Step drill bits or unibits are beloved by some and despised by others. They make drilling holes of various sizes quick and easy but are not suitable for drilling deep holes.
But why should you use a step drill bit instead of a regular twist bit? What are they used for, and why?
What Is a Step Drill Bit Used For?
A Step drill bit is primarily used to drill holes in sheet materials up to 1/8″ thickness. You can also use it to enlarge existing holes. Step drill bits allow you to cut different size holes without changing the bits.
Here are the 10 most common uses of step drill bits or unibit.
1. Drill Holes in Sheet Metal
Straight-flute step drill bits are best for drilling holes in sheet metal and other flexible materials. The straight flute doesn’t relay torque to the material, and so the material won’t be twisted or warped once the drill punctures the sheet.
When you use a regular twist bit on thin sheet metals, it tends to pull the sheet and walk around resulting in a somewhat triangle-shaped hole. Unibits eliminate these problems.
Step bits are perfect for cutting holes in sheet metal. Here, you progress along the steps until the hole reaches the desired size. To deburr the edges, lightly touch the beveled edge of the next step to the surface. Do the same on the other size, and you have a perfect, clean hole with no other prep work needed.
You can use this bit to drill sheet metals, metal doors, angle irons, aluminum channels, steel pipes, etc. In short, anything with a cross-section of up to 1/8 of an inch. The downside is that you cannot use the unibits to drill uniform diameter holes deeper than the step height on the bit which is usually limited to 4mm.Tip Use a titanium or cobalt bit for longer tool life. If you want to resharpen the bit, get a straight flute step drill bit. They can be easily sharpened by grinding inside the straight flute with a Dremel or die grinder.
2. To Drill Acrylic and Other Plastics
Drilling acrylic, plexiglass, or any other plastic using a step drill bit is a far better option than using a traditional twist bit. When using a twist bit, two cracks typically form once the bit punctures through the material. Step drill bits don’t cause these cracks, making for a neat, clean hole.
When drilling through new plexiglass or plastic sheets, leave the protective film on the sheet while drilling. This protects the surface from scratches, accidental nicks, and bumps.
3. Enlarging Existing Holes
Enlarging existing holes is easy when using a step drill bit. Since each chamfered step has a diameter larger than the one before it, simply drill down until you reach the desired measurement. It’s quick and easy, and the step drill bit generally removes burrs while drilling, so the hole will be clean.
4. To Drill Carbon Fiber
Carbide-tipped step drill bits are well suited to drilling carbon fiber. These won’t damage the material while drilling and will create a neat, clean hole. The benefit here is that you can drill holes of varying sizes without changing the drill bit. Unfortunately, though, drilling carbon fiber will dull the bit relatively quickly, so if you’re working on a large project, you may need to replace your drill bit halfway.
5. Wood: Can step drill bits be used on wood?
Step drill bits are suited to drilling holes through thin materials. For this reason, you can use it on wooden sheets thinner than 4mm, but not a large block of wood. Ensure that you choose a drill bit made of a material compatible with wood.
You should use a wood bit such as a brad point bit to drill deep holes in thick lumber.
Step drill bits are a staple for many electricians. This tool allows them to drill the correct size hole in any panel, junction box, or fitting without changing drill bits. The holes are also neat and burr-free, minimizing the amount of finishing work involved.
7. HVAC and Sanitary Engineering
The step drill is well-suited to HVAC, or heating, ventilation, and air-conditioning applications. As with electrician-related applications, many installations require holes of various sizes or holes that must be resized on site. Here, the step drill bit allows technicians to drill holes of various diameters without changing drill bits.
8. Automotive Industry
Step drills are often used in the automotive industry when carrying out installations and repairs, specifically related to car audio systems and auto-body work. Again, the step drill bit speeds up work since the technician can drill holes of varying sizes and deburr them without changing drill bits.
9. General Construction
In general construction, the step drill bit has many uses, mainly in the finishing steps. Examples include installing electrical infrastructure, cabinetry, underfloor heating, plumbing fixtures, and any features that require neat, clean holes.
