Shelf sag

[Gritineye]

Sounds similar to post tensioning a brick gatepost to stop it bending under the weight of the gate, which works because the brick post is usually wide enough. Not sure if a shelf would have enough thickness to make it work though.

 

[prepman]

Well it works for guitars. It’s called a truss rod, but it really needs to be put into a groove that is curved along its length, so that when the two pieces are glued together it forms a bow shape. When the nut is tightened at the end it will pull the shelf into a shallow curve, counteracting any sag due to the load (assuming you’ve installed the shelf the right way up!).

Interesting...obviously you know about guitar builds? Got a couple of questions regarding bridge bowing/bulging. This isn't the section for it needs to be over in
https://www.mig-welding.co.uk/forum/threads/guitar-players.46974/post-2161422

 

[chunkolini]

Google search sagulator to calculate saggage on shelves.
Truly a tragic sight

 

[dave h 2]

I would wonder about a metal strip screwed to the back edge of the shelf

 

[knighty]

Would it not be easier to use two pieces of MDF, bend then the wrong way then glue then together?

A bit like some kind or pre tensioned veneer?

Gives you extra debth to add the metal rod if needed... But I think you'll need to have the nuts on the end of the rids sticking out the sides of the shelves to have any hope of stopping them.just pulling into the ends of the mdf

 

[ukracer]

Everything is expensive nowadays.

Price gouging is the cause of much of the rises. Profiteering is another..

Then you get the fall out and manufacturers having to pay extra for raw materials passing it on to the customers who in turn need more wages to be able to afford the increased prices....or the manufacturers will go out of business...meaning workers loose their jobs. This has a knock on effect as other businesses can't sell to those workers who are now out of work.

The MONEY must be going somewhere. Mainly to those who do not need it sadly.


The end result is the OP struggles because his customers simply cant afford what they WANT and the OP WANTS to produce.

 

[Kram]

I dont think tensioned rods will work. MDF will creep over time. It does not have the compressive strength that proper wood or other materials have.

Better would be to use thicker mdf shelves, route out the edges and insert 10mm or so steel box section and a strip of mdf or veneer to hide it on all sides.

 

[ukracer]

I would wonder about a metal strip screwed to the back edge of the shelf

Or a T piece steel (aluminium) rebated into the shelf.

 

[ukracer]

I dont think tensioned rods will work. MDF will creep over time. It does not have the compressive strength that proper wood or other materials have.

Better would be to use thicker mdf shelves, route out the edges and insert 10mm or so steel box section and a strip of mdf or veneer to hide it on all sides.

Great minds think alike...I had not seen your reply...honest.

I have just been using Aluminium T pieces to install my suspended ceiling. Amazingly strong.

 

[Kram]

I have some Lidl metal frame shelving and the shelves are OSB. The shed one is ok but in the garage, where its slightly damp, all are bent like a bananna in the middle and with very little weight on them. At some point it will need replacing!

 

[Gareth J]

My thinking/hope is that it would eliminate any sagging in the first place (to a point) as opposed to being a way to counteract it over time.

Or at least constrain it to the point where it doest draw the eye.

When I say "as the shelf bends" I don't mean the shelf will deform (it will, but that's not the point) I mean, imagine what will happen to the rod, as the shelf is loaded and it begins to bend. If the rod is bang on the centre of the board, it will just bend. If it's towards the top of the board, it'll be compressed, if it's towards the bottom, it'll be in tension. For maximum impact, it'd need to be as far to the bottom as possible (or below the bottom!)

 

[grim_d]

Google search sagulator to calculate saggage on shelves.
Truly a tragic sight

I use it. However the answer with MDF + books is always going to be unfavorable.

Price gouging is the cause of much of the rises. Profiteering is another..

Then you get the fall out and manufacturers having to pay extra for raw materials passing it on to the customers who in turn need more wages to be able to afford the increased prices....or the manufacturers will go out of business...meaning workers loose their jobs. This has a knock on effect as other businesses can't sell to those workers who are now out of work.

The MONEY must be going somewhere. Mainly to those who do not need it sadly.


The end result is the OP struggles because his customers simply cant afford what they WANT and the OP WANTS to produce.

Nail. Head.

Better would be to use thicker mdf shelves, route out the edges and insert 10mm or so steel box section and a strip of mdf or veneer to hide it on all sides.

Already using 26mm @ £120 a sheet.

Thing is with MDF as it gets thicker it gets insanely heavy, and start sagging under its own weight.

Tension rods work for large format doors, but yes perhaps not in this application, glue is drying so I'll find out soon.

Box section thing doesn't seem to make a difference, it's as bendy as the MDF though it would probably constrain the sag from getting worse over time.

 

[sako243]

Radical suggestion - veneered steel box section frame

 

[grim_d]

Radical suggestion - veneered steel box section frame

Would be similar to a torsion box shelf, which works but they are far too thick sadly.

 

[eLuSiVeMiTe]

I use it. However the answer with MDF + books is always going to be unfavorable.



Nail. Head.


Already using 26mm @ £120 a sheet.

Thing is with MDF as it gets thicker it gets insanely heavy, and start sagging under its own weight.

Tension rods work for large format doors, but yes perhaps not in this application, glue is drying so I'll find out soon.

Box section thing doesn't seem to make a difference, it's as bendy as the MDF though it would probably constrain the sag from getting worse over time.

View attachment 382597

Last dresser I did I doubled up the 18mm MR MDF. No sign of sagging as yet. giving me 36mm shelves. Could route / cut a 10mm grove both sides for 20mm box pre glue up.

 

[Gareth J]

Block board?

 

[Trevorleach]

Two grooves in the bottom of the sehlf and some of that thin walled c section extruded aluminium inserted into the grooves?

 

[Pond frog]

I think the sad truth is mdf is fundamentally unstable for long spans so the best solution is that use short spans or multiple supports as in kieth 66s design

 

[voipio]

Use a wedge-shaped cross section, so that it is 2x or even 3x thicker at the rear of the shelf compared to the front, which can be the same thickness as the other shelves for appearances sake. it would be barely noticeable to to most people. Doubling the thickness for the full depth of the shelf would decrease the sag to 1/8th, and tripling decreases it to 1/27th. Using the wedge shape wouldn't give as dramatic a reduction in sag as having the full depth made thicker, but it would still be a considerable improvement.

 

[Kram]

^ but it would cost just the same as a full thick sheet with half the benefit.

Tbh I cant see box or T section bending. ID weld up using sheet steel rather than alu extrusion just as itll be much cheaper and thinner for the same effect.