Shelf sag

[grim_d]

Something that bothers me greatly in my line of work is shelf sag, particularly with bookcases, in this case, with MDF, the damn stuff sags under its own weight.

There's all sort of methods for avoiding sag such as hardwood edging, metal capping, underbracing....none of which I like.

I recently saw a system from Hafele intended for straightening bowed doors, in essence it's a bit of 6mm threaded rod that is tensioned. Seems to work great.

Complete Set, Recessed Mounted, Planofit Door Straightening System - Häfele U.K. Shop

Sliding & Folding Door Gear for Furniture For min. board thickness 16 mm - order in the Häfele U.K. Shop.

www.hafele.co.uk

I make my shelves from 26mm but I was thinking of routing out a nice fitting groove in two pieces of 13mm, I can then sandwich them together with some threaded bar inside.

I can tension via a couple of holes on each end for some nuts/washers.

Do we think this would help to increase the stiffness of the MDF?

 

[Newlands]

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!).

 

[Barking Mat]

Don't buy MDF shelving ?

Alu 90° extrusion, the length of the shelves ?

Proper wood ?

 

[grim_d]

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!).

Of course! Well in theory there's no reason the groove can't be curved, cut it with the CNC.

Don't buy MDF shelving ?

Alu 90° extrusion, the length of the shelves ?

Proper wood ?

I'd love to supply real oak or other hardwoods to my customers, but even getting MDF into their budget is challenging currently. It's not just the additional timber cost, the additional labour in dimensioning and glue up too.

Ally extrusion is unsightly, anything external is unsightly IMO.

Birch ply is now almost unobtainable, where it is available it's disgustingly expensive, have just tried alternative ply (premium manufacturer not builders merchant crap) but it was so bowed and twisted it was unusable...£2.5k worth.

Trying to avoid melamine.

So veneered or painted MDF is about all that's left unless the the budget is there for real wood...

 

[Barking Mat]

Of course! Well in theory there's no reason the groove can't be curved, cut it with the CNC.



I'd love to supply real oak or other hardwoods to my customers, but even getting MDF into their budget is challenging currently. It's not just the additional timber cost, the additional labour in dimensioning and glue up too.

Ally extrusion is unsightly.

Birch ply is now almost unobtainable, where it is available it's disgustingly expensive, have just tried alternative ply (premium manufacturer not builders merchant crap) but it was so bowed and twisted it was unusable...£2.5k worth.

Trying to avoid melamine.

So veneered or painted MDF is about all that's left unless the the budget is there for real wood...

Everything is expensive nowadays.

 

[eLuSiVeMiTe]

Something that bothers me greatly in my line of work is shelf sag, particularly with bookcases, in this case, with MDF, the damn stuff sags under its own weight.

There's all sort of methods for avoiding sag such as hardwood edging, metal capping, underbracing....none of which I like.

I recently saw a system from Hafele intended for straightening bowed doors, in essence it's a bit of 6mm threaded rod that is tensioned. Seems to work great.

Complete Set, Recessed Mounted, Planofit Door Straightening System - Häfele U.K. Shop

Sliding & Folding Door Gear for Furniture For min. board thickness 16 mm - order in the Häfele U.K. Shop.

www.hafele.co.uk

I make my shelves from 26mm but I was thinking of routing out a nice fitting groove in two pieces of 13mm, I can then sandwich them together with some threaded bar inside.

I can tension via a couple of holes on each end for some nuts/washers.

Do we think this would help to increase the stiffness of the MDF?

What about routing a 6mm strip on the edge of shelf glue in steel rod them cap with stripwood

 

[grim_d]

Everything is expensive nowadays.

I could just about deal with the rising cost if the quality came along with it but sadly it's cost up, quality down.

What about routing a 6mm strip on the edge of shelf glue in steel rod them cap with stripwood

I'm really not keen on the strip on the edge look, even though a beefy enough strip of oak on its own would largely solve the problem.

I think the rod would need to be under tension for it to work satisfactory, 6mm, even 8 or 10mm is pretty bendy on its own?

I though about putting a bit of c-channel Inbetween two 13mm boards but it doesn't leave much meat left in the board.

