How Close To Edge?

[custard]

I want to put up some shelves inside a window "bay" in my workshop. I plan on fastening a wooden cleat to the wall with two 5mm x 50mm screws, using 8mm rawlplugs drilled to a depth of 50mm. The shelf will simply sit on top of the cleat. Nothing fancy, after all it is a workshop. This photo shows the general arrangement, the wooden cleats will be about 200mm long.

Here's the question. The further apart the two screws the more stable the shelf. But if the front screw (ie the one furthest away from the window glass) gets too close to the breeze block edge then it risks blowing out. So how close to the edge should I drill?

My guess is 20mm, but does anyone have better advice? When I say "better" I mean not a guess, but advice based on industry guidelines, or at least on first hand experience!

 

[clogs]

I guess they are hollow....?
the edge fixing I would use a stud held with a 2 part epoxy.....
it won't blow the wall and u could be as close to the edge as u want...
thats provided the drill doesn't blow it out by wandering.....
tricky jobs like that I have some masonary drills with an extra point, so they follow where you guide them...
have used this stuff a lot, even in wet stone (with the correct product)
when fitting steel barn legs close to the edge in old or new concrete I always use epoxy.....
it even got used on my 2 poster car lift...totally secure....

 

[Cabinetman]

Crikey Custard what are you putting on the shelf? I can’t really see a problem at all unless the cleat is extremely flimsy, over 200 mm you could almost put the screws wherever you wanted, but I would suggest the one nearest the edge isn’t as close as 20mm, there is just no need for the cleat to be supported that near the end. Ian

 

[sammy.se]

in that arrangement, I'd put a screw in the mortar line, and one half-way across the block (the block you have your question mark on).
I'd much rather have to patch up mortar than holes in bricks/blocks, as long as the mortar was sound.

Two 50mm screws will hold a shelf very well, even if they are not on the edge. Just secure the shelf to the cleat with screws as well, for stability.

Edit, this is based on my personal experience - not industry guidelines or anything like that...

 

[MikeG.]

Thirty mm. Get your hole size right (ie don't undersize it, and it's useless oversize).

-

Epoxy? To hold a little shelf in a workshop? Really?

 

[Cabinetman]

Yes I really don’t think you need epoxy, but I certainly wouldn’t put it into a mortar joint that’s asking for trouble.

 

[Inspector]

Have you thought over and under? A cleat long enough to put a screw in the centre of two different blocks. One above the shelf and one below it. A groove cut across the cleat the shelf will slide into. You can slide the shelf out to clean the window every decade or so. If you really want to overbuild it to stick some construction adhesive squirted between the blocks and cleat when you screwed it to the wall would make it permanent.

Pete

 

[Racers]

I would put the screws 50mm from the edges, that would leave 100mm between the screws.
Closer to the edge the more unsupported shelf it's not that important as it is narrow shelf.

Pete

 

[MikeG.]

A shelf across the window, though? That seems a little unusual. I thought you'd loads of space, custard.

 

[MusicMan]

The general rule applied in precision engineering and metrology is to minimise the deflection of the beam (cleat in your case). This is achieved by supporting it, not at the ends but at a certain distance in from the ends, ie shorten the span. My memory is a bit dim, and it is a slightly miserable calculation (maybe the Sagulator will do it), but I think the optimum distance is approximately 1/6th of the span in from the ends. So I would use screws at 200/6 ~ 33 mm in from either end. This seems far enough in for the breeze block not to crumble. [edit: see correction in next email]

You don't see this much in textbooks as they usually focus on beams supported at each end. Not because they deflect less (they don't) but because that is how most buildings are made.

Keith

 

[AJB Temple]

A 200mm shelf is not at risk of deflection....

 

[MusicMan]

Ah, found it: Airy points - Wikipedia

The points for minimum sag of an evenly loaded beam are separated by 0.5536 of the span. ie 110.72 mm for a 200 mm beam. 1/6 is wrong.

So put your screws at approx 45 mm in from each end. Pete Maddox's estimate was pretty close!

You will have the best designed short shelf in the forum!

 

[novocaine]

I wouldn't get within a Bono of the Edge or u2 could find yourself on a street with no name and you still wont find what you are looking for.

30mm as Mike said.
I havent try block inserts yet.

Don't get why you want a shelf in fornt of a window, but as i prefer not to have wondows at all i cant really talk.

 

[Doug71]

I often use concrete screws instead of screws and plugs in your situation. Screws and plugs rely on the plug expanding which can cause the breakout but concrete screws just thread into the block so don't cause any expansion, that's the theory anyway!

https://www.screwfix.com/p/easydrive-countersunk-concrete-screws-7-5-x-60mm-100-pack/3313h

 

[Trevanion]

Ah, all ye need is just plenty 'o Pink Grip there! One tube on each cleat should do it!

 

[Ttrees]

How many windows do you have?
If it was only one or two, I would weld up a frame and make it wrought iron or handmade "style" to make the workshop secure, and make the shelf as an add on.

Curious to see how you could do so effectively
All the best
Tom

 

[Sgian Dubh]

I want to put up some shelves inside a window "bay" in my workshop. I plan on fastening a wooden cleat to the wall with two 5mm x 50mm screws, using 8mm rawlplugs drilled to a depth of 50mm. The shelf will simply sit on top of the cleat. Nothing fancy, after all it is a workshop. This photo shows the general arrangement, the wooden cleats will be about 200mm long.

Maybe this is daft, but couldn't you simply cut two pieces of wood (plywood for the lot?) ±200 mm wide to the height required and lay your shelf or shelves on top or in between, with appropriate joinery (glue and screw, for e.g.). Essentially it's a free standing shelf unit that just 'happens' to fit in the opening, and the edges butt up against the window frame.

You did say it's just a shelf(ves) for a workshop, so I'd guess that's maybe "nothing fancy" enough, ha, ha. Slainte.

 

[MikeG.]

I wouldn't get within a Bono of the Edge or u2 could find yourself on a street with no name and you still wont find what you are looking for........

.... with or without trying, you've shown that sometimes we can't make it on our own.

 

[MikeG.]

Ah, found it: Airy points - Wikipedia

The points for minimum sag of an evenly loaded beam are separated by 0.5536 of the span. ie 110.72 mm for a 200 mm beam. 1/6 is wrong.

So put your screws at approx 45 mm in from each end. Pete Maddox's estimate was pretty close!

You will have the best designed short shelf in the forum!

I'm not absolutely convinced that sag is the major issue here!!!

 

[Doug71]

Maybe this is daft, but couldn't you simply cut two pieces of wood (plywood for the lot?) ±200 mm wide to the height required and lay your shelf or shelves on top or in between, with appropriate joinery (glue and screw, for e.g.). Essentially it's a free standing shelf unit that just 'happens' to fit in the opening, and the edges butt up against the window frame.

You did say it's just a shelf(ves) for a workshop, so I'd guess that's maybe "nothing fancy" enough, ha, ha. Slainte.

I did that for a window display in an off licence, worked well, especially as the window had horizontal glazing bars so I could line the shelves up with them.