by Gary BrownClick image to enlargeby Gary Brown


Machinists and programmers alike know how demanding cross-hole drilling can be, as it often exacerbates many of the difficulties inherent in metalworking. 

Deburring is already a painstaking process, but when burrs are difficult to inspect and access, as is the case in cross-hole intersections, traditional deburring methods are time consuming and inefficient. 

Regardless of size, or whether the hole is threaded, angled or off-center, any time a hole is drilled into a part, it will create a burr: ragged edges, particles, protrusions or shavings not removed by the initial drill pass. 

Drawing of a cross hole deburring situation with slanted cross bores.Click image to enlargeThese imperfections can create off-spec parts or increase the likelihood of injuring a worker that handles machined parts or blanks. In many manufacturing applications, it is vital that through-holes are chamfered and absolutely free of metal burrs, as flawless fit and durability are the top priority when parts are assembled. When the intersecting parts move, the importance of fit increases exponentially, as any additional source of friction at the edge breaks will abrade the part, leading to premature failure. When the part is used in applications involving fluid or liquid, burrs in the pipe can slow down or obstruct the flow of the liquid. 

The closer the bore gets to a 1:1 ratio, the more difficult and expensive the bore is to deburr. Intersecting bores result in elliptical-shaped bores where burrs bimage.pngClick image to enlargeClick image to enlargeuild up in the areas where the bore dips. The burrs are difficult to see, and even more difficult to access–but all the more important to remove. 

image.pngClick image to enlargeClick image to enlargeHow automated tools work
As the rotating tool is fed into the hole, the front cutting edge deburrs the top of the hole and the blade rocks upward, creating a tapered, radiused edge break. When the blade is in the hole, the blade slows itself down and does not cut as it passes through–only the ground and polished non-cutting ball touches the surface, protecting it from damage while the tool is fed through the part. 

As the blade reaches the bottom of the hole, it springs back into cutting position, and the back cutting edge deburrs the bottom of the hole as the tool is withdrawn. When the blade is inside the hole, the tool can be rapid fed out and on to the next hole. 

Machine shops who replace hand benching with machine deburring tools report an average of 20 per cent or more increase in productivity while producing higher quality parts. By deburring parts in-house rather than outsourcing, or even taking the part off the line, shops maintain manufacturing momentum. 

Heule's Cofa-X tool for automated cross hole deburring.Click image to enlargeWithout automated deburring, it falls to the machine operator to decide when a burr is getting too big and the drill needs to be changed. Most operators do a subjective “fingernail test” to determine whether too much of a burr is developing. This decision varies from operator to operator, and often results in either increased costs for changing out the drills frequently or a lower quality product due to large burrs at the bore intersections. 

Automating burr removal takes the subjectivity out of the process and allows for consistency in part quality, as well as a superior quality part. It also results in cost savings from fewer drill changes, longer drill life and more efficient operators who can attend more than one machine at once. 

These tools can be applied to virtually any metal because they can be custom-designed to fit the requirements of the job, and blades can be quickly swapped out. Tools are available in different grid selections and abrasive types, as well as sizes for various hole diameters. Different blades allow for flexibility in varying hole geometries; and different spring strengths allow options for deburring various materials. 

To stay competitive, many shops are automating the burr removal process, especially in tricky cross-hole intersections. Machinists can use automated finishing tools to deburr parts on the line. Keeping parts on the production line frees manual labour to operate other machines, and increases productivity in the shop. Operators can deburr parts of multiple sizes and materials one after the other, quickly and effectively, because the blades are easy to exchange. Automated tools deburr parts, even in cross-holes, consistently, saving time, money, and an expensive part from being scrapped. SMT

Gary Brown is president of Heule Tool Corp

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