Though the old extruder worked fine there were some parts which needed improving.
- An aluminum bar was keeping the hot end in place; this leads to loss of energy causing long warm-up times and heating of the extruder's plastic part in the places where the bolts are attached (see here).
- The hot end was very short making the placement of the thermistor difficult. basically the thermistor was taped with kapton on the nichrome wire which is not the best place.
Because the old hot end was kept in place with a aluminum bar with m3 bolts and the new PEEK bar has m4 holes in different positions, an adapter piece (copper) was made to make it fit.
The old thermistor and new nichrome wire attached again (old nichrome wire had turned white and the insulation was falling off when taking it off the old hot end).
Since the new hot end is a bit longer I decided to insulate the it, just like the original makerbot extruder (see here). The insulation tape was bought locally in Finland from www.robomaa.com.
The temperature of the extruder seems to be much more constant. It seems the actual temperature is always about + or - 1degree of the set temperature. The old hot end had + or - 5 degrees.
The extruder with the rebuilt hot end has been printing all day and seems to be OK again. There are some small issues with precision of placement of plastic (belts?) but that is a worry for later.