getting to grips with Skeinforge 40

I printed my first test object a little over a week ago. I used skeinforge 39 to slice and repsnapper to send the code to the RAMPS setup. The print quality was poor so I started to figure out how to optimise it. It turned out that skeinforge 40 was released recently and is a little different to 39 – see RepRap forum here – so I decided that I may as well get used to it instead of ver 39.

First thing was to figure out E_steps_per_mm: to do this I nicked the filament at 50 mm intervals using a blade, took the extruder off, ran the extruder as far as required to go the 50 mm using Repsnapper and plugged the 50 mm value, repsnapper value and old firmware E_steps_per_mm into Josef Prusa’s calculator calculator to get the new steps per mm. I followed all as per the forum link above for the setup (for material type, diameter etc).

To optimise I then looked at Dave Durant’s blog and started printing off cubes. For the moment things are running ok at a really slow 5mm/s. I’m going to increase the temp and see if that allows me to extrude faster and hence up the feed/flow rate and do things a bit quicker as I suspect the higher temp may allow me to introduce material into the nozzle and melt it faster.

Something that puzzled me for a while was the Perimeter Width over Thickness ratio (PWoT) and layer thickness (mostly the former!). My current understanding is that its basically the resolution at which you build your object.

So Layer Thickness (T) is the vertical resolution: the lower the thickness value the more layers you will have in your object. For example imagine 0.25 mm v.s. 10 mm layer thicknesses – the object with 10 mm thick layer will be much coarser than the fine detailed 0.25 mm one – like a 791×791 pixel image vs a fine 10M pixel photo  (3162×3162 pixels).

So far so good. What about the PWoT? This is the same horizontally – how closely lines will be spaced across the surface. PWoT * T = PW or width. Increase PWoT to spread the lines further apart and thus lower the resolution, decrease for the opposite effect. Maybe they should be called vertical resolution and horizontal resolution and let the software calculate the ratio if it needs it but there are probably good reasons for being as it is. According to Dave Durant you need to set/fix these values (choose/decide your print resolution) and find a feed/flow rate to achieve good quality at the chosen level of detail.

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2 Responses to getting to grips with Skeinforge 40

  1. Dave Durant says:

    Bit slow to respond.. 🙂

    Just like layer thickness is the height of threads being laid down, w/t is (a litttle indirectly) the width of threads being laid down. The actual width is just w/t times layer thickness so if you have a .25mm layer thickness and 2.0 w/t, your threads are .25mm tall and .50mm wide.

    There are 2 flavors of w/t: perimeter and infill. The short story is that perimeter is the stuff on the outline of the object – bits that touch the air on the final product and infill is everything else.

    With SF40+, you shouldn’t really have to mess around with tweaking feed/flow values any more. Skeinforge should be figuring all that out for you. You (in theory) just tell it the height and w/t values and it will make things come out right..

    • amk says:

      Hi Dave,

      Thanks for the comment.

      Recently I’ve started using SFACT which is a fork of skeinforge 40+ (v41 i guess!) by Action68. He has moved away from the w/t viewpoint to the more intuitive height and width – you now specify eg 0.25 mm tall and 0.5 mm wide! Anyway you can read more here: http://www.reprapfordummies.net/index.php?option=com_content&view=article&id=49:sfact-homepage&catid=44:gcode-generators&Itemid=66
      Its all on github and it integrates with Kliment’s Pronterface host which is also on github (Both are in active development and Action68 and Kliment are always in IRC #reprap channel).

      Naturally, being new, it was a bit buggy for a few days there but that seems to be ironed out now. Its touted as having default settings that work out of the box and I’m getting pretty nice prints with minimum messing (just by tweaking filament diameter in the Dimension plugin).

      Alan.

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