Determining milling bits

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mun

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Hi

I'm going to make an egg-shaped part. Does anyone know how to determine what and how many milling bits I'll need? Also, is there a way to determine the time it needs?

Sorry, I'm very new.

Any help appreciated.
 
Sounds more like a lathe job to me. You've got a real challenge on your hands for a new mill job.

CHuck the grumpy old guy
 
PS welcome to the group! The combined knowledge contained here in enormous an friendly.

CTGOG
 
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ch2co said:
Sounds more like a lathe job to me. You've got a real challenge on your hands for a new mill job.
Click to expand...

Sorry, I should have been more accurate. I'm actually trying to make an egg shape cavity in a block, so I think CNC is probably the way. But how do I determine how many and which milling bits I'll need?
 
If you're milling an ellipsoid pocket in a block, typically rough with a 1/2 inch 4 flute center cutting end mill with a 1/32 radius, and finish with a 3/8 four flute ball end mill. I assumed an inch mean on the ellipsoid. That will work for larger pockets too..

The basic rule is to use a ball em that has a smaller radius than the profile you need to cut.

Coated carbide is the way to go. It is rigid, and holds its edge.

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Welcome aboard mun! :)

The answer to your question is: Yes. But, in order to be able to calculate a good guess there are a lot of variables that need to be taken into account:

  • Material?
  • Part size?
  • Machine size?
  • CAM program used to generate the G-code, some are more efficient than others.
In some CAM programs, there is a simulator that will give you a pretty good idea of the machining times. The formula is pretty much length of tool path divided by the feed speed.

As far as end mill requirements, it really depends on the other factors. Material removal rates are normally rated in cubic inches per minute or CC's per minute. But this is highly dependant on the material, machine size, and part size. If you can use a larger end mill then you can apply more horsepower to it and thus have higher material removal rates. But this is limited by the machine spindle horsepower and machine mass.

Number of endmills required is dependant on the material and operations, if it's a free machining plastic then maybe one, but if it's 304 stainless steel then maybe it's going to require more than one. You may need to use different endmills for roughing and finishing.

I hope this helps. :)
 
Last edited:
Well put JimDawson, if indeed one needs to produce many parts in a limited time and the price is right then the number of tools used is unimportant, add the tool change time and tools to the overall estimated cost.
Buy lots of extra tools.
 
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