Backreamers are the workhorse of every HDD drilling operation. As HDD tooling experts, we see too many drillers make the mistake of thinking that one backreamer can do it all. The fluted reamer that comes with the rig is great–under certain conditions. However, drillers try to use the default drilling reamers in situations where a specialized reamer would increase production.

What can happen when you rely on the wrong reamer?

At best, picking the wrong backreamer can make your drilling proceed slowly and drag your efficiency way down. At worst, your reamer can snap off in the hole, causing you to stop drilling to retrieve it or forcing you to abandon the hole altogether and re-drill a new pilot. Pick a reamer that pulls back too fast and you may cause road humping that you’re on the hook to repair. Too slow and you get cratering.

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:

Ground conditions you’ll encounter

Know the type of material you expect to encounter before you drill your pilot. 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 drill fluid mixed together to support the borehole wall, and not allow the sand to collect on the bottom of the hole.

Cutting action you’ll need

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 rocks 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.

The size of your rig

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 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.

The right volume of drilling fluid

Always be sure you have plenty of drill fluid flow when backreaming. 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.

Here are some do’s and don’ts when picking your backreamer:

  • DON’T just assume that your OEM reamer is right for every job
  • DO try to get a sense of every ground type you’ll run into on one job
  • DON’T hesitate to stop work to swap out your reamer if ground conditions change
  • DO ask your HDD supplier’s opinion before you begin the job
  • DO stay open-minded. HDD tooling experts are there to help


Choosing the right backreamer before you begin a job saves time, saves stress and saves money. If you have questions about which drilling reamers are right for your job, call your local Melfred Borzall distributor to talk options. We can’t get enough of this stuff.