UKC

I need to drill some holds for T-nuts for my board. I have some 4 pronged T-nuts.

Am I correct in thinking that standard T-nuts are M10, that this will need a Ø13mm drill bit, and that a Brad point bit would be the best for the job?

All I have is an old wired drill that only goes up to around Ø9mm so I think it's time to invest in a new cordless combi drill. I have other Makita 18V tools so I think I'll be looking at something like the Makita DHP485Z 18V LXT Brushless Combi Drill. I think this uses standard drill bits so you aren't locked in to buying Makita specific bits?

I can't see many places selling Ø13mm drill bits which has me questioning whether I've made an error. Apologies for all the basic DIY questions!

12mm is fine.

13mm (or 12mm, 1/2", whatever) flat bit would fit in your current drill:

https://www.screwfix.com/p/flat-wood-bit-set-5-pcs/4139v

12mm as commented above.

corded is fine IMO

I use paddle bits and allow for 1 bit for every 2 sheets of ply. With the repetition the bit heats up, loses temper and then gets dull quick. Be aware of blow out as you drill through the other side, drill from the face side and ideally drill into a scrap on the other side. I also like to stack sheets, clamp them together and then drill them. It saves on time and you only have to draw layout on the top sheet.

Don't apologise for asking questions, its great that you are trying something new and want to learn! Have fun building!

Thanks for all the help everyone. It looks like 12mm is the way forward.

I used this one and it went through stacks of 4 boards with surprising ease: https://www.amazon.co.uk/gp/product/B00BJ3QMLI/ref=ppx_yo_dt_b_asin_title_o...

When I was drilling a lot of holds for a mini climbing wall I found the auger type of drill bits were a good option for speed plus neat finish. They went through 4 sheets of ply pretty quickly with minimal chipping -think it was a 12mm bit. 

Also lots of hammering to look forward to.

Enjoy..

Most corded drills might work but I don't think mine will. I inherited it from my Grandad, I'm in my mid-thirties and it predates me! It doesn't go wide enough to accept the 10mm bits that I already have. It's probably worth upgrading anyway, I'm sure I'll find plenty of other uses for a cordless drill and/or wider bits.

The board is already installed with lots of screw on holds but I've recently acquired some bolt on holds so I want to fill in some gaps rather than drilling a whole grid of empty ply. It would be a lot of effort to take the board down so I'll be (carefully) drilling with the board and existing holds in situ.

I'll be very aware of blow out as my board has an LED system so I'll need to make sure I don't risk punching through to any of the wiring.

Corded is fine, but variable speed is v helpful so you can start slow.  If the OP's corded drill is just on or off single speed - there's the requisite excuse to buy a shiny new one.

^ Apologies to the OP if I'm stating the bleedin obvious, but this bit bears repeating.

A flat bit will do nicely, but the 'exit' side of the hole can be messy if you're drilling right through into fresh air.  (This is a problem with any kind of bit to some extent.)  So drill from the 'good' side of the board, and have a sacrificial noggin of wood pressed against the back side so you drill through the board and part way into that to prevent any 'tear out' on the back of the board.

You may want to consider the screw type t-nuts rather than the 4 prongs then if you are doing it in situ. You might get a lot of bouncing going on if you are not hammering onto a solid surface.

I used a 13mm auger bit. The auger is good because it maks no damage on the face side of the board.

Larger bits typically have a narrower or 6.35mm hex shank so plenty will fit in your antique drill no problem. (The ones already linked above have hex shank)

Being that old, it will be an imperial drill and therefore won't work with metric drill bits...

If the flex is too much to hammer them fully home, then an option would be to partially insert them and then clinch them fully home by tightening a hold on them.

great recommendation, I've never come across mini augers, they look super useful!

Thanks

Maybe not! When I asked a similar question I got two separate PMs advising me to just use screws and both linking to these washers:

https://www.accu.co.uk/solid-countersunk-washers/24503-HKW-M6-A4

This has worked of for me on a 25 degree board and a 75kg climber. I’ve used additions screws with most holds (new resin holds come with these already but you can drill older holds with a masonry bit). It’s a lot easier than T nutting.

Or have someone hold a sledge hammer against the other side of the board to the nut being hammered.

OP: Might be worth drilling the holds or screws instead, depends how many you have I guess. You can get drill+countersink all in one bits to speed the job up.

jk

When I did my board, initially 2.4 x 3.3m with hammer-in T-nuts on a 100x100mm grid, I just hammered them in with the boards on the floor before mounting them on the structure. I don't remember it being difficult or taking more than 1 - 1.5hrs. I did wear ear defenders though! I had a couple of 'spinning failures' though over the years but it was a lot quicker than using the screw in equivalent T-nuts.

My initial reaction was to post asking if the chuck on the old drill was compatible with either Whitworth mm or BSF mm. But out of concern that OP thinks any of this is serious, I have to point out all the mm/imperial twaddle here is humour (this always ruins a joke, sorry)

In reply to Ram MkiV:

^^^ The above!
Why consume more and more "stuff" - if the old drill still works? reduce, reuse, recycle etc etc

I had realised that this was to be filed along with the left handed hammer.

I've decided to go this route until I find a job that the old drill isn't up to. I hadn't realised that most larger bits had hex shanks (shows how little I know).

12mm is the hole size, and as others have said a couple of 12 mm spade bits will do the job and will fit any standard chuck. Wear ear defenders when you knock the r-nuts in. The next level up is to use a plunge router with a 12mm cutter and stack your ply sheets to do several sheets in one go. I’ve never had any problems with t-nuts spinning as long as they’re inserted squarely into clean holes. It’s also possible with the 4 prong tnuts to obliquely drive in a wood screw to stop them spinning and being pushed out.

Wrt why bother with tnuts in the first place? I’m just about to move and will build a new home wall there. It’s really down to personal taste and how much you want to spend. I’ve mostly got wooden screw on holds, which are easier on the skin, and tend to take more training effort because they have a smooth surface. Again really down to you

Large twist drills with small shanks are often sold as 'blacksmith's drills'. 

Jk