Mdf Versus Ply

18mm MDF will be fine.
The hinges you want are called 35mm concealed hinges often called Blum hinges after a major manufacter of them.
If you go on the Blum or Hafele, a supplier, website there should be a chart showing how hinges you will need for the size of door, probably 3 for the larger size and 2 for the smaller.
You need to decide wether you want the doors to cover the carcass, which is the most common method, if you want the doors to sit inside the carcass or if you want a frame in front of the carcass and the doors to sit inside this.
When you paint the doors you must paint both sides in fairly quick succession to avoid warping.

 

25mm will be too heavy for an overlaid door. You would need extra blums to take the weight. I use 25mm in a jointed and framed door, set in a face frame. But I assume you are not set up for that type of thing.

In general mdf should come straight and true thoughout, so long as it has been handled and stored well. But you do get some which can have a slight bow. Which would be noticeable on the bigger doors. In which case have the bowing in the middle facing out, and if it needs it; it can be straightened out with a catch at the centre. Quite often mdf will straighten out nicely with painting.

If the cabinets are side by side they will have enough for the screws to bite into and hold the blum hinges. Blums have a lot of adjustment and if you get the basic siting about right the doors can be tweaked into place thereafter.

I have not used ply for a long time in such things. Its nicer to work with. But I think having two different materials means a noticeable difference in the finishes, or more time and effort in achieving a consistent finish.

 

I agree with the above - 25mm will be very heavy and is simply not required.

IF the MDF starts off flat and IF you paint both sides equally as Chips says, then it should remain flat. Especially if you are using moisture-resistant stuff.

Wear a dust mask... Really.

 

Sorry if this is a dull question, but what is the bit about being painted at the same time got to do with being flat?

 

So that's what this is for...

 

Hi Fats;
I think the point about painting both sides at the same time or in quick succession is to stop the MDF from warping

Not a problem with a fixed panel that is say screwed to a wall or a carcass, but with a door, painting just one side may cause the board to warp. Painting both sides seems to equalise the warping and you end up with a flat board

Maybe not the most scientific of explanations from me but in lay mans terms, it seems to work

I assume that para is being humorous above

 

Drywall screws are not the best for MDF. They are best for fixing plasterboard. Use the Spax MDF screws.

 

Ed,
You have some excellent advice here. I would just add that wearing a dustmask as someone has said is mandatory but do not attempt to cut the mdf in an enclosed space without proper dust extraction and ventilation. Mdf is terrible stuff and will cause you problems.

 

I can only concur with VM. I've always cut MDF outside.

 

and a the best face shield you can afford.

mdf fibre is horrible