50mm Drill bit

[Elthrin]

I need to drill through 2x 8"x2" timbers sat next to each other and through a thermolight block wall behind it for a 40mm shower waste.

Do I just go ahead and use my diamond core drill bit or is there something I can use to go through the wood first?

 

[durhamplumber]

Before you start attacking the timbers..might i suggest you seek proffesional help..what are the timbers for...and you are seriously reducing there strength drilling 2inch holes in them

 

[Elthrin]

Let's assume that I know what the timbers are doing and drilling holes in them is not an issue.

 

[durhamplumber]

Go for it...if the bit does not work...get a bit that drills timber

 

[Elthrin]

I know that diamond core drill bits are not designed for wood and I am pretty sure it is going to heat up and ruin the bit, does anyone have any helpful comments about how to solve the problem?

 

[Agile]

Well I would be drilling a circle of holes about 8 mm with a wood drill and then open them up with a 12 mm wood drill.

What that has been completed then the diamond drill.

Tony

 

[Elthrin]

Thanks Tony, that was sounds like a sensible plan. I was hoping that there may be some sort of tool or Special drill bit I was missing.

 

[Elthrin]

For anyone else reading this thread it should be pointed out that even if the timber was a structural floor joist (which is it not) it is usually acceptable to drill a hole up to 1/4 of the timber depth. Which in this case would be 50mm. Although it would need to be along the neutral axis, in a zone that is between span x 0.25 and span x 0.4 from the end of the joist and not closer to another hole than 3 x hole diameter. This is because most of the strength in a horizontal timber comes from the compression of the top and tension on the bottom.

 

[JimCrow]

its 1/4 the the depth of the joist not 1/3rd,

and one of these,
https://www.google.co.uk/search?q=h...w=1047&bih=504#tbm=isch&q=hole+saw+for+timber

 

[Phill Peck]

I can't help but picture a Venn diagram consisting of
A- those with structural understanding of timber joists
B-those who have not heard of a holesaw

With @Elthrin standing lonely in AnB

 

[Dan Robinson]

 

[Elthrin]

Quite right JimCrow 25% of the depth, I have corrected my comment so as not to spread misinformation.

I have a hole saw, I just don't have one that will go through 200mm of wood. typically they only go about 35mm deep. There does not seem to be such a thing a wood core drill bit for that size.

I have a feeling I am going to end up using a hole saw as deep as it will go, chisel out what is there and repeat.

 

[nickjb]

Go through the wood with a forstner bit. Not depth limited like a hole saw, as long as the shank is long enough. With a 50mm you should be able to get the chuck in as well so 200mm should be OK, if not you can buy shank extenders. Cheaper ones from ebay or toolstation are a bit rubbish but for one hole will probably be fine.

 

[Elthrin]

Thanks nickjb that is the name of the thing I need.

 

[Steelmasons]

A hole saw will go through any depth as long as hole is cleared after cutter depth has been reached.