Product Development Inc.

When I rough it does not cut out the small holes and then when I finish the small tool goes into the hole and gets broken why?

3 different scenarios to consider with this question

1. Soft Material, Wax, Modeling Foam, You do not need to do roughing passes with each tool, roughing passes are mainly used to remove the majority of the material then the smaller tools are able to handle the cutting of the rest of the material in the finish passes. Since the step over is so small on finish passes normally .003 for ball mill tools and smaller .0015 for conical tools then the tools are only cutting very little material each pass.
2. Hard Material, Aluminum, Plastic, and a model that has holes smaller then the roughing tool, for example roughing tool is 1/4" and there are 1/8" holes and the finish tools is smaller then 1/4". When roughing the tool will not go all the way to the bottom of the small hole because it does not fit, 1/4" tool and an 1/8" hole. So material will be left behind in the 1/8" hole, no material will be removed. Then when you finish with a smaller tool it will try to enter the hole which has not had any material removed and it can break the tool,will it break the tool it really depends on how deep the hole is and also how hard the material is. A nice work around is to rough a part with the larger tool but in the case of an 1/8" hole I would rough with an 1/8" tool however it will not go into and 1/8" hole because it needs to leave the skin material that the finish tool removes, so next create a toolpath that is the smaller finish tool size and contour only and it will cut down the contours and into the holes to remove the material before finishing, or finish first with an 1/8" tool and do the final contour last with a 1/16" tool. This will cut out all the small holes, if you have a lot of small holes then using the drilling command it is faster if it is the same size as your endmill.
3. Jewelry wax and conical tools this does not apply because the wax is so soft and the conical tool is stepping over .0015" then you do not have to worry about it breaking the tool when entering holes like these that were not cut out during the roughing pass.