Manky Monkey Motors

How do you know what size drill bit to use  for the tap size or bolt size you want to use? and does the rule apply to metric and imperial a like?

Ive got a Helicoil guide and a Tap & die guide that tell me what size goes with what,I will dig it out tomorrow...Voodoo....

Cheers Voodoo  ;D

You need the Zeus book, a must have  ;D

http://www.amazon.co.uk/Precision-Reference-Drawing-Toolroom-Workshop/dp/B0000CLZUO

Drill 5mm for a 6mm tap
Drill 6.5mm for a 8mm tap
Drill 8.5mm for a 10mm tap
Drill 10.5mm for a 12mm tap 

These might help..............

http://www.engineering-supplies.com/info/15/tapping-drill-sizes/


http://www.physics.ncsu.edu/pearl/Tap_Drill_Chart.html

maybe some that knows how too could put this at the top of the tech section  sort of a ,sticky, subject thing  ;) ;)


i,d try  but i aint  ,puter, clever :D ;D

I generally use a Zeus book, but a "cheerful" method,which is usually accurate enough for most applications, is to choose a twist drill that just passes through the nut of the size to be tapped! a simple method shown to me as an apprentice over 50 years ago, and handy when on site and miles fr om the workshop and reference books!! Morrag

Thats a handy tip Morrag, i will remember that thanks.

Just had a look at the charts oily bike has put on here and i think they could be a big help to every one.Could someone put them on our Trike Bike and car  help section  "Motors". I aint very good on the computer and dont know how to do it. :'(

That saves me scanning my charts then lol...Voodoo.....

yeah cheers though voodoo,this might help others too  ;D

Best thing I ever spent out on is a quality Tap & die set and a full Heli-coil set...they aint cheap but I would never be without a set now...Voodoo...

The tap gives you the info. A normal 6mm thread has a 1mm pitch so it needs a hole 1mm smaller.
A 12mm thread has a 1.25mm pitch
The pitch is marked on the tap
Fine threads and wierd thread sizes have different holes need

Never a truer word has been spoken, it truly is the engineers bible, not just for drilling and tapping but all sorts of formulae, tolerances etc etc.

Agree, the book for all that stuff.

Going off tack a wee bit, did you know we can thank good old Mr Whitworth for us all having standard threads (those with old motors will be familiar with whitworth theads), as it was he that decided that it was a good idea to standardise.

Before him, the idea of going to a store and buying a fastener to match one you had simply didn't exist, you had to make one that fitted what you had.

Some interesting reading:

http://en.wikipedia.org/wiki/British_Standard_Whitworth

http://en.wikipedia.org/wiki/Joseph_Whitworth

I find I can make any nut fit any bolt if I bash it hard enough wiv an 'ammer.

Drill the nut out and weld it ;)
I knew a bloke who was laying a steel conduit for a petrol pump and couldn't get the die on the pipe (already in ground) so he used a holesaw to cut the threads out of the couple an araldited it in place. Ruff as guts

Mr Whitworth also made a very accurate rifle with a hexagonal bore/bullet. Queen Victoria tried it out at the great exhibition I believe and was very impressed. Idiots at the War Department went for the cheaper, less accurate and less reliable "Enfield" rifle.  ;D ;D ;D ;D