noob needs help for my rep-strap

I just built a rep-strap recently. I'm using a Sanguino board to drive the stepper motors of a CNC milling machine. I added an extruder on this milling machine. The extruder speed has not been calibrated since I can't print anything correctly yet.

I have teacup firmware running on the Sanguino. On my PC I'm running ReplicatorG with Skeinforge (50). I'm using the "replicator slicing default" profile because I just don't know what should be used.

I'm using 3mm ABS filament, and I set temperature of the extruder to 250*C. The heated bed is set at 70*C.

With all that said, I tried to print a first print: the thin-wall-square box. I canceled the print in the middle because I got 4 big blobs on the 4 corners of the square (please see the attached photo) .

My hot end is home made and is about 0.6mm in diameter. It seems extruding the ABS just fine.

I would like to know how to set the software so that this doesn't happen? There are gazilion settings in skeinforge and I have no idea how to set them up. I'm not sure what other info that someone would need to help me. So please let me know if you need any info. Please help.

Thanks

-Thanh

Your heated bed should be at 110°C for ABS.
Check your distance from the bed when hot @ Z=0.
There should only be space for one (or two) sheets of paper.

---

Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

rhmorrison Wrote:
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> Your heated bed should be at 110°C for ABS.
> Check your distance from the bed when hot @ Z=0.
> There should only be space for one (or two) sheets
> of paper.

Thanks for your help. I will increase the the bed temperature up. I had a feeling that they are not warm enough since the extruded plastic didn't stick very well. I adjust the print head by running every 0.1mm until the head almost touch the bed and raise it up 0.1mm. I do this when both of them have reached the set temperature. I hope it's enough?

How do I get rid of the big blobs at the 4 corners? I see it runs the wall fine but then stops at the corners and extrude a lot of ABS there. The ABS has no where to go but make a big blob, then when the head moves away from the corner to make another wall, it drags the molten plastic from the blob away.

Thanks

First make sure it sticks to the bed.
Are your E_STEPS_PER_MM calibrated properly, i.e. when you tell your host to print 100mm of filament it should pull in 100mm of filament. This is critical to getting good prints.
Do you have cool turned on?

---

Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

To get rid of the blobs you need to change your slicer from "absolute E distnces" to "relative E distances", or you can change your firmware from relative to absolute. Also you can calibrate E without printing.

rhmorrison Wrote:
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> Are your E_STEPS_PER_MM calibrated properly, i.e.
> Do you have cool turned on?

What do you mean by "cool turned on"? Is it the fan to cool the cool/cold end of the extruder? I don't have this fan.

I've not calibrated the E_STEPS_PER_M yet. I have not found a solid tip how to do so. I thought I needed to print the thin-wall-cube or some standard objects before I could calibrate my settings. The problem is I can't print the cube properly due to the blob problem that I got. I tried to print the 20mm cube and the 20mm thin-wall cube.

Also I see another problem is that the extruder doesn't spin to extrude anything on the first layer. The extruder step motor doesn't spin until the head has gone about 3/4 of the square. If I use prontface interface to manually play with the extruder, the extruder motor would spin right away when I click on the button to extrude some fillaments. So I think the hardware is working. Just the software settings are not right.


> when you tell your host to print 100mm of filament
> it should pull in 100mm of filament. This is

Thanks. I've thought the 100mm length was the 100mm extruded and not the 100mm that was pulled in.

Thanks

-Thanh

konwiddak Wrote:
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> To get rid of the blobs you need to change your
> slicer from "absolute E distnces" to "relative E
> distances", or you can change your firmware from
> relative to absolute.

How do I do this in ReplicatorG & Skeinforge?
I check the Teacup config file, and it is using relative E (because it has the E_ABSOLUTE commented out). Uhh, confusing. I will check it out.


>Also you can calibrate E
> without printing.

