Boring heads are basically the cutting end of a boring toot, such as the cutting head of a diamond drill or the cut holder on a boring rod. Boring heads are used to produce large diameter holes when a drill bit is not large enough or do not have the required tolerance for a drill bit. A boring head can also be utilized for enlarging holes or adjusting hole centerlines in certain situations.
Rough boring heads, the essence of this article, are designed for heavy duty rough boring and semi-finishing operations. Rough boring heads are typically designed to be compact and short that come with a positive and friction locked connection between the insert holders and tool body, which then offer optimal strength and superb cutting performance.
Rough boring is essentially a metal removal process that prepares the hole for finishing. Roughing machining is carried out to enlarge an existing hole created by methods such as casting, forging, pre-machining, etc. Rough boring tools can be set up for productive, step or single-edge boring.
Despite the size of a rough boring head, it is of utmost importance is the operation of rough boring and definitely more feature-rich than you think. Some of the typical features include:
● A rough boring head is ideal for single bit boring, twin-bit boring, and step boring with diameter range based on the operation requirement.
● Rough boring heads can be easily adjusted to accommodate various boring needs for machining on demand. The boring depth can also be extended using tool connection.
● Rough boring heads typically have thickened cartridges for superior rigidity and cutting efficiency, making it the idea option for a variety of boring operations.
● A tool-setter is not needed to make adjustments on a rough boring head as it usually comes with clear side division.
● Rough boring heads are ideal for boring on boring mills or various other machine centers. They come with universal designs which make them compatible with all brands and models of machine tools they complement.
The inset style along with your rough boring head should be carefully selected as well to achieve optimal machining performance and chip control. Inserts can typically be divided into the positive inserts and negative inserts:
● Positive Inserts: It is definitely advantageous to use positive inserts along with your rough boring heads because they offer lower cutting forces as opposed to negative inserts. Positive inserts are typically equipped with a small nose and angle and small nose radius, both of which contribute to the reduced cutting force.
● Negative Inserts: Stronger negative inserts should be chosen in tough applications where process security is required to be maximized. They are also ideal in stable conditions for better insert economy.
A common question posed is whether we should use a rough boring head or a finish boring head? On a general rule, if finish boring heads are typically preferred for a much tighter tolerance. If not, a roughing boring head should be used instead to ensure optimal accuracy. As for material stock, the nose radius of the insert should never exceed 1 millimeter in diameter in conventional applications. In other words, any amount of stock larger than that number will require the use of a rough boring tool unless you take multiple finish passes.
Moreover, keep in mind that crooked holes are likely to happen when a drill deviates from the center while producing the initial hole, which occurs if the drill is fed too abruptly or has a damaged tip. A finish boring tool is very sensitive to these out-of-round holes because of its one-insert preference, meaning it will only experience radial force applied from one side. And a finish boring tool has a higher possibility of being damaged from radial cutting force because it does not receive support from an insert on both sides and takes off very little stock.
Having any of these tools fed into the crooked hole will make them follow the path set previously. In fact, the longer the crooked hole, the more likely a boring tool will bend during the cutting process. As opposed to a finish tool, a rough boring tool is not affected by how straight the initial hole is, meaning that it will always bore true regardless due to the fact that most forces are axial.
In a nut shut, a rough boring pass surface finish is typically acceptable, but a specified finish in some applications may not be achievable using a rough boring head. It probably goes without saying that a fine boring head will always be more precise than a rough boring head when it comes to surface finish.
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