extruder ripples in outer wall (3 replies)

or my corexy i tried a direct drive extruder with a mk8 hobb . I am getting these wierd ripples in the prints. ( the rippples are visible in the plan like inconstant extrusion. The steps per mm for the motor are right, the hot end is new and not clogged. the nozzle is 0.5mm so the force needed to extrude is not so much ( u can easily push with 2 fingres ) . Up until now i have been using geared extruders and never had this problem

I tried 2 different motors and drivers ..

motor 1 :
12v
27 ohm
40mm nema 17
dont have any more details

motor 2
6 v
7.5 ohm
7.5 mh
0.8 amp

drivers :
1 drv 8825 in 1/16 mode
2 a 4988 in 1/16 mode

motor 1 works better with drv 8825 but has the ripples like in the pics, with the a4988 the ripples are double the amplitude( deeper and higher )

motor 2 works better with a4988 but again with the same ripples as the pics . With the drv 8825 the ripples are doubled

controller :
ramps 1.4
drivers for x and y sd 6128 in 1/32 mode
hot end e3d v6 with 0.5 mm nozzle
print z resolution 0.25

firmware repetier ( downloaded from online configuration wizard )

steps per mm for x, y : 160
steps per mm z : 400
steps per mm e : 140

any idea why this is happening ?










i did the following tests


printed with ALL DIRECT DRIVE MK8 ).4 nozzle e3d
a4988 stepper drivers at 0.8A ... ripples exist
drv 8825 1/32 0.3A-0.8A
sd 6128 1/32 0.8A

Then I did tests with a 1:3 geared extruder with mk8 hobb 0.4 e3d nozzle

Last i printed with twisting the belts so that the back side of the belt goes over the pulleys

I even tried two separate hot ends and two separate power supplyies . One a 6 Amp and the other a 30 AMp

the ripples exist in all prints..

they are least with the belt reversed and the print with a flow ratio of 150%

It looks like a under extrusion issue ( like on other forums ) but the measured extrution with is coming to 0.44 mm and the specified width is 0.4mm (auto in slic3r)


a4988



sd 6128 at 1/32 and 0.8 A



geared extruder with belt revered on pulley and sd 6128


[lh3.googleusercontent.com]

detail
I am stumped that the frequency of the pulsing is same for the direct and the geared extruder.. If it was the extruder creating the problem the frequency would vary with the gearing of the motor. Reversing the belts and increasing the flow helps but doent remove it completely



firmware : repetier

slicr : slic3r 1.1.7



Any guesses whats going on?

thanks