Deep hole drilling using precision tooling can present numerous challenges. To produce a quality final product while keeping costs under control, shops must be able to achieve accuracy, repeatability and sufficient surface finish while maintaining predictable tool life. What are the common challenges operators run into when drilling and how do you solve them?
Challenge #1: Tool Runout
Runout is differences or variations in the diameter of a cutting tool at certain points along the outside edge while the tool is rotating. The level of runout, or total indicated runout (TIR), can be measured with a dial indicator. Tool runout can lead to oversized holes, poor surface finish, bad burrs, and decreased tool life. When drilling, the challenge of maintaining control of runout increases when you increase the length of the drill. Replacing a drill that is 5 x diameter with a drill that is 30 x diameter will result in significantly larger runout.
As seen in Table 1 from “Production Machining”, one drill test they ran showed that by increasing runout accuracy from 0.0006” to 0.00008” resulted in 2.9 times longer tool life.
Solution:
First, make sure you are using the proper drill length. You want to make sure your drill is as short as possible to safely drill your desired hole depth. This may seem obvious, but it’s always good practice to remind your operators to choose the “right” tool for the job.
Another tip we normally recommend to improve drill runout is to regularly disassemble the drill and the tool holder assembly to check that parts are clean and not worn out. Chips and debris that get into the holder and/or collet system can affect TIR. Proper maintenance on your current drilling system is the easiest and most cost-effective way to improve drilling runout.
Using a proper toolholder is imperative to precision drilling. When drilling, you want to choose a toolholder that applies equal pressure around the periphery of the tool. Some options include shrink-fit, hydraulic, and collet chucks. Your budget, hole tolerance, current toolholders, and shop set up can all be factors in determining the best option for your shop. Your local Butler Bros. should be able to make a recommendation that best fits your needs.
Challenge #2: Drill Walking
Another common challenge when drilling, especially deep hole drilling (12 x diameter and over), is drill “walking”. Because the tool is rotating, it will want to move across the part surface instead of entering downward into the part. Longer drills have a higher tendency to walk, which can quickly lead to tool breakage. Dull cutting edges can also lead to drill walking so it is important to examine tools before starting a job to know when your tool needs to be replaced or resharpened.
Solution:
Depending on material and part shape, there are a few solutions we recommend to avoid drill walking. If the drill is entering a workpiece that is flat and the drill is still walking, you may want to use a spot drill. The spot drill’s point angle must be larger than the point angle of the drill. That way, the deep hole drill is guided into the centerline location.
If your application requires more guidance and accuracy, you may want to use a pilot hole. A pilot hole should be considered when drilling holes at a depth of 16 x diameter or greater. The pilot hole acts as a guide to help stabilize the longer drill at the beginning of the drilling process.
If your hole location is on an irregular surface or incline, the drill will have a greater tendency to walk. In that instance, we recommend milling a flat surface before drilling.
Challenge #3: Chip Control
When beginning a new drilling operation and application, inspecting the chips is just as important as inspecting the hole. Poor chip control can lead to a myriad of issues such as poor hole quality and bad tool life. The chips should look like Cs and 6s. There will also be conical shaped chips formed by the center of the drill. If you notice your chips are long and irregular, you should examine your chip control. If you are producing a “bird nest” chip, then you are losing significant life on the tool. It is also imperative to listen to the machine when drilling. If the machine sounds like it is struggling and cutting noise is irregular, then chances are good you are not getting the proper chip evacuation.
Solution:
Use coolant. If you can, use internal coolant. Depending on the age of the machine, or diameter of the tool, you may not be able to use internal coolant. The advantage of internal coolant when drilling is that the coolant is flushed down to the bottom of the hole which pushes the chips back to the top. It also keeps the edge of the cutting tool cool to prevent buildup. If you do not have coolant-thru / internal coolant capabilities, flushing coolant at the tool and hole can assist with chip evacuation as well. Using external coolant, you may have chips that refuse to break. In these instances, you may want to consider peck drilling. This process can help pull the chips out of the workpiece. The process may not be as quick, but if poor chip control happens long enough, the drill can seize and snap, destroying an expensive cutting tool and resulting in a scrapped workpiece.
Another potential solution that plays a role in chip control is tool coating. With the evolution of workpiece material, tool manufacturers have had to develop innovative tool coatings to increase drill performance. Now, more than ever, manufacturers are releasing special coatings on tools that are designed to be material specific. We understand some material you run may be proprietary, but the more you can share about the material, the more it can help us choose a coating that would best fit your application.
Drilling can be a tedious operation. Understanding some of the challenges before starting can help. For personalized assistance at the spindle, please feel free to contact your local Butler Bros. sales representative for help. If you’d like to find out who your local representative is, please email your company name and location to sales@butlerbros.com and ask for the contact info of the local Butler Bros. representative in the area. Or, please give us a call at 888-784-6875 and our staff will point you in the right direction.
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