Hammer Care

DTH Hammer Lubrication and Break-In: The First 30 Minutes Decide the Hammer’s Life

By Windrilling Technical Team – Updated October 2026 – 12 min read

A 5 inch hammer came back to us last season with 11 hours on it. The piston was scuffed blue down one side and the cylinder bore was scored like a file. The customer was certain we had shipped him a bad hammer.

We asked two questions. Was the oiler filled? Yes. Was the oiler turned on? Long pause.

Eleven hours of dry running will do that. Not to a cheap hammer. To any hammer.

Lubrication is the least exciting subject in down-the-hole drilling and it is the one that decides whether a hammer gives you thousands of metres or one bad week. The break-in window matters even more. What happens in the first hole a hammer drills sets up the wear pattern for everything that follows.

What Actually Wears Inside a DTH Hammer

A DTH hammer has no gearbox, no hydraulic circuit and almost no electronics. It is a piston moving inside a cylinder, driven by compressed air, hitting a bit. That simplicity is why it lasts so long when it is fed oil, and why it destroys itself so fast when it is not.

The parts that carry the load:

Component	What it does	What lubrication failure looks like
Piston	Fires up and down thousands of times a minute	Scuffing, bluing, chipped striking face
Cylinder bore	The running surface the piston works against	Longitudinal scoring, loss of impact energy
Check valve	Stops water and cuttings entering the hammer	Leaking, hammer floods between holes
Chuck and top sub threads	Transfer torque and hold the string together	Galling, threads picked up and unserviceable
Bit splines	Drive the bit while letting it slide	Wear, slop, broken splines

Notice what is not on that list: the rock. Rock wears bits. Lubrication decides whether it wears the hammer. When we strip a returned hammer, we can usually tell within a minute whether it was oiled properly, because dry-running leaves a signature – a bright, polished bore in one part of the stroke and a scuffed piston where the film broke down.

If you want the wider maintenance picture, our DTH drilling rig maintenance checklist covers the rig side of the same discipline.

The Right Oil: It Is Called Rock Drill Oil for a Reason

The oil for an air-operated hammer is an air-line lubricant, usually sold as rock drill oil or hammer oil. It is formulated to do three things that ordinary oil will not do well: stay fluid enough to be carried as a mist in an air stream, cling to metal after the air passes, and resist being washed off by the condensate that comes down the line.

Oil you might be tempted to use	Why it is the wrong choice
Engine oil	Not designed as an air-line mist; leaves deposits and does not cling as the air expands
Hydraulic oil	Built for a sealed circuit at high pressure, not for lubrication carried by compressed air
Grease pushed into the air line	Does not atomise. It arrives as a slug, or not at all
Gear oil	Too heavy for most lubricators to meter reliably, especially in cold weather
Diesel or kerosene as a thinner	Washes the film off instead of adding to it

Rock drill oil is sold by viscosity grade, and the grade you need depends mainly on ambient temperature. Air-line oil has to atomise at the temperature on site. A heavy grade that works in a hot quarry can arrive at the hammer as a thick rope in a cold morning start, and a light grade that misted beautifully in winter can thin out too far in desert heat.

The DTH machine manuals we work from usually name a specific product rather than a generic grade – one common example recommends a Mobil Almo 525 or Shell Torcula 100 type air-line oil, or a fluid equivalent. If your manual names a product, use that product. If it does not, give us the ambient temperature range on your site and we will tell you which grade of the oil we supply suits it.

The Oiler: Reading It and Setting It

The oiler, or air-line lubricator, is the small reservoir on the rig that meters oil into the compressed air stream. On most rigs it hangs off the air line between the compressor and the hose that goes up the mast, with an adjustable valve or dial that controls how much oil is picked up.

Four things go wrong with oilers, and all four are cheap to prevent:

• The oiler is never filled. Somebody assumes somebody else filled it. On a five-day job nobody checks.
• The setting is never adjusted. The valve is left wherever it was when the rig arrived, which may be right for one hole size and wrong for the next.
• The oiler is downstream of the wrong point. If it sits after the point where the air is split, part of the air goes to the hammer un-oiled.
• Water gets in. Condensate from the compressor receiver moves down the line, and a slug of water will strip the oil film off the piston in seconds.

Setting the oiler is a two-step job. Start low. Then walk the setting up in steps until you can see what you expect to see – a light oil film on the drill pipe, and a visible mist carried out of the hole with the exhaust air. When you can see it, mark the position. From then on, that is your reference, and any change from it is a signal.

How Much Oil Is Enough?

