Hotend problem - bad construction?

Hey!

I have big problem with my hotend. I found this model on ebay... i heard that this is tested and working hotend, but this experimental hotend not working good.
Here are some photos: This is build - but green PTFE is replaced by alu radiator: [tnij.org] and this is my hotend: [tnij.org]

when the cooler fan is ON heater reach only 160 C, so i replaced resistor to ceramic 40W heater.
But filament inside hotend is melting and going up in hotend, by the nozzle (0.3mm) going only some mm of flament. Inside diameter between radiator and heater block is around 3.8mm. I guess its to big so this is problem im right ? Maybe i must have better cooling fan for cold end part?
I dont have more ideas for this shit! Please give me some solutions ; )

Thanks!

Simple advice - get a known good hot end from a trustworthy dealer. There is a lot of bad stuff on eBay. There also is a lot of good stuff on eBay, but you need experience to sort it all out.

Almost all metal hot ends need a fan that is close to the hot end and blowing across the heat sink. One of your pictures does not come through, only going on the second one - the fan is not close enough to the hot end.

Hey! thanks.
I will try this hotend with better cooling fan. I hope that helps.
Maybe I should remove this yellow plastic part behind hotend and mount extruder in another way ?

Now neither of your pictures are coming through...

You need good air flow past the top end of the hot end. You do not need air on the bottom (for the hot end it's self). Anything that gets the air moving past the top is a good thing.

Okey, But what do you think about inside diameter? I disassemble hotend and check dimension at entry to the heater block - there is 0.8mm above filament diameter, its doesnt matter?

Im waiting for J-head hotend now... I hope that this be better.

A hot end is a full design. You can do it a lot of different ways. Some people do it one way and it works. Other people do it a very different way and it works every bit as well. There is no single dimension that is universally right or wrong, other than the initial opening must be greater than the filament diameter.

If the dimension you are talking about is the clearance between the outside of heated tube and the inside of the heat sink tube, then there should be a pretty good separation there. If you are talking about the inner diameter of the bottom of the heated tube where it goes into the heater block, then it depends a bit on the diameter of the hole (and taper) in the heated block. Some believe that a fast transition into the block is a good idea. Others have different ideas. I would not design it with that big a feed tube, but others might get it to work with some brands of filament.

Bottom line is the same regardless. If you can’t get that head to work with your filament and you have tried a range of temperatures and cooling – get another hot end or different filament.

Thanks Uncle_Bob.
Now im fighting with another hotend: [tnij.org] Its require cooler fan to? - I mounted small fan.
Here is problem too: extruder working good only for first 10-15 cm of filament, then filament go more slowly and the hobbed bolt destroys filament ;d Maybe problem is in idler block ? bearing ? filament to hobbed pressure ?

(sorry for my english if you sometimes cant understand my words : ) )

I build my first reprap printer since 4 months (its prusa i3 box frame) and i freaking out, problems and problems

You could have any one of several problems:

1) Your hot end may not be hot enough. That could be your set temperature or your thermistor may be wrong in your firmware.
2) You filament may be bad, either just plain bad or full of water bad
3) You may not have enough pressure on the drive bolt in your extruder (or to much)
4) You may be trying to feed to fast (Pronterface will let you try various speeds).
5) You bed level may be out (to high) and it's blocking the filament (will it feed into mid air?)

I'm sure there are other possabilities. Those are just the ones that have happened to me over the last week or so...

hey!

Thanks a lot! Now is working good. Problem was in to low temperature(maybe thermistor setting is wrong) and bearings on the drive bolt. Now im trying to calibrate all axis : )

Thanks for help

The clamp that holds the filament against the drive needs to be *tight*. It's amazing just how much force is needed in most of these designs. Yes you can over do it. Yes it the filament can't go in or out of the extruder when the clamp is pulled back by your thumb it's to tight. Most people get it to loose rather than to tight.