A Bridge too Far

I believe I sorted most of the X/Y drift by adjusting the MAX_TRAVEL_ACCELERATION_UNITS_PER_SQ_SECOND_X Y and Z values in the repetier firmware to be the same as my lowered MAX_ACCELERATION_UNITS_PER_SQ_SECOND_X Y and Z settings (1000, 1000 and 100).

The creep has not completely gone away but it is now down to one strands thickness, mainly in the X direction, every 10-20 layers, sometimes I can manage 40+ layers without any creep.

I have been using this new found lack of creep to print out the parts for the Revised Fully Printable Eggbot.

Here are the parts I have printed so far:

These have mostly avoided creep. The two idler ends needed opening out in order for the bearings to fit, this I did with a boring head on my mini mill.

Next I wanted to improve the X axis motor and idler ends as mine don’t really hold onto the LM8UU bearings very well.

This thing looked to be a good basis for some new ends that would grip the outside of the linear bearings a bit better.

I modified the ends I had previously drawn in Sketchup.

I mount my motor on the opposite side to most people so I can have a sturdier frame with shorter X rods and still have the same available print area.

This Part was going to be an exercise in bridging no matter how I printed it, so I thought I had better do some bridging calibration using the Bridge torture test so I did not end up with filament hanging down in a mess.

The gap being bridged in these tests is 50mm, each test takes about 5 minutes to print (all test prints are shown upside down for comparison purposes).

The settings were as follows starting with the top left bridge and finishing bottom right, in two colums:

Test # Temperature Bridge Flow
1 200 0.85
2 200 0.65
3 200 0.35
4 195 0.85
5 190 0.85
6 188 1.00
7 188 0.85
8 186 0.85

The first bridge was using the settings I had recently been using for general printing, the best bridge is arguably the last one at 186C and 0.85 bridge flow, however, I feel that the temperature was a little low as it is also the most “stringy” of the various prints and had the worst bed adhesion.

Having settled for 188C for the print, I set it off and all was going well at first, then the printer seemed to be creeping in the Y axis which up until now had been pretty stable.

I halted the print after about 20 layers, as the print had moved too far and tightened the belt, then started again from scratch.

This next print was still creeping but nowhere near as bad as before, and then after about 65 layers, whilst I was having dinner, disaster struck, the Y belt holder sheared.

The printer just printed a mess from then until I stopped it wasting any more filament.

On closer inspection of the Y belt holder it looks like the person who made the part was using ridiculously low infill values as there is next to no material inside the part to give it any strength.

Needless to say, this piece or a suitable substitute are now up there at the top of the list of items to make once I can get the printer working again.

On the plus side, at least the bridging of the wide gap in the middle of the print went fairly well, with only a few mm of bowing to be seen in the middle of a 20mm wide gap.

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