Wednesday, March 11th, 2015
There are several small factors that can make it much easier or much harder to penetrate safe hardplate. Here are a few common problems, their symptoms, and their remedies.
The need for safety should also be highlighted at this juncture. The use of good quality safety goggles is important and leather safety gloves can often prevent the operator’s hands getting burned by very hot swarf or drill bits. When drilling smaller items, it is always a wise policy to ensure that the work is held securely while drilling, particularly when the work is thin or has sharp edges.
There may be instances where drilling is enhanced by the introduction of a suitable coolant/cutting fluid, while other materials such as Nimonic and Manganese Alloys should be cut dry. In order to use a safe drill bit with maximum pressure, a large supply of fluid is needed to keep the tip temperature to an acceptable level. Usually the resultant spillage and splashing is not tolerable in anything but a workshop environment, so you must drill dry. There are a few gel and spray fluids available and users may find some improvement by using one of these. The danger here is that the use of small quantities can sometimes cause rapid variations of temperature as the tip heats, and localized partial quenching occurs. This can result in thermal stress cracks developing in the tip and rapid deterioration of the drill bit. Also, some gels or sprays are prone to make unpleasant smoke.
Using the safe drill bit at too high a speed is usually evident when the safe bit will not bite and the tip quickly becomes burnt or dulled. You can use higher than normal speeds if you use a cutting fluid to draw excessive heat away from the cutting region. Using the safe drill bit at too low a speed will still cut, but you will find that your progress will probably be slow and exhausting. The best plan is to start with a slow speed and increase it slightly until you find the most efficient speed.
Too much pressure results in the safe bit tip overheating and quickly loosing its edge. Insufficient pressure will give little or no progress or it will cause the material being cut to burnish and glaze.
Usually when a safe bit has irregular or incorrect angles, the problem is due to using a wrong type of sharpening stone or an improperly set jig. The result is usually little or no cutting ability and rapid overheating. If an inspection of the tip prior to drilling failed to highlight this fault, lack of chippings should make the user aware that something is wrong. The remedy is to have the safe bit sharpened on the correct “green grit” or diamond wheel using a properly set jig to ensure correct and uniform angles. (Sometimes it is cheaper to buy a new safe bit.)
Drilling without a drill rig is often the prime cause of the fault. In this situation the tip will tend to skate around the surface. In addition to damage to the cutting edges, the drill flutes can become damaged above the tip and can add to the risk of breakage.