How thick for a door jamb?

[Gerrydelasel]

I'm making an internal door lining and I'm wondering how thick to make the jamb on the hinge side. I can get 21mm (after planing) boards very easily, but this looks kinda puny, especially after rebating for hinges. Next size up is 33mm which is rather too thick and will reduce the available width of the aperture (I'm trying to keep it as wide as possible but am limited by the length of the lintel).
No one seems to stock 27mm round here which looks ideal.

That said, I have seen off-the-shelf door linings that are as thin as 19mm! Am I being too conservative?

 

[big-all]

your hinges will use no7 x1 1/4" screws so 32mm
you may get away with 27mm and 1" screws ??

 

[Gerrydelasel]

you may get away with 27mm and 1" screws ??

Historic linings appear to be 1 inch thick so 27mm would definitely be OK if I can get it. Glad I'm not the only one who thinks ~20mm is too wimpy.

 

[Doggit]

With the architrave mouldings on the outside of the door jamb, you wouldn't really know what the depth of it was. In theory, if you could securely fit a piece of backing wood where the screws are going, then 21mm could be achieved.

 

[foxhole]

I needed a few very wide linings, beyond what is readily available so ripped down 25mm mdf.

 

[Gerrydelasel]

I needed a few very wide linings, beyond what is readily available so ripped down 25mm mdf.

Seriously? No way my doors would hang off MDF. They'd rip the screws right outta there...

In theory, if you could securely fit a piece of backing wood where the screws are going, then 21mm could be achieved.

I think I'll do this -glue some strip wood behind the areas where the hinges will be.

 

[big-all]

as an aside

you only need the 33mm on the hinge side the lock side can be 18mm
indeed iff you get an 18mm frame then double up on the hinge side
although i think thats what you have just just suggested
is this in a studwall or brick wall ??
if its a stud then assuming its flat and level then fix the hinge side to the stud and go with 18mm and 35mm/1 1/2"screws

 

[Gerrydelasel]

iff you get an 18mm frame then double up on the hinge side although i think thats what you have just just suggested

Yes more or less. It's a brick wall, but only single skin. There enough thickness of plasterboard for me to fit some stripwood behind the hinge area without even needing to gouge out the brick. Problem solved I think!

 

[foxhole]

Seriously? No way my doors would hang off MDF. They'd rip the screws right outta there...


I think I'll do this -glue some strip wood behind the areas where the hinges will be.

Your door would have to weigh a few hundred kilo to rip out the screws from mdf.?
Much stronger than same thickness of timber as it's far denser.

 

[Gerrydelasel]

Much stronger than same thickness of timber as it's far denser.

But it's so fibrous? Then again I've been wrong before.

 

[foxhole]

But it's so fibrous? Then again I've been wrong before.

Its only weak when screwing into end grain which should be avoided.

 

[big-all]

mdf is a great and a horrible material in equal amounts

its very heavy for its strength as its short random wood fibres compressed so about 5 times the volume to get a workable material
it de-laminates in the end grain or near the edge
screws that will normally move the wood fibers and go in between can delaminate and or cause bulges in the board
it is useless if it gets wet

then the good points
very easy to machine and cut without splintering as theres no grain
it gives you a fantastically smooth face for painting
iff you do a pilot in the face you will find it very difficult to lever any screw out because off the densety

 

[Doggit]

Gerry, you're trying to get the maximum width possible, but you haven't mentioned the depth of your door stops you're going to use, as this is the normal place to try and increase the width.

 

[Deleted member 174758]

But it's so fibrous? Then again I've been wrong before.

Believe it or not quite a few door casings installed in public buildings such as colleges, office blocks, etc use MDF casings carrying relatively heavy doors. The trick is to ensure that the MDF casing is properly fixed to the stud work (often using double rows of screws) and that good quality screws are used for the hinges and that they are driven into correctly sized pilot holes

 

[Gerrydelasel]

Gerry, you're trying to get the maximum width possible, but you haven't mentioned the depth of your door stops you're going to use.

Oh I'll just buy some stripwood or something. Basically I have two doors available, one 700mm wide, the other 800mm wide. I'm trying to get the doorway as wide as 780mm so I can use the 800mm one (cut down).