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1-flute mills cuts POM much better, trust me. More than this you can run the spindle at his max-speed and exploit the full torque of it.MagIO2 wrote: I always used 2 flute endmills, for example the 2mm one with cutting depth of 2mm, 16000rpm, 6mm/s. And I don't go down in steps but cut down to the full depth of 10mm in 5 steps. No broken endmills so far.
Nice argument. But I think that the difference between the speed of cutting in one, or in the other, direction should be very small when compared to the turning speed of the tool (in my case between 16.000 and 20.000 rpm).MagIO2 wrote: Going one direction the portal speed adds to the cutter (turning) speed from perspective of the material. In the other direction the portal speed is subtracted from the cutter speed. Maybe that makes the difference.
The overlap in the above photos was 10%, when I increase it I just obtain more thin grey/white stripes. For now the unique solution I found is to force milling just in one direction (i.e. increasing Y coordinate). But this is not a real solution at all (milling became a very slow operation)MagIO2 wrote: How big is the overlap when cutting forth and back? I tend to use a overlap of 70% if surfaces should be nice. Meaning with each pass in one or the other direction there is only 30% of the endmill cutting material. Maybe you can play with this parameter to improve the result.
Yep! I subscribe your point of view. I think that the problem is there. Anyway I still cannot understand why a 2-flute bit doesn't suffer of the same problem. I mean... ok, maybe the tool is not perfectly perpendicular, and a 2-flute bit has 2 tips cutting the material, the 1-flute has just one. But when the rpms are so high (e.g. 20000 rpm in my case) I think that even the 1-flute bit should have enough time to cut junk material that it leaves behind.MagIO2 wrote: But I think that it is really important that the endmill is perpendicular to the table.
Yeah, I've made this test too, no results. Same stripes even if you use a "Staubsauger" or not...MagIO2 wrote: It might also be worth to try out a vacuum-cleaner. It removes the cut material which might get stuck in between of the uncut material and the cutter and increase friction (which produces more heat). Second the airflow will cool down the cutter.
No, I never broke an end mill until now (I'm crossing my finger). In my previous posts I just speak about broken material 'cause of excessive vibrations of the tool.MagIO2 wrote: Maybe this is why your endmills broke in the other thread. This problem should not be fixed at the spindle/collar. The root cause is somewhere else.
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Yeah, I know that. Since many days I have adopted the 1-flute bit to half the amount of material cut and put less stress on the machine (and reduce also vibration). As you suggested, it works.Rory wrote: Machining with a 2 flute - and then with a 1 flute - with the same parameters - means you are machining at "feed per tooth rate A" (2 flute) and "feed per tooth rate A/2" with the single flute - so you will see differences.
By adoption of the right feed rate I can avoid to bend the tool or flex the machine. Obviously one has to make several tests to get the right moving speed.Rory wrote: The cutter stickout you have is high also so its likely the cutters are flexing the STEPCRAFT frame.
Aaaaaaargh!Rory wrote:
First of all: at max speed you do not have full torque. Torque is max well below full speed. It would be interesting to have a torque curve for this spindle. Strictly speaking - motor torque curves will show that max power is not actually at 100% RPM but lower - However in our experience its still better to be at 70% or higher for these types of Motors.
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mmmh... this means that the max torque is at the max speed? Rory said this is not true.drilldevil wrote: hi,
watch in wikipedia "torque/turning moment" of an electrical motor (i used the german section) there u will find the following:
P = 2 Pi n M
if u dissolve this to M:
M = P/(2 Pi n)
and you use the known parameters:
P = 500 W,
n = 20000 rpm = 333,33 rp sec
you get the following:
M = 500 /(2 Pi 333) = 0,2389... Nm
and thats nearly the value you will find on the stepcraft homepage given for the 500 watt hf spindle.
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mmmmh... I don't know... description states that the HF350/500 motor is asynchronous, while brushless motors are synchronous.drilldevil wrote: as this spindle uses a brushless motor.
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