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📅 Mon February 04, 2013 - Midwest Edition
Randy Stevens - SPECIAL TO CEG
Pneumatic concrete dowel drills have one purpose — to drill holes. While their intended use is easy to recognize, operation of this equipment isn’t quite so simple. In fact, it’s a bit of a science. That’s not to say they’re difficult to operate. But there are certain best practices and processes to keep in mind for proper drill operation, whether it’s an on-grade, slab-rider or equipment-mounted model. Operators who adopt these guidelines and implement them on every job are rewarded with better performance from the machine and fewer hassles overall.
First Things First
Before even getting the drill close to a concrete slab, a few simple preparations are needed. A pneumatic dowel drill virtually comes out of a box, poised to go to work; all it takes to ready it for a job is air, a drill bit and a couple simple steps. Specific instructions vary with each make and model, so follow the exact recommendations in the owner’s manual. Generally speaking, the basic items begin with attaching and securing the air hose from the compressor to the drill. Next, install the drill bits. When doing so, it’s necessary to have the correct bit guide bushing to match the bit. This centralizes the bit and keeps it from moving around too much. The bit also must be the proper chuck size for the drill. Adjust the drill spacing and height, level the drill and set the drilling depth.
Finally, be sure to start with the proper lubricating oil in the oiler. Most manufacturers recommend rock drill oil, as it’s heavy and thick enough to run this large of a piece of equipment. Some operators may try to use pneumatic tool oil or even automatic transmission fluid. These types of lubricants are much lighter and almost a watery consistency. While ideal for smaller tools, like impact wrenches, these lubricants often won’t stand up to the demands of a large dowel drill.
After these basic preparations, a dowel drill is almost ready to begin its job. Prior to any actual drilling, every operator should know the basics of proper use to ensure a smooth process and end result. Following a few guidelines will result in projects that are completed efficiently, safely and without equipment failure whether they’re new pours or full-depth repairs.
Most highway paving, airport repair and smaller residential roadwork projects have one thing in common: deadlines. Every piece of equipment must perform at its maximum efficiency level so the company can keep up with strict timelines and avoid penalties.
Setting a drill to the proper feed pressure is the first step to optimal drilling. There is a common — and incorrect — belief that increasing the feed pressure will increase the drilling speed and efficiency, but that’s simply not true. Finding the proper feed pressure is the best way to ensure maximum efficiency, and also to prevent unnecessary damage to drill bits and the drill itself. This greatly minimizes downtime for replacements, as well as costs for new bits or more significant repairs to the drill.
Whether using an on-grade, slab-rider or equipment-mounted drill, each has virtually the same process for setting and adjusting feed pressure. Feed pressure varies based on the drill and application, so there’s not a specific setting that’s going to work for all scenarios. The best approach is to set a logical starting point and then adjust as needed based on the results. Most manufacturers recommend a starting point between 18 to 25 psi for horizontal drilling applications. From there, the operator simply needs to watch the machine’s performance and adjust if necessary.
For example, if the drill is “bouncing” on the concrete’s surface rather than drilling into it, the pressure is too weak and the operator needs to increase it. Conversely, if the pressure is too great, the bit’s rotation will slow down or even stop. In this case, adjust the pressure down until normal rotation resumes. Most drills have an easily adjustable regulator knob that simply needs to be turned one way or the other to adjust pressure up or down.
On job sites with multi-gang drills, it’s recommended to go through this process one drill at a time. After proper adjustments have been made to each individual drill, they can be run simultaneously. However, after they’re all turned on simultaneously for the first time, it’s also the first time they’re all being run off the same air compressor, so slight adjustment may be needed to be sure they’re all still receiving adequate pressure.
Some on-grade and slab-rider drills can be converted to vertical drilling and there also are specific models designed just for this application. In the case of vertical drilling, the same process can be used with a minor adjustment. Feed pressure should be reduced anywhere from about 5 to 9 psi from the start, then adjusted up only. This is a common safety precaution because, if the pressure is set too high, the drill can tip over.
Keep in mind the two factors that affect ideal feed pressure before the bit ever meets the concrete: drill bit size and the hardness of concrete. It’s important to remember this when the drill is moved from one job site to the next. What worked for one airport lane addition may not be ideal for another one in a different setting. Again, it all goes back to monitoring performance and adjusting pressure as needed.
Another key to achieving optimal operation and minimal stress on the drill is a relatively simple concept: every drilling application should be approached in a series of strategic steps.
Keeping Things in Order
Imagine a homebuilding project. The only way to succeed is to follow a proper series of steps. Pour the foundation, put the framing in place, put up the drywall and, finally, install the fixtures. Mess with the sequence and the project won’t make it very far. Similarly, there’s a proper sequence for before and after drilling. Following it prevents damage to the drill and components and makes a successful project more likely.
Spawling is a great example of an issue one can avoid with proper pre- and post-drilling procedures. This common problem results in excess concrete chipping away from the hole area. While some spawling is natural in a concrete drilling application, following the proper sequence will keep it to a minimum and is the best way to avoid any issues with inspectors.
