Making Mdf cabinet carcasses

[Wilson joinery]

Evening all

If you were making a simple cabinet from mrmdf what’s the maximum width you’d design the carcass to be before having to design in some sort of bracing to avoid sagging to the top of the cabinet. I’m using 18mm for the top and sides and a 6mm back panel which will sit in a grove in the back of the sides. Also do you think glueing and screwing top and sides will be sufficient or would you use additional fixings (biscuit or domino).

Many thanks
Pete

 

[rogxwhit]

Say 600mm span max?

As for jointing, the trouble with mdf is that the hard surfaces are thin and all the middle part is useless fluffy stuff, not up to much for glueing or screwholding. I wouldn't have a lot of confidence in biscuits either. Not by themselves. From what you described, the rear panel could act as anti-racking at the back, but you haven't implied anything at the front. A properly jointed (tenons or Doms) face frame of some sort would help ...

I've assumed a free-standing piece. If it's fitted in an alcove or some such then that lets you off the hook.

 

[petermillard]

600mm. Maybe 700, depending on environmental factors eg is there enough space above to stack heavy things on it. Unless the sides are exposed, consider just stapling the back on; faster, easier, just as effective.

I probably made thousands of MRMDF carcasses when I was a working the fitted furniture game, most had dominos for alignment, but many of the early ones didn’t - never had a complaint about any of them, glue and screws works really well.

HTH P

 

[Wilson joinery]

Hi both

Thanks for the replies. I suspected it would be around 600mm. My design is going to use cabinets closer to 850mm width so I’ll have to factor in a brace underneath the cabinet tops.

And yes, rogxwhit it’s fitted cabinets so they will be fixed to the floor via 2 4” wide brace pieces front and back.

Cheers
Pete

 

[BrandonB]

Hi

A few factors determine the maximum cabinet width. If you were to build a double wardrobe for example. You wouldn't want 2x 600mm width cabinets joined together as it divides the hanging rail and doubles the amount of runners needed for the drawers.

A single unit with a single door can only be 600mm in width maximum. If you have anything wider with a single door the hinges will begin to struggle. 650mm is max for a door I would say and obviously would have to take into account the length of the doors.

The back panel if it's a large unit should be 15mm minimum and 12mm if it's a smaller unit such as a alcove unit etc. 6mm is way to flimsy to give any support and will warp/bounce in the middle.

If you do go 800mm - 900mm or even 1000mm -1200mm in width. You can always add a central support for the overhead shelf - similar to a kitchen cabinet central support or by using hardwood for the face frame and fixed through the back and sides.

Cabinets generally all domino'd and screwed. I don't tend to glue cabinets as they're generally pre finished and it gets messy and can stain in the corners. Once it's domino'd and screwed it isn't going move, plus if you need to de assemble to get it through an opening or dry fitted it before loading up it saves alot of hassle.

All the best.

 

[Wilson joinery]

Hi Brandonb sorry for my ignorance but I’m not sure what you mean by a central support for the overhead shelf similar to kitchen cabinet central support. Do you just mean a framework underneath?

Cheers
Pete

 

[BucksDad]

Have you seen Alastair Johnson of Freebird interiors? He has a fitted furniture for business and has a members site where you can subscribe and discusses everything he does in great detail

https://www.buymeacoffee.com/Freebird/posts

 

[BrandonB]

Hi Brandonb sorry for my ignorance but I’m not sure what you mean by a central support for the overhead shelf similar to kitchen cabinet central support. Do you just mean a framework underneath?

Cheers
Pete

Hi,
I have added a photo showing the support in place. They're two doors that will meet on the post and it doesn't hinder the access too much. I feel this is the best option to prevent any movement and to offer support. It's similar to a kitchen carcass as it'll be 18mm x 100mm.

 

[baldkev]

As you probably know, theres different grades of mrmdf. Don't go for caberwood 'trade', go for 'pro' or medite, they have a higher resin content..... heavier, but the middle isnt fluffy, better to machine and finish