Biscuit Question

[robin_shepherd]

Hello all,

I am currently designing (to make) a large shelving unit. It is going to be fitted in a bookshop and will store books.

The client has specced that it will be 4 metres long, thus longer than a standard 2440 x 1220mm sheet. My question is: considering the weight of the books is it safe to biscuit join the shelves together?

To give a bit more information on this, each shelf will be made from 18mm MDF and will be 290mm deep. The verticals of the unit will have routered out slots for each shelf to sit it (please see attached pic). The other option would be to position the biscuit join in one of the slots however I'm not sure if this would cause a whole other set of problems!!

So to reiterate my question, are biscuit joins strong enough to join lengths of 18mm MDF together when they will be carrying books?

Any answers, thoughts or ideas would be much appreciated.

Many Thanks.

 

[neilyweely]

Hi Robin
Assuming the diagram you have shown is reasonably accurate it shows 7 units over the 4m span. This indicates that each unit will be over 500mm wide. Working on this assumption I would suggest some sort of timber frame may be in order. If you wanted to keep things looking 'clean' and as in the diagram then perhaps some sort of frame made from 18mm mdf with an 18mm face frame on the front would help to make it more rigid.
The obvious alternative is to use plywood instead of MDF. Or to simply use a frame around the rabbets which would be strong, but maybe not so aesthetically pleasing.
I know this is a point many will dispute but in my experience, albeit limited in this instance, biscuits are not very strong. They are more useful for locating the shelves rather than strengthening them. Bearing in mind they would sit in rabbets I think this is covered anyway. I did make a smaller version of this, for a restaurant's wine collection - so bearing a deal of weight, some time ago. Made from MDF with a Poplar face at the front tongue and grooved (with a long tongue) to the MDF, and located in the rabbets with some glue and biscuits. It has held up far better than I imagined ( I was worried about sag over the years, but it still looks great; should've charged more! :roll: )
There are folk here with FAR more experience than I in this area, Dr Bob and mailee are two who spring to mind; it would be advisable to wait for an answer from a 'real' expert!!! (as opposed to me, a fake one :lol: ).
If you wanna hang a door I can be more help.........

Sorry, but HTH

Neil

 

[Chrispy]

If you need to make the shelves run through as drawn, then I would be tempted to suggest that you make the middle section slightly deeper than the rest to make it into a break front bookcase, this will disguise the joins in the shelving. ie make it in three sections, three bays to the left and right with one in the middle.

 

[Sgian Dubh]

You won't need to join any shelves with biscuits to increase their length, which is what I think you are asking-- this wouldn't be very strong if a join was at the mid-point of a shelf, and I wouldn't do it. You have eight verticals, which will take up 144 mm of the 4000 mm width, assuming you use 18 mm thick MDF for these parts. Next you cut each shelf to fit between the two ends and the six vertical dividers, meaning they are all approximately 551 mm long, plus a bit to sink into the verticals, say 4 mm at each end resulting in each shelf being ~559 mm long. If this was built on-site that would be about all you'd need to do, plus a bit of jiggery-pokery for the different layout at the far right.

If you are building the thing off-site and installing it later, you'd probably build it in three or maybe four units that could be screwed together on-site once everything is levelled up on the floor, and possibly fixed to the wall. In this case you would need to incorporate more verticals so that each unit would be a discrete item each one ready to be screwed to the next unit.

I don't see evidence of a plinth in your drawing, but I'd probably incorporate one because this can be set up level on the floor, which certainly won't be level, and then you simply place your shelving on top it and fix it to the plinth.

There is just then the question of the strength of the shelving and the load it's expected to carry. Typical loading for a bookshelf is 25 lbs per linear foot (or about 11 kg per 300 mm length), and you have just under 2 feet length per shelf, so you're looking at just under a 50 lb load per shelf-- large format books weigh more per linear length when stacked together. You will get some visible bending if there is no further bracing of the shelf, eg, a fixing in the centre back of each shelf into a wall or a back panel, or possibly a vertical return about 45 X 18 mm along the back and/or front edge of each shelf. Without the additional support you'll need to make sure your customer is willing to accept some visible bending, which might be up to about a 3 mm sag at the mid point. Slainte.

 

[Racers]

Hi,

If the horizontals are continuous then the weight will be transferred through the verticals without placing any strain in the joints.

I have used this method my self for bookcases.

Pete

 

[Shultzy]

Another way would be to make them in a series of boxes with 9mm sides and glue together. Obviously the outer edges will be 18mm and the front edges covered with "iron-on" or hardwood lipping. If you are worried about sagging use 18mm box horizontals to give 36mm shelves.

 

[Hudson Carpentry]

I would stess to the client that having then built in 1 or 2 column units is the better way to go and recommend 25mm mdf. If the client wants the shelves to be continuous then push for the use of either timber planks or a custom order of 4m long mdf.

 

[NLH]

If the client wants it 4m long make it in four 1m sections,

That way you can fix each unit to the wall and then to each other for added strength,

Also I would use 25mm plywood for the shelfs and clad them in 3mm mdf, yes it's more work but the shelves will never sag.

Good luck mate make sure you get some pics up when your done

 

[AndyT]

You might not like this comment, but before you commit to the work... it looks the sort of thing where the labour of cutting up sheet materials and edging them will be difficult to cost realistically. If I were you I would have a look at what it would cost to build using Ikea's 'Billy' range.