People don't really seem to care about long term stuff like this, I've seen a few things from a well respected cabinet maker near here, after a couple years all the shelves and longer carcass spans are all bowed and unsightly due to sag. I'd like my stuff to look good for years even if it's made of sawdust glued together.

 

[Blue Chips]

Something that bothers me greatly in my line of work is shelf sag, particularly with bookcases, in this case, with MDF, the damn stuff sags under its own weight.

Can you post a photo or two of some of the typical shelves you're making? That might help spur some specific suggestions. I've built bookshelves out of various materials, including MDF (which I avoid when possible), and the most useful technique I've found to stiffen a shelf is to attach/glue a hardwood strip to the front edge of a shelf that's about twice as high as the thickness of the shelf material. I'll admit that it gives the shelves a heavier appearance, but some people might actually like that look, and it definitely stiffens the shelves. Ideally, the backboard should be thick enough to cut a dado in it to receive the rear edge of of a shelf.

As to shelves in a workshop, rather than finished shelves for interior home/office use, there are lots of interesting approaches. In my workshop, I have several 'suspended' shelves (hanging from the ceiling joists) that are fully supported along the rear edge of the shelves against the wall by a wooden strip screwed to the wall, and the front edges have steel angles under the full width of the shelves. I have some very hefty items on the shelves, and there is no sag anywhere. I can take a photo or two if you're interested.

I'm really not keen on the strip on the edge look, even though a beefy enough strip of oak on its own would largely solve the problem.

Yes, I agree. As I mentioned here, a tall enough strip of hardwood along the front edge could help greatly.

 

[mike os]

Pretty much a waste of time ... by the time you have messed about with rods, strips, tee or angle and made it look right it is cheap to buy wood ... if it's painted then tulipwood or similar is good and relatively cheap

 

[eLuSiVeMiTe]

I could just about deal with the rising cost if the quality came along with it but sadly it's cost up, quality down.



I'm really not keen on the strip on the edge look, even though a beefy enough strip of oak on its own would largely solve the problem.

I think the rod would need to be under tension for it to work satisfactory, 6mm, even 8 or 10mm is pretty bendy on its own?

I though about putting a bit of c-channel Inbetween two 13mm boards but it doesn't leave much meat left in the board.

People don't really seem to care about long term stuff like this, I've seen a few things from a well respected cabinet maker near here, after a couple years all the shelves and longer carcass spans are all bowed and unsightly due to sag.

My own stuff I make from ply. Not birch but decent quality to avoid it.

I give em the choice it's up to them if they want to pay.

Could always face frame. Adds a lot of support to shelves.

 

[keithski122]

Today I dismantled some shelving that I put up in my garage at least 15 years ago.15mm chipboard over a 4ft span, it had at least 3 inch of drop in the middle where it had sagged, only had spray paints on it.Got a couple of scaffold boards I might make new ones up from.

 

[grim_d]

Can you post a photo or two of some of the typical shelves you're making? That might help spur some specific suggestions. I've built bookshelves out of various materials, including MDF (which I avoid when possible), and the most useful technique I've found to stiffen a shelf is to attach/glue a hardwood strip to the front edge of a shelf that's about twice as high as the thickness of the shelf material. I'll admit that it gives the shelves a heavier appearance, but some people might actually like that look, and it definitely stiffens the shelves. Ideally, the backboard should be thick enough to cut a dado in it to receive the rear edge of of a shelf.

As to shelves in a workshop, rather than finished shelves for interior home/office use, there are lots of interesting approaches. In my workshop, I have several 'suspended' shelves (hanging from the ceiling joists) that are fully supported along the rear edge of the shelves against the wall by a wooden strip screwed to the wall, and the front edges have steel angles under the full width of the shelves. I have some very hefty items on the shelves, and there is no sag anywhere. I can take a photo or two if you're interested.


Yes, I agree. As I mentioned here, a tall enough strip of hardwood along the front edge could help greatly.

All and any external and visible supports are no good to me here unfortunately.

Shelves are also positionable so can't dado or attach to the back panel which further increases the need for stiffening.

This type of thing, first picture that came to hand, I didn't pick the colour.