In addition, both the pre- and post-hole techniques help to prevent dry-firing, a situation in which the drill is in operation but there’s no pressure on the bit. Dry-firing adds unnecessary stress to the drill and can damage its trunnion bolts. Every bit has a latch, which is held in place by a trunnion bolt. The stress dry-firing places on the drill can eventually cause the bolt to break. With proper operation, a trunnion bolt can last the entire lifetime of the drill. At around $80 apiece, it isn’t a part most operators want to replace frequently, if ever.
Whether it’s for a single hole or set of holes, the first step is to properly position the drill along the designated area of a slab where holes are to be drilled. Next, feed the drill. Place it against the concrete and move the feed control valve to the “In” position. When the bits make initial contact with the concrete, place the main power switch in the “On” position and the drill will begin operating.
After the drill has reached its desired depth, it’s crucial to turn it off immediately to prevent dry-firing. Then, there’s a proper removal sequence to follow as well. Prior to taking the drill out of the hole, stop the drill by moving the main power switch to the “Off” position. Do the same for the feed control valve and that will cause the drill to retract. Occasionally, the drill bit can become stuck in the hole and make it difficult or impossible to retract the drill. If that’s the case, simply turn on the power valve. This will allow the bit to rotate enough that it should easily begin to retract. At that point, shut off the valve. If a drill has an auto align switch, it’s wise to place it in the “Up” position before fully pulling it away to move to the next location. This slightly raises the drill away from the concrete. When the drill has been moved and placed in its next location, move the auto align switch to the “Down” position and repeat the sequence.
Some operators neglect to turn off the drill before removing it from the hole and others even leave it running when moving to a new location. While it’s tempting to skip the proper steps in an effort to save time, it’s not safe and will end up causing more headaches.
Safety is one area on the job site where there’s no room for compromise. As with any major piece of machinery, dowel drills have their own set of safety guidelines that everyone on site needs to follow.
Dowel drilling isn’t a dangerous process. However, as with any piece of equipment, negligent operation or a complete disregard for safe practices can create serious hazards. Just like ignoring proper operational sequences, ignoring safe operation practices may put more than just the operator in jeopardy; it also can lead to a damaged drill or component.
Begin with the basics, proper work attire. Workers should wear earplugs to prevent damage from drill and air compressor noise. Debris flies during drilling, so the operator and other workers on the site must wear safety glasses and hardhats, as well.
Concrete dust is often emitted during the process too, so dust masks are a must-have for all on site workers. But concrete dust can pose other risks too. If large amounts are emitted, the dust can cloud a site and create a low-visibility environment for workers or, worse, for nearby live traffic. To help minimize dust emissions, many companies offer pneumatic drills with dust suppression kits or dust collection systems. Dust suppression kits include a spray nozzle, which attaches to each drill system and sprays water on the bit as it’s drilling. A dust collection system runs on the same compressor as the drill and vacuums dust as it’s emitted. The system’s dust collection head typically mounts to the end of the bit guide, where the bit penetrates the concrete. The vacuum draws out dust straight from the hole and into the collection bag. Both systems keep airborne dust and related hazards to a minimum.
A few areas of the drill pose specific danger to operators. Every drill has pinch points where fingers, hands or limbs can become caught. A primary example is the carriage assembly. Keep clear of the carriage assembly to avoid being caught between the carriage and frame. When moving a drill, be sure the carriage lock is set to prevent the assembly from sliding onto fingers and hands.
Furthermore, improperly moving a drill can cause operator strain or a serious accident. When moving a drill on the ground, operators should use the unit’s designated handles. If the drill is lifted improperly, it could cause a strained back or other muscle and joint problems. If a drill needs to be moved a greater distance, a lifting device might be necessary. In this case, use a properly weight-rated strap or chain and attach it to the drill’s lifting bale. Be sure the carriage lock is in place.
Compressed air is required to run a pneumatic drill and the great pressure can pose safety issues. The operator should monitor the air compressor’s gauge to be sure pressure doesn’t inch up too high. If the pressure is too high, it can damage the drill. This may void the warranty altogether, but even more detrimental is the lost productivity as a result of downtime. Additionally, before moving, disconnecting the air hose or any parts or disassembling the unit, the operator must first shut off the air supply and bleed off any air in the system. Taking just a few minutes to do so will help eliminate potential injuries.
One final note to ensure efficient operation and long drill life is perhaps the simplest of all — keep the drills clean. At the end of each workday, use the air compressor to blow off all dust and debris from the drills. While it doesn’t seem like much, it can pay off greatly. Doing so prevents clogging issues and excessive dust build-up. In the event of rain, any dust accumulated will quickly harden to concrete when it dries. If choosing to pressure wash the drills post-operation, be sure to dry thoroughly to prevent any potential concrete accumulation.
No matter the project size, timeline or logistics, the need for correct drill operation is one component of a job that’s always a constant. Proper operation isn’t difficult or complicated, it simply boils down to a few best practices. The small investment of time and thought pays back large dividends in job site safety and productivity. And, ultimately, the result is a piece of equipment that costs less to own and offers more years of reliable service.