Choosing correct screws fo MDF cabinet

[lymmranger]

Hi guys - well next on the list of jobs SWMBO has thoughtfully provided for me ( ) is ........

2 of MDF display units

these will be constructed out of 18mm MDF (and then painted)

I have designed the units and worked out my cutting plan

but I am unsure on suitable screws

the units will be 500mm deep by 1000mm wide and I was stuck between using a 6 or an 8 and also 50mm or 70mm

any expert views on my choice will be gratefully recieved

 

[speed]

you can buy mdf screws
id use some 2"6s or if you are new school 3.5 x 50mm

depending on the style etc biscuits and/or dado joints could be worthwhile for a strong joint

 

[lymmranger]

Simple box construction is my way

...intention is to drill a pilot through both pieces (countersunk & subsequently filled) and pukka woodglue (green)

I have mimicked a kitchen base unit design with strengthening cross rails.

my trouble is I tend to overdesign, I was worried that a 50mm no 6 was too light (mind I will probrably use hundreds!)

Thanks for that, now then off to tradepoint!

 

[speed]

. i find when using 8s it expands the mdf and you will see the ripples down the corners, even when pre drilled, wood glue will give a strong hold also

 

[lymmranger]

6`s it is!!!!!!!!!

thanks alot

 

[JohnD]

wouldn't dowels be better?

doesn't need a special cutter like biscuits do.

 

[Jasonb]

I use carcase screws, drill 4mm clearance in the top part and 3mm pilot in the edge of the other board. Some form of dowel or biscuit would help with strength.

Screwfix sell the screws

Jason

 

[joinerjohn]

Last place I worked at made display units for shops etc. We used tons of MDF. Was usually screwed and glued together. Combined pilot drill/ countersink in one drill and screws similar to the ones suggested by Mr Bellamy. Some of the flat pack displays (for assembly on site) had the proper cam and dowel fixings. The MDF for these was usually machined on the cnc and dedicated machine for the holes in end grain.

 

[lymmranger]

I was going over my cutting plan last night when a terrible feeling of "Doh" hit me.....

.....I haven`t allowed for the saw blade

Anyone know how much to allow for the thickness of the blade? If it helps I will be usingf B & Q (due to being a tradepoint customer and they are the only place who will cut it at 7pm on a saturday night!)

 

[joe-90]

Give them the size you want - blade thickness not a problem.

 

[lymmranger]

sorry did not explain myself properly

I need 5 full sheets cutting down into 34 component parts

I drew a scale plan (which does have tolerance) but forgot that the blade will use some material and may/will effect the calculations. Or are you saying it wont?

 

[Jasonb]

On a wall saw its likely to be about 3.2mm kerf.

I always like to rip the last 10mm off the edges of any boards as the "grain" is a bit open and they may also be a bit bashed about.

Jason

 

[joinerjohn]

On a wall saw its likely to be about 3.2mm kerf.

I always like to rip the last 10mm off the edges of any boards as the "grain" is a bit open and they may also be a bit bashed about.

Jason

It's not unknown for boards to be very slightly out of 90 degrees on the corners either. We always used to mark a known 90 degree line and cut around 10mm off one edge.

 

[foxhole]

Keep any screws at least 80mm from edge of mdf to avoid splitting board.Glue with a few screws is more secure then a lot of screws .

 

[lymmranger]

....just by way of an update

For the first time in my life a project involving wood (well mdf) is going well

B & Q happily and carefully cut it all up (and didnt charge!!!)

Yesterday the first unit was built and installed and....

it is all square and vertical and looks mint

....long way to go yet but so far so good - thanks for the help guys