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Solve the problem of poor surface quality of CNC machining parts

For a layman not familiar with CNC machine shop operations, once the chips stop flying, the CNC milled part is dropped, and another precision machine part is rolled out, they may assume that the final product is accurate and to specification. Unfortunately, this is not always the case. In any relevant CNC machining shop, the finished product is not delivered to the customer until it passes the inspection service process. Dimensions of parts must meet the tolerances set by their design, including a thorough inspection of the finish of all machined surfaces.

In general, a part may conform to a specific size, but must be scrapped due to substandard overall appearance and surface finish. Not only can this cause aesthetic problems, but more importantly, it can negatively impact the functionality of the part.

Best of all, the amount of work that has to be sent to the dumpster at the end of the milling and machining process is less than expected. CNC machinists are detail-oriented by nature, take pride in their work, and want to see a completed project. Scrap parts due to surface finish issues can also be a real profit killer for a job shop. Poor quality leads to increased costs, increased downtime, delayed deliveries, and in worst cases lost orders.

1. Improve tool speed

Faster speeds (measured in surface feet per minute) mean less contact time between the material and the cutting tool. This reduces edge buildup that causes poor surface finish and increases tool life. Tool failure is the leading cause of damage to precision machined parts. Never estimate or guess how fast your work will take you.

2. Always clear/control chip

Removing excess chips or built-up edges during machining and not allowing them to contact the workpiece is a critical task and key to producing a high-quality surface finish. Chips and BUE tend to build up and can easily damage the surface finish of the tool if not removed. Chip breakers, compressed air and best of all solutions, flooded coolant can be used to remove chips for better control and less scratching/damage of parts.

3. Different tools should be used for roughing and finishing

Do not use the same tools used for roughing to complete the service. Instead, a small number of roughing tools should be used to remove most of the material, while newer, sharper tools should be kept and used for finishing only. When used in conjunction with roughing or finishing tools, the tool insert radius, rake angle, feed rate and insert material itself can lead to higher quality.