I’m in the process of shortening some cranks for my 8 year olds bike and have done some research on the correct drill bit for tapping in 9/16″ pedals.

It is recommended by Park Tools to use a 33/64″ (13.1mm) drill bit to open the hole.

Is there anyone out there who has used a 13mm metric UK drill bit to do the operation?

Thanks,

John

I doubt it will matter, if the hole is too wee just shoogle the bit around

That’s terrible advice. You’ll end up with a hole wider at the entrance and exit and probably bigger over all.

You can’t ‘shoogle’ 0.1mm with a power tool.

Run it through to 13mm and accept you’ll need to work more with a tap. Do not rush.

33/64s aint hard to get youll just need to hit up an engineering specialist not bnq.

I see them at £6.48 in my toolrunner catalogue

How do you plan on getting it paralel to the crank have you a drill press ?

Plenty of 13.1 drill bits on eBay for 7.99 delivered.

You can also get your left and right handed taps on the bay for about 17 quid, or the pair for 11 if you wait for delivery from HK.

Edit – you’ll need a big enough tap wrench too.

Make sure you thread each side correctly for the relevant pedal!

I’m doing something similar OP, I worked 33/64″ out as 13.096mm so rounded down and got the taps and a 13mm bit, when I actually get some spare time I’ll do a practice hole before the proper one just to be sure it works with a pedal…

13mm will be fine, your biggest worry should be keeping the tap perpendicular to the hole. And also getting the left/right on the correct cranks 😉

What cranks are you using? I’m planning on doing this for my daughter’s bike at some point.

Drills tend to drill oversized so I expect if you measure the a hole drilled with a 13mm it will be over. If you want to be correct drill (pillar drill) and ream it to 13.1 mm.

33/64 is the hole size required for the tap already has tollerance built in (and assumes your using an alu crank and not a steel crank otherwise youll be wanting a 17/32″ drill)

. a close fit clearance hole would be 37/64″ and a free fit hole would be 19/32″

If using a pillar drill i certainly wouldnt be bothering to ream out to get exactly 13.096 for tapping it out.

as swavis said there are bigger issues to worry about.

Yep used a Pillar Drill.

done it this weekend – homemade jig, nice and steady away – 13mm drill bit – correct pedal taps and wrench – I used 3 stage taps, 1st, 2nd and final to get the threads square – As for right hand and left hand thread on the correct crank arms, sorted that with the correct tools.

SRAM S600 powerspline cranks were used to do the job.

I’m going to try it out on Shimano Zee Cranks that I got for £23 – as the Hollow Tech II bottom bracket weighs so much less than square tapered and power spline BB’s

Cheers

John