Which countersink bit to use for a 7g 40mm screw?

[ZenZhou]

Im building a fish tank stand using 18mm water-resistant MDF, the screws i was advised to use was either a 8g 50mm screw, or a 7g 40mm screw. The only problem is that i cant find a countersink bit thats long enough to fit either one of them. they have 8g and 7g but its just not long enough. I also need advice on which hinges to use for this, and the screws that are needed for the hinges. 

Many thanks.

[EricL]

Hello @ZenZhou 

Welcome to the Bunnings Workshop community. It's sensational to have you join us, and thanks for sharing your question about counter sinking.

I suggest using the Ryobi 4 Piece Countersink Drill Bit Set RHSS-CDB4. It has four-gauge sizes which should work for your cabinet project. Drilling pilot holes and counter sinking them is a two-step process. First you drill the pilot hole with an ordinary drill bit, you then remove that drill bit and use the counter sinking one to create the bugle seat for the screw.

There is a drill bit that does an all-in-one like the Starborn No.8 Smart-Bit Trim Head Countersink Drill Bit. Keep in mind that using the counter sinking bit does not need to go very deep unless your timber is very easy to split then the pilot hole will need to go deep.

For the hinges I suggest using Hafele Salice 110° Hinge Full Overlay Slide On - 1 Pair if you want it fancy. But if you only want an ordinary hinge, I propose using non mortise hinges.

If you have any other questions we can help with, please let us know.

Eric

[ZenZhou]

Thank you so much @EricL,

Im just worried my MDF will split if i dont go deep enough, i read online that a rule of thumb was 10mm more than the actual screw. Is this true?

Many Thanks, Zen

[MitchellMc]

Hi @ZenZhou,

With MDF you'll typically need to pre-drill for the entire length of the screw. Going 10mm further is a good assurance that the timber further in from the screw doesn't also crack. There's nothing wrong with pre-drilling a little further than needed if you have the space.

Mitchell

[ZenZhou]

Thank you @MitchellMc,

Thats the problem im having with all-in-one counter sinks. I would prefer to use a all-in-one as ive never done much woodworks or ect. Majority of them go 300mm. Is there a solution to this?

Zen

[MitchellMc]

Hi @ZenZhou,

I believe it's these P&N 4 Piece Quickbit Pilot Drill / Countersink Bit Set where the drill bit can be extended out to around 50mm.

Mitchell

[ZenZhou]

Hi @MitchellMc,

thanks for the quick response. I have those bits right now however the 8g one is still not long enough. Should i be going down in length then? Will it still hold a 74kg tank?

Many thanks, Zen

[EricL · Accepted solution]

Hello @ZenZhou 

I'm a big user of MDF, but there is one thing I always do and that is to add actual timber supports in the corners. Unfortunately, MDF tends to tear itself apart under heavy stress. I don't think it will be strong enough to hold the weight of your fish tank.

However, I suggest using 70 x 35mm Framing MGP10 Untreated Pine 2.4m at the top to hold the weight of the tank. This will also allow you to drill the panels together without worrying about splitting it in the middle. As you will be drilling into the timber frame.

As for the bottom and back panel, I suggest using 42 x 19mm 1.8m DAR Pine Premium - 1.8m. This will strengthen the bottom and back panel and prevent the MDF from coming apart.

I've drawn up a sample sketch to give you an idea of how to install the frame.

If you have any other questions we can help with, please let us know. 

Eric