In directional drilling, blade choice will make or break your success straight out of the gate. Of course, your blade’s bolt pattern is dictated by the drill rig you’ll be attaching it to, but there’s more to selecting the right blade for your job. Here’s what you need to know.
The type of ground you’ll be drilling is the most important part of determining the directional drilling tools you’ll need. Different tools are carefully engineered with specific features to address the challenges of various materials. Using the wrong tool might get the job done–but at a cost to your time, equipment and sanity.
Hard and compact– For dense, compact soils, use a tool with a point that will help with penetration as you change direction. Because you’re applying a forward push with no simultaneous rotary cutting action as you turn, a tool with a steep taper will help puncture the soil during directional pushes. Blades with conical carbides are best, since these pointy teeth are excellent at fracturing hard materials.
Cobble– A tapered tool like the above is also ideal for cobble-like conditions if you want to stay with a typical bolt-on blade (in place of a specialty bit). The bit’s steep point will help it wiggle through your bore, displacing the cobble as you maintain steering capability. For cobble or gravel conditions, your carbides should be dome-shaped. You’re not trying to gouge or shatter the material. Instead, the carbides work to displace the small rocks, preserving the life of your blade.
Soft ground conditions–In softer conditions like sand, clay and dirt, avoid bits with a significant taper because they won’t supply sufficient surface area to facilitate your drill’s directional changes. In soft conditions, you need surface area to push against in order to achieve a controlled change in direction. The force of the ground against top of the blade is what causes the blade to steer. The less surface area you have, the easier it is to push–but there is less force available against which the blade can interact. In these scenarios, you need a bit or blade with more surface area or a wider nose.
In soft, non-abrasive conditions (ex. clay), you can get away with fewer carbides and less hardfacing. Blades with less protection will be less expensive, but will likely wear out faster. Ultimately, it’s a trade-off: pay up front for a longer-lasting blade, or replace your blades more often.
For instances of direct pullback, you’ll want to choose a blade that will drill a hole that is slightly bigger than the pipe you’ll be pulling. Just like when backreaming, your backreamer should measure 1.5x the diameter of the pipe or cable you’ll be pulling. The same logic applies to your blade during direct pullback, although for shorter bores you may be able to get away with less clearance.
Some products have features that have been specially designed to optimize a direct pullback. Melfred Borzall engineers have integrated a hole for your pullback device or swivel. Our bits and blades also feature a keyway that allows you to attach a Quick Swivel or Quick Link to the blade, while holding everything in line with the center of rotation. By creating this rigid connection, you protect from the chance of breakage or getting stuck in hole.
During direct pullback, make sure there are plenty of carbide cutters–or at least sufficient hardfacing protection–along the edges of your blade. Since you’re pulling that blade back though the hole, you’re exposing your directional drilling tools to twice as much wear.
Remember, if you try to use a blade too long, it may still be cutting fine up front but the back of the blade can get worn down. This hidden wear can become costly. When the back of the blade is spent or the main cutters have worn significantly, the blade’s diameter can become reduced to about the same diameter as your transmitter housing, so your housing will see greater wear and tear. Ensuring that your blade diameter is sufficiently wider than your transmitter housing will protect you from having to replace your transmitter housing, which is a significantly more expensive tool than a blade.
Choosing the right blade before you begin drilling will save you the headache and added expense of lost time or broken or insufficient equipment. If you’ve got questions about which blade would be best for your upcoming job, give us a call. Tell us more about your job’s specifics and we’ll let you know which blade would be best.