CNC Machining Cost - Saving Design Skills: A Practical Guide+ View more
CNC Machining Cost - Saving Design Skills: A Practical Guide
+ View more
Date:2025-01-20 09:36
The CNC machining field has been my professional home for many years, mostly as a senior CNC machinist. From this perspective, I have gained a deep understanding of the pressing need to save money in any and all projects that involve CNC machining. What I am sharing here is not a treatise on design for CNC machining. It is much closer to a tip sheet, almost like a series of post-it notes, on some practical and well-proven design skills that can—if their intent and use are understood—save time and money in any project that involves CNC machining. To start with, there is a principle that, when followed, allows a part to have smooth internal vertical edges and gives the cutters a much better place to work.
Controlling the depth of the cavity is also crucial. The depth must not exceed a condition of modesty in which metal or plastic begins to look bad. Speaking very generally, you'd want it to be less than four times the longest linear dimension. For a guinea pig I once worked with, the cavity length was 80 mm. We controlled the cavity depth to 300 mm. Not only does excessive depth increase tool stroke, but it also negatively impacts several factors crucial to near net shape precision. These factors include cutting speed, which directly affects processing cost, and machining speed, which is usually a term reserved for the appearance of near net shape parts once the tool is retracted, but which also affects processing cost in that the faster you can get the job done, the less you spend on labor and overhead.
The specifications also state what the thread length must be. It may not exceed three times the diameter of the aperture. Thus, if the 10 mm is the aperture diameter, then the maximum preferred thread length is 30 mm. Anything beyond that length not only is more difficult to command through the body of the work but also takes more time and talent to do so. If you must process a thread to fit through an aperture, it really is best to keep the thread length manageable. If you are choosing the aperture diameter, it really is best to keep to standard sizes. You will find standard tools for making through holes to be much more common and versatile than tools for making blind holes.
Be careful when assembling tolerances. Specify them only where it's absolutely necessary, and use GD&T for the parts that need tight control. Don't go after high precision throughout your design. Instead, aim for reasonable tolerances that allow your parts to do what they're supposed to do and fit together well. Also, consider how many setups a machinist will have to do to finish a part. Your designs should allow for setups that make all the important operations a part needs happen in the fewest and easiest steps possible.
For small features, it's crucial to keep aspect ratios from getting too large. If large aspect ratios can't be avoided, then it is absolutely necessary to add structural supports and make strategic connections to the wall to give the feature some backbone. Be careful when creating features that are "text" in nature. If text features can be left out, they should be. If they must be retained, the engraving process should be used. The embossing process is far more complex and much more risky—because it has many more steps to manage and a lot more that can go wrong—that it simply shouldn't be done at all when the engraving process will work just as well.
One of the most significant components affecting costs is the choice of materials. For large-scale orders, we should choose materials with good processing performance. We recommend selecting materials that are easy to process—that is, easy to cut and easy to form. They may not be the cheapest option, but we believe they will give us the best return on investment. For small orders, we should choose materials that keep unit costs low while still performing their necessary functions.
Unless absolutely necessary, the surface treatment should be chosen appropriately and tailored to the item at hand—without inflicting upon it the multiple, unnecessary treatments that have, until now, subjected the appearance of items to degradation and made us question the very integrity of the items themselves.
Controlling the depth of the cavity is also crucial. The depth must not exceed a condition of modesty in which metal or plastic begins to look bad. Speaking very generally, you'd want it to be less than four times the longest linear dimension. For a guinea pig I once worked with, the cavity length was 80 mm. We controlled the cavity depth to 300 mm. Not only does excessive depth increase tool stroke, but it also negatively impacts several factors crucial to near net shape precision. These factors include cutting speed, which directly affects processing cost, and machining speed, which is usually a term reserved for the appearance of near net shape parts once the tool is retracted, but which also affects processing cost in that the faster you can get the job done, the less you spend on labor and overhead.
The specifications also state what the thread length must be. It may not exceed three times the diameter of the aperture. Thus, if the 10 mm is the aperture diameter, then the maximum preferred thread length is 30 mm. Anything beyond that length not only is more difficult to command through the body of the work but also takes more time and talent to do so. If you must process a thread to fit through an aperture, it really is best to keep the thread length manageable. If you are choosing the aperture diameter, it really is best to keep to standard sizes. You will find standard tools for making through holes to be much more common and versatile than tools for making blind holes.
Be careful when assembling tolerances. Specify them only where it's absolutely necessary, and use GD&T for the parts that need tight control. Don't go after high precision throughout your design. Instead, aim for reasonable tolerances that allow your parts to do what they're supposed to do and fit together well. Also, consider how many setups a machinist will have to do to finish a part. Your designs should allow for setups that make all the important operations a part needs happen in the fewest and easiest steps possible.
For small features, it's crucial to keep aspect ratios from getting too large. If large aspect ratios can't be avoided, then it is absolutely necessary to add structural supports and make strategic connections to the wall to give the feature some backbone. Be careful when creating features that are "text" in nature. If text features can be left out, they should be. If they must be retained, the engraving process should be used. The embossing process is far more complex and much more risky—because it has many more steps to manage and a lot more that can go wrong—that it simply shouldn't be done at all when the engraving process will work just as well.
One of the most significant components affecting costs is the choice of materials. For large-scale orders, we should choose materials with good processing performance. We recommend selecting materials that are easy to process—that is, easy to cut and easy to form. They may not be the cheapest option, but we believe they will give us the best return on investment. For small orders, we should choose materials that keep unit costs low while still performing their necessary functions.
Unless absolutely necessary, the surface treatment should be chosen appropriately and tailored to the item at hand—without inflicting upon it the multiple, unnecessary treatments that have, until now, subjected the appearance of items to degradation and made us question the very integrity of the items themselves.
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