Backreamers are the workhorse of every HDD drilling operation. As
HDD tooling experts, we see too many drillers make the mistake of trying to adapt a single reamer to every job or ground type. The fluted reamer that comes with the rig is great–under certain conditions. However, when using the default reamer in situations where a specialized reamer would increase production, you’ll lose time… or even a tool.
At best, picking the wrong backreamer can make your drilling proceed slowly and drag your productivity way down. At worst, you can lose your reamer downhole, forcing you to retrieve it or even abandon the hole altogether and start over. Also, picking a reamer that pulls back too fast can cause road humping…and you’re on the hook to repair it. Equally, choosing a reamer that goes too slow and you’ll get cratering with similar profit-eating implications.
All these scenarios eat up time and stall your progress. Broken backreamers require replacement of the original reamer and an investment in a reamer that is better suited for the job. Add on extra for the rushed air freight to get the reamer to your jobsite as fast as possible. That’s a lot of cash that you could have saved if you had the right reamer in the first place.
Before you decide which reamer you need for the job, think about these factors:
With all of the different types of reamers, knowing the type of material you expect to encounter before you drill your pilot is optimal. If you’re in ground that is unstable or sticky (like clay), you need a reamer with excellent mixing action and enough fluid pressure to make sure the material doesn’t ball up or leave big chunks behind in the hole. For unstable conditions like sand that face the risk of collapse, you need to have an efficient mixing action that keeps the cuttings and the drilling fluid mixed together to support the borehole wall, and not allow the sand to collect on the bottom of the hole.
The type of cutting action you’ll need also depends on your ground conditions. Shale and soft limestone require backreamers with more cutters for fracturing material, then grinding it up. Softer ground like clay or sand requires fewer cutters or you risk balling up. Harder conditions like cobble or river rock mean you don’t need to break up baseball-sized cobble as much as you just need to push it out of the way, so you need reamers with a gradual, tapered body that help push the rocks aside. This is where a solid, tapered body reamer like the basic fluted or stacked plate reamer performs best. Finally, solid rock conditions need cutting action that pulverizes the rock as it’s spinning, making small rock chips that are easier to pump out of the hole.
Using an undersized tool (not the cutting diameter but the shaft it’s built on) on too powerful of a drill rig can damage the backreamer and stop your job. Choose a backreamer that is strong enough for the size of the rig you’re using. Don’t use a 20,000 lb. drill tool on a rig with 40- or 60,000 lbs. of pullback. If you must mix and match, it’s better to use a big rig reamer on a smaller rig than the opposite.
Always be sure you have plenty of drill fluid flow when backreaming. The pressure isn’t as important as making sure you have enough volume passing through the shaft. If you’re not using enough fluid, you’re not going to be able to get all the cuttings out. Pulling back too quickly without enough fluid to carry the cuttings out of your hole can just push the material forward with the reamer, causing it to get stuck or create a speed bump. If you’re using a reamer meant for a small rig on a big rig, the fluid holes in the reamer could be too small—not allowing enough flow to carry your cuttings out. The opposite applies, too. Using a big reamer (with big fluid holes) on a small rig means not enough pressure, limiting your flow and causing the whole thing to ball up.
Choosing the right backreamer before you begin a job saves time, saves stress and saves money. If you have questions about which types of reamers are right for your job, call your local Melfred Borzall distributor to talk options. We can’t get enough of this stuff.