Carving and surface finish
Posted: Wed Jun 20, 2012 12:39 pm
Attached is a chart I worked on in jpg form.
Basically it lists the the 3 common sized ball endmills and then calculates (by using the Pythagorean theorem) the height of the theoretical peak left between stepovers. Theoretical because this assumes zero runout. Runout would tend to lower the peaks but ruin the details if excessive.
So if you are happy with the finish that you get with an 1/8 ball at a 10% step over, but feel you would like to see extra detail on depths that a 1/16 ball mill would give you, go to this chart where it shows your .00031 height for a 1/8 ball nose at 10% step. You can see that you'll get the same step height with a 1/16 ball nose at 14% but since the step is about 1/3 less it should take you about 1/3 longer to cut then your 1/8 ball nose.
I actually cut my very detailed celtic cross in cherry (also attached) at an 18% stepover with a 1/16 ball nose in 58 minutes. The step was slightly smaller than you would get with an 1/8 at 10%(.001125 vs. .0125) with a .00051 height but this also required only a light sand mopping to finish as the peaks between stepovers are easily removed.
So this chart would help anyone who wants to see what adjustments they could make to balance finish and speed. It’s daunting to look at the estimated time for machining and not know if it’s worth letting your router hum for 3 hours. This would allow a comparison for evaluation before committing to 90,000 lines of g-code.
The level of finish required is something that you have to determine based on how the carved object will be used, the detail you want to see, and how long you want to machine. It is at a point that you determine there will be no advantage to going to a lower stepover percentage.
I hope this chart can help make that decision easier for you.
Basically it lists the the 3 common sized ball endmills and then calculates (by using the Pythagorean theorem) the height of the theoretical peak left between stepovers. Theoretical because this assumes zero runout. Runout would tend to lower the peaks but ruin the details if excessive.
So if you are happy with the finish that you get with an 1/8 ball at a 10% step over, but feel you would like to see extra detail on depths that a 1/16 ball mill would give you, go to this chart where it shows your .00031 height for a 1/8 ball nose at 10% step. You can see that you'll get the same step height with a 1/16 ball nose at 14% but since the step is about 1/3 less it should take you about 1/3 longer to cut then your 1/8 ball nose.
I actually cut my very detailed celtic cross in cherry (also attached) at an 18% stepover with a 1/16 ball nose in 58 minutes. The step was slightly smaller than you would get with an 1/8 at 10%(.001125 vs. .0125) with a .00051 height but this also required only a light sand mopping to finish as the peaks between stepovers are easily removed.
So this chart would help anyone who wants to see what adjustments they could make to balance finish and speed. It’s daunting to look at the estimated time for machining and not know if it’s worth letting your router hum for 3 hours. This would allow a comparison for evaluation before committing to 90,000 lines of g-code.
The level of finish required is something that you have to determine based on how the carved object will be used, the detail you want to see, and how long you want to machine. It is at a point that you determine there will be no advantage to going to a lower stepover percentage.
I hope this chart can help make that decision easier for you.