Drilling Holes in Rock

  In the development of the MICRO-BLASTER we learned a great deal about drilling small (5/16 inch diameter), deep (9 inch) holes in rock and masonry. Normal rotary drills even when equipped with carbide tipped masonry drill bits proved to be almost totally ineffective and are not recommended. Drills described by their manufacturers as "hammer drills" are usually only slightly more effective. From what we can gather these "hammer drills" utilize a mechanism which imparts a strong vibration to the drill bit when rotating.

This aids the progress of the hole drilling operation in hard rock only marginally. The most effective class of tools are known as "rotary hammers" and seem to be the best choice for efficiently drilling the type of holes required for the MICRO-BLASTER system. Within this class of tools, drills which are rated for drilling 3/4 to 1 inch diameter holes will perform quite well giving a good balance between cost and drilling speed. Drills rated for larger diameter holes may overheat the relatively small 5/16 inch bits required for the MICRO-BLASTER, causing premature failure of the bit when drilling particularly hard materials. Within this class of tools several drill shank (the end of the drill bit that connects to the drill) and chuck (the part of the drill that holds the drill bit) configurations are available.

The most commonly available style is known as SDS or SDS+. This shank/chuck configuration allows the bit to be rotated and yet free to move in response to the relatively heavy hammering action of the "rotary hammer" mechanism.SDS "rotary hammers" and bits are available from many large hardware outlets across the country (US). Most of the models we have seen in stores operate on 110 volt power and will need an accessory generator for use in remote areas.

There are also some rechargeable battery operated "rotary hammer" drills which eliminate the need for a generator. However they are usually several times more expensive than the 110 volt powered models. If your use requires extreme portability, i.e. equipment must be packed to the work site, these tools are highly recommended.Manufacturers of these battery operated tools that we have had good experiences with include: Hilti, Bosch, and Dewalt. The 36 volt TE6-A Hilti is our favorite, the Bosch Bulldog second and the Dewalt 24 volt model third in overall performance. As in most things the most expensive tool performed the best.

If you have a generator and rarely need to drill in locations remote to where you can easily transport it, the cheaper 110 volt "rotary hammer" drills are the the recommended way to go. These tools are as a rule just as effective as most battery operated models at up to 1/5th of the cost. Of course if all your drilling will be within 100 ft. of a 110 volt outlet all you will need is an appropriately sized extension cord and cheaper 110 volt "rotary hammer" drill.

Drilling Holes for MICRO-BLASTER

Regardless of what drill you use you will need to drill holes in the material you wish to crack as straight as possible. The tip of the MICRO-BLASTER actuator tube, which fits in the drilled hole is exactly 5/16 in in diameter. SDS carbide tipped drill bits, marked 5/16 inch, when new, will drill holes slightly larger than this. This extra clearance will allow for the slight unavoidable variances in straightness in the hole as it is drilled. As drill bits wear from use their diameter can decrease so it is important to use relatively new and sharp bits with the MICRO-BLASTING process. The manual supplied with the MICRO-BLASTER KIT goes into detail on this subject.

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