Trenching MDF

[ldoodle]

I have made an 18mm MDF cabinet and I am going to use 3mm MDF for the back panel, which I would like to slide into the unit, so thought about trenching the 3 pieces (2 sides and top) so it slides in from the bottom.

Only question is how close to the edge can I do this without what's leftover snapping off. Thought about going 3.2mm wide by 5mm deep, and 5mm in from the edge to get it as close to the back as possible.

Alternatively I can trench out right on the edge (a sort of TnG effect) and nail the back panel on?

PS: All the cuts are bevelled so no visible but joints, so just pinning the back panel on is a no-no.

 

[big-all]

i just rebate 6mmx6mm and glue and nail 6mm/5.5mm mdf/ply
3 mm is to thin

 

[ldoodle]

Thanks. Do you mean 3mm MDF is too thin for a back panel or that is too little to leave on one side of the trench, as I planned 5mm at least.

The overall width of the unit is 540mm (making the back panel 514mm with a 5mm rebate in each side) so I don't know if that has any bearing to the thickness of the back panel, as in it's not too long a run?

Saying that if I was trenching in 5mm from the edge to fit a 3mm thick sheet, that's over 8mm coming in from the edge, whereas rebating on the edge using 6mm MDF is just over that so gives me more room, so makes sense to do that. Tiny amount I know....

If I rebated in 6x6mm, what size nails should I use to avoid splitting the edge of the pieces the nails go into? Or would pilot holes plus screws be better?

 

[Deleted member 174758]

Thanks. Do you mean 3mm MDF is too thin for a back panel or that is too little to leave on one side of the trench, as I planned 5mm at least.

3mm is far too thin - it will wobble and get knocked out far too easily - it's the same thickness of stuff you get in the cheapest, low-quality kitchens. You can get MF-MDF (melamine faced MDF) and MFC (melamine faced chipboard) in 8mm thickness which is designed for the task, or alternatively 12mm MDF, although a more sturdy job is done by grooving the sides and top and sliding your back in from the bottom of the cabinet. Personally I'd happier with 15mm or even 18mm material for the backs because they are very sturdy indeed. When grooving (trenching is really for full thickness BTW) in MDF you need at least 10 to 12mm material from the edge of the stock to the rear face of the back - less than that and there is a high liklihood that the rear edge of the cab sides/top will potentially just crumble away if mis-handled

If I rebated in 6x6mm, what size nails should I use to avoid splitting the edge of the pieces the nails go into? Or would pilot holes plus screws be better?

Don't use nails on MDF - use screws. 3.0 x 15/20mm and pilot/countersink them, too. Make your rebates 9 otr 10mm wide (1/2 the thickness of the MDF) - 6mm means that you'll risk spalling out the inside of the cabinet. If instead you groove and slide your back in all you will need is a few spots of glue in the grooves and a couple of dabs on the last edge with a few screws to hold it whlst the glue goes off (although you'd really need to have done this before assembling the cabinet - same goes for rebating although that is possible in a post-asssembly scenario)

Alternatively I can trench out right on the edge (a sort of TnG effect) and nail the back panel on?

You mean rebate (helps if you learn the right terminology). If so see response above. This is done a lot with factory-made furniture