Adding molding to slab mdf

[Yorkshire1]

Hi , new to the forum thanks for the the approval , initially looking for advice but hope to be able to contribute aswell!
We need to build some wardrobes for a client , the doors will be 18mm mr mdf roughly 1800 x350-500mm wide with dado style molding running 100mm in from the edge on 3 sides the molding is to be roughly 40mm wide and 16mm deep
Now we know usually whats done to one side needs to be done to the other to maintain equilibrium However has anyone any tips for acheiving doors that will remain true
The plan is to use mdf molding in the hope that its flexibility will allow the doors to remain true with the help of 4 hinges / door when fitted
Thoughts gratefully received, thankyou
Photos show how badly the doors would bow with pine molding

 

[Chippyjoe]

I think you would be better off using 22mm MRMDF personally if the budget allows.

 

[Yorkshire1]

Yeah we ve tried that previously and its worse because you get more tension the thinner the mdf the more flex you get

 

[Cabinetman]

Even though your last statement seems contradictory I know exactly what you mean, we started off with 18 mil MR MDF just like you for my sons wardrobe doors, he wanted a geometric slashed design right across six of them, I knew I should’ve run away but Dad's being Dad's got stuck in and this is what we ended up with, six mil MR with aluminium angle iron glued on the back with pink stuff, hinges in blocks and almost a nervous breakdown.
I am not recommending you try it this way. NO definitely NOT!! It was a nightmare.
On more expensive wardrobe doors when they glue a mirror on the front they have vertical grooves with aluminium fittings running full length of the height of the door which can be adjusted/tensioned to take movement out. Ian

 

[Droogs]

I would suggest that it's best to make the mouldings out of the same material as the doors, esp if being painted. Or to make the moulding and leave it in the customers house for a couple of weeks to acclimatise and then fit it to the doors just before painting and fitting.

 

[Jones]

Have you tried a glue that is not water based? The tension causing the bow presumably comes from the glue drying and shrinking so a pu glue or coating the panel both sides with sealer first might work.

 

[Doug71]

I had the same happen on 2 pairs of doors I made for an airing cupboard, wasn't sure if it was the heat or the wood strips shrinking which made the doors bend, either way I won't be doing it again.

Luckily as they were pairs of doors both doors bent the same so you couldn't tell, I think it was only me who noticed it

 

[Spectric]

The nice thing about MDF is that when it does move it is usually only in one direction unlike real wood that bows and twist.

 

[Yorkshire1]

I would suggest that it's best to make the mouldings out of the same material as the doors, esp if being painted. Or to make the moulding and leave it in the customers house for a couple of weeks to acclimatise and then fit it to the doors just before painting and fitting.

Hi thanks yes thats the next plan we do have an an insulated cabinet we use to replicate indoor conditions

 

[Yorkshire1]

Even though your last statement seems contradictory I know exactly what you mean, we started off with 18 mil MR MDF just like you for my sons wardrobe doors, he wanted a geometric slashed design right across six of them, I knew I should’ve run away but Dad's being Dad's got stuck in and this is what we ended up with, six mil MR with aluminium angle iron glued on the back with pink stuff, hinges in blocks and almost a nervous breakdown.
I am not recommending you try it this way. NO definitely NOT!! It was a nightmare.
On more expensive wardrobe doors when they glue a mirror on the front they have vertical grooves with aluminium fittings running full length of the height of the door which can be adjusted/tensioned to take movement out. Ian

View attachment 126458View attachment 126459

Even though your last statement seems contradictory I know exactly what you mean, we started off with 18 mil MR MDF just like you for my sons wardrobe doors, he wanted a geometric slashed design right across six of them, I knew I should’ve run away but Dad's being Dad's got stuck in and this is what we ended up with, six mil MR with aluminium angle iron glued on the back with pink stuff, hinges in blocks and almost a nervous breakdown.
I am not recommending you try it this way. NO definitely NOT!! It was a nightmare.
On more expensive wardrobe doors when they glue a mirror on the front they have vertical grooves with aluminium fittings running full length of the height of the door which can be adjusted/tensioned to take movement out. Ian

View attachment 126458View attachment 126459

Striking set of doors there Ian yeah Ive seen those adjusters are they the hafele ones
The strange thing is why some doors stay true and others dont when everything is in equilibrium am going to clamp a bowed door flat and add molding to reverse side and see what happens

 

[Yorkshire1]

Have you tried a glue that is not water based? The tension causing the bow presumably comes from the glue drying and shrinking so a pu glue or coating the panel both sides with sealer first might work.

We use mitre glue and activator its slightly baffling as to what the issue is currently 8 500 mm wide tall doors are sfraight and all 4 300+mm doors have bowed all the same materials all built the same day

 

[Yorkshire1]

Just as a matter of interest and to show the random nature of the bowing this is a mock up we made a couple of months ago thats just been sat in the workshop its 18mm mr 2200x500 and its stayed dead straight

 

[Yorkshire1]

And another this time 2100x600 same 18mm mr with mock mr molding to one side and its bowed although i think with 4 hinges on itll straighten out as the bow doesnt have the tension of the pine

 

[BrandonB]

From my experience, 18mm MRMDF is no good for doors as it reacts to changes in moisture so badly and quickly. I have used 18mm MRMDF for doors in the past and would avoid it as not matter if you store them perfectly flat in your shop and take good care of them before arriving to the clients home it doesn't take alot for them to bend or bow slightly ruining your hard work.

