Lately, I have been asked several questions about hole finishing. Many are concerned about the best method to use. Should I use a boring bar, multiple cartridge boring head, reamer, or what is the best method to finish my part?
As you know, numerous things will help determine an answer. We’ll need to look at the amount of stock being removed, the finish required, the total tolerance we must work with, the machines we have available to produce the part, and any fixturing issues that may exist.
The most common mistake I see from customers is the length-to-diameter (L:D) ratio used when boring parts. The best practice is to use the largest diameter boring bar that fits into the bore. This will also give you the most stiffness and eliminate tool deflection. The second consideration is the depth of the bore and again the diameter of the bar. By using the larger diameter bar, you’ll achieve greater depths as well.
Tooling suppliers offer a wide range of boring tools. Most of them offer tools with diameter adjustment and at least two cutting heads. This type of tool maximizes metal removal while providing a more stable cutting condition to help eliminate tool deflection. Single head or pocket boring bars offer multiple pocket designs that allow you to change the geometry of the cutting insert and provide the flexibility you need to produce your parts. Most of these tools come in steel or carbide shanks with replaceable heads.
Another area of concern is the machine tool you’ll use. Often, we see machines that are too small or lack the horsepower to produce the parts. In these cases, we must look at the safety of the operator first and make sure we safeguard against machining a part that is too large for our machine.
So, what’s the answer to our original question? There’s no one answer. Variables are numerous. All questions must be answered to determine the best way to bore the part. In some cases, reaming may be the best approach, a dual-headed boring bar may be best, or a plain single-head boring bar may be the answer. However, we should always look at our L:D ratio and maximize the diameter of the boring bar we’re using. Consider chip removal and use through-the-tool coolant, if possible, to help chip washing.
I suggest working with your tooling supplier. They have the application expertise and can help guide you to the proper tool selection. Go ahead and lead a boring life!
CMR Consultants miker2468@aol.com