Note that the step drill bit is only suitable for thin sheets, which is the main limiting factor.
10. Deburring and Chamfering Holes
The step drill bit easily deburrs and chamfers holes. Once you’ve drilled to the desired diameter, simply touch the beveled edge of the next step to the material’s surface. This removes any burrs left on the edge.
This avoids the extra step of changing the bit to a countersunk or chamfering bit and hence saves time.
When chamfering the hole, allow the next step’s beveled edge to cut slightly deeper into the material’s surface. This creates a neat, clean chamfer in one easy step.
How to Use a Step Bit?
Using a step drill bit is easy and considerably cuts down on working time.
Note that you require the correct PPE (personal protective equipment) to use this tool safely. These include safety glasses, closed shoes (preferably rubber-soled and steel-tipped), gloves, and a safety vest if you’re working in a high-traffic area.
Step-1: Select a Drill Bit
Select your drill bit according to the material you will drill. Ensure that the drill bit’s material is compatible with the project’s material, and inspect the drill bit for any damage. You should focus on the edges of the steps since most damage and dulling occur here. These drill bits aren’t easily sharpened at home – if your Unibit shows signs of dullness, replace it with a new one or enlist the help of a professional.
Step-2: Choose a Power Tool
Step drill bits fit into various power tools, most commonly drill portable drilling machines and drill press. Select the power tool best suited to your application.
Step-3: Clamp the Workpiece
To prevent the workpiece from slipping or spinning during drilling, clamp it in place. Ensure that the clamps are secure since the drill bit could exert considerable force on the workpiece, dislodging it in the process.
Step-4: Make a Center Mark
If you are drilling metal with a cordless drill, use a center punch to create a center mark. Do this by placing the center punch’s tip at the desired point and tapping the back end using a hammer, or use an automatic center punch. This enables the drill bit’s tip to catch the material and not drift once drilling commences.
Self-starting step drill bits typically have a sharp, non-slip split-point tip. You can use it without punching the center when drilling soft materials such as wood, plastic, etc.
Step-5: Drill a Pilot Hole
Technically, this step is only applicable when you’re using a larger step drill bit. You could use the tip of the unibit to directly penetrate into the material. However, if you do it this way, the tip will have to cut every hole you drill and this is often one of the first cutting edges that get damaged. Using a pilot bit will prevent your unibit tip from getting damaged.
Drilling a pilot hole is highly recommended before cutting large diameter holes.
Here, you would first use a smaller step drill bit or a pilot bit to drill a smaller hole. This hole should be at the diameter of your large step drill bit’s smallest diameter. Doing this enables accurate work, preventing the larger step drill bit from slipping or crumbling the material.
Step-6: Apply Cutting Fluid
Most metals, and some other materials, could potentially overheat while drilling, warping the material and compromising the finished product’s quality. To prevent this, select a suitable cutting fluid to cool the cutting interface. This could be water, oil, or other lubricants and coolants, depending on the material at hand.
Step-7: Drill the Hole
Before connecting your power tool to any power source, install the step drill bit by placing the shank into the power tool’s chuck. If appropriate, apply lubricant to the step drill bit and center mark.
Set the power tool to a low drilling speed and commence drilling vertically into the workpiece. Apply steady pressure as you drill, adding cutting fluid to the power tool as applicable.
When nearing the desired hole diameter, slow the drilling speed and reduce the force applied.
Once you reach the desired diameter, chamfer the hole to create a clean, deburred surface. To do this, gently touch the beveled edge of the step drill’s next diameter to the workpiece’s surface.
Step-9: Clean Up
Once the project is complete, wipe the step drill bit down using a dry rag. Store it in the appropriate place. Clean metal chips from the workplace using a magnetic chip collector. Use a broom or vacuum to clean any remaining debris from the workstation and floor.
Back to Contents
- What Is a Step Drill Bit Used For?
- How to Use a Step Bit?