx PC unit) weighs 8kg and that's bolted into the ceiling with 3 5cm screws :D
 
Last edited:
srichards said:
I was thinking of just adding a third support with much longer screws to spread the load as the shelf is in the right location so I don't want the faff of re drilling the other 4 holes.
Click to expand...

This. With the 40mm screws and plugs to suit.
I think the hook & chains is a bit over the top! (excuse the pun!)
 
neil_g said:
How heavy is the projector?

Edit - must learn to read..

What projector are you going to get? I don't even think the huge Epson at work (size of an atx PC unit) weighs 8kg and that's bolted into the ceiling with 3 5cm screws :D
Click to expand...

Epson 3200. It's the only one I can find with lens shift, decent throw and not silly money for bulbs!

Ceiling mount ones are usually fixed into joists or anchored into metal beams. I dare you to swing from it ;)
 
As said...40 mm x 10's or even 12's should easily be ok but is it brick, block, thermalite, dry lined or studding
Edit...and if brick use brown plugs with a 7mm masonary drill bit (sorry if I'm stating the obvious)
 
Last edited:
Nod said:
Well, if I was going to stick £800 worth of projector on a shelf, I would go to the faff of ensuring a pretty bloody solid fixing. http://www.toolstation.com/shop/Ironmongery/Shelving/Strong Stay Bracket 400 x 355mm/d170/sd2230/p59007 and 2" screws IMO.
Click to expand...

My thoughts exactly! Shelf will be over engineered :)

The brackets on it are supposed to be good for 10 kg each. But sounds like the screws used may not have been long enough for that weight.

Wall is solid. Plaster over I'm assuming brick work. Dust would be grey if it is breeze block. Pretty sure it was orangey when it was done originally.
 
As a kitchen fitter, I normally use 50mm x 4 turbo gold screws from Screwfix into red wall plugs- 6mm- for kitchen wall units. 2 screws per cabinet, standard 500mm wide unit.
This holds the unit and everything it can hold- probably about 20+kg.

I'd never use 30mm screws for this.
 
Have you tried the pull test? I.e put some downward force on the shelf with your hand.

I can't help thinking this is being overthought. I mean today I hung my 13kg mountain bike and 10kg (partially resting on ground) chain from a storage hook secured into the wooden shed roof with 2 40mm screws.
 
neil_g said:
Have you tried the pull test? I.e put some downward force on the shelf with your hand.

I can't help thinking this is being overthought. I mean today I hung my 13kg mountain bike and 10kg (partially resting on ground) chain from a storage hook secured into the wooden shed roof with 2 40mm screws.
Click to expand...

I did do that and pulled reasonably firmly. Seemed ok to be honest but I'd rather not have an expensive projector fall on the floor for the sake of a bracket and a couple of extra screws. :eek:
 
Martyn D said:
That's 12 mm diameter, I'd be inclined to beg, borrow or hire a 240 volt sds drill
Click to expand...

For this job it'll be the best. I did drill into a wall with a cordless Quattro once. No hammer. That was a bit of a chore it has to be said!
 
A standard drill should be fine, hammer action if possible.
I use 18V Hitachi cordless drills (I have 3 of them :) ) A good quality masonry drill makes the job easier. I use DeWalt drills.
 
Martyn D said:
That's 12 mm diameter, I'd be inclined to beg, borrow or hire a 240 volt sds drill
Click to expand...
Don't need SDS for drilling holes in masonry for a shelf, a hammer drill will be absolutely fine. Perhaps if drilling over 5/8" holes, but that's not the case here.
 
This thread reminded me I needed to strengthen the side rail to my decking :lol:

Whoever constructed it used a long screw through the end post into the kitchen wall, over time movement of the rail has caused the screw/plug to move and it's not created a slot in the wall meaning the side rail (now with attached trellis) wobbles all over the place when it gets a bit breezy. Used some 2x2 to create a couple of little batons either side of the end post, fixed to the wall with 50mm size 10 screws. Not that pretty but it'll do for now..... (or ever ;) ) :lol:

Certainly didn't need and SDS drill, I didn't even use the hammer action :)

Provided the wall is sound, a few 50mm 10s is going to hold most things on the wall in a domestic environment. Think there are 6-8 of those screws holding my 21" LCD TV on the bedroom wall.
 
