I used ordinary rods 5/16" - 18 tpi + these
lead screws just because they fit the "rollerblades" ball bearings. I have no tools to handle metal and I was not convince the whole shebang was going to work. So I went for cheap stuff.
Now, looking back I think it is worth spending some money in acme screws. The lead screws I have definitely will not cut it for a decent load on the machine. On the other hand I have no idea how much I will use this (don't forget this is a just hobby for me)
As for "stealing" ideas. There is not much to steal. All ideas are coming from one build or another on this forum.
I just tried to pay attention to what was important and what not that critical in the build.
Just some decisions I made (that proved good)
1. I didn't like to much the idea to use pipes because to build support for them (to avoid bending) required a complex structure (hard to build without another CNC). Using V profiles 1" x 1/8" x 3' I managed to create a very strong support (because they stay on the table itself and I used 2 layers of plywood where the V rod is supported (
see here).
2. Also I wanted to make sure the parallelism is easy to control. As a result to use the table as the support worked just nicely. The support for pipes using screws to align them were, again to much for me.
3. Everybody was complaining about bending. As a result T frames all over for
X Axis,
Y Axis,
Z Axis. I'm happy about choosing plywood instead of MDF. Although plywood is not stable in one direction using T frames made it extremely robust. MDF worked for a lot of people. So probably what I did was an overkill.
Some ideas that were not that good:
1. Rods & lead screws are not good. Although 18 tpi can provide a good precision, you cannot run this at high speeds. The best I was able to run it without loosing steps was 40 ipm with minimal load. They cannot support high speeds and also they cannot support load.
2. I threaded the coupler for the steppers to fit the rod (they were 1/4 and I threaded them to 5/16). They are not properly aligned. This is not the way to do it for sure.
My conclusion is that the overall design is OK (and also very simple) but using ACME screws is almost a must.