Need Help!- chatter on countersink operation

[AchillesGr]

hi,
guys i need your help.
i am new to milling and i have some problems that i do not know what to do.
i am trying to make cut a small lip around a 1/2" hole for an o-ring to seat abought 1/16 depth.i get so much chater that it ends up in a polygonal shape.

my machine:
optimum bf20 vario
mt2 drawbar 10mm
20mm hss countersink
hand tightened chuck
no cooling
aluminium 7075

i tried 70-2000rpms and i get the same.

i also tried to form a side of a aluminium 7075 1/2" thickness with the side of a 3/8" hss endmill on a er25 collet and the finich is not good. it is shiny but there are noticeable waves.
also tied low and high rpms (100-2000)

what is going on?
is there flexibility from the machine?
i am asking too much from a small machine like this?

thanks!

[djr76]

try a single flute chamfer if you are using a multi flute. Otherwise try increasing feed rate with a slower spindle speed.

[AchillesGr]

thanks!
i will try that!
my countersink is a 5 flute one.should i have bought the 3 flute ones?
how slow speed do you mean?

is there a way to measure the machine flexibility or rigidity? why i am taking a waving surface when miling with the side of a 3/8 endmil? what is the cause of this?

thanks

[underthetire]

And get that thing out of a drill chuck, and in to a short holder.

[djr76]

Originally Posted by AchillesGr thanks! i will try that! my countersink is a 5 flute one.should i have bought the 3 flute ones? how slow speed do you mean? is there a way to measure the machine flexibility or rigidity? why i am taking a waving surface when miling with the side of a 3/8 endmil? what is the cause of this? thanks

if its wavy, then it could be the hole is not concentric, work holding/rigidity issues. with 5 flute, you really need an aggressive feed rate.

[AchillesGr]

i have a similiar problem with a 1/2" enmill cuting from the side a 1/2" aluminium plate. i get a wavy surfase with diagonal marks and i have tried speeds from 50-2500 and varius depths and rates.
.i measure my spindle runout at the er25 collet body and there is a 0.01mm runout per revolution.if i remove the er 25 holder and measure it at the spindle inself there is a runout of 0.006 mm .

my question is if this is normal and causes any kind of problems. as the endmil rotates i hear the sound changes in every recolution .
is this amount of runout normal?

thanks again!!

[DareBee]

Use flood coolant or cutting oil

[neilw20]

Keep it short, close to the spindle, low speed, aggressive feed, with a .5s pause before retract.
3 flute not good.
Even flute count helps one side react against the other.
Rigidity is everything.

[Ed from NY]

Waviness in general is a sign of lack of rigidity. Could be the work holding, tool holding, gibbs, machine column, etc, etc.

Originally Posted by DareBee Use flood coolant or cutting oil

+1 on that!

If all else fails you could try a 45* mill and circle it around as you would do if you were chanfering the piece's outside edge.