Nobody can give you one number for this, and anyone who does is guessing. Oil consumption depends on hole size, air volume, hammer model and how long the hammer is in the air rather than on the rock. What you can do instead is measure it.

Fill the oiler to a mark. Drill a known interval – say one rod, or one hour of steady drilling. Refill to the same mark and note how much oil it took. That is your real consumption figure for that hammer on that job. Repeat it after you change hole size. Now you have a benchmark, and a benchmark is what turns “I think it’s fine” into “it used a third less oil today, something changed”.

Signs you are starving the hammer:

What you see	What it usually means
Hammer comes out dry, with a bright bore	Oil is not reaching the hammer at all
Oil level in the reservoir does not drop over a shift	Oiler blocked, empty feed line, or setting at zero
Penetration rate falls off earlier than usual	Film breaking down; piston and bore wearing together
Hammer is hot to touch at the chuck	Friction from metal-on-metal contact, not rock cutting

Signs you are over-oiling are rarer and much cheaper: excess oil mist on the deck and extra oil consumption for the same metres. If you are choosing between the two, the dry side is the dangerous one.

Break-In: The First Hole a Hammer Ever Drills

A new hammer and a freshly rebuilt hammer behave the same way on day one. The running surfaces are not yet matched to each other. There is no established oil film, no polished bearing surface, and the clearances are at the tight end of tolerance. Break-in is the process of getting those surfaces to settle in gently, under a full oil film, instead of hammering them into each other dry.

This is the procedure we ask customers to follow, and it is the same one most hammer manufacturers describe:

1. Oil the hammer before it goes down the hole. Coat the entire inside diameter of the hammer – the cylinder bore and the piston – with a light film of rock drill oil. Do this on the bench, by hand, while the hammer is open. A hammer that starts its first hole dry from the inside has already lost the argument.
2. Grease the threads and the splines. Coat all the threads – top sub, chuck, and the bit shank – with thread grease, and grease the bit splines. Dry threads gall under torque, and a picked-up thread turns a serviceable chuck into scrap.
3. Check the check valve before you commit. With the hammer vertical, pour a small amount of oil into the valve and watch whether it holds. If it leaks, the hammer will flood the moment you pull it out of the hole and water will wash out the oil film. Fix it now, not after the first hole.
4. Set the oiler richer than normal for the first hole. Start-up lubrication is a deliberate exception to your normal setting. The aim is to guarantee a full film while the surfaces are still finding each other.
5. Collar the hole at reduced throttle. Start the hole with the impact and feed turned down, let the bit cut its own seat in the rock, then bring the parameters up. Full impact against a bit that is bouncing on a rough collar is exactly the load you do not want on an un-bedded piston.
6. Keep rotation in the normal band. Most hammers in this class run somewhere around 15 to 25 rpm. Do not spin a cold hammer faster than you would a warm one to “get the hole going”.
7. Pull the hammer after the first hole and look at it. You are looking for an even, faint oil film across the piston and bore. A dry bore, or bluing on one side of the piston, tells you the oil never arrived.
8. Reset the oiler and log it. Record the rod, the hole, the oiler position and the oil used. That log is how you catch the next problem before it costs you a hammer.

Two things are worth adding to that. First, break-in oil quantity is not the same as running oil quantity – do not leave the oiler turned up for the life of the hammer, or you will buy oil by the barrel for no benefit. Second, break-in is not only about the hammer. It is also the first time your compressor, your air line and your rig are working as a set. If the air volume and pressure are wrong for the hammer, the hammer will run hot on its first hole no matter how much oil you feed it.

Daily and Weekly Lubrication Checks

These take four minutes a day and they are the difference between a hammer that reaches its wear limits and one that reaches your scrap bin.

When	Check	Pass condition
Start of shift	Oiler oil level and setting	Filled, valve at the marked position
Start of shift	Drain the compressor receiver and water traps	No free water carried into the air line
Every rod change	Oil film on the drill pipe and mist in the exhaust	Faint film, visible mist
Every rod change	Thread condition on rod and sub	Clean, greased, no picked-up metal
End of shift	Oil used against metres drilled	Comparable to your benchmark
Weekly	Oil feed line and oiler valve	Clear, metering consistently, no blockage
Weekly	Bit splines and chuck wear	Within wear limits, no slop beyond spec

If your rig runs in a hot climate, add a mid-shift look at the oiler. Oil consumption rises with air temperature, and a setting that was correct at seven in the morning may be lean by two in the afternoon.

