Used Gun Drills & Deep-Hole Drilling Machines for Sale
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About Used Gun Drills & Deep-Hole Drilling Machines
Gun drills and deep-hole drilling machines produce straight, precise holes with depth-to-diameter ratios far beyond what conventional drilling can achieve — 20:1, 50:1, even 100:1 and more. Originally developed for gun barrels, deep-hole work is now essential for mold cooling lines, firearms, medical instruments, hydraulic manifolds, crankshafts, and aerospace components. Modern CNC gun drills feature multiple spindles, programmable feeds, and high-pressure through-tool coolant that evacuates chips out of the hole as it's cut.
This machine is single-flute gun drilling. A gun drill is a tool with one flute, coolant down the center, and chips coming back along the outside V. A bushing at the start keeps the tool from walking, and high-pressure coolant is what pushes the chips out of a hole that may be twenty, fifty or more diameters deep. A twist drill in a machining center will not do that. It packs, it wanders, and it burns. Mold cooling lines, oil holes, barrels and long pins are the work.
Stroke has to clear the depth plus the tool. Hole diameter is the range the spindles and the bushings were built for, generally the smaller deep holes rather than a large bore. Coolant pressure and a filter are part of the machine. A pump that cannot hold pressure, or a filter full of chips, will stop a straight hole even when the iron is sound. One spindle is the simple machine. A second spindle drills two holes, or two parts, when the work repeats. The whip support and the bushing have to match the diameter you will run.
Honing is a different process. It finishes size and surface on a bore that already exists, and those machines are on the deep-hole drilling and honing machine. Go there when the print cares about roundness after the hole is drilled. Larger bores that send chips back through a tube are a different method on that same machine. This range stays with the single-flute gun drill. Mollart is the gun-drill builder that appears as a line. Sunnen is the honing name in the same deep-hole family, listed here so you can see it and then open the honing machine for the stones.
On a used gun drill, run a bar. Watch coolant pressure with a tool in the cut, not only with the pump switched on. Look at the bushing and the whip guides. Measure stroke against your longest hole. A machine that reaches pressure and will not hold a bushing on size will drill a curve. EDM can start a hole a flute cannot enter. It will not replace the gun for a long cooling line.
How to Choose Used Gun Drills & Deep-Hole Drilling Machines
How to Size a Gun Drill
Size diameter and depth together. The hole has to be inside the tool range the machine was built for, and the stroke has to clear that depth plus the drill and the bushing. A machine that is short of the cooling line is the wrong length, whatever the pressure says.
Coolant pressure and filtration are the rest of the size. The pump has to flush chips up a single flute for the whole depth. A second spindle is useful when you have two holes or two parts, and it is idle iron when you have one. The bushing has to match the diameter. If the print then calls for a honed finish, the hone is the next machine, on the deep-hole machine, not a setting on this one.
Single-Flute Drilling, Then Honing
The single flute is the chip path. Coolant goes down the tool and chips come out along that flute, which is why the hole can stay straight and small. A bushing starts the tool. Without it, the drill walks in the first diameter of depth.
Honing does not drill. It corrects size, roundness and finish after a hole exists. Those machines, and the larger-bore methods that are not a single flute, are on the deep-hole drilling and honing machine. Use this machine to buy the gun drill. Use that machine when the bore has to be finished, or when the diameter is no longer a gun-drill hole. A machining center still starts a short hole. It does not follow it twenty diameters down.
Gun Drills & Deep-Hole Drilling Machines Specs to Compare
| Spec | Typical range | Why it matters |
|---|---|---|
| Hole diameter | Smaller deep holes, often well under 2 in | The spindles and bushings are built for a range. A larger bore is a different method on the deep-hole machine. |
| Depth-to-diameter | Often 20:1 and much deeper | This is the ratio a twist drill will not hold. Stroke still has to reach the actual depth. |
| Stroke (in) | Stroke has to clear the hole plus the tool and the bushing. A short machine cannot be programmed longer. | |
| Coolant pressure | About 1,000 psi through the tool | Chips leave along the single flute only if the pump can push them. A weak pump drills a packed hole. |
| Guide bushing | The bushing starts the tool straight. A worn or wrong bushing is a wander in the first inch. | |
| Spindle count | 1 spindle, or 2 for a repeated hole | A second spindle helps when two holes or two parts run together. It does nothing for a single cooling line. |
Hole diameter
Typical range: Smaller deep holes, often well under 2 in
The spindles and bushings are built for a range. A larger bore is a different method on the deep-hole machine.