You can still provide your client with a complete supply and fit service and they would get something on a properly level footing, fixed securely to the walls. It might be more profitable for both of you.

It's also very strong and well finished!

 

[Sgian Dubh]

... it looks the sort of thing where the labour of cutting up sheet materials and edging them will be difficult to cost realistically.

I don't really understand that Andy. Estimating or quoting for work is a basic requirement for a furniture designer maker... and if it is too challenging for someone to estimate then perhaps the person trying to price it up, but can't, is in the wrong business. In reality the job is pretty basic, albeit quite large, but there's very little really that's difficult in the design shown, although I'd modify it to make it do-able in sections along the lines I suggested in my earlier post. Slainte.

 

[RogerBoyle]

You might not like this comment, but before you commit to the work... it looks the sort of thing where the labour of cutting up sheet materials and edging them will be difficult to cost realistically. If I were you I would have a look at what it would cost to build using Ikea's 'Billy' range.

You can still provide your client with a complete supply and fit service and they would get something on a properly level footing, fixed securely to the walls. It might be more profitable for both of you.

It's also very strong and well finished!

Agree with the post above from Sgian Dubh

Could you explain how you think it would be difficult to price /cost realistically
Just curious

 

[AndyT]

Sorry, I didn't mean that the estimate would be wrong - just that it could come out at a high price which might not be to the customer's liking. I've not done the sums for this project, but I've looked at similar things for myself in the past and realised it would cost me more to buy the basic sheet materials than the finished flatpack from Ikea.

 

[robin_shepherd]

Wow thank you to everyone for your input. It has been very helpful and I really appreciate it. As you may have guessed this is my first large job (I'm fitting the whole book shop however the other units are much smaller than this one).

I have read through all the comments in detail and created a different design. As I am making it off site and then fitting it seems that making 4 seperate units is the way to go, thus totally avoiding the need to create a 4m length.

I have two more questions...

I agree that making a pedestal to level off first is a good idea. Instead of making it from MDF, could I instead make a simple timber (2x1) frame, slightly less deep and then screw down into it when fitting the units. To me, doing this seems sensible as it would create a shadow gap and give me a surface to level off. I would like to make it out of timber to keep costs low.

I am concerned that the shelves will sag (the gap between verticals is 600mm) if I make the units out of 18mm MDF. I originally suggested plywood but the client can't afford it. If I was to fit braces into the back of each shelf (see attachments) would this remedy the problem? I was planning on doing this anyway to give me a point to fix to the wall. However I was not planning on doing it for every shelf.

As before advice and ideas are much appreciated.

 

[RogerBoyle]

Sorry, I didn't mean that the estimate would be wrong - just that it could come out at a higher price which might not be to the customer's liking. I've not done the sums for this project, but I've looked at similar things for myself in the past and realised it would cost me more to buy the basic sheet materials than the finished flatpack from Ikea.

LOL I actually thought the same from the home woodworkers point of view after I posted

Thanks for the clarification

Roger

 

[petermillard]

Lots of sound advice here, and as always, many different ways of achieving the same end result. I make a lot of shelves and bookcases, and I'd go for 25mm MDF personally - even over a short span of ~600mm I'd be a bit leery of 18mm MDF when you know it's going to be fully loaded with books. I always lip my MDF shelves in a hardwood 'D' profile, which I've found adds significantly to the stiffness of the shelf.

Is there space to fab these onsite, or are you making up the individual units and delivering them pretty much complete? If the latter, I usually make up the bookcases as single individual units, with the sides half the thickness of the shelves e.g. 12mm sides for 25mm shelves, then as mentioned above, simply glue & clamp the sides of the adjoining bookcases together (packed out if required) and lip the exposed edge with the same profile as the shelves. This is a quick and easy construction method as, apart from any exposed ends, the shelves can simply be glued and screwed into the housings - no other fixings needed.

I presume you're fitting backs to the bookcases? Securing the shelves to the back is a good way of reducing shelf sag, even if it's just pinned through. At the base I'd definitely use a plinth to level things off, though I prefer 3x2 CLS on its side - gives a solid area to work from - easier to ensure the noggins support the joins between individual units, too. Level it up with wedges, then screw little MDF "L" shapes into the inner sides of the plinth to act as feet, then scribe a thin MDF skirting to tidy things up nicely.

And finally, just a personal observation; I'd be a bit cautious of any customer who commissions a piece of this size but says they can't afford the difference between MDF and Ply. Just sayin'...

HTH Pete

 

[Jacob]

MDF not good for shelves. Tends to sag unless it's so thick it weighs a ton.
500mm perfect for 12 to 18mm softwood. 22mm would do 1000m bookshelves.
I'd it in three pieces as suggested. The owner could then arrange them differently at a later date.
I'd have the top bottom and middle shelves jointed into the sides but the others all sitting on supports - simplest being 2 short dowels into holes at each end. Then they are adjustable and the whole unit lighter and easier to install. The dowels can be housed into the underside of the shelf with a simple chisel cut nicked out - to keep the shelves from moving or dowels from dropping out.

NB forget biscuit joints, do it properly!

PS I'd also suggest doing a bit of research first, as your measurements look a bit odd - why 290 deep? Measure a few books. Creep into a book shop or library and measure a few shelves - and look at how/what made.

Seems to be a basic assumption with beginners that you design from the top of your head. Unless you are a very unusual genius this is a mistake. Somewhere not far from you there will be some excellent examples to copy - you don't have to make mistakes to develop your design/making skills!