Hotend temperature drops

Please respond me!

1)I am printing lithophanes, I increased my retraction from 6.5 mm to 7.5 mm still little zits/blobs can be seen on the surface of lithophanes.

2) I am using pronterface for printing, My printer gets slow down at some layers while printing . When it's slow downs, I just click the button of mouse randomly on pronterface interface then printing speed becomes normal. I don't think this is mesh size issue. What could be the reason for this?

3) currently I am facing another issue, my printer stops printing after 2-3 layers. on close observation,I found that this is because of temperature drop. Initial temp stables at 205 deg cel.but after 2-3 layers when part cooling fan gets turned ON, temperature drops by 9-10 deg.cel. then printer gives me heating error and printer beeps.
Then in cura, I changed my settings for cooling. I set initial fan speed same as that maximum speed i.e. 100%. That time also , after bed leveling when part cooling fan starts for 1st layer, temps drops and gives error. How can I resolve this?
I also tried by setting initial fan speed as 50% and then 100%after 3-4 layers but again got a same error.

Please respond to above queries. waiting for your support.

Thanks and regards,

1: Presumably you are using a Bowden setup. Long retractions might be a result of loose fitting of the filament inside the Bowden tube. Some tubes (e.g. Capricorn) are a better fit than most others. They might also result from looseness of the fittings at either end of the tube.
Perhaps try faster retraction rather than longer retraction.

2: I expect that using Proterface means that the communication between computer and printer is via USB. Works OK, but is often slowed down by the computer for reasons that only the computer knows! Reading a file from an SD card or a USB stick is often more reliable because it is not at the whim of a computer.

3: In general it is not always easy to avoid the part fan blowing on the hotend, but that is what you should aim for. Do you have an insulating silicone sock on the hotend? If not, then that might fix your problem. If an appropriate sock is not available then you can hack an alternative using high temperature silicone or fibreglass and Kapton tape. I used the fibreglass and tape solution for quite a while.
Perhaps you could ramp up the fan rate gradually over a few layers so that the hotend heater can more nearly keep the temperature constant so that the heater failure detection is not triggered.

Thanks for your response,

1) yes. I am using Bowden type arrangment using silicon tube. Now I have kept my retraction at 6.5 mm as default in cura and retraction speed increased from 25 mm/s to 40mm/s. Still I observed some blobs/zits intermittently/randomly on the wall of printed part. Should I increase retraction speed further?

2) yes. I tried to give prints directly from SD card inserted but my SD card sometimes shows "media inserted " and sometimes shows "media removed". It actually fluctuates. I don't know why this is happening. That's why I give prints via computer and usb cable.

3) currently I don't have silicon sock, high temperature fiberglass or kapton tape.
How can I increase fan speed gradually ?
In cura I can see only initial speed and regular/maximum speed.
For uniform distribution of temp , I have set initial temp at 25% and final temp at 80% (after 2 layers)
But how can I increase speed gradually?

1. Silicon tube is too stretchy for use as a Bowden. You need PTFE (which I'm guessing is what you meant to write).
See this site for an extensive set of instructions and files for tuning retraction and other aspects of the printer: [teachingtechyt.github.io]

2. I don't know what is going on with the SD card. Can you print from it? Does the slowdown happen?

3. Get a sock; you won't be sorry.
Increase the fan gradually by setting increasing fan speeds for different layers in your slicer. I have never used Cura, but I imagine that it allows you to set fan speed on the basis of layer.