Registered: 16-08-2021
Messages: 3
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1. Preparation is a precondition for success.
The longer the drill takes, the deeper the hole is. When drilling a longer hole (with a greater distance between the tool tip and the spindle nose), the extent to which runout can affect results increases. In some deep-hole applications, even the slightest wobble can cause tools to wear out prematurely and compromise both straightness and surface finish, resulting in premature tool wear.
Metal Cutting Techniques Include a Variety of Methods [wignar.com]
However, the requirement for meticulous setup should not be used as an excuse to spend excessive amounts of time identifying and correcting for runout with each tool or insert replacement. A modern manufacturing environment does not allow for the climbing into workzones to mount indicators or the holding of pieces of paper in place for tool touch-offs, to name a few examples. With any deep-hole drilling operation, the likelihood is that using an offline tool assembly system with a presetter will save significant amounts of time.
2. The Chip is Created by the Coolant
Apart from using X-ray vision, chip formation is the only way to assess the performance of the drill while the cut is still in progress and there is still time to take corrective action. Curlicue shapes (also known as "sixes" and "nines") are ideal, whereas longer, stringier chips are less effective at transporting heat away from the cutting zone. Color is also important. With increasing overheating of the cutting zone, the chips become progressively darker in color, progressing from gray to black to blue. It may be necessary to reduce heat by slowing the spindle rpm, whereas stringy chips may indicate that the feed rate should be increased until the machined material breaks rather than peels.
Other issues may be more difficult to notice at first. According to Mr. DeLuca, "one of the most underappreciated inputs in any machining process, even beyond drilling, is coolant." In light of the significant influence that coolant has on the formation of chips, adjusting coolant concentration and flow can also aid in the resolution of problems with discolored "bird's nests."
3. Pecking Is Associated with Issues
It is possible to create 187 different combinations of standard insert geometries and coatings with Allied's T-A drills, and this is just one line of tools from a single manufacturer. Strategies for insert drills that were once standard procedure may no longer be applicable in the face of the wide range of application-specific options now available.
Pecking is an example of this. It should not be necessary to reverse the tool's feed during the cut to ensure that chips are evacuated from the hole on a regular basis. The majority of the time, when you see pecking these days, it's because someone misapplied a tool or used the wrong tool entirely, according to Mr. DeLuca.
4. Inserts are self-centered in their design
Another outmoded practice is the use of a 90-degree spot drill with a smaller diameter for the pilot hole, which is another outdated practice. The intuitive reasoning behind this is sound, and, as is the case with pecking, it can still be a useful rule of thumb for toolroom applications. Indeed, a hole of smaller diameter that is slightly off-center is easier to correct than a larger hole of larger diameter. A sharp point angle helps the drill penetrate the part more quickly and easily, allowing it to settle more quickly into position. Most CNC machine tools, on the other hand, are accurate enough that the pilot drill can be the same diameter as the main drill. They are also capable of driving duller points into virgin workpiece material with sufficient force.
In fact, the vast majority of replaceable-tip drilling inserts have self-centering tips with point angles that are less than 90 degrees in degree angle. As a result, the insert may have an impact on the major diameter of the hole before it reaches the self-centering point. According to Mr. DeLuca, if a standard spot drill is followed by one of our tools, the drill will have a tendency to walk slightly, causing premature wear and possibly causing the tool to lead off. Because the insert diameter and point angle are the same as the spot drill, the longer drill is able to pick up where the spot drill left off perfectly.
5. Caution is a virtue in this situation
Increased speeds and feeds are required immediately after starting a deep hole drilling operation, which can cause safety concerns and compromise the work. Therefore, many of the standard recommendations for general-purpose T-A insert drills from Allied can be summed up in a single phrase: proceed with caution when drilling the pilot hole. See the images in the picture gallery above for more information on the specifics.
According to Mr. DeLuca, approaching a pre-existing hole cautiously can help avoid scarring or damage. This gives the drill margins time to engage with the material before you accelerate the drill. The hole begins to function as a bushing, which helps to keep the drill centered while also keeping the parts and people safe."
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