drill size for tapping 10BA hole?

[jon price]

I've looked at the charts you can find online, and they are far too complex for me to understand. Can anyone tell me what size drill bit to use to drill the hole prior to using a 10BA taper tap into paper reinforced phenolic (like Tufnol) to take brass screws?

[David B]

1.4mm. Drill No. 54

[jon price]

Excellent. Thanks

[Terry Bendall]

And for those who may need them, and don't like complicate charts, here are the tapping and clearance drills in mm for all the BA sizes

Size Tapping Clearance

OBA 5.1 6.1
1BA 4.5 5.4
2BA 4.0 4.8
3BA 3.4 4.2
4BA 3.0 3.7
5BA 2.65 3.3
6BA 2.3 2.9
7BA 2.05 2.6
8BA 1.8 2.25
9BA 1.55 1.95
10BA 1.4 1.75
11BA 1.2 1.6
12BA 1.05 1.4
13BA 0.98 1.3
14BA 0.8 1.1
15BA 0.7 0.98
16BA 0.6 0.88

In practice, where a tapping size is given to 0.05mm or less, it is normally possible to use a slightly larger size, e.g. 1.1mm rather than 1.05mm for 12BA tapping and 2.3mm rather than 2.25mm for 8BA tapping. On thin material going a little smaller, e.g. 1.0mm rather than 1.05mm is sometimes useful.

In 4mm scale I rarely need anything larger than 6BA and I have not used the odd number sizes, apart from 5BA for many years.

Terry Bendall

[Lindsay G]

Very useful info, Terry.

To complete the picture, what diameters should rod be turned down to before getting going with the dies? Altho', like many, I only have the even numbered taps/dies.

Lindsay

[Alan Turner]

Very useful info, Terry.

To complete the picture, what diameters should rod be turned down to before getting going with the dies? Altho', like many, I only have the even numbered taps/dies.

Lindsay

0- 6.0 mm
1 - 5.3
2 - 4.7
3 - 4.1
4 - 3.6
5 - 3.2
6 - 2.8
7 - 2.5
8 - 2.2
9 - 1.9
10 - 1.7
11 - 1.5
12 - 1.3
13 - 1.2
14 - 1.0
15 - 0.9
16 - 0.79

regards

Alan

[Terry Bendall]

what diameters should rod be turned down to before getting going with the dies?

Alan has provided the answer to Lindsay's question but a littler explanation may be helpful to some.

The size of a bolt, or screw is given by the diameter over the top of the thread. If you want to thread a turned down part then the diameter of the part to be threaded has to be the same as the screw size since the thread is cut into the bar. A thread in a hole is cut into the side of the hole so the tapping size hole is always smaller than the size of the thread.


Terry Bendall

[Lindsay G]

Thanks Terry and Alan for this info, it will all now be transferred to the lid of the tap and die box to save me having brain-ache and Googling each time I come to use the things!

Lindsay

[grovenor-2685]

Of course we do have this in the Digests, http://www.scalefour.org/members/digests/dl.php?f=10-8-2.pdf
which you can keep at the workbench.
Regards
Keith

[Terry Bendall]

Of course we do have this in the Digests

Yes we do Keith and it is certainly useful but in my view it is probably too complicate for those new to the hobby. Small booklets that give tapping and clearance sizes for screw threads are also useful but again often include information that the majority of railway modellers will not need.

Terry Bendall