CNC Machining Various Precision Holes Guide
Date: 2022-09-07
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CNC Machining Various Precision Holes Guide

We largely underestimated hole punching, since most holes don't require precision, are small in depth, and are mostly reserved for bolts. However, modern technology industries such as automotive and aerospace are increasingly using the services of CNC companies because we can create precise deep holes that are precisely positioned.

What problems do we face when CNC machining holes?

From a manufacturing point of view, the entire creative process is very heavy. Workpieces and tools can easily overheat because injecting coolant into the hole is tricky. Ideally, the process is not fully visible to machinists, who mostly blindly cut workpieces with little machine information input. Fortunately, advances in machining strategies over the years have allowed us to create precise holes, and these new tools and tools allow us to meet the needs of our esteemed customers.

Deep drill

Drilling is a basic process that involves creating short holes with ease. However, we found it difficult to create deeper holes as it was tasked with maintaining a straight axis due to the fact that longer drills are less rigid. Although they may have two cutting edges, we cannot make them the same length. As a result, different drill flanks will generate different cutting forces, and the drill will eventually deviate from the set linear axis. So we end up with unbalanced holes, which is unacceptable for CNC precision parts.

We are using gun drills to solve this problem. Gun drills have one cutting edge, so there is little deviation in their process. In addition, it has a larger chip flute that also acts as a cooling channel. When we pump coolant into the grooves at high pressure, it removes chips. At the same time, it cools the drill bit, allowing it to last longer, its only downside is that we can't mount it on a CNC milling center. However, our experts have figured out a way to install special tools.

At Xiehe, we use gun drills for extreme projects. In general, we try to stick to standard tools as there are special ways to drill deep holes even with simple drills. First the length of the hole needs to be divided into sections between 3-4 hole diameters deep, each time the drill reaches the end of a section, we pop it. Then, let the workpiece and tool cool while we empty all chips from the hole, which is one of our CNC deep hole machining methods.

High-precision hole machining

We use a variety of tools for CNC drilling to create a precise hole. The first tool is usually smaller than the hole diameter. The diameter of the next tool is larger than the diameter of the previous tool. Our expert machinists do this to reduce cutting forces and thus reduce the chance of misalignment, and then we do coring drilling immediately after drilling. Core drills include 3 cutting edges instead of 1 for better stability. The core drill facilitates a depth of cut of about 0.5 mm, and its main advantage is the ability to correct a skewed axis.

The next advanced CNC fine hole machining method involves reaming. We do this on projects where clients require holes with IT6 tolerances, and the same goes for a truly smooth finish. Using a reamer reduces the machine feed rate. Reamers have a lot of very small cutting blades, therefore, they have a cutting depth of 0.05mm-0.1mm, which makes them very accurate when cutting edges. For smaller holes, we have to do the reaming manually.

Another advanced CNC hole making method is honing, which refers to the grinding process that we carry out using CNC machine tools. Honing machines include reamers with abrasive plates in place of cutting blades. Also, we can change the planks to get different diameters. When the honing machine is pushed out, the direction of rotation is reversed. As a result, the surface of the hole ends up with microscopic grooves that criss-cross, which makes lubrication more effective.

Types of hole threading strategies

Most holes require threads, which are complex thin surfaces that are a difficult task for the machine. Fortunately, our experts come up with specific threading methods. But before that, we have to perform a counterbore or counterbore. Both processes require a tapered groove to be formed at the entrance of the hole, which allows proper access to the threaded tool for actual part assembly.

An advanced method of hole threading is tap drilling. It involves using a tool that looks like a bolt but has a tapered front area and flutes that help increase cutting depth. The machining feed we use in threading is similar to the pitch. The tap drill first slowly inserts into the hole, each of its rotating cutting edges severing a piece of material, creating a line. If you are looking for other precision CNC machining methods for designing holes, please contact us.


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