Advice drilling 32mm holes in 80mm joists

[joncooper27]

Hi
I have to drill lots of holes in joists 32mm diameter for copper pipes. I will be drilling from underneath as the ceiling is not fitted but the floor is.
How and with what can anyone recommend?
I have about 100 holes to drill

 

[Wilson joinery]

Hi Jon

A 32mm flat wood bit should do the trick. I guess it doesn’t have to be neat (there will be breakout where the bit exits).

Cheers
Pete

 

[Jake]

Max permissible diameter of holes anywhere in span is 25% of depth of joist so this doesn't work.

 

[ChaiLatte]

What size pipes? A 32mm hole suits a 28mm pipe, which is unusual in a domestic situation. A 32mm hole is excessive for a 22mm and 15mm pipe. The smaller the hole, the less material has to be removed, the less effort and time on your part. Buying two different sizes of drill bit over more than 100 holes will have a time and labour benefit that exceeds the tool cost.

Flat wood bits are good because you can cut the shank down if space is limited, but do need to be pressed on to get them to bite. They need relatively high speed to work.

https://www.screwfix.com/p/erbauer-hex-shank-flat-wood-drill-bit-32mm-x-152mm/422PH

An auger-type bit will pull itself into the hole, so is semi-self-feeding. However, to have a controlled feed, they are better spun a little slower than a flat bit. That means a high torque, low RPM machine.

https://www.screwfix.com/p/armeg-wo...flute-auger-wood-drill-bit-32mm-x-165mm/91676

https://www.cef.co.uk/catalogue/products/615703-32mmx100mm-short-auger-drill-bit

What is the clear space from face of joist to face of adjacent joist? Something like 400mm - 50mm = 350mm? Your motive power plus drill bit needs to have an overall length smaller than this.

Use a laser or stringline to mark the line of the holes and then a combination square to mark the height of the holes. Having all the holes aligned makes fitting the pipe less stressful.

 

[Jake]

I think you'd be better lowering the ceiling with battens (could combine with a notch of up to 10mm, so 25mm roofing batten could work). A lot simpler to get the pipes up then than feeding them through 100 holes.

 

[ChaiLatte]

Max permissible diameter of holes anywhere in span is 25% of depth of joist so this doesn't work.

Is it possible that the 80mm is the width of the joist?

Given he says it has a floor above and ceiling below, an 80mm deep joist does not seem practicable.

 

[Jake]

Is it possible that the 80mm is the width of the joist?

Given he says it has a floor above and ceiling below, an 80mm deep joist does not seem practicable.

Oh I suppose so, hadn't considered that.

 

[joncooper27]

The depth of the joists are 250mm x 80mm thick sorry did not make it clear. The joists are @ 400 ctrs
I have plenty of tolerance with hole diameter.
I was just concerned threading the pipe through if the tolerance was to tight

 

[Jake]

The wood beaver type will make for much quicker going compared to a flat bit. I think they are about 150mm so that doesn't leave a great deal for the drill (even allowing for some in the chuck) unless it's in a right angle chuck or drill. That said, if you can feed the pipe in later, you can also feed a longer auger in once you've done a few holes (as long as your drill has the power to cope with the extra friction).

 

[Spectric]

How are you going to feed copper pipe through the holes when the joist are at 400mm spacing and there is a floor above ?

@Jake 's idea is much better .