Drill bit, spade bit, or hole saw?

Spade bit with some sort of jig to hold it straight

I like the Bosch Expert Wood Drilling Spade Bit. It has a threaded end so pulls the bit through the wood.

Another vote for the Bosch spade bits. Best I’ve ever used.

Long series forstner bit.

Forstner bit

If you need the matching holes to be exactly opposite these may help.

https://www.amazon.co.uk/Centers-Alignment-Points-Accurately-Aligning/dp/B08R9PVTFR/

The holes also need to be straight,

so long as the chuck on your drill will take it - a 13mm Hss drill will give a more reliably straight, cleaner hole than a spade bit.

The only drawback with the Bosch spades is the thread on the top is fairly course This means they cut through faster , but faster isnt always better. ie If its going wrong , you will be further on till you realise.
If you use a long spade bit . get an assistant to eyeball the vertical drop from the side. You can do the horizontal ,or visa versa . Should keep things squarer that way .Be fine , unless they are oak doors

Screwfix sell Blacksmiths drill bits that are tapered , so will fit a smaller chuck , but go to 18mm iirc . These will give you a nice hole

As above, I’d favour a regular drill bit over a spade/auger/Forstner/holesaw, since regular drills are always easier to control in a hand drill. And 13mm happens to be exactly the max size of common hand drill chucks.

But I wouldn’t use a regular hss bit, I’d use a Brad point bit (aka lip and spur) because these are better suited for wood than a regular hss twist drill. Brad bits have a point to aid starting without wandering.

Also, you say “it has to be 13mm”. Well, is there much problem with going a bit bigger to allow some tolerance?

This bit would suit, 14mm dia Brad point (weirdly screwfix don’t have 13mm but I’m sure you can find one if you want) and has a reduced shank to fit in a standard drill with 13mm chuck :

14mm Brad point

Edit: these are the blacksmith bits singletrackmind mentions with the reduced shank.

Edit again: no they’re not lol. I thought blacksmith bit meant reduced shank, which it usually does, but if you look for blacksmith bit on screwfix they are hss twist drills with reduced shank. You definitely want the Brad point bit I’ve linked for wood work IMO.

Probably a daft question, but have you checked that the frames are actually 70 mm deep?

I'd use a brad point (aka wood) drill bit.
The point means they are quite good at drilling into wood in a controlled and tidy fashion, unlike a flat bit.

If you wanted to go old school, a auger bit in an old school manual brace is a good option.

Standard HSS can wander, as can a spade bit. As above a brad point, or even auger. Both are designed not to wander.

These are handy.

I wouldn't drill anything with one of those Bosch bits if I wanted something with a fixed depth and good angle. They're fine for cutting holes for conduit and cable in studwork and joists but absolutely not for anything more than first fix work. They rip through wood like it's not there and you'll be out the other side before you know it.

Armeg Wood Beaver FTW

I'd use an auger bit. Old school or powered.

You get to line everything up and correct the angle but checking the nickers draw a circle then you re locked in

6 holes, try 6 different drills and report back.

As @mc says, a brad point wood bit is the badger.

Threaded augers can be a bit of a bugger as they tend to pull your bit in aggressively and not necessarily straight.

A spade bit is fairly difficult to keep straight as the shaft of the bit is so much smaller than the hole and therefore doesn't self-guide at all.

If I'm drilling freehand and it needs to be straight, I'll often pre drill a block of wood on the pillar drill and use that pressed up against the work to get it started nice and plumb. Can also work well as a depth stop.
But then, you might not have a pillar drill.

Another little aid to straight drilling is to get the hole started using a similar technique to below.

If you can get it started like that, then carry on freehand you should be good.

Nice simple idea that kayac23, to quote Burglar Bill "I'm having that"

Another little aid to straight drilling is to get the hole started using a similar technique to below.

The quickest - easiest way to make those little drill guides - if you're not someone who has nice right angles scraps of wood kicking about - is out of lego (if you're someone who has plenty of that kicking about)

I was suggesting a regular HSS over a brad point simply on the basis that its more likely to a be a drill bit that someone already has - that they've got in their old tool box or can blag from a neighbour, and something that would find a larger variety of uses in future. Its only 6 holes in a shed door.

The quickest – easiest way to make those little drill guides – if you’re not someone who has nice right angles scraps of wood kicking about – is out of lego

😊👏

Cheers all. Looks like a brad point is the way to go, I just need to check what girth of shaft my chuck can take, ahem.

Top secret tip: Spade bits are for impact drivers, and leave a much cleaner hole when used with one.

I would suggest a brad point bit, but in reality would probably reach for the spade bit because ive already got it.

How do you use a spade bit with an impact driver? There's no chuck?

Another tip is to use centre punch or similar to put a little 'divot' where you want to drill, it'll help stop the bit from wandering

How do you use a spade bit with an impact driver? There’s no chuck?

A lot of spade bits come with a hex shank.

Take steps to stop breakout on reverse side