belt tensioner

June 9, 2011

Generally most things print pretty well… with the exception of the small RepRap pulleys which need a lot of ‘cleaning’. I could feel some backlash in both pulleys when the motors weren’t powered up. So, like other folks, I put a pencil on the nozzle and plotted an 80 mm diameter circle with fill.

I used the lash option in SF 40 to compensate but pulleys looked a bit odd.  So I designed up some crude adjustable belt tensioners in openSCAD which I could fit to both y-axis and x-axis without dismantling anything (except loosening the x-axis belt to fit the tensioner!).  The x-axis one fits under the prusa x-carriage onto existing bolts and the y-axis one fits under the bottom plate using the belt clamp bolts.

X-belt tensioner:

Y-belt tensioner (the bolt is too short so there are some other bits jammed in to raise the belt a bit more!):

Printed pulleys (left to right, original, SF40 lash, tensioner, tensioner with more tension):

It mightn’t be that obvious from the photo but there is a decent improvement, although there is a bit more tuning to do!


getting to grips with Skeinforge 40

March 7, 2011

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.