my new prusa i3 make me hard times

hi guys
I'm new in this world and just bought my prusa i3 before amount
i already success with some printing but still have unclear problems and questions:
1. my printer controlled by "melzi" and i read somewhere that the hot head fan should always work so,i need connect it directly to 12V and do not connect it to the "fan" connection on the board. can it be?
(currently i added micro switch to the fan and set it always on after the first layer)
2.I tried to print a part with some studs on it and the sticking between the stud and the base of the part is not good,and it very easy to break it ! (please see attached photo)
3.This part is a section of full circular part and when i try to print the full part (140 mm diameter) the connection between the infill layers is bad and definitely
not in the same quality like the connection between layers in the small section . what is the reason ? my thinking is that in small part the material is still hot when the printer add one more layers and than the sticking is better , and if that the reason so how can i print a big part and to keep verify good sticking between layers?
hope i am clear with my questions
i will appreciate your response
shai

1.- That is correct, the fan to the hot end needs to be powered by the power supply and stay on all the time, the fan used to cool down the PLA while printing is the one you need to connect to the board.
2.- It looks like you are using 2 STL files combined? if so, need to lower the connecting Z distance.
3.- If you are printing with ABS then what you mention is correct since you need to keep the lower layers warm to allow good interlayer adhesion, if part is too big, without a chamber the part will cool down and suffer from bad interlayer adhesion. If you are printing with PLA then you might be printing too cool for good adhesion.

hi
thanks for your quickly response
1. when you said fan for "hot end" do you mean the number 1 or number 2 ? (in the attached photo)
2 no i'm not using 2 STL files combined. this is the same file (printed with fans "on" (both of them) during all printing if it make you sense)
3. i'm printing with pla and i don't get good adhesion in the big part (if compare it to printing small part). its look like it's doesn't work with cold part.
one more question : the bed should be always warm or only at first layers? (currently it always on 60 degree)

Quote
shaip
hi
thanks for your quickly response
1. when you said fan for "hot end" do you mean the number 1 or number 2 ? (in the attached photo)
2 no i'm not using 2 STL files combined. this is the same file (printed with fans "on" (both of them) during all printing if it make you sense)
3. i'm printing with pla and i don't get good adhesion in the big part (if compare it to printing small part). its look like it's doesn't work with cold part.
one more question : the bed should be always warm or only at first layers? (currently it always on 60 degree)

Fan one would be the hot end fan, used to keep the heat from the hot side from creeping up and melting the extruder plastic or softening the filament at the driver wheel.

Fan two is used to cool the extruded plastic to help with adhesion and bridging.

By the way you are better off with the hot end fan on all the time because it doesn't take much heat creep to start the extruder slipping.

I am looking for drivers for the Melzi board. Do you have them for Windows 7 or MAC?
Also, when you started up the printer what LED's came on? I only have 1 red LED and I am not even sure the printer is working. I just finished putting it together.

hi
sorry i don't have driver , i bought the printer and driver was already inside the board
the led in the bed is the only one that i have and its start only after start warming !

thank you .
i change it and now the hot end fan always run and the second one connected to the board.
its look good , but i am still have some problems , there are some parts that success only by using cura and some part only by using slic3r
one of the problem is that i don't get good adhesion between the external wall to the infill .

Inter-layer adhesion can be poor if your print temperature is too low. Try upping it by 5 degrees at a time and testing the strength of the print after each increase.

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