Jay’s Seco TechTalk: How much stock should you leave prior to your finish pass with Solid End Mills?
Check out these tips and tricks for maximizing tool life and surface finish.How much stock should you leave prior to your finish pass with Solid End Mills? It’s a good question. Seco Product Manager, Jay Ball has the answer.
Defining the optimal amount of stock to leave prior to the finish pass is a delicate balance that depends on various factors. You must consider material characteristics, toolpath strategies, and desired surface finish.
Excessive stock can lead to longer machining times and increased tool wear. Roughing complex 3D features will leave behind additional stock in corners and tight areas. One of the easiest ways to put yourself in a solid milling bind is by leaving too much stock behind to finish. It’s a sure way to reduce output and wreak havoc on tool life and surface finishes.
Leaving sufficient stock ensures there's ample material for the final pass, reducing the risk of chatter or tool deflection. It will also give you a more consistent tool life and surface finish.
Precision and efficiency intersect in this decision-making process.
Don’t leave too much stock for finishing in your hard-milling machining applications. When machining tool steels above 48 HRc, leaving too much finish stock will not only reduce output but also wreak havoc on surface finishes and tool life. A general guideline for finish stock allowance is 1%-2% of the finish cutter diameter. Most cutting tool manufacturers base their finishing cutting data on 1%-2% of the tooling diameter engagement. Leaving more than this will result in lost productivity.
For example, when using a ½ diameter tool it is best to not leave more than 0.005”- 0.010” of finish stock.
Leaving too much finish stock is bad for tool life and surface finishes but leaving inconsistent stock for finishing causes a negative impact as well. After a complex surface has been roughed, it is important to run a “rest-rough” and even a “semi-finish” tool path, to ensure a consistent finish stock on all surfaces.
Take this example into consideration: A complex 3D surface has just been roughed out with a 12 mm ball nose end mill with an intended finish cutter diameter of 8 mm. A safe practice would be to “rest-rough” with a 10 mm ball nose end mill. Then, “semi-finish” with an 8 mm ball nose ensuring there is only 0.003”- 0.006” of stock on all surfaces. Finally, finish mill with a new 8 mm ball nose end mill to achieve a consistent surface finish as well as extend the life of the finish tool.
This strategy may even lend itself to using the finish ball nose end mill as a “semi-finish” tool once the finish tool life has been met.
Check out some more information about what solutions can help you achieve successful hard milling applications here.
Once your tool is below 3mm diameter range, leave on average 2% of the diameter to ensure you get sufficient bite on the pass.
Inspired by a long list of things he wishes he was taught in school, Jay focuses his Seco TechTalks on his hands-on machining experience.
Catch more episodes of Jay’s #SecoTechTalk on Seco’s Instagram. Be sure to let him know what you want to hear about next.
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