Tips on surface milling with ballnose endmills.
November 18, 2013, 1:13 amArticle Summary
Eldar Gerfanov (Admin)
November 18, 2013, 1:13 am
September 19, 2024, 11:50 pm
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Fri September 20, 2024, 7:51 pm
Fri September 20, 2024, 7:51 pm
Since surface milling is more than half of what I do for a living, I decided to share some of my tips on that topic.
Step-over considerations
Generally, you want to create a continuous toolpath that does not change directions too often.
Changing directions slows the machine down and reduces the feed rate, which changes the deflection of the cutter, and causes gouge marks on your surfaces.
When you have a long narrow piece it's better to go along the long side to save on time and machine wear.
Also going along the longest side reduces the number of direction changes.
It often helps to make circular lead-ins on step-over.
Finish allowances
When surface-milling you often need to first rough, then semi-finish then finish.
- Leave 15 thou after roughing, 3 thou after semi-finishing, and finish to zero. All with progressively smaller tools.
- 5 thou stepover will give you a good finish on most ball mills
- 3-5 thou chiploads are very common for finishing surface finishing.
When shallow surfacing
The ball mill will always give a bad finish on shallow areas - the center is not cutting, but dragging around.
Proper step-down and milling direction
The straight portion of the flute acts as a wiper and reduces the scallop that the ball portion creates.
This is why going from top to bottom is safer and yields a better surface finish.
The closer the wall taper angle is to the taper of the flutes the better finish you will get:
There is another reason for always trying to go from top to bottom.
When taking material top to bottom you engage stock closer to the tip of the tool.
It makes the cut more stable. It is safer because you are less likely to bury the tool in stock unexpectedly.
Do not go from climb milling to conventional UNLESS you need to save some rapid time.
Pick up only climb milling and you are good to go.
Changing from climb to conventional will cause the tool to deflect away from the work on the climb and into the work during the conventional pass. You will see zebra marks all over your surfaces.