Today I tried some settings in Slic3r. Doing so I printed a U-shaped testcube of PLA on a heated mirror. I printed the first layer at 200°C and the subsequent layers, too. It looked quite well, but at one corner it hadn't stuck to the bed as perfectly as I wished. Actually I wouldn't call it warping already, but maybe the very very beginning of it.
So I cleaned the mirror with alcohol. Then I printed a second cube with 200°C at the first layer and the other layers at 170°C. My expectation was a reduction of the warping, as a layer with a lower temperature wouldn't shrink that much like a hotter one.
The result was puzzling. The second cube showed strong warping.
To be sure I repeated the printing and printed a third cube with 200°C/200°C and a fourth with 200°C/170°C. While the third one again showed no warping, the fourth cube warped so much that it got off the heated bed and I had to abort the print.
Obviously the reduction of temperature at the second layer weakens the bond of the first layer to the bed. Maybe the "cold" second layer cools down the first one and causes it to shrink. Once the first layer got off the bed the whole part is an easy prey to warping.
Possibly this temperature difference explains a lot of cases of mysterious warping. A little option in the slicing software turns out to be a trap ...
Well, crimping a stainless steel tube actually isn't very easy, as I had to learn. So a solder free solution isn't really in sight.
Furthermore I do not like the gap between the screws caused by the crimping, as it hinders the flow of molten plastics. Therefore I came up with a solution, where the barrel is soldered to the upper screw.
I think this solution is the best one as it leaves no gap open and allows me to change the barrel and/or the nozzle. In fact I only need two barrels (one for ABS and one for PLA).
I am thinking about a hotend which can be made without soldering. The idea of crimping the barrel came up in the reprap forum. After some discussion I suggested something like the following solution.
To be honest I don't know, if I prefer such a solution. What I don't like about it is that the nozzle has no contact to the bottom of the heater block. The head of the screw will have a cooling effect on the nozzle this way. It should touch the heater block thus.
Today I saw that the organ pipe hotend isn't the only descendant of my former Longsword Hotend Project.
Wolfgang (Stoffel15) has built a new all metal hotend which is based on it.
Instead of a fan he uses a self paced water cooling which allows him to keep the hotend very short.
The stainless steel tube runs all along through the cooling bar and is widened up at the top, so it can't slip down. Like in the case of the organ pipe hotend the nozzle and the tube are virtually one part. Unlike with my pipe Wolfgang pressed the tiny brass nozzle into the tube. This is clever, because that way he doesn't need to solder them together. But on the other hand that means to build a very tiny nozzle on the lathe, which is rather difficult.
As he has widened up the top of his pipe, the only way to pull it out of the cooling bar is upward. That means, if he wants to change the pipe, he must take the cooling bar out of the extruder block. Not very comfortable yet.
The pipe is fixated to the cooling bar and the heater block by grub screws. I wouldn't have chosen this solution for two reasons.
The grub screw presses the tube against the opposite wall thus opening a gap on the side of the screw. A gap blocks the heat transmission from and towards the tube.
The grub screw can damage the tube.
The water cooling consists of a wound up brass tube touching the cooling bar. It is difficult to say, how efficient this method is, because a round tube touching a plane doesn't have much contact.
Apart from the fact that this design has room for improvements, I like it a lot. Good job, Wolfgang. ;)
Building some more pipes revealed that there is still room for further simplification.
Soldering the nut onto the threaded rod probably isn't the best idea because of annealing the brass. Besides it is an unnecessary step, because I could take a screw instead. Taking a brass M6 x 8mm hexagon screw would fit perfectly. All I had to do is tapering the head and drilling the holes.
This looks promising and easy to make. But there are two problems I need to solve yet. The first is to find a convenient way to taper the head on the drill press. The second is a way to improve the sealing.
Here the nozzle hole is drilled. The drill is a 0.5 mm PCB drill. As I found out they are well suited for drilling those holes into brass, since they are a little bit flexible. I use my ordinary drill press for it. The threaded rod is clamped into the chuck of the drill press, while the drill is hold by a little chuck from the watchmakers (look at my sources). The small chuck itself is clamped into a drill press vice. It is important that the drill press vice isn't fixated on the drill press table. The drill automatically finds the center of the rod this way. I drill at 600 rpm.
The nozzle part is ready now. Even the chamfer was made on the drill press by holding a file against the rod.
This is the other side of the nozzle part. The whole procedure took approx. half an hour.
The soldered pipe. A M6 nut is soldered onto the thread, so it is easier to screw the pipe in and out of the heater block.
ABS comes out of the pipe some minutes later. It works!
Two shopping coins. Still uncalibrated. Not bad for the beginning. The right one was printed at first. Both 36 mm/s @ 240°C.
I should have known better. A little bit of ABS is leaking out above the heater block. Every time when I solder only once it seems to get leaking. If I solder twice, it gets sealed.
In summary. I am quite satisfied with the results. The organ pipe hotend performs very well. I guess I will stick with it.
I expect this version to be easier to make and less prone to leaking. Instead of 15 mm this version now has a soldering zone of only 5 mm. That should lead to less influence of thermal expansion and thus less danger of leaking.