A couple of points. Well maybe more than a couple.
1) If the ABS filament has been open for a while, it may have absorbed moisture. Place in an oven at 165 deg F. The specifications for drying ABS say it may take up to 7 hours to dry. I periodically put it in for 2-3 hours. Much over 165 deg F will melt the spool which usually is Polystyrene, which has a much lower melting temperature. Ask me how I know.
2) Store ABS in sealed freezer bags. Squeeze as much air out as you can and seal the bag. Place in a second bag and again squeeze out the air.
3) Reduce the number of shells to 1. Try that. It looks like you are using 4 shells. The Makerbot slicer seems to be a little off when multiple shells are being used.
4) Increase the infill percentage when you reduce the shell count.
5) Increase the thickness of top and bottom surfaces. It is under Settings | Custom | Model Properties | Roof Thickness and Floor thickness. Increasing this value improves surface finish of top face.
6) Don’t go much over 243 - 245 C for extrusion temperature. Some plastics change their behaviour when extrusion temperatures are too high.
7) The belt gripper on the 2X head carriage does not have enough pinch. Remove both heads and nozzles. Slide belt fully into the gripper. Drill through the gripper and belt with a 1-1.5mm drill and use a 1 - 1.5mm bolt and lock nut to pinch the belt tight. Before starting this, you can prove this is a problem by pinching together the carriage left - right drive belt about 50 mm away from print heads. This locks the belt from moving. With the belt locked, now when you push the print heads left and right, you will see that they move and the belt does not. The play you see is in the belt gripper. The drill and bolt fix it. Make sure the belt is fully seated in the gripper and drill through the centre line of the belt.
8) The heated bed rises up in the centre of the platform as it heats up. This gets worse as the bed heat-soaks. So I set the bed level when it is cold. Then when I heat-soak it by preheating for 30 minutes, I then use the bed leveling utility and lower the bed evenly on all three adjusters until the gap in the very centre of the bed is just right. Now all the gap checks at the edges of the heated bed are too high, but the one in the centre is just right. A high temperature glass bed is next on my shopping list.
9) Tighten the left right carriage belt tension. Pluck the belts like a guitar string. They should all have similar tones or pitch. The deep tones are the loose ones.
10) The short vertical belt on the right rear is hard to tighten. Make sure it is very tight. Loosen both bolts holding the motor. they should be so loose the nuts almost fall off. Pull down on the motor. Tighten the upper nut first all the way. Then tighten the bottom nut. Pluck the belt to gauge the tension. I found it was best to remove the front door and side panel to do this. It takes a few minutes but is quicker than fighting your way through and around the front door and reaching in from the top.
11 ) High Speed printing is not your friend. You can easily go too fast. You seldom can go too slow.
Let us know how you make out.
Jim H
