Small drills run slowly are much more likely to break than if run faster. A high speed and light feed is required for small drills. Due regard must be given to the article being drilled, if the article is able to carry off the heat being generated quickly then the drill can be safely run much faster than if small articles are being drilled. Also when drilling these small articles they should be held by or rested on a metal surface, so as to help the radiation of heat. Again when drilling deep holes the speed should be reduced. Many drills are broken when just on the point of passing out of the drilled hole, this is due to a sudden movement forward, either through spring in the work, or too much pressure on the drill so forcing it through before the hole is properly finished. To avoid it use a piece of metal in line with the hole, even a piece of lead will do, and drill through into it, also make sure there is no looseness anywhere in the machine in line with the drill. Provided the drill is properly ground it is a sure sign that the feed is too great if the cutting edges chip off. See the article on Grinding Twist Drills, as bad grinding can cause a drill to wobble, to cut holes oversize or with rough sides, or to refuse to cut at all. Care should be taken that small drills never get so hot that the temper is likely to be affected.

Drilling Glass Or China

Difficulty is often found in hardening the drill point so that it will stand up against the china glaze, etc. Try heating the drill to a bright red heat and dipping the point into mercury, then into cold water. The drill should now be hard enough, and may require care not to break it. Not much mercury is needed. Camphor dissolved in turpentine makes a good drill lubricant ; also alum dissolved in acetic acid, dip the drill into this and so convey a drop to the spot to be drilled.