Pretty much a waste of time ... by the time you have messed about with rods, strips, tee or angle and made it look right it is cheap to buy wood ... if it's painted then tulipwood or similar is good and relatively cheap

It's not just material, you have to remember the labour cost. Once set up running a couple grooves and glueing two boards together would be pretty quick.

Plus tulipwood isn't much use when the spec is oak, IMO tulipwood is only any good if you're painting, it's not a nice looking timber.

@eLuSiVeMiTe what ply do you use? My experience of ply has sadly been that it's utter crap unless it's birch, even from the bigger names like Garnica, £180 a sheet for birch faced poplar 18mm is beyond a joke, their poplar face/core stuff looks nice but every one of the 30 odd sheets I had delivered were so bowed in both directions they could be used as bowls.

 

[mike os]

All and any external and visible supports are no good to me here unfortunately.

Shelves are also positionable so can't dado or attach to the back panel which further increases the need for stiffening.

This type of thing, first picture that came to hand, I didn't pick the colour.

View attachment 382552





It's not just material, you have to remember the labour cost. Once set up running a couple grooves and glueing two boards together would be pretty quick.

Plus tulipwood isn't much use when the spec is oak, IMO tulipwood is only any good if you're painting, it's not a nice looking timber.

I thought you were using mdf?

 

[bricol]

I've got something like 50x30x3 angle at the back of my bookcase shelves - its got lots of holes in as it really the main supports for industrial shelving.

The back of the shelf sits in it, the books on the shelf hide the bit that sticks up above. I've got a lot of heavy hardback books on them - previously they sagged under the weight over a year or few - so I reversed them (so they bowed upwards initially) - but I got fed up after a decade of clearing, flipping and reloading them.

Having now seen your piccie - probably won't work for you.

 

[grim_d]

I thought you were using mdf?

Oak veneer

 

[JOEPRO]

I buy all metal shelving good used from shops etc. Never sags etc I would not use timber myself as I know it will bow overtime in our damp cold climate especially. I have about a dozen metal bays of different depths in my garages

 

[Agroshield]

Two observations:

1. You need to consider how to resist the compressive force of the tensioned rod at the sides of the shelf. You do not want the nuts sinking into the MDF and the rod losing tension over time. First thing that springs to my mind is a long barrel nut. One side would need the threads drilled out for a nut on top of it.

2. Make sure you know which is the top of the shelf when you put the curved groove in. Installing it upside down will accelerate the sag.

 

[Keith 66]

If using mdf for shelves avoid long spans if at all possible & put supporting partitions under shelves. Idea of a truss rod as used in guitars is sound but the groove on the necks i have seen was straight, the truss rod is made up of two straight bars, both joined at one end with small gap between, other end one bar has a threaded end going through a block welded to the other, adjusting the screw adjuster alters the tension or compression in one bar & it will bend them one way or the other, as its trapped in a recess under the finger board it alters the bend in the neck.
Other way to stop sag is increase thickness or add hardwood edgings, Bookcase below i made 3 years ago was made this way as i dislike sharp corners & wanted radiused corners, All made in cherry faced mdf with cherry edgings.
It was built up with housings for partitions & all glued & biscuit jointed together, effect is some partitions support the shelf hanging below them as well as others holding shelves up. It was built in sections as it is bloody heavy. Wont be coming out any time soon!

 

[Gareth J]

I think the rod would need to be under tension for it to work satisfactory, 6mm, even 8 or 10mm is pretty bendy on its own?

It wi need to be under tension. And, for it to do anything meaningful, it'll need to be put under more tension as the shelf bends. That means offsetting the rod so it's biased as much as possible to the bottom.

Have you looked at ladderax shelves? They use a simple, but nifty way to make the most of properties of wood and steel. A thin strip of flat, vertically, holds the shelf up. While a closely matching slot in the shelf holds the steel in place and resists buckling/twisting if the steel. It's not perfect but it's simple and effective.

 

[grim_d]

It wi need to be under tension. And, for it to do anything meaningful, it'll need to be put under more tension as the shelf bends. That means offsetting the rod so it's biased as much as possible to the bottom.

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.