If the USB cable gets hot there must be significant current through it. I would suspect a difference in ground potential between your 12V PSU and your computer. Measure the voltage between them before they are connected.by nophead - RAMPS Electronics
How much does your Y carriage and bed weigh? It is probably more than the extruder.by nophead - Prusa i3 and variants
If the PTFE makes a good seal then it should prevent plastic getting to the hole in the PEEK. I am not sure because I have never encountered that before.by nophead - Mendel90
Yes the PTFE liner should form a seal against the brass, however the PEEK should not have any holes in it to allow it to escape where you indicated. I think Brian machines the PTFE liner (it has a chamfer on one end). He sells spares @ . No sign of the washers but I am sure he could include one if you ask. There are some on eBay as well: but I have no experience of those.by nophead - Mendel90
My advice is never disassemble a hot end. It isn't necessary to fix any jamb and it is difficult to reassemble correctly. For jambs at the cold end: heat the cold end with a hot air gun or in a glass of boiling water, then nip the filament with needle nosed pliers and pull it out of the hex socket of the grub screw. That is the only place it can jamb. Anything below the cavity will slide throughby nophead - Mendel90
I suspect you have a bad ground or 12V connection between the Melzi and the PSU. That would cause the voltage to the motors to drop when the bed was on, hence why you can jog but not start a print. A bad ground can cause some of the bed current to flow down the USB cable. That could conceivably damage the USB port on either the Melzi or the computer you are attaching it to, although I haven't knby nophead - Mendel90
Poor layer alignment is normally a mechanical problem. I am not sure how the slicer would affect it, other than if you only have rounded corners you don't have as much stress on the mechanics. If you have backlash then the order and direction of the outlines can make a difference. If you always approach the start of an outline from the same direction the outline will be in the same place but ifby nophead - Slic3r
What do you mean exactly by layer evenness?by nophead - Slic3r
Quoteklbarie How exactly would that work? Do you have a schematic or sketch to better explain? I don't entirely understand how 12v and 24v and be wired in the same circuit and not cause problems. Electricity is basically magic to me. I know the basics, but only the circuits class us mechanical engineers have to take, and that was 3 years ago. Here is a sketch: - How much current the Melzi canby nophead - General
If you use a second 24V PSU you can keep the Melzi on 12V and simply connect the bed's positive lead to +24V instead of the Melzi bed+ terminal that is 12V. Then link both PSU grounds. The MOSFET on the Melzi will connect bed- to 0V to complete the 24V circuit.by nophead - General
I think the inner rounding is just a progression of the outer rounding when you offset inwards by the filament width. The difference comes from the outer perimeter. KISSlicer seems to round the corners where the model has sharp corners. To some extent that makes sense because you can't actually print a sharp corner. It will have a minimum radius of half the filament width. However KISSlicer seemsby nophead - Slic3r
It might be worth swapping the X and Y stepsticks to see if you have a faulty one. Seems like it might not be microstepping correctly.by nophead - Mendel90
Looks like a wiring fault then. Could be the at the Melzi terminal, the IDC connector or the soldering on the extruder PCB.by nophead - Mendel90
Also check the warm up order in the start code does not heat the hot end sooner than necessary.by nophead - Mendel90
What temperature are you using? What speed is the first layer? If you print too slowly with PLA the heat can creep up it, particularly on the first layer because the fan is off.by nophead - Mendel90
Also check continuity between the fan- pin on the Melzi and the black lead of the fan and between fan+ and the red lead. There isn't actually a wire in fan+ because it shares the connection with the heater.by nophead - Mendel90
I never use a fan when printing ABS, not sure why you would get a mess, but it would be more likely to warp and de-laminate with a fan. Check the voltage at the fan connector on the Melzi. There should be 12V across the two terminals when the fan is on.by nophead - Mendel90
If the current is set too low it won't microstep accurately but I don't know how that would make the prints so bad. You should aim for about 1A which means Vref is 0.4V or 1.6V depending on the Stepsticks. I can't really explain the prints. They look to have vertical waves which would be difficult as Z should be constant during an XY move.by nophead - Mendel90
It is normal for ABS, PLA tends to come out smaller. Die swell depends on viscosity and flow rate. When building an object it gets stretched to the cross section defined by flowrate over feedrate regardless.by nophead - Mendel90
Yes ramps should be able to do everything a melzi can in theory. We use melzi because the ones we supply have better connectors, MOSFETs and stepper driver heatsinking on the PCB, so they don't need heatsinks and fans. On ramps you have to crimp connectors on all the wires and might have to short out the bed polyfuse as it will be right on the limit with the bed PCBs we supply that are less thanby nophead - Mendel90
Looks nice. How does it function?by nophead - Mendel90
You just need to change the board number to the one for RAMPS and make sure you use the correct endstop connections and jumper the unused three. I.e. X min, Y min and Z max. You will also need to turn the current down to about 1A because stepstick format boards generally can't do 1.25A.by nophead - Mendel90
I didn't try with J-head because the shape is more difficult. The PEEK insulator is bigger than the heater block, whereas my own design hotend uses smaller diameter PEEK to get less thermal conduction. I don't think I had considered kits at this point.by nophead - Mendel90
Also keeping the flow away from the hot end is less critical now that it is insulated. The insulation could be improved with a couple more turns of tape and perhaps a piece stretched across the bottom. In the past I made a cast silicone boot to fit a hot end of my own design but never tried it as I switched to J-heads. The mould and a core were printed of course and I measure the volume needed iby nophead - Mendel90
Yes finally have time to experiment again. The duct only really works with objects bigger than its inner diameter so it cools parts of the object laid down some time before. I have seen people use a jet that points directly at the nozzle. Not sure how that affects the bond strength but it would allow smaller objects and probably better bridges.by nophead - Mendel90
Hi Neil, I am pretty sure the fans we use are 24 CFM. A crude test with a hot diode acting as an anemometer confirms it has a higher flow rate than a Gelid Silent 6 which I bought to compare. As it has the same dimensions and blade count, etc, I think the only reason it is a bit quieter is that it spins slower. I can't see any reason why it would improve print quality unless your original fanby nophead - Mendel90
I think extrusion width and nozzle diameter also affect how much round holes shrink.by nophead - Slic3r
It should really be 16 AWG for the 16A that the machine takes but I think you will get away with it if you keep it very short as the heat will be dissipated by the thick bundle soldered to it.by nophead - Mendel90
Screw terminals are more reliable than pins as long as you tighten them properly and don't use too much solder. In fact the best way is probably to solder the bunch to a short piece of thick cable and leave that without solder where it goes into the terminal. I have read it is a bad idea to tin wires in terminals as the solder creeps but I have never had a problem with it on any of my machines tby nophead - Mendel90
Check that the screw terminal for the ground connection on the Melzi is tight. It looks like the ground has a high resistance so the bed is only getting part of the voltage and the rest is across the USB cable.by nophead - Mendel90