Extruder Flow Delay...

[Chuck B]

So as newbie I have been delighted that my machine works! Made the fans with no problem... but I did notice that when the program began the machine often traveled 4 inches before the filament began to come out of the extruder. This was not a problem for the fans because the program created long lead-in paths before it came to the actual fan.

But now I am attempting to make a small part I downloaded from thingiverse out of ABS - and the program does not have that long lead-in path so the extruder does not start producing its stream until well into the first layer. So when the second layer gets put down it has nothing to adhere to, curls up, and then creates a gooey mess.

So a couple of questions:
1) Is the delay in my extruder to produce filiment flow normal? Does your produce instant filament flow? If my delay is not normal, what do I do to fix that?
2) If it is normal, do I have to make some program changes in the way of a lead-in path? Suggestions?

Thanks.
Chuck Bailey

[Earthbound]

Chuck,

Your best bet is to add a perimeter ring around the object (the "lead-in path" as you called it). Doing so means that the hot end is already flowing normally at the point that it begins the first layer of the object. The extrusion lag is caused by the heating cycle at warm up. When using the heated bed during a print, it will always warm up slower than the hot end. So hot end is ready first and molten material in nozzle will ooze out under gravity, expansion, or any residual pressure until it is partially empty. Once the bed is warm and the machine begins to print, the first few moments the extruder runs, the material is refilling the void in the hot end. You can try to avoid the problem by turning the extruder knob manually when the heated bed is one or two degrees shy of ready and then wipe the ooze quickly just before the head starts moving.

Another solution would be to create some add-on G-code to extrude/wipe and add that to every print. A perimeter seems easier to me.

Mike

[teoman]

There is a setting in the mattercontrol where you can specify the minimym lentgth of the skirt.

You can manually extrude a bit from the extruder while the nozzle is warming up. Or as you have already found the number 4 inches, you can plug that in to the software.

[Captain Starfish]

I have added code to the cancel and end print custom g-code that retracts the filament 100mm at the end of a print. It stops the filament cooling in the nozzle and becoming impossible to remove to change to something else the next time I want to print.

Accordingly, I need to prime the nozzle before the print. Usually I do that from the host software: let everything come up to temperature, do all my settings fiddling, and right before I start the print I either manually push filament down or use the extrude button on the control panel to push filament until it starts squirting from the nozzle.

Most of the time it still takes a few centimetres of travel before filament appears on the print. So a 5cm minimum length or 3-4 loop skirt is handy.