Printed object is bigger at the base. How to fix it?

Somehow the object I print has this problem: it's bigger at the bottom (the 6 bottom layers) than it is at the top. It creates something like a half parabollic curve. Please see this photo:

Could anyone please tell me what causes this and how I should fix it? I'm using ReplicatorG 40 with Marlin 1.0 firmware and SkeInforge 50.

Thank you in advance

-Thanh

Your print bed is too hot. Also helps to run a fan.

Please put the details of your settings: speed, layer height, etc. With these data, we can help you.

Your slicing software also may be putting down twice as much plastic on the first layer to help adhesion, so that may be something to check.

Thanks for all the helps guys! I'm sorry I didn't provide enough data earlier.

I reduced the bed temperature down to 80* celcius (as compared to 110* earlier). And I tried another print of the same object. Print speed: 10mm/s. Layer thickness: 0.3mm. Filament: 3.0mm. Nozzle: 0.6mm. Filament is ABS. It looks better, but it still gives me different dimension between the bottom 6 layers and the rest of the object.

I don't have a fan to cool the object down. Not sure why we need a fan to cool the object down while we need a heated bed? If we need to cool it down would it be more reasonable if we turn off the heated bed too?

A zip file of the generated G-code is attached SunOrPlanetGear.zip. If someone can find if I have some wrong Skeinforge settings

Thanks again, everyone!

-Thanh

Edited 1 time(s). Last edit at 03/08/2013 02:35AM by ThanhTran.

Are you printing with ABS or PLA?

110°C for the print bed is correct for ABS.
For PLA you should use ~60°C.

What temperature are you extruding at?

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

Hi Bob,

I'm printing ABS. The extruder temperature is set at 230*C

The temperature of the bed was originally 110*C (which you suggested me to use when I asked about the blob last week) and it had problem. But this problem exists with either 80 or 110* bed temperature.

Thanks

-Thanh

In the German forum we call this effect Elefantenfuß (elephant foot) and it is caused by the heated bed temperature being too high. But 80°C is definately too cold for ABS...

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

Do you have any way to check the tempratures are what your printer is saying they are?

This is can also be caused if your first layer is too close to the bed. Try raising your first layer very slightly.

lazzymonk Wrote:
-------------------------------------------------------
> Do you have any way to check the tempratures are
> what your printer is saying they are?

Thanks for your help.

I just made couple more test prints with thinner layer (0.27mm) and 20mm/s feed rate with temperature set at 100 and still have that problem.

I checked with a voltmeter / temperature probe which I haved used to check temperature of boiling water before) and it tells me the temperature is 95*C. I stick the probe on top of the kapton tape on my heated bed. I also used a infrared temperature gauge to read the temp on various places on top of the heated bed, and the temperature values is varied from 95 - 103. The place where I had the printed object earlier 98*C. So I with all 3 reading agree with each other, I think my temperature is in that 98 - 101 range.

Thanks

-Thanh

rhmorrison Wrote:
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> In the German forum we call this effect
> Elefantenfuß (elephant foot) and it is caused by
> the heated bed temperature being too high. But
> 80°C is definately too cold for ABS...


Thanks for the cute name. Now I can google for this symptom I guess .

Looking at the teeth of the gears I print, I see that some teeth are actually better than other. Some teeth look quite straight until the bottom layers, but some teeth are like the size of a trapezoid. This gear is quite small (the base of it is about 15mm in diametter), longest diametter from top of the teeth is about 22mm. The teeth are quite porus and not completely solid due to the filling. Some teeth are just not filled and can see through from top to bottom. Would that makes the heat goes up too high and make this big foot problem worse in some teeth?

I just printed a test cube with the same settings & feed rate, and I don't see this elephan foot problem in this test cube. I'm also printing another gear with 100* at first to help with the sticky of the first layer, as soon as it starts printing the second layer, I turned off the heated bed. Will see how that turns out.

Thanks for your help, again.

-Thanh

konwiddak Wrote:
-------------------------------------------------------
> This is can also be caused if your first layer is
> too close to the bed. Try raising your first layer
> very slightly.


Thanks for the suggestion. Yeah I'm aware of that. I can't yet judge consistenly the initial gap I need to leave the print head at, especially if there are some ABS sticking out of the nozzle. Sometime if I see if the first layer is too thin, I just cancel the print and restart again. But I think it would be a problem for first layer only if it's too smeared off. In my prints, I see at least 5 - 6 bottom layers are bigger than the top.

Thanks

-Thanh

I tried to print the gear again with the bed originally set at 100*C. As soon as the first layer is finished, I turned off the power to the bed and wait for the print to finish. By the time it finishes the print, the bed is about 40*C. The gear teeth are now straight (as compared to earlier prints). I'm so happy.



There are still inconsistency between layers, which I'm not sure what causes it yet, but I'll leave it for another day

Thanks everyone for helping me. Really appreciate your effort.



Thanh

Turning the heat to the bed off is dangerous as the objects can come loose from the printbed.
If you are not using a fan try printing 4 of the gears at one time and see if that makes a difference.

---

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