Danger of a high-speed rotating chuck

Most applications do not require the lathe to run at 6,000 r/min or more. If an unreliable chuck rotates too fast, it will be very dangerous to workshop personnel. It is at the risk of breaking the bolt thoroughly. In a car factory, when a machine tool ran at 4,000 r/m, a small piece of copper sheet flew off the chuck and embedded into a steel structure nearby. So, you can image how dangerous it is if the workpiece flies off the machine tool. Every machine tool should be made in the standard of being able to provide enough safety for workers. In the United States, if someone is injured, lawyers will line up to visit.

Safety must be a primary consideration. Not all the chuck manufacturers use the same rating value when announcing the data that a chuck clamps the curve. SMW Autoblok measures the maximum rotary speed of its chucks when the clamping force loses by 50%, while the parameter of another competitor is measured when the clamping force loses by 66%; therefore, their safety level is not the same.

High speed does not necessarily mean high rotary speed. Chucks running at 8,000r/min are seldom applied; and what are more often used are 254mm high-speed chucks running at 5,000r/min.

Faster chuck speeds are becoming more common. But in some cases, for high speed application occasions, compared with conventional motor chucks, flexible collets may be more suitable. Workpiece holder project manager of Hardinge Company thinks that high speed is indeed a trend; several high-speed chucks available in the market, even now, are ahead of machine tools. But machine tools tend to develop towards higher spindle speeds, which plus the function of improving productivity makes such high-speed chucks may have a certain market. As to whether it will be dominant or nor, it is another question.

Correction Methods of Three-jaw Chucks

Three-jaw chucks will appear reduced coaxility and horn mouth phenomenon, which will impact the processing accuracy and clamping reliability directly. Practice has proved that the following correction methods are simple and practical. Just have a try!

Take a positive-jaw chuck for example, clamp a section of round bar with a proper diameter externally, start the machine tool, and turn the cylindrical part of the chuck jaw. Then, clamp a ring unit in an internal support way, start the machine tool and turn the internal part and ends of the jaw.

Obviously, this will be able to significantly improve inner circle of the processed chuck jaw and the coaxiality of the machine tool spindle and eliminate the horn mouth phenomenon, obtain a higher precision and achieve the purpose of correction. The following points should be paid attention to during specific applications:

1.The gap between the claw and the chuck of the chuck is inevitably present, and the direction of the force on the jaw during correction is opposite to that on it during actual work, so the corrected chuck will appear the horn mouth phenomenon in use. Therefore, the inner circle of the chuck jaw should be processed into a reserve horn mouth with a certain taper (large inside and small outside) during correction; the tamper value adjusted can be confirmed through test, and this is the key to success.

2.The outer circle of the round bar and the inner circle of a ring unit should be pro-processed and have certain accuracy. Besides, the inner diameter of the torus shall not be too small, or it will make the concave of the jaw surface too deep, which will easily damage the surface of the workpiece when holding large-diameter workpiece, so it must be paid great attention to.

3.Because the hardness of the chuck jaw is high and it is used for intermittent cutting, the depth of cutting and the amount of feed should be small during correction and the cutting speed should not be too high. The tool material is preferably made of cemented carbide. If a small power head is installed on the planker and grinding wheels are used for grinding, the correction effect will be better.

4.The first step is to require the aim of cutting jaw’s outer cycle should be establishing a good benchmark to improve the precision of correction, and this step should better not be saved.

5.This method can also be used to correct errors due to improper installation or other causes and improve the precision of processing.

6.The same principle can be used to correct reverse jaws.

Manual for Safe Use

Matters Needing Attention in the Use of Chucks:

Customers that just use front-mounted pneumatic chucks, hydraulic chucks and oil-pressure chucks must pay attention to the following questions, which shall prolong the lifetime of our chucks very well. General service life of a chuck is over 3 years (but very few customers do not pay attention to the use of chucks and will have the chuck break down within a month). Under normal situation, the well-protected chuck can be used for 5-10 years.

1.Be sure to wipe some butter before the first time use of the chuck and the dosage of the butter is twice that the usually used amount. There is no limit to what brand the butter should be but you must use cooled butter when the chuck is running at a high speed.

2.For chucks working every day, spend 1 minute in clearing the iron dregs, grease, etc. with a blower before and after work.

3.For assistant jaws or collet chucks in front-mounted chucks, it is recommended to change a new pair when clamping every 100,000 pieces, which is conducive to maintaining the precision.