PrntDGW by DavidWalker

Last crawled date: 3 years ago

I started from AndyCart's PrntQB V2 9 months ago and have been making gradual "improvements" to end up at this. Some key features:
The offset pulleys at the front avoid the string rubbing, this doesn't affect the corexy geometry.
Aluminium carriages, I found the printer I used to make the initial carriages couldn't make straight holes so I turned to the milling machine.
X Y carriage are 75mm wide the initials ones were 25mm and this proved much too narrow, resulting in significant slop at the print head.
The bushes are simply made on a lathe from nylon rod with a 8.1mm hole.
I'm currently trying dry lubricant to protect the silver steel rods from corrosion.
The small 623 bearings are quite sloppy, the 625 ones are much better.
After some experimentation with the Z drive the best configuration seems to be to have the threaded rod butted up against the motor shaft inside the flexible coupler. The bearing at the bottom stops the rod moving down when the carriage is being lifted.
The brackets for the z axis are separate parts so that the spacing is only determined by the carriage.
I've changed from a straight drive pulley to the figure of eight style idler. This stops the string moving up and down the drive pulley which seemed to be affecting the accuracy as the angles change. However this has been quite problematic to date, there seems to be a small amount of creep of the drive string on the pulley causing subsequent layers to become offset. I have since reverted to the old system of a plain pulley and no idler, this works much better but the accuracy isn't great (plus or minus about 0.3%). So good enough for a lot of things.
Video: https://youtu.be/n_YZ6EtYQfY
Edit: Thingiverse isn't letting me post comments, to reply to mbthor:
Thanks. I've uploaded a video from before I reverted back to the old drive system. The groves were made using a tool with an insert which had a radius of roughly 0.5mm on, so they are rounded. My idler bearings/supports are poor and not entirely vertical which could be contributing, I'm not sure. With the idlers there is a much greater length of line between the in and out of the drive system which might have something to do with it.