Thread: Need advice about making flat pack bookshelves

I don't like the sound of masking the rebates. Best case, you'll end up with a sharp ridge (this can be removed by scraping over it backwards with a razor blade). Worst case, the paint will completely cover and fill over the masking and you'll need to cut it free with a razor blade (this usually doesn't end well).

I'd be cutting the dados a bit wider to allow for the paint and just spray the whole thing.

Another tip for 2-pack paint on panels that will be assembled after (and just in general, really): Don't have sharp edges. The paint is much more likely to chip off sharp edges so whenever we do this sort of stuff at work every painted edge gets a 2mm radius. At the very least, just take the sharpness off with 120 grit sandpaper (this is fine for rebates and dados).

A few points to consider.

MDF is available in 32mm but is very heavy and will sag under its own weight over an 1800 span unless very well supported. 30 mm is not a standard size. From memory the few times I have used 32mm, a 2400x1200 sheet is around 45kg, and definitely requires 2 people for every movement. A 450x2400 panel would be manageable but awkward for a single person to manoeuvre.

Standard sheet sizes are in the order of 2400x1200, 2400x1800, and 3600x1200 or 3600x1800. I used to handle a lot of coated sheets in 2400x1200 and plain sheets in 2400x1800. We occasionally had things cut outside from 3600 sheets but that is outside the length our machines handled so I never got to see the full sheet to identify the width. However you will not be able to source material for the back as a single sheet.

Is there any particular reason for wanting the 30mm (32mm) thickness other than the chunky look? I am not a great fan of the chunky look so have never looked at commercial products made for that look, but I suspect that it is made using the concept of a torsion box (2 thinnish (6mm) sheets top and bottom separated by a grid of 12mm strips on edge. Much stronger and lighter, and considerably less sag.

Two pack tends to be a brittle finish. If you cut dados in the uprights then fill them to keep the paint out of them, how do you intend to remove the filler blocks without chipping the coating, as it will be a continuous coating over the fillers?

I am not a fan of dados in MDF. Unlike real timber, strength and crush resistance are variable with the position in the core. The skin of the sheet provides most of the strength and crush resistance, while the core is primarily there to hold the skins at a specified separation. Once you cut dados into the skin, particularly from both sides at the same height, most of the strength of the sheet is lost because the remaining core has little crush resistance. Attempting to lift a dadoed 32mm x 2400 long section from a horizontal position would most likely cause it to bend and fail at the dado as the skin integrity has been lost and a stress concentration point created.

Also
Even 2400x1200x25mm MDF is a 2 person lift unless you have big arms and a back of steel

Originally Posted by Glider

I'm planning to make a built-in bookcase 2900 wide x 2300 high using 30mm MDF with beading on the open faces. All joins would have dados.

I want to have all the component parts sprayed with white two pot PU prior to assembly on site. I think I could mask the dado slots with MDF offcuts and leave all the shelving and vertical separating panels un-masked.

I'm pretty inexperienced in the use of MDF much less trying to work with pre-sprayed pieces. I'm hoping someone will tell me if the whole idea would work or not

mick

Hi Mick

without commenting on your choice of MDF thickness ...
for 2900 wide I strongly suggest at least 4 if not 5 bays -- for 4 bays, each would be approximately 660mm wide (or approximately 545mm wide if you went with 5 bays)
don't use dados -- instead use a combination of shelf pins and knock down connectors -- look at an Ikea bookshelf for how the two go together

in my limited experience with MDF, I suggest applying the finish after cutting the components to size and applying the beading, but before drilling for the shelf pins / knock down connectors.


good luck

First things first. Commercially MDF is NEVER two pack painted, it is simply too soft on an exposed edge. The norm is a HDF that is prefinished in a white finish on two faces. This is available from Laminex Industries and Polytech. All the two pack kitchens etc. out there today use this product as less paint is required and it is a more staple product.

Originally Posted by kph

First things first. Commercially MDF is NEVER two pack painted

Ummm, yes it is. MDF with a white satin finish is a very commonly used product for 2-pack paint.

Originally Posted by elanjacobs

Ummm, yes it is. MDF with a white satin finish is a very commonly used product for 2-pack paint.

Sorry you are wrong, check the specification for the MDF board then the then satin board. There is also more glue in the product. I have just checked with the Laminex MSDS and their technical specifications and they different. We use it every day and I can assure you it is. We also use different tooling to cut it.

Originally Posted by kph

Sorry you are wrong, check the specification for the MDF board then the then satin board. There is also more glue in the product. I have just checked with the Laminex MSDS and their technical specifications and they different. We use it every day and I can assure you it is. We also use different tooling to cut it.

http://tradeessentials.thelaminexgro...tial_Guide.pdf
http://tradeessentials.thelaminexgro...wood%20TDS.pdf

Both are pretty much the same density.

Fine have it your way, I will let my technical rep, my foreman, paint shop supervisor, CNC operator and the cabinetmakers and joiners on the floor tomorrow that we are all wrong! By the way just got off the phone from my sales rep and he told me I am right, so I will have to let him know also, that he is wrong as well.

You told me to check the specs, so I did...
They might be different products, but if they have the same density you can't call one MDF and the other HDF. Even the data sheets call them both MDF.

Originally Posted by kph

First things first. Commercially MDF is NEVER two pack painted, it is simply too soft on an exposed edge. The norm is a HDF that is prefinished in a white finish on two faces. This is available from Laminex Industries and Polytech. All the two pack kitchens etc. out there today use this product as less paint is required and it is a more staple product.

before the thread goes nutz, did u mean MR white satin MDF? HDF is a different beast altogether and I doubt anyone uses it for kitchens, since as far as I can recall HDF doesnt get produced in Oz anymore.

I think I will bow out from this as I am at a different level. I run a large commercial fit out company and we work on major projects both here and overseas. I thought wrongly that I could contribute with some of my 40 years experience in the industry.
Anyway good luck to you all with your projects.

dont get upset. im actually interested if u are in fact using HDF for kitchens. do u have a link to the product that you use? I cant find anything from laminex in which i would describe as HDF. I still reckon you are using "white satin finished melamine moisture resistant medium density fiberboard", but I would love to know that I am wrong.

Hi Mick
Having used mdf a fair bit would agree with others comment regarding using 32mm thick, it is just too heavy to work with in my opinion

You could probably get away with 18mm if well constructed.

The main issue with mdf id no matter how thick it is when used for shelves is is incapable of even supporting its own weight without sagging, let alone adding books.

Adding a solid timber lipping to the front edge and preferably the back aswell will give the shelves sufficient rigidity for your requirements, you can also give it a moulded edge if required.

I much prefer using bookcase studs for the adjustable shelves as opposed to cutting lots of dados.
You can even use a bookcase strip that is already pre slotted/drilled.
The design would probably require some shelves to be permanently fixed for the whole structure to have some strength.