Things to change when you use 2020 aluminum extrusion instead the 1515 one on the bill of materials.
According to Kossel_Mini_Assembly_Guide_V1.0.pdf,
One bottom vertex frame requires:
M3 Allen key
M3x8 cap screw x10
M3 nut x10
Three of the bottom vertex frames needs total 60 M3x8 screws and M3 nuts.
One top vertex frame requires:
M3x8 cap screw x5
M3 nut x5
Three of the top vertex frames needs 15 M3x8 crews and M3 nuts.
The total number of M3x8 screw is 45, and M3 nut is 45.
However M3x8 screw and nut dimension is too small to attach the vertex frames.
Slot width of DF2020 is 5.4 mm on top, 8.3 mm in the middle.
Let’s calculate dimension of M3 nut.
D is 3 mm.
Length of s is 4.8 mm (1.6 x 3.0).
Length of e is 5.4 mm (1.8 x 3.0).
Outer diameter of washer is 6.0 mm (2.0 x 3.0).
Well, the slot width of DF2020 is 5.4 mm which makes M3 nut useless without washer.
The wall thickness of vertex frame is around 4.1 mm plus 2 mm of the DF2020’s edge gives 2 mm clearance.
So if I gonna use M3 screw and nut for mounting the 2020 aluminum extrusions on the frames, I’ll need to buy 45 pairs of M3x10 screw and M3 nut or simply uses M4 screws and nuts.
Second thing you have to consider is that extra cost of six vertex frames or labor time to make the square holes bigger.
When you buy the printed parts kit, make sure what linear mechanism it uses. Original Kossel Mini uses steel rails to handle vertical movement of the push rods. Price of one steel rail is over $34 with shipping and handling fee, buying a set of three rails probably increases the total cost 1/3.
At the moment I have to deal with these two problems.