Opening up holes in joist

[pc1966]

A friend of mine is looking to have an electric shower fitted and has floorboards up already (mostly, long story). Anyway there is a run of 2.5mm T&E already following a sane route that the 10mm T&E for the shower could take, but the holes are just a bit bigger than 2.5mm and certainly not enough for both.

It seems like a bad idea to drill more holes in the beams, so I would prefer to open those holes out to around, say, 22-25mm to take both cables. Most auger or flat-blade drill bits assume no existing hole so the pilot can keep them centred, so I was wondering if anyone has good suggestions for doing opening such holes out in a sensibly controlled manner?

TL;DR drill options when existing hole is present in a wooden beam

 

[ipf]

They are not where they should be in the span, at least following UK guidance (the USA has a different figure for distance from end-support as 3*depth, not 0.25*span), but they have been like that since it was rewired in the 90s. But the beams are big and the holes, even if made larger, are a lot less than the max allowed.

My feeling is the least-worst option is opening one hole enough for the additional cable, but going to look at just how wide it would be needed to get the various T&E through without drama (can try-drill some scrap wood to see).

After all this lot mate, I'd be reaching for the wood saw, hammer and chisel for notching

 

[ferg]

FWIW I think the Dewalt triflute bits are garbage.
I have a lot of Dewalt gear that is great but the wood bits are absolute guff.
Bosch self feed spade bits are great as are Irwin triflute bits.

 

[nicebutdim]

FWIW I think the Dewalt triflute bits are garbage.
I have a lot of Dewalt gear that is great but the wood bits are absolute guff.
Bosch self feed spade bits are great as are Irwin triflute bits.

I'd noticed Dewalt's bits, but hadn't tried them. Armeg are good, although pricey and I hear mixed reports about their 'nail proof' version - not that I'll be trying them at the current price. Irwin are reltively cheap and last well if you can avoid nails.

 

[Vortigern]

You can sometime use a jigsaw quite safely when cutting away from the wire or maybe a multi tool with a small blade???

 

[pc1966]

FWIW I think the Dewalt triflute bits are garbage.
I have a lot of Dewalt gear that is great but the wood bits are absolute guff.
Bosch self feed spade bits are great as are Irwin triflute bits.

Ah, too late as I got on on my way in to work this morning (different work).

It reminds me of how much I hate working in homes, especially old homes with lath and plaster, etc. Yes, I know if is a valuable job and the bread & butter of most sparks, and would never look down on folks who do this all the time obviously, but I really don't want to be doing this!

But if I don't the friend will probably end up with the plumber doing it...

 

[pc1966]

You can sometime use a jigsaw quite safely when cutting away from the wire or maybe a multi tool with a small blade???

Notching is a possibility, but this friend of mine is the sort who might try putting in screws/nails to stop floorboards creaking, so I really don't want a 45A circuit just below them!

 

[Dustydazzler]

Small notch and Nail plate

 

[brianmoooore]

Notches!!!! Only if you have red/black VIR to wire it with.

 

[7029 dave]

If you do decide to make the existing holes bigger, hope you remove the cable and how easy will that be? additional joints etc.
Please say your not going to drill with the cable insitu

 

[pc1966]

If you do decide to make the existing holes bigger, hope you remove the cable and how easy will that be? additional joints etc.
Please say your not going to drill with the cable insitu

No, not trying that!

One of the cables needs partly moving/joining anyway as a wall socket needs moving, so I was thinking along the lines of just taking it the whole length (2-3m or so) and then bring it back along with the shower cable.

 

[davesparks]

Notches!!!! Only if you have red/black VIR to wire it with.

Whats wrong with notches? Sometimes it is necessary.

 

[ipf]

Whats wrong with notches? Sometimes it is necessary.

No chance....wood chisel's gone all rusty....

 

[nicebutdim]

If you do decide to make the existing holes bigger, hope you remove the cable and how easy will that be? additional joints etc.
Please say your not going to drill with the cable insitu

I'm fairly certain he isn't completely mad

 

[brianmoooore]

Whats wrong with notches? Sometimes it is necessary.

I've notched out hundreds of joists over the years, but only to fit copper pipes. Nail plates won't deter a determined DIYer.

 

[7029 dave]

I'm fairly certain he isn't completely mad

Lol just wanted to clarify