Two 50mm size 4 or 5 screws will hold a full kitchen cabinet up.. No need for overkill- that costs money

I use my SDS drill when I'm removing floor tiles. Set to 'hammer' and put a chisel attachment in.
The only other times I use it are for large or long holes- 100mm holes for extractors or when using my 1 metre drills.
 
Last edited:
onomatopoeia said:
Don't need SDS for drilling holes in masonry for a shelf, a hammer drill will be absolutely fine. Perhaps if drilling over 5/8" holes, but that's not the case here.
Click to expand...

You can cut a piece of cheese with a piece of cardboard, I'd prefer to use the best tools and get the job done quickly.
This thread seems to be getting a few DIY experts who buy a book from b&q and can suddenly build a house!
 
Last edited:
I don't *need* an SDS drill. I just thought it seemed daft not to when they were only £10 more than a normal hammer drill... :)

Another thing I read rated the 7mm brown wall plugs at 30kg each. I'm fairly certain the brown ones were used so as they're 4 of them wouldn't they be more than enough for an 8kg load?

I'm going to have to stick a few bricks on and find out for certain :D
 
Last edited:
srichards said:
I don't *need* an SDS drill. I just thought it seemed daft not to when they were only £10 more than a normal hammer drill...
Click to expand...

My point was that you don't need one for this job, but if you want to get one - go for it.
I have tool GAS too!
 
kendo1 said:
My point was that you don't need one for this job, but if you want to get one - go for it.
I have tool GAS too!
Click to expand...
(y)

I was lured by the dob off drill specs. I do fear I'd have a sudden urge to drill holes everywhere because it was suddenly really easy ;)
 
Epson have exaggerated the weight of this thing. It turned up today. It might be the quoted 7.3KG with all the mahoosive cardboard packaging but the actual projector is probably about 5kg +- 0.5kg A bag with 2 bricks in feels heavier.

Looks like I won't need the forklift to get onto the shelf after all ;)
 
Result!
 
Double result as its on the shelf and the shelf is still on the wall :) Still have to keep checking on it though . . .
 
It's daft, whilst I understand that a bolt is not just a bolt, because of stress, loading etc. until reading this thread I had never even thought about loading on a wall screw before
 
munch said:
It's daft, whilst I understand that a bolt is not just a bolt, because of stress, loading etc. until reading this thread I had never even thought about loading on a wall screw before
Click to expand...
You've obviously never had a curtain pole fall down in your house then (admittedly mine was 'guided down' by a friend's kid ;))
 
Thankfully never had anything fail, but it has got me thinking.
 
Simple Rule of Thumb:-

If it looks as if it would do the Job, then use the next size up, Simple
 
An ex girlfriend said something similar.;)
 
munch said:
It's daft, whilst I understand that a bolt is not just a bolt, because of stress, loading etc. until reading this thread I had never even thought about loading on a wall screw before
Click to expand...

I always do. Everything secured to walls in my house is massively over-engineered.
 
I think that's called "a safety factor"!
 
Have you ever tried to lever out even a one inch screw that has been properly plugged.
What you are talking about is going to be massively strong.
The problem is rarely the screw the main problem is always the wall. Plaster or plasterboard is not intended for fixing screws.
 
Fortunately the wall is plaster over solid brick. Fixings should be long enough to get stuck into the brick.

I've even put bits of sticky tape over the uprights so I can tell if they move. Not that I'm paranoid at all...nor checking twice a day that it's still looking the same...

If I'm putting up anything then I'd just use the brown wall plugs even though it isn't always necessary. I figure if I'm going to be drilling a hole I'd rather do it once and not have to re-do it later when it's fallen off.
 
You must log in or register to reply here.
Back
Top