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Small Diameter Radius Fillets and Price Increase (CNC)

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rfer

rfer

Mechanical
Oct 4, 2019
19
Excuse my ignorance on this subject, but why does using small radius fillets increase the price of the part for CNC machining? Radius size I am talking about is R0.20-R0.40 mm (R0.008"-R0.015").

The geometry I am talking about is top down vertical milling when removing a rectangular shape from the material - the radius of the 4 fillets at the corners. The rectangular depth is small compared to the width of the cut - depths in the 0.5-3.0 mm range.

I am not a machinist so please correct me if I am wrong, but isn't it just a simple tool change to cut these?
Also, is this price increase per fillet or is it per tool change? Where say the price jump for 4 small fillets on one rectangular cut is large, but the price jump for 8 small fillets (2 rectangular cuts) is only slightly larger?

Thank you for any insight you have on this!
 
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What is the material you are cutting? Canyou post a drawing or picture showing the desired cut shape.

Ted
 
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Material is PEEK. I can't post a drawing of my specific part, but here is a pic of what I am talking about. Basically having these four fillets be R0.20 mm.

square-with-fillets_qkguoz.jpg
 
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The smaller the internal corner radius size, the smaller the maximum end mill diameter that can achieve that radius size. Smaller diameter end mills are more likely to break and will also cut less efficiently than a larger diameter end mill. Very small diameter end mills may also be less available and therefore more expensive. All of these factors are likely to drive up cost.
 
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A .008" radius is crazy small. I'd also like to add that you can't just grab an endmill that matches the corner radius. You have to go slightly smaller or you will get chatter in the corner and in this case you would probably break the end mill.
 
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