✔ Predrill the large holes.
When the hole diameter is higher than 5-6 mm in steel the feed force necessary starts to exceed that which can be obtained with handheld drilling. More than 70% of the feed force is consumed at the chisel edge. If you predrill with smaller bit diameter than the final one you can reduce the feed force just as much. Very large holes can be predrilled in several stages.
✔ Locate the hole in the exact place.
When you start drilling, the bit easily slips out of position, specially if you are using bits with a chisel edge. Thereby, you can avoid it by using split-point or web thinning bits, marking the center with a center punch or using a drill that can be creep-started. You can also use templates, a helpful way when several holes are to be positioned in specific places in relation to one another.
✔ When drilling through two parts simultaneously, keep them fixed together.
This is very common when using handheld drills. For the large and heavy structure it may be a good idea to secure the parts together with a bolt or screw in the first hole before the other holes are drilled.
✔ Again about predrilling…
About 70% of the feed force is consumed in getting the chisel edge (the first bit part to be drilled) to work its way through the material. Consequently, as soon as the point has made its way through, the penetration process becomes much easier and the bit can pass through quickly, what means that it probably will not have time to cut the hole cleanly. And the bit jams. Avoid this problem by predrilling.
✔ Drilling deep holes.
When the lengh of the hole is 5x bigger than the bit diameter, the bit must be withdrawn at regular intervals for chip removal. This procedure must be repeated as frequently as the hole gets deeper. Dip the bit in oil or water to cool it.
✔ Get quality for your hole.
Basically, the quality is related to roundness/straightness, angular trueness and burrs on the back of the hole. You can get better quality holes by choosing the right type of drill
. It’s also important to have a perpendicular angle to the work surface to have a right-angled hole. You can also avoid burrs on the back of the hole by drilling against an underlay and making sure that the bit is sharp.
✔ Crosswise holes in shafts and pipes.
Mark up the hole with a center punch