Screwing gussets to rafters

[OldKettle]

Hi,
I am planning on attaching some plywood gussets to some 2x4 rafters.

The rafters are circa 1960, and so are actually 51mm, and the ply gussets are 18mm each side, for a total thickness of 87mm.

I'm planning on screwing through all three pieces with 6 x 80mm screws.

Is there much chance of splitting the original joist? Would nails be better?

EDIT: If I can use screws, do I need to pre-drill? These are the screws I am planning on using.

https://www.screwfix.com/p/turbo-ii...k-multipurpose-screws-6-x-80mm-100-pack/8930h

 

[opps]

Both nails and screws provide a stronger fix if pilot holes are drilled first, and the risk of splitting the wood is decreased.

 

[OldKettle]

Thanks. Would a 4mm pilot be OK for those 6mm screws?

 

[opps]

I'd go with a 3.5 or 4mm pilot (depends on how soft the wood is) and a 6 or 6.5 clearance for the ply.

3.5mm bits are often a tad shorter though.

"I'm planning on screwing through all three pieces with 6 x 80mm screws."

But they will only poke into the opposite ply by 9mm (assuming that you have used a flush countersink), I am not convinced that will do much other than trying to push the ply away as the screw hits it.

I will defer to others but personally I would for much shorter screws that almost reach halfway through the rafters and additionally use glue with the gussets. Another advantage of shorter screws will be that there is more space to get your screwdriver in between the rafters.

 

[foxhole]

I would use 50mm from both sides, lots of screws out there that require no piloting .

 

[OldKettle]

I would use 50mm from both sides, lots of screws out there that require no piloting .

Thanks. I'll take the 80mm back and get a box of 50mm instead (I have some PZ 4 x 45mm, but they easily cam out with the impact driver, so I'd rather use TX).

What would be best 4, 5 or 6mm?

 

[blup]

Maximum 5mm screws but 4 x 45mm should be fine. Use a conventional cordless drill on low speed setting to minimise the cam out.

Blup

 

[foxhole]

Maximum 5mm screws but 4 x 45mm should be fine. Use a conventional cordless drill on low speed setting to minimise the cam out.

Blup

Never have a problem with cam out , must have weak wrists? Bits can snap though .

 

[blup]

Likewise, it can be controlled with experience, but I assume the OP is new to this.

Blup