Depth-to-diameter
Typical range: Often 20:1 and much deeper
This is the ratio a twist drill will not hold. Stroke still has to reach the actual depth.
Stroke (in)
Stroke has to clear the hole plus the tool and the bushing. A short machine cannot be programmed longer.
Coolant pressure
Typical range: About 1,000 psi through the tool
Chips leave along the single flute only if the pump can push them. A weak pump drills a packed hole.
Guide bushing
The bushing starts the tool straight. A worn or wrong bushing is a wander in the first inch.
Spindle count
Typical range: 1 spindle, or 2 for a repeated hole
A second spindle helps when two holes or two parts run together. It does nothing for a single cooling line.
What to Inspect on Used Gun Drills & Deep-Hole Drilling Machines
Drill a test bar
A pump that runs with no tool in the cut has not made a hole. Look at straightness on a bar you can section or indicate.
Watch coolant pressure
Pressure should hold with the tool drilling, and the filter should not be packed with chips from the last job.
Inspect the bushing
A worn guide bushing lets the flute wander at the start. Match it to the diameter you will run.
Check whip supports
The supports that steady the tool have to be there and on size. A bare drill will whip before it cuts.
Measure the stroke
Depth plus tool length has to fit. A machine that stops short of your cooling line is the wrong length.
Look at the flute tooling
Single-flute tools for your diameters should be with the machine or in your plan. A bare spindle is not a process.
Confirm alignment
The bushing, the tool and the part have to share an axis. A crooked setup drills a curve no pressure will straighten.
Related Equipment
- Deep-Hole Drilling and Honing
Honing and bore finishing after the hole exists
- Machining Centers
A twist drill when the hole is still short
- EDM Machines
A spark start when a flute cannot enter
Related Manual & Tool-Room Machines
Manual Mills, Drills & Lathes
Manual and tool-room machines are the general-purpose machine tools that keep a shop running alongside its CNC equipment — manual knee mills, engine lathes, drill presses, and radial and gun drills.
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Top Brands for Used Gun Drills & Deep-Hole Drilling Machines
Mollart
UK builder of CNC gun drills for deep holes.
Sunnen
US builder known for honing and bore finishing.
Common Applications
Frequently Asked Questions
What is a gun drill used for?
A gun drill makes a deep, straight hole that a twist drill will pack and wander. One flute, coolant down the center, and chips returning along the outside V let the hole stay small and deep, often twenty diameters and more. Mold cooling lines, oil holes, barrels and long pins are the usual work. A bushing starts the tool so it does not walk in the first diameter. Stroke has to cover the depth plus the tool. A machining center can start a short hole. It should not follow it that far.
What is the difference between gun drilling and BTA drilling?
Gun drilling uses a single-flute tool with coolant down the center and chips coming out along the flute. It is the method for smaller deep holes, such as a mold cooling line. BTA drilling, also called STS, is a larger-bore system: the chips come back through the center of the tube and the coolant is outside. BTA suits bigger diameters and higher metal-removal rates, and the machine, the pressure head and the tooling are different. Do not put a BTA head on a gun-drill spindle and expect the same hole. Match the process to the diameter before you match the stroke.
What should coolant pressure do while the tool is cutting?
Hold. The number depends on the diameter and the tool, so a universal pressure is not a spec you can copy from another shop. What you can check is that the pump reaches a real pressure with the tool in the cut, that the lines are not crushed, and that the filter is serviceable. Chips recirculated into the pump will end the pressure and the hole together. Ask what diameter the machine last ran and whether the bushings for your size are there.
How do I check the bushing and the whip guides?
The bushing should match the tool diameter and should not be bell-mouthed. That is the support for the first part of the hole. The whip guides, or the steady supports along the tool, should be present and on size, or a long drill will flex before it ever reaches the part. Missing tooling is a common used-machine problem. The iron can be sound and the process still absent. Put a tool in, line it up with the bushing, and see the supports touch. Then drill.
Where do I look if the bore also has to be honed?
On the deep-hole drilling and honing machine. A gun drill makes the hole. A hone corrects size, roundness and finish with stones after the hole exists. This machine does not size hones, and a hone will not start a solid bar. Sunnen is the honing name you may see near these listings. Mollart is the gun-drill builder. If your print is a cooling line that only has to be straight and open, you can stop at the drill.
Which stroke should I match to a mold cooling line?
The length of the line, plus the drill, plus the bushing, with a little room to enter and to retract. A cooling line that is longer than the stroke cannot be finished by a second peck the way a twist drill pecks. The tool has to reach. Diameter of that line has to fit the bushings you will have. If the mold is large, the table or the fixture has to present the hole on the spindle centerline.
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