what should I use oil or grease to help the motion on my M16 thread rod?

also I have some little pb...the rod is little bit bended. I checked and all the bars you can buy are very little bend. If I increase tension on the rod, It seems that it does'nt t help much...

I am using Stainless steel...should I use something more soft so that the tension can make it strait?

Well in my experience if you can oil something regularly (or make it automatic) use oil. But if its a hard to get to area or you are just plain lazy use grease.

Grease is afterall just a vehical to deliver what is essentialy oil. Grease is usfull for its viscosity its ability to act as a bearier (to moister on whatnot). The down side on grease is that everything sticks to it so it has to be used in a fairly clean environment it tends to build up on the moving parts like a squeegy (this could be a good thing, depends on the ap.) and if the evironment dosn't generate enough heat to make it flow the pressure of operation could squeeze out the grease after the first run and then your running dry.

personaly i use oil lube systems (either bought or make your own) to oil my screws. that way you know its getting oil and when you disassemble to service something its not as gunked up as grease usually makes it.

Oil systems don't tend to need as much in the way of engineering as grease does. In a greasing system you have to engineer something to make the grease stay where its needed. Oil on the other hand is pumped to the location (either by splashing or active pumping)

just my thoughts on the subject and I am not a expert on this subject or even that well informed. But these are the same things that I thought of when I was in the design stages of my mill.

dont know the softness or hardness of the stuff your using but don't think that stainless (which is pretty soft (300series) already ) is going to make that much of a dif.

I am using stainless and I was asking myself if I should move to something else...
maybe the best is buying a homeshopcnc ballscrew system...it seems to be not too much expensive and I hope can be better.

the only point is I don t really see on the website how the ball nut is attached to the structure...is there any hole? a face view might help to understand...or is it the metric thread that is used?