Thanks I will try Rhmorrison tip above to calibrate my extruder:
> when you tell your host to print 100mm of filament
> it should pull in 100mm of filament. This is


Thanks so much

-Thanh

After adding the " #define E_ABSOLUTE" in the Teacup firmware, now I see no big blob at the corner. Yay!
I also calibrate the extruder stepper so that it pulls in 50mm of fillament when I command the extruder to extrude 50mm. But I now see another problem: before each of the print, the extruder runs in reverse for a large amount, and this results in a first empty layer with no extruded ABS (I'm still trying to print the thin wall cube object). Any idea what settings should I change so that this doesn't happen?

Thanks very much for all the help so far!

-Thanh

I reverted the firmware back to use relative E and also set the Skeinforge to generate relative Extrusion distance, and I was able to do some prints. Got a thin wall object after couple tries and with the help of my finger to push down the first layer to the bed for it to stick.

The string of plastic is the early extruded plastic that didn't stick. Maybe I need to change to the Kapton tape instead of the white masking tape. Eagerly waiting for the machine to cool down so that I can apply the tape

Thanks
-Thanh

250 C is also a bit on the hot side for ABS. A lower temp will help with blobbing, and oozing in general. I'm usually around 220-230 for regular printing, 210 for slow/small/detail printing.

When using absolute you must add a "G92 E0" to your start.gcode.

---

Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

Dirty Steve Wrote:
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> 250 C is also a bit on the hot side for ABS. A
> lower temp will help with blobbing, and oozing in
> general. I'm usually around 220-230 for regular
> printing, 210 for slow/small/detail printing.

Thanks for the tip, Steve! I'll keep that in mind.
Thanks

rhmorrison Wrote:
-------------------------------------------------------
> When using absolute you must add a "G92 E0" to
> your start.gcode.


Thanks for the info. I think I'll stay with relative extrusion now

I have another question: When the print first starts, many times, the extruder takes some time before the ABS starts flowing out, but the machine is already running as if the ABS is already running. How do we solve this?

I tried using Oozeband, but it gives me another problem.

Thanks very much

-Thanh

A skirt will help, as it lays an outline before printing the object. If you are printing smaller objects the skirt may not be enough to prime the extruder, but you can do that by hand before you start the print.

Andrew Smith Wrote:
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> A skirt will help, as it lays an outline before
> printing the object. If you are printing smaller
> objects the skirt may not be enough to prime the
> extruder, but you can do that by hand before you
> start the print.


Thanks so much for your help, Andrew. That really helps with the consistency of the first layer. With that on, I the extruder is always ready when the machine starts actually printing the object.

I still have a weird problem which I don't know if it's the Teacup firmware or what but if I print a thin-wall-square box (no filling) then my box is printed and form nicely. Every layer is exactly on top of the previous layer.

But when I switch to print the solid 20mm cube, I get a weird shift. The upper layer is shifted to the right (in both X&Y axis) about 0.5mm. The third layer is also shifted 0.5mm compared to the 2nd layer and so on. The end result is a skew box. It skews to the direction between 1&2 o'clock. This problem doesn't happen when I print the thin wall square box.

I deleted all the comments of the generated G code, change letter "E" to "A", and then load this G code file into EMC to visualize the box, and I don't see any shifting or skewing. The cube's layers are drawn nicely by EMC. My stepper driver & my CNC machine have been used to mill some parts before and I didn't see any shifting or skewing. What left seems to be the Sanguino & Teacup firmware or maybe the combination of the Teacup firmware and the stepper drivers.

Anyone has any idea what causes this?

Thanks

Thanh

Figured out what caused my printed objects being tilted / slanted. The steppers were loosing steps when they change direction. Bypassing the direction & steps optos on the Chinese TB6560 stepper driver helps fixing my problem.

The reason, I think, is because the Sanguino firmware (Marlin) has only 4us (micro seconds) delay between direction change signal and the step signal. When I tried running the same G code (that would print the object on Reprap) on EMC, I didn't have this shift / tilt problem because the signal on EMC has a delay of 13ms (millisecond) between direction change and step pulse

-Thanh