Natural ABS extruding Brown(ish)

After printing many partswith great success from day one using the Green PLA in the Mendel90 Kit I have bought some Natural ABS from RepRapKit (via Amazon).
When I extrude the filament is comes out with a faint brown tinge. I have tried lowering the extruder head temperature to 220 Deg C but still cannot get it to extrude the colour of the feedstock.
If I stress the extruded filament it will turn white again.

I am also having problems getting a good print as the lower layers(about 1 mm) of the print turn a tan colour. I have the bed set to 130 Deg C. Do I need to reduce this throughout the printing? I think that because of the small diameter of the object (about 12mm) the lower layers are not cooling enough before the subsequent layers are added. I am using Skeinforge and I know that nophead does not use the fan when printing ABS. In this case is there a minimum time to let the layer cool that I can enter in the 'cool' profile?

Richard

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Bearded Flyer
After printing many partswith great success from day one using the Green PLA in the Mendel90 Kit I have bought some Natural ABS from RepRapKit (via Amazon).
When I extrude the filament is comes out with a faint brown tinge. I have tried lowering the extruder head temperature to 220 Deg C but still cannot get it to extrude the colour of the feedstock.

Very odd. I have never known ABS to do that below 260C as long as it is not left heated in the extruder for a long time. I would ask the supplier about it.

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Bearded Flyer
If I stress the extruded filament it will turn white again.

That is normal for ABS, even if it is pigmented.

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Bearded Flyer
I am also having problems getting a good print as the lower layers(about 1 mm) of the print turn a tan colour. I have the bed set to 130 Deg C.

Again I have never known that to happen unless the extruder has been sitting hot for a long time or the bed is far too hot.

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Bearded Flyer
Do I need to reduce this throughout the printing?

When printing onto PET tape I set the bed to 130C all the way through as it is only about 110C on the top of the glass.

When printing on glass with ABS juice I use a surface temperature of 130C for the first layer and 110C after that but it isn't possible to get a surface temperature of 130C with a PCB bed and a 12V PSU.

If the surface was actually 130C all the way through it may go brown on a long build but it shouldn't be possible to get that hot with a standard kit and a small object would not be building for long enough.

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Bearded Flyer
I think that because of the small diameter of the object (about 12mm) the lower layers are not cooling enough before the subsequent layers are added. I am using Skeinforge and I know that nophead does not use the fan when printing ABS. In this case is there a minimum time to let the layer cool that I can enter in the 'cool' profile?

Small objects shouldn't go brown but they may be grossly distorted if they don't cool enough between layers. There is a minimum layer time on the cool tab and I set it to 20 for ABS and 10 for PLA. For tiny objects I print more than one at a time, even if that means throwing some away.

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[www.hydraraptor.blogspot.com]

Thanks for the comments Chris.
I have emailed the suppliers but I appear to get a bit better colour by extruding at 210 deg C. I might even try 200. I am trying to print a foot for my aluminium garden furniture. It consists of an inverted trucated cone with a bottom dia of 10mm, top dia of 16mm and a height of 7mm. Whilst this prints well in PLA the ABS printed one shows, what I think is, signs of shrinkage and whilst the infill is at the correct height the top dia is only 14.3mm and it's edge is 7.5mm tall. This means that the edge is higher than the infill and is deforned by the extruder nozzle as it tries to create the next edge layer at the correct height. I think that this due to the fact that the slope length of the cone is correct but the shrinkage is pulling the cone more into a cylinder making the top of the edge higher.
I have rechecked the e-steps and the filament diameter and all is well. Bed temp is set at 130 at start and eeduces to 120. If I increase the fill to 100% from 20% will this help? I am also thinking of slowing down the print speed and 'orbiting' between layers or using the fan. Do you have any other suggetions? I expected some shrinkage with ABS but this seems excessive.

Richard

200C is very low for ABS, it must be weird stuff.

Yes ABS will shrink a lot more than PLA and that does give the effect you describe with overhanging curves. You can try using the fan but you may end up with a weak object. Orbiting usually gives time for some ooze so you end up with blobs on the perimeter.

More infill might help or might make it worse. I never use more than 95% to give some room for the flow rate not being spot on due to filament size variations.

Also different layer heights and W/T will affect it.

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[www.hydraraptor.blogspot.com]