After a perfect raft the first layer messes up

Hi guys,
my makerbot got a strange error since a while.
The printer prints the raft in a good quality and than suddenly messes up the first layer. Most of the time just the center of it.
It looks like the nozzle is too close to the platform, but why is it printing the raft and the "outlines" of the cube correctly?
If I don't stop the print it will print the rest of the cube normal and the bottom has the holes from the first layers…
Anybody knows why?
Attachment 10033
I print ABS on a Makerbot Replicator 2 with an upgrade heatbed.
Thanks

Attachment 10034
If you don't cancel the print it comes out like this.

Having similar problems with ABS. The guys suggest I try PLA.

Give us some setting to work with...

Attachment 10047Attachment 10048Attachment 10049Attachment 10050

I just used a new roll of ABS and the same settings and the effect almost didn't happen.
Can moisture cause that effect?
Thanks

Attachment 10051
this is the bottom of the cube with the new filament and same settings. It's much better, but still not perfect.

Don't see anything obviously wrong with your settings. Form the photo it looks like material that gets too hot. If you were running PLA at those setting you'd get a finish like that...

Strange.

Well, now that's interesting...

When I first tried "Replicator G" it used 220C for the extruder temperature. Makerware has been using 230. Perhaps I'll cut it back to 220 and see what happens.

Hi there
make First Layer Raft = 30mms
temp of Right = 230
Heated bed temp to 105
And don't forget to turn off FAN from 1 layer if you are printing with ABS

Try increasing the bed - extruder gap a little. It looks like the slightly thicker first layer is catching on the extruder. Half a turn might do it.

Do you need to print a raft? I find with Buildtak I never need to. It keeps the print attached and with no warping.

Quote:

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Originally Posted by Roberto

Hi there
make First Layer Raft = 30mms
temp of Right = 230
Heated bed temp to 105
And don't forget to turn off FAN from 1 layer if you are printing with ABS

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Still the same problem :(
It feels like it happens less if I turn the filament fan on from the beginning, but maybe it happens just random?!

Quote:

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Originally Posted by noiseboy72

Try increasing the bed - extruder gap a little. It looks like the slightly thicker first layer is catching on the extruder. Half a turn might do it.

Do you need to print a raft? I find with Buildtak I never need to. It keeps the print attached and with no warping.

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I increased the gap, but it still happens on some areas of the print.
Attachment 10068Attachment 10069
I tried to take a picture. On some areas, some "strings" of the first layers lift from the raft just before the nozzle moves to the same spot. Than the nozzle hits the "strings" and burns them. But I can't see why this happens. The areas next to them are fine again…

Without raft I can't even print the first layer. I don't have a Buildtak, I use "ABS Juice".
Thanks

Did you try to reduce Model to raft distance?
By Default it is 0.23. Reduce it to 0.18 maybe.