Five Lubrication Failures That Cost Hammers

1. The dry start

The hammer sits overnight, the oil film drains down, and the first thirty seconds of the morning are run at full impact with no oil arriving yet. This is why morning start-up deserves the richest oiler setting of the day. If you want to know how much damage a dry start does, look at the top of the stroke on a stripped hammer – the wear is not evenly distributed down the bore. It concentrates where the piston was sitting.

2. Water in the air line

Compressed air is wet air. Every compressor produces condensate, and in humid conditions a receiver that is not drained daily passes that water straight into the hammer. Water does not mix with rock drill oil – it displaces it. The symptom is a hammer that is oiled properly on paper and dry in practice. Drain the receiver, drain the traps, and check that the oiler is positioned so the air reaching it is as dry as your setup allows.

3. The wrong oil, chosen for the wrong reason

Usually this starts with a shortage. The rock drill oil runs out, somebody finds a drum of hydraulic oil in the container, and the hammer keeps working – for a while. By the time the shortage is over, the piston and bore have a wear pattern based on an oil that was never designed to be atomised into an air stream. Keep a spare drum of the correct oil on site. It is the cheapest insurance in the container.

4. Threads that were never greased

Lubrication is not only about the piston. Chuck, top sub and bit shank threads carry the torque of the whole string. Un-greased threads gall, and a galled thread on a chuck is a replacement part, not a repair. The same applies to bit splines, which slide under load every stroke.

5. Running a hammer that already has wear damage

Once a piston is scuffed or a bore is scored, more oil will not undo it. The clearance is already wrong, so the hammer runs hotter, wears faster and eats the parts around it. If you are seeing lost impact energy or a hammer that will not fire cleanly, work through the seven field problems and fixes before you blame the oil.

Storage and Re-Commissioning

A hammer that has been stored for six months behaves like a new hammer on its first day back, with one extra risk: whatever is sitting inside it has had six months to become a grinding paste. Dust, dried thread grease and corrosion all end up in the bore.

Before a stored hammer goes back into service: drain and flush it with clean oil, re-oil the bore by hand, re-grease every thread and spline, check the check valve, and treat the first hole as a break-in hole rather than a production hole. Twenty minutes of preparation against the cost of a hammer – it is not a close decision.

What to Have on the Shelf

If you run DTH hammers seriously, these are the items that turn a lubrication failure from a week of downtime into an afternoon:

• Rock drill oil in the grade that matches your site temperature – enough for a full job, plus one spare drum
• Thread grease for chuck, top sub and bit shank threads
• A spare oiler or a spare oil feed line
• Check valve and seal kit for the hammer models you run
• A rod of the same hammer model, if your fleet is big enough to justify it

We supply DTH hammers in 3, 4, 5 and 6 inch sizes together with the oil, thread grease and spares that keep them running, and the same consumables fit most common hammer models in the field. If you are building a consumables list for a project, or you want to know what a hammer and a spares kit cost as a package, the hammer price guide covers how the numbers stack up. Everything we ship for hammers, rods and bits is listed on the drilling tools page, and the bits that go with these hammers are on the DTH drill bits page.

Questions We Get Asked

Can I substitute engine oil or hydraulic oil if I run out of rock drill oil?

You can, and the hammer will keep working for a while, which is exactly what makes it dangerous. Neither oil is formulated to be carried as a mist in an air stream or to cling as the air expands through the hammer. You will end up with a wear pattern built on the wrong film, and you will usually notice it as a slow loss of penetration rather than a failure you can point at.

How do I know the oiler is actually working?

Two checks, both simple. Watch the oil level: it should fall at roughly the same rate over the same drilling interval, day after day. And look at the machine: a faint oil film on the drill pipe and a visible mist in the exhaust mean oil is arriving. A static oil level with the rig drilling is a fault, not a saving.

Does a new hammer need a different oil from a used one?

No. It needs more of the same oil, hand-applied inside the hammer before it goes down, and a richer oiler setting for the first hole. The grade stays the same; only the quantity and the timing change.

My hammer has lost impact energy. Is it the oil?

It can be, if the film broke down and the piston and bore have worn into each other. But loss of impact is more often air-side – pressure too low, volume too low for the hammer, or a leaking string – so check the air before you strip the hammer. Lubrication and air supply are partners, and blaming one without measuring the other wastes a day.

How often should I check the hammer’s wear limits?

Every service interval, and always after a job where the oil ran short or the hammer came out of the hole wet. Wear limits are the objective test – measuring is the only way to know whether a hammer goes back in the hole or onto the rebuild bench, and lubrication is what keeps you on the right side of the number.