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How to attach piece of Pine to a Jarrah roof joist?

Winniemac

I need to screw a small piece of heat treated pine to a jarrah joist in my roof cavity. (I need this for an inline exhaust fan as the joist is not quite wide enough to attach the fan to directly.)

I am seeking advice on how to do this, which drill bits are recommended and which screws are best. I have had bad experiences with drilling into jarrah in the past so now want to know how best to do this!

I have a Ryobi hammer cordless drill.

Thanks

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EricL

Hello @Winniemac

Thank you for sharing your question about drilling a piece of pine to your jarrah joist. Drilling into a dense Australian hardwood like a Jarrah joist requires caution because the wood is extremely hard, abrasive, and prone to overheating tools. Watch out for bit burnout, smoke, splitting if near edges, and structural weakening of the load-bearing timber.

When drilling into dense hardwood, use a low-to-medium drill speed, as high speeds create excessive friction and heat that can quickly damage the drill bit. To clear packed wood dust and allow the bit to cool, pull it out of the hole approximately every 10 mm of drilling before continuing. Always use sharp, high-quality drill bits suitable for hardwood.

But, when drilling through a joist, keep holes close to the centre line (neutral axis) wherever possible. As a general guide, holes should not be larger than one-quarter to one-third of the joist’s total depth and should remain at least 50 mm (2 inches) from the top and bottom edges.

Finally, when installing screws or other fixings into dense hardwood, pre-drill suitable pilot holes first. This reduces stress on the timber, makes the fixing easier to install, and helps prevent the dense grain from splitting or cracking. I suggest using small drill bits first to start the pilot holes and then work your way up to the larger bits.

If you can share a photo of the joist and panel you'll be attaching together, our members will be able to provide you with more recommendations.

Let me call on our experienced members @Dave-1, @Noyade and @DIY4Knuckleheds for their recommendations.

Please remember to wear personal protection such as gloves, goggles and a mask.

If you need further assistance, please let us know.

Eric

Dave-1

Good Evening @Winniemac

Drilling holes in hardwood is a hard slog :) Tho the good side is you know its not going anywhere lol

@EricL has covered all the points I was thinking of but I will add one more and also give you a link to things we have done wrong, for me it was trying to use a hammer styled drill to turn the screws into the hardwood. Nope, bad move. You need a graduated torque drill (Its the drill where you can see a bunch of 1-10 settings and also a drill setting on the chuck of the drill (Not sure for Ryobie) but Ozitto have them :)

I have also used dry soap over the thread of the screws to help them screw home. (into the pilot holes)

Mistakes with tools that we have done? Have a read through this thread, There are a lot of things we all have done that afterwards we go mmmm maybe not such a good thing :)

Take it easy, the classic slow and steady wins the race especially for not overheating drill bits into old hardwood. Clean out the swarf frequently (sawdust) and go a little deeper then you think. (the wood shavings as you screw might need somewhere to compress to

DIY4Knuckleheds

G'day Winniemac, l think EricL nailed it…..so to speak 😊 Drilling the smaller pilot holes prior to driving in the screws is a must. Generally speaking, particularly when screwing into hardwood, the finished pilot hole should be roughly the same diameter as the shaft of the screw.

It was also a good suggestion from Dave-1 regarding the dry soap coating the thread of the screw. You can also use wax as a substitute or even run the screw through your hair which some of the old timers used to do. The oil from your hair (if you still have any 😂) adds a bit of lubricant to the screw.

Good luck 👍

Noyade

With hardwood, as per @EricL 's thoughts on regularly cleaning out the hole as you progressively drill. If it's only a few screws - I always use a hand held screwdriver so I can 'feel' the torque involved and hopefully prevent screw snapping. If it gets too tough, remove the screw and increase the drill bit size by 0.5mm. For me, it's all about the pilot hole.

Winniemac

Thanks everyone. Attached is a photo. I won't be drilling through the joist - just into it. The two joists are slightly different measurements - one is 75mm wide by 45mm high and the other is 65mm wide by 35mm high. The timber doesn't need to hold up the house - just be sturdy enough to screw an inline fan into. What gauge and length screws would be sufficient to attach the pine to the jarrah?

pine timber to attach to jarrah joist.jpg

EricL

Hello @Winniemac

It all depends on the thickness of the panel, I propose having a look at using https://www.bunnings.com.au/zenith-6g-x-40mm-zinc-plated-hinge-long-thread-countersunk-head-timber-screws-100-pack_p2434142 . My best advice is to make sure that 50 percent of the screw length is anchored onto the joist.

If you need further assistance, please let us know.

Eric

Winniemac

I thought I would message to say I successfully attached the pine to the jarrah joists! I started small and used cobalt drill bits which worked a treat. I also used torx head screws rubbed with candle wax, low speed screwing and it all came together without any hassle. Thanks for all your advice.

EricL

Hello @Winniemac

Thank you for the update. That is definitely a win! If you can share a photo of your handy work that would be great.

Eric