I recommend only to use 22mm MRMDF fordoors as it's less likely to change and isn't so 'whippy' compared to 18mm doors. The 22mm seems to stay alot flatter for longer and isn't so bad with changes in moisture. I've found it to be more stable and elimates alot of the problems using 18mm caused such as 'fighting' with the hinges. When you use 18mm for doors, because the material is farily thin and can be quite 'whippy' given the length of the door say anywhere between 1700mm - 2200mm when you attach the hinges, because the material isn't rigid when you hinge up the door, they anchor to the carcass and sometimes you can feel the material resisting to open and close or not wanting to move in sync with the rest of the hinges. You don't get this with 22mm as it's alot more ridig.

I'm not sure about the effect of timber mouldings being fitted to one side of a door as from my prespective it's just fixed to the door. It isn't a part of the door whereas if you were doing 'faker shaker doors'.....it's just beading pinned to the center of the door? I can't believe people mitre mate 6/9mm MDF to a 12mm/18mm sheet of MDF for a shaker effect as that is crying out to bow and bend. There's such a large surface area being stuck to one side of the door....Two different materials on one side of the door it's literally screaming to bend and move? But everyone has their own ways I guess.

From my experience everyone battles with these flaws and they just find good ways of hiding them. Even if you made the door from solid tulip you'd have the same problem if not worse...if you used solid oak or ash it's bow and twist with no chance of getting them back to shape. What I have done before is heat one side of the door up with a heat gun and leave it in clamps which solved a bowed door but apart from that it's just another plate to spin!

 

[Yorkshire1]

Ha funny you say that we make both 22 and 18mm slab doors at times and to be honest we find the whippiness of the 18mm an advantage as the hinges (usually 4/full height door) will keep the doors straight whereas its the 22mm that tends to fight and as you say yes you can feel the door connteri g the hinges/carcass
I removed the trim detail from the bowed door and both the trim and the door are perfectly flat unbelievable
I do wonder what properties the mr has over standard mdf as measuring the edges of both that have been layed about the workshop for a while show about the same level of expansion .I mean what is mr if it cant stand ambient moisture!
We tend to use the medite sandwich board with the green centre and the green is a lot less dense than the outer brown layers which makes you think the moisture resistance is just the top surface

 

[BrandonB]

Ha funny you say that we make both 22 and 18mm slab doors at times and to be honest we find the whippiness of the 18mm an advantage as the hinges (usually 4/full height door) will keep the doors straight whereas its the 22mm that tends to fight and as you say yes you can feel the door connteri g the hinges/carcass
I removed the trim detail from the bowed door and both the trim and the door are perfectly flat unbelievable
I do wonder what properties the mr has over standard mdf as measuring the edges of both that have been layed about the workshop for a while show about the same level of expansion .I mean what is mr if it cant stand ambient moisture!
We tend to use the medite sandwich board with the green centre and the green is a lot less dense than the outer brown layers which makes you think the moisture resistance is just the top surface

Sometimes you could hang the door on concealed hinges are there will be a massive bow but if it's put back on a bench and led down under its own weight it won't show the bow. It's not until you tip it on it's edge and sight down it will you see the bow, so it makes it very difficult and frustrating. I found the 18mm a nightmare for any door as it would bow alot easier and alot worse compared to the thicker 22mm. I also use only the medite MRMDF which has the sandwich appearance on the edges. It's much denser and more compact than the horrible fluffy standard MDF.

I have a feeling that moisture is causing the grief for you. The changes in moisture and how it's stored can play a big part of why things move. I typically throw a transit cloth over any doors and stack doors on top of each other on a bench or flat area over night to prevent any moisture settling on one face side. It all really boils down to uneven moisture content levels on each face etc, but I mean no one OR it's very rare to have a workshop which is the same temperature and moisture level as a clients home and even if it is, when you store it in the van over night i.e if it's a large install for example, it will change there....it's never ending all we can do is try and elimate things to prevent problems later down the line.

But like I mentioned in my last reply, I don't know how people do not have this problem or prehaps they don't mention it but adding thin MDF to create the look of shaker doors (known as faker shaker) doors. They must bow like crazy, I can't see a timber trim doing that to a door or have the same effect...

There is also a guide from Blum on using concealed hinges and measurements given on width of the door, weight of the door and height of the door. It's very useful and stops alot of overthinking. I generally try and keep them around 450 - 550mm apart min/max.

I'm not sure if this helped but should be some reassurance the atleast.

 

[Yorkshire1]

Yeah looks like se re on the same path as a rule we dont have too many issues luckily and we do have an insulated cabinet we store stuff in to keep material at similar humidity levels to end useage
Most of our painted work is in frame shaker 25mm styles/rails sandwich core mdf with 9mm centre panel

 

[doctor Bob]

Not a type of door I generally do. However we sometimes do 18mm veneer doors with oak strip slats on the front 50 x 14.
I route in the door straightening kits in the back and cover with an oak plate. Just takes the worry out of the job.