Workshop Practice
Cross drilling jig
John Walker
Article from Gazette Volume 20 number 1 - Nov 2016
There are times when I need to drill a small – 0.6mm – hole through a piece of brass rod 1.5mm diameter. One example is the tap on a steam heating pipe – why don’t I use one of the many excellent castings available instead of making my own? – because none of them seem to have sufficient ‘tail’ for secure fixing. Also, I prefer to fix them and the vacuum pipes after painting which makes final detailing of the buffer beam easier. A longer tail can be run along the underside of the body where it doesn’t conflict with anything else and fixed with solder or epoxy. For tenders I often run the tail vertically behind the buffer beam and up the inside of the tank and secure with a blob of epoxy.
Now, back to drilling holes. The jig is a short piece of ¼ inch or similar size brass rod drilled centrally to accept the rod you want to drill – this hole needs to be a snug fit on the material – too tight and it may be difficult to withdraw after drilling – too slack and the hole will be off centre or the drill may jam and break. Brass rod may be 1/16 inch or 1.5 mm. diameter so make sure you know which size you have before you start.
The cross hole is drilled next – I assume that any serious modeller has a small drilling machine – by setting the rod horizontally in the machine vice I bring the drill down to slide over the end of the rod and adjust so that the 0.6mm drill crosses the hole centrally – this needs a good light and the eye looking directly at the hole – Fig. 1.
The 0.6mm drill is replaced by the smallest centre (Slocombe) drill and the hole started about 6-8 mm. from the end – it helps to file a small flat on the top of the rod to give the drill a starting point – Fig. 2.
The 0.6mm drill is now used to drill right through – very gently, a little at a time – as soon as it starts to squeak, withdraw and brush away the chippings and dust. It also helps to put a scrap piece of the 1.5mm rod in the hole – this guides the delicate drill and avoids breaking through and re-starting across the gap which are the points where it is most prone to breaking – Fig. 3.
If you use a short piece of the ¼ inch rod – say about an inch long – you could drill right through its length and cross drill other size holes – 0.7 – 0.8 or even 0.5mm, if you are feeling brave!
