Mendel Printed Object not coming out vertically straight.

Dear all,

I have been printing parts these few days on my mendel. But something is puzzling me.

As you can see from the picture, my parts are not coming out exactly the way it should be. No warping. The part never left the print bed. It stuck on VERY WELL. I had to wait minutes for it to cool before I can pop it out of the bed.

1) the vertical sides should be vertically straight. However, it is curved near the base.

2) The tower on top have nice, straight vertical walls.

3) There is this wavy texture along the length of the object that I cannot explain.

4) Blobs along the edges (z-direction) of the objects

My configuration

1) Adrian's extruder
2) 0.35mm nozzle
3) RepG 23, SF 35
4) glass, Heated bed with no temperature control. 100W pumped in from variable power supply. A set up of 3 nichrome wire in parallel, total R 3.5 ohms
5) 24mm/s , flow rate setting = 4.2, 30% infill
6) layer thickness 0.25mm
7) No fan
8) reverse capable extruder

My guess:

1) There is huge temperature difference near the base, causing the layer above the base to shrink, causing the vertical curvature

2) Temperature difference eases at the top.

3) My ABS filaments are too stretched, causing the wavy texture

What do you guys think?

tc

Edited 2 time(s). Last edit at 02/09/2011 06:12AM by TianChang.

It looks like the temperature of the heated bed is too high to me.
Why is your heated bed not temperature controlled?

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

Nophead couldn't get ABS to stick on glass at 140C. Do you have anything like Kapton or PET on top of your glass bed? You might have a harder time getting it to stick to glass once you lower the temperature to prevent the curvature in the bottom unless you can run it hot for the first layer and then turn the temprature down for the other layers.

Yes the bed is way too hot. It needs accurate temperature control. 10C makes a lot of difference. It needs to be hot for the first layer but then cooler for the rest.

As brnrd said, PLA will stick to glass but for ABS you need Kapton or PET tap on it.

The wavyness in the edges is the infill pattern showing through I think. That might be due to the infill overlap being too high, or the fact the your bed is so hot the outline is shrinking in against the infill.

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[www.hydraraptor.blogspot.com]

Thanks guys.

I wanted something simple so I didn't work on temperature control. Initially I thought of just lowering the voltage but since i need it to be lower after the first layer, looks like control is a must.

I fried 2 out of 3 (learnt a thing about measuring currents) power transistors that is on the Gen 3 extruder board. I am left with no spares to control the bed. But I'll figure out a way; desolder and solder in an equivalent transistor.

My glass has Kapton on it so it sticks REALLY well. Like I said, I had to wait in excess of 10 mins of things to cool before I can pry it open. And the poor object always take off into the air when I pop it out. It's almost like a ritual.

I have gone through much broken glass but it seems normal glass holds up ok at 100 W, 200mm by200mm. I am using it as primary and secondary print surfaces. As long as i don't impart sudden shocks to it through bulldog clip bloopers, it holds up alright thus far. It is so flat it behaves very weirdly while adjusting for flatness. It seems one corner's adjustment also affects the corner diagonal to it.

Once again, many thanks from tropical Singapore,

Tian Chang

You don't need the power mosfet on the extruder controller anyway so you can probably still use you board it to control your bed. The Reprap firmware is set to use D15 which controls the third power mosfet from the 12V supply connection. Look here. If that digital signal is bad, you can reprogram the firmware to use the other one.

Edited 1 time(s). Last edit at 02/09/2011 10:10AM by brnrd.

Quote

It is so flat it behaves very weirdly while adjusting for flatness. It seems one corner's adjustment also affects the corner diagonal to it.

Yes when the bed is stiff it makes no sense having four adjustments, you can only have three independent ones. Three point leveling work much better because you can then fix one and have only two to adjust.

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[www.hydraraptor.blogspot.com]

Another long day at the lab.

Because I have only the variable power supply and no thermistor rigged into my bed yet, i did a simple experiment with voltage and current.

I printed the first layers at 19 V, 5.3 A. Then I experimented with a few lower values.

19 V 5.3 A => too high, parts shrink
• 11.7 V 3.2 A => too low. Parts warps
• 17.2 V 4.8 A ==> too high, Parts still shrink
• 16.1 4.5 A V ==> Does not warp, slight curvage, some holes along breath, surface of length is perfect,

So yes, it is correct. lower bed temperature helped but it has not eliminated. I have yet to try with 15 V.

I am wondering if it has got to do with my infill pattern. I didn't have this problem so pronounced when I did octagonal pattern.

I can see some of the 30% infill layers is a little what I would describe wriggly. no straight, nice and flat.

To Brnrd:

I am using RepG with MB v2 firmware, Gen 3 electronics. Is the same D15 pin also used to control heated bed? How do you suggest I go about doing it? I'll probably need a relay board?

To Nophead:

I re-looking the posts and I have one question: What would be a good temperature for 1st Layer, and temperature for subsequent layers?

For the white ABS I get from reprapsource.com on PET I use 140C for the first layer and 110C for the rest. I don't wait for it to cool down though.

I am not surprised you cannot make it work with a fixed temperature. For the first layer to stick it needs to be above the melting point so you can't do more than the first layer at that temperature as it is basically a very viscous liquid, so won't hold its shape. After the first layer you need to drop the temperature so the base just solidifies but not enough that it shrinks.

When I was using Makerbot natural ABS on Kapton I used two lower temperatures: [hydraraptor.blogspot.com]

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[www.hydraraptor.blogspot.com]

Quote
TianChang
I am using RepG with MB v2 firmware, Gen 3 electronics. Is the same D15 pin also used to control heated bed? How do you suggest I go about doing it? I'll probably need a relay board?

If you follow the link to Adrian's page in my previous reply, there's a picture showing where to solder a pin or wire to get D15 from the on-board power mosfet. On that page, there's also a diagram showing the connection to an external power mosfet and a thermistor to measure the temperature.

Alright.

Thank you very much.

To Brnrd: I was actually concerned about the RepG / MB v2 firmware portion. If I hack it through D15, is it the same way the Makerbot HBP interface with the extruder controller? I saw the MB wiki docs but it wasn't too clear whether they are the same, what more I am using techzone's stuff. So I won't / will have to change the firmware? It would nice to have some insight before I start playing with it.

To Nophead:

Yes. I understood the concept so i went back and tried to print with one high temperature and after that one low temperature bed setting (altering volt & amps of PSU) That's why it improved, but still have some curvature. Will add control. =)

Back to the lab.

Edited 2 time(s). Last edit at 02/11/2011 10:08PM by TianChang.