Getting a PRECISION print - what parameters affect it?

Hi all -

- Prusa Mendel I2
- Repetier Host
- 3mm filament/0.5 mm extruder

I have been running a number of parts, all successful, but somewhat coarse in their precision. When I try to run a part like one of the gear wheels for the printer, the teeth are all munged together in a big cylinder. Small features like holes are also not as crisp.

I have read about calibration exercises, and have the calibration block, but still am unclear on what things I can do to come up with a higher precision print. What I assume is the case:

1) Filament dimension doesn't matter - 3mm or 1.75mm are equally good at making precision prints.
2) Print speed is important
3) X and Y belt tension is important

Are there other things I should be taking into account? Any help here would be appreciated!

Rob

Outside of the mechanical stuff, extrusion width matching what what the Slicer is specifying is the single most important item.
After that, you want to make sure you're not printing too hot, if the part is small you'll probably need a fan.

[reprap.org]

I've found this really useful - you want to scroll down to the section with "extrusion - PLA" (it works for ABS just as well mind you)

The "thin wall cube" is great for checking your "Perimeter width over thickness" (I'll be using skeinforge references, slicer will possibly call it something similar but different)

The 20mm box is good for basic starting point and for checking 100% infill does not overfill / underfill your objects

The 50mm tower is a good one to "turn down 5 degrees, print 5 layers, turn down 5 degrees, print 5 more" until your extruder stalls or something and using this to find your "minimum extrusion temp" (keep in mind that this is subjective, if you are printing at 40mm/s and 190 is your min temperature, you will find it will need to be higher if you start printing at 60mm/s)

The hollow box is great for testing your bridging - you will want to know your minimum temperature first though so do these tests in order!

There is a "perimeter width" test, with 2 parts which are supposed to fit together - for some reason this is a BOGUS test - I spent days on this trying to get it to fit and it turns out that lowering / raising your "perimeter width over thickness" does not change the outside dimensions of a part - so don't waste time calibrating your perimeter width on this one - instead this can help final calibration of your flow settings... (aaaand that's about where I'm up to, so I'll end my post here - but there's a few more tests which look helpful too!)

Your gear problem though sounds like it's a temp thing, I'd say do the tower test and find your minimum temperature (different for different materials obviously!) MARK the temp on your spool - that way you will know next time u change filaments what temperature u can print it at ;-)

The hot end diameter will have a slight effect on the resolution of your prints... for example any gear teeth will have a 0.5mm radius at the top of the tooth with a 0.5mm hot end and a 0.3mm radius at the top of the tooth with a 0.3mm hot end. So if the teeth are too fine/small then they might get blurred into a cylinder.

If you draw one of the gear teeth and then apply a 0.5mm radius / fillet to the tip of the tooth then you will see you will effectively lose some of the tooth height... on small teeth this could have the effect of printing a wobbly cylinder!

Wobbly cylinder - I like it!

This is true, nozzle diameter will affect print resoloution, but, the extruder gears should be quite printable even with a .5mm nozzle - I would be more inclined to look first at your settings in slic3r...

I can print fairly good detail at 40mm/s - but NOT if it's running too hot...

Thanks all for the great suggestions! I will let you know how the investigation into these areas goes!
Rob