The Delta-Pi motor mounts allow the stepper's position to be adjusted vertically by a few mm, thereby adjusting the GT2 belt tension, however this is far from practical since the steppers are mounted under the base. Once the printer is assembled and running it is highly unlikely that it can be disassembled / decommissioned for such trivial maintenance as adding a little bit of tension to one of the GT2 belts.
I started thinking about this a couple of weeks ago and since I was unable to find anything similar to what I wanted, this week I began writing my own OpenSCAD code for a much more convenient system to adjust the tension in the GT2 belt of each column. My design uses an extra assembly for each column, placed on top of the printer opposite of the top clamp, whereby the belt tension is adjusted simply by turning a knurled knob.
Actually I decided to base myself on a belt tensioner design that I have been using for the X-axis idler end in the P3Steel, which has worked very well so far:
I redesigned the whole assembly to fit the dimensions defined by the column clamping system designed for the Delta-Pi by Mike Paauwe. I also tried to strengthen all the parts, since the Delta Steel's GT2 belts are quite long and will require a reasonable amount of tension to keep tight and avoid backslash.
I managed to print some parts of the idler assembly today:
The pulleys (an earlier design which you can find on Thingiverse) use the same small and inexpensive 623ZZ bearings as the carriages, just like in the original Delta-Pi idler. They spin around an M3 20mm hex screw inside the tensioner (the part on the left in the picture above).
I sized the parts correctly so that the tensioner slides inside the idler with little play, as shown above.
For the knurled knob, I am reusing my previous design published on Thingiverse a few months ago:
Yes, it has an Open Hardware logo on top. :-)
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