Calibration Advice?

The attached photo shows some of my first few test prints on a Prusa Mendel form RepRapPro.

I'm pretty happy with the results but would like to improve them and am a little confused by the wealth of variables!

These were all printed at 200c on a bed at around 50c. White PLA 1.75mm.

I'll try and keep it to three questions:

1. You can see on the two solid cubes at the very back of pic, not enough PLA is being extruded to fill the final top layer.
I have increased extruder steps from 660 to 670 which has helped but still isn't perfect - trouble is my calculated steps for 100mm is 646 so I don't want to just ram more filament down if there is better way to adjust.

2. Dimensions - my 20mm boxes consistently measure 20.03mmx19.38mm. What would cause and how do I compensate for this?

3. Wobbly towers - the hollow cubes at the front right all go wobbly after about 10 layers. This only happens on smaller prints so I figure this is due to previous layer not having time to cure. What's the best solution? Slow it down? add cooling fan? lower print temp? If I could get these walls printing straight I could move on to adjusting the bridging setting for the 'lids'!

I found the calibration wiki a bit short on detail as to what adjustments to make and how!
Thanks in advance for any advice,
Sim

hmm - what kind of cubes are you printing? are they solid? its difficult to tell. if not solid then you cannot print an unsupported surface - so you cannot do a hollow cube. if you print a solid cube you will see the software takes care of the filling and will print just a loose supporting layer inside.

Sim,
I also have a RepRapPro Mendel and have been printing for a few months now.
I am using 1.75 mm PLA, with a .5 mm nozzle, the first thing I would say is reduce the hotend temp to 185.
Addressing your questions in order, I would suggest
1. Increase the extruder feed rate, mine is usually around 880( M92 E880 ) experiment, if the extruder
sounds like it is straining set it a little lower
2. If you are using the printed pulleys, make your first upgrade metal pulleys. You could adjust the x or y
feedrate with a measured print, ( again M92 Xxxxx Yxxxx ) M500 to save the changes.
3. A good strong fan, I use a big old computer fan.
And bridging , I find 1.75 or 1.8 works well
Hope this is of some help
Myles

If your printing with the fabedashery supplied pla I would also say 200 is too hot, 180-185 is good for that stuff.

Ben

Hello,

I have just mounted mine. These are the results.

I have carefully calculated the exact lenghts of X,Y,Z,E with M92 and calculations.
- Did you calculate the exact steps x units (M92 command) ?
Have a look at RepRap Wiki

To do in my case:
- check the pronterface skeinforge settings
- align X versus Y axes (not exactly 90 degrees)
- If I plan to print small surfaces I will need to add an additional fan.

Dunno how you came about this statement spezzer

You can print unsuppoted surfaces its called bridging and there are settings for it in Sli3er
takes some fine tunning to get it to work but it definately does work

spezzer Wrote:
-------------------------------------------------------
> hmm - what kind of cubes are you printing? are
> they solid? its difficult to tell. if not solid
> then you cannot print an unsupported surface - so
> you cannot do a hollow cube. if you print a solid
> cube you will see the software takes care of the
> filling and will print just a loose supporting
> layer inside.

make sure your machines esteps are calibrated as per the wiki then leave them alone once calibrated

you can make adjustments as to how much material is actually extruded in your slice software
( in Sli3er its called Extrusion multiplier and in Cura its called packing density )

the fact you measure different measurements for the x and y of your cubes
could be
different estep values for x & y in your firmware
slipping/ hopping belts
stepper motor occasionally stalls ( unlikely)
slipping drive cog on stepper motor

I get the best prints for PLA at 168 C and with a fan. Its trial and error, i find the 20mm hollow cube and 0.5 mm thin wall
the best for set up testing

Good luck