Bowden issues

The addition of the Bowden tube has introduced some fairly major hysteresis into the system, this required an increase in the retraction distance to overcome the stringing and blobbing that has appeared since the Bowden got put in place.

Carried on with the Atoms of the VAWT (3 required for a complete VAWT) unfortunately my overzealous retraction settings had an undesired effect on the leading edge of the VAWT wing section at the bottom where the print head moves from the wingtip to the centre

Printed all 3 Atoms of the VAWT regardless of the quality issue purely as a build volume test and so that I could tweak the retraction settings to try and eliminate the malformed leading edge issue (and although I saw a slight improvement I think I may need to shorten the Bowden tube as much as possible to avoid or at least improve upon the hysteresis issue)

Chopped out approx. 70mm of Bowden tube and tested, slight improvement in the hysteresis suggesting I am correct in the assumption that the Bowden tube is causing the loss of quality.

As I am still getting issues with bed leveling/flatness I decided to upgrade to a glass bed on top of the heated bed PCB, this cured the leveling and flatness issue completely but introduced a large delay in the heat up time of the hotbed, from approx. <5 minutes to around >10 minutes, this is annoying as it considerably slows the whole process down, I must find some thinner glass, (maybe from an old picture frame)

After much testing of many prints, I remembered the other reason for upgrading to a Bowden tube, speed so I began experimenting with pushing up the speed from 20mm/second to 30 then 60 then 100!

Yes 100mm/second and everything seems to be working flawlessly, wicked!

In fact at these speeds I start to notice mechanical wobble appearing in my y axis print bed, need to shorten the screws mounting the hot bed above the wooden build bed.

I also noticed that I am getting warping again possibly due to the fanning effect of the rapidly moving Y axis.

I am currently finishing the hotbed upgrade to shorten the screws and properly insulate the hotbed underneath so that the hotbed holds its heat better.

Almost finished this last night 21/09/2012 other than the need to re-level the bed properly and fix it in position properly.

If this does not solve the warp issue I will probably need to move the whole printer into a heated room as I am currently doing all my printer stuff in an unheated room and now that summer is ending and winter is on its way it is starting to get cold again.

last year this had major warp implications with the plastic I was using at the time, which I had assumed was PLA but may actually have been CAPA (I am still not exactly sure what plastic this is as It was gifted to me with the original Darwin machine)

It took me a long while to realize that this was due to the local temperature conditions in the room as when summer arrived the problem promptly vanished proving that local temperature conditions in the room need to be warm not cold.

Need to investigate a heated build chamber or at least temperature monitored.

The hot bed should be good enough to heat the chamber assuming it is fairly small and well insulated but I would need to figure out where to connect the chamber thermistor to the sanguinololu electronics set, more web research required here.

I also fell fowl of trying to implement the pronterface control of a fan on small layers recently, as when I looked into this I discovered information (ref) suggesting  that the hotbeds Mosfet on the Sanguinololu board was not rated for use on a PCB of this fine a track width.

Following the advice, I removed the Mosfet from the board completely and rewired it as suggested, basically connecting the hotbed’s Mosfet directly to the ATX power supply and just wiring the gain to the PCB, this means that the Mosfet draws most of its current from the PSU rather than routing it through the Sanguinololu’s PCB tracks.

It was suggested that this is a possible safety issue with the Sanguinololu’s design, At the same time I also replaced the screw terminal power connector with a proper 4 pin ATX 12V PSU socket doubling the copper connecting the PCB to the PSU.
I had noticed also before these upgrades that the power regulator (on the other end of the PCB from the PSU connection) was getting extremely hot and was in danger of meltdown (in fact it was manifesting as the sanginololu resetting itself during prints, which is how I first spotted the problem.