On completing the build of my K8200, I was disappointed with the quality of the print. Searching the forum only to find
it’s the ‘norm’ with this machine. On close inspection of the print the deep ridges are an exact match with the shaft
thread pitch.
The suggested remedy is to replace the Z axis threaded shaft and connector. Not being happy to wait for replacement items
to get to me, I decided to at least replace the rigid connector with a flexible coupling. After trying in vain to source
such a coupling (to fit a 5mm shaft and 8mm thread), I decided to make my own. After all I now have a machine that should
be capable of printing such an item, if I could design one.
After some thought, I had a basic shape that may work, saved to STL and sent to Repetier. The printed item as expected
was very rough, so a bit of filing and drilling was required. After the old connector was replaced with the printed one, a
test was in order. Resulted in a nice even print, a quantum leap from my previous prints.
I then printed a new version of the flexible coupling, for ongoing use.
Apart from the PLA used (a bit over a 1hr print), the only other items required were; a 5mm and 8mm drill bit, an 8mm nut,
a 5mm nut and grub screw, three small pieces (10mm X 24mm) of 1.5mm sheet rubber.
As a first item to print, the manual suggests a box for the electronics. With such a poor surface with the supplied
connector, buying an ‘off the shelf’ box is far more cost effective/aesthetic. But a flexible coupling (like this) would be a far
more practical first item to print. This item may not be the best design but it does fit, and fixes the problem.
Can supply STL and further details if anyone is interested.
Yes, Steve, I’d be interested. I have exactly the same problem. I have requested a replacement coupler from velleman and they very promptly responded saying they would. but Im not sure how long it will take to get to Australia.
Tony.
Apologies for not getting back sooner. Living in Australia (W.A.) was also my decision to look for an alternative coupling.
For me it was a good introduction to the overall printing process by practicing with 3D CAD. The coupling was my first attempt, so it may not be the best design. So I’ll just describe my coupling and allow you the ‘joy’ of designing your own. Need can be a good instructor. I may at a later date replace this with a ‘proper one’.
The printed coupling doesn’t have to be pretty, as long as it functions. My coupling is basically two pieces,each about 24mm diameter and 20mm long. As the print quality may not be great, all holes/recesses will likely require cleaning to their correct dimensions.
One piece has a 5mm hole through the centre, with a 4mm hole through the side about 8mm from one end. Along-side the centre hole is a square recess for a 4mm nut, in line with the 4mm hole. That gives a better ability for a firm attachment to the motor shaft than just threading the plastic. At the other end are three grooves across it (forming six hollow ‘spokes’) about 2mm wide and 5mm deep.
The second piece has a 8mm hole through its centre, with a similar six hollow ‘spokes’ across one end. At the same end but deeper in (below the ‘spokes’) is a recess for a 8mm nut. This does greatly reduce the area of the spokes in this piece, but hasn’t to date caused a problem.
Cut three pieces of 1.5mm rubber 10mm wide and 24mm long. Partially score them across the middle.
Take the first piece and place the 4mm nut in the recess, insert a 4mm grub screw through the side hole and into the nut. Place and tighten this piece on the motor shaft, bend a piece of rubber into a V and insert into two adjacent spoke recessess. Place the other two likewise, to form six raised rubber spokes (giving the flexibility).
Place the 8mm nut into the second piece, insert the Z axis threaded rod into it and tighten, so the thread does not extend beyond the nut, or the rubber spokes may not fit fully into the recesses.
When the two pieces are slotted together over the spokes, this makes a simple/cheap flexible coupling. Though this works well for lifting the arm, it may come apart when lowering the arm (did for me), so place something to prevent the top bearing from lifting out of its holder.
This improved the print quality immediately, I have since also changed the 5mm toothed belts for 2.03mm pitch belts on 24 tooth pulleys (for an almost identical X/Y resolution) for a smoother surface.
Hope that helps! Steve.