Do you use a fan for ABS?

So I have been tuning my machine for some time now. I used to have some issues with the extrusion temperature (see the top part of the calibration pyramid):



This model was printed with ABS @ 210°C with no cooling. In order to extrude ABS so that is solidifies quickly enough on small surfaces (like the top cube) I have to extrude at 205° and even then it is not perfect. I cannot go below 205° because my ABS material doesn't flow continuously anymore and clogs the hot end.

I experimented with 220°, where I get my best accuracy. At the point when the top layers were extruded I took a straw and used it to blow air (so that I can simulate the effects of cooling) and the cube pyramid turned out to be perfect.

So there is my question: Do you use cooling for ABS? I've read that using cooling for ABS is a bad thing to do. Why? Is it not better to use cooling, especially when small objects are being printed?

I don't use a fan for ABS printing. The problem you're having is that when you're printing a small area layer, such as those near the top of the pyramid, the plastic doesn't have time to cool before the hot nozzle is there adding heat and plastic again. It might be possible to use a fan to cool the print, say when a layer gets below a certain area, but I use different techniques. Sometimes I print multiple objects. If you print multiple objects, you can space them apart on the bed and reduce the travel speed setting to a low value to give the prints time to cool a little before they get revisited by the nozzle. Another technique is to print a sacrificial object that will keep the nozzle away from your print for a while as each layer is printing. It wastes a little plastic annd adds to the total print time, but plastic is cheap and time required to reprint is not.

I think the problem with using a fan is that when you're printing an overhang, the fan will cause the plastic to shrink rapidly and curl upward. This is already a bit of an ABS specific problem without a fan.

It would not be too difficult to add gcode upon every layer change to have the nozzle move away, wait maybe 20 seconds, then move back and start printing. The problem there would be dealing with the snot that oozes out of the extruder while it's waiting. It will end up leaving boogers on the print when it starts printing again. Maybe the boogers would flick off easily and wouldn't really be a problem. Or you could do something like Stratasys does and have the nozzle wipe itself on a brass wire brush before it starts the next layer.

I noticed a similar problem to yours a while back- but in my case I chalked it up to retraction. The original (green) is one of several antirotation pins on an object that was designed to be mounted on a stryofoam cooler box. I thought the cones looked pretty ugly so I designed and printed an object to show the retraction performance. The blue object is the result after a few prints while tweaking retraction settings. The tips of the cones are 2mm dia and the base is 6mm dia. IRIC they are 10mm tall. IRIC, I printed four of these objects at once, and maybe spaced them apart on the bed so it would take some time to go from one to another.

Before:


After:

---

Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Thanks Could you please elaborate on the retraction settings? I have a bowden setup and have experimented with 4mm and 7mm retraction. Better retraction setting would mean less oozing and consequently less extruded plastic on small surfaces.

Maybe another solution would be to add a line in the G code to simply reduce the flow rate at certain areas. Would be great if there were such an option in the slicer settings.

I ended up with the acceleration for retraction set to 3000mm/s^2, and the speed to 30mm/sec. I'm using a direct extruder so my retraction is a very short 0.5mm. Bowden tube setups usually require a bit more fooling around because of the filament that bunches-up inside the tube. The retraction has to be longer to take up the slack then finally pull the filament back out of the melt zone in the hot-end.

Here are STL files for my test object. I added one with 4 cones, too.

---

Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Can you set the acceleration for retraction only in Slic3r? I found the speed settings and the retraction length settings but where can I adjust the acceleration?

In Marlin there's a line in config.h or config.adv where you set acceleration for X, Y, Z, and E. E is the extruder acceleration.

---

Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

I am new to 3d printing, so I may be way off base here, but in Cura there is a setting for minimum layer time. I believe this is the minimum time it will spend printing a layer, and if that layer is printed faster, it will pause until the minimum time has passed before printing the next layer. Perhaps there is a way to do this with GCode, or maybe your slicer/printing program will allow for this?

I haven't tried it for a while, but I think Cura just slows printing down until the layer takes as long as you set. That can be a problem because on a small area layer the hot nozzle will be in contact with the print longer, turning it to goo.

---

Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]