[jcoats]

Most steppers do 200 steps per revolution.

Let's start with some numbers:

If you use it direct on a 1 start with a 20 pitch thread, you get 4000 steps per inch.

If you do the same thing but have a 4 start, that basically turns it into 200 steps x 20/4 = 1000 steps / inch

So with the 4 start, every step goes 4x as far.

This also assumes you do NOT do microstepping. Microstepping generates more steps and most controllers can do up to 8 if not 16 microsteps per step. Effectively increasing the theoretical resolution.

Also depending on the stepper you use. If you use the ones with 7.2:1 ratio, it takes 200 * 7.2 steps to make a revolution or 1500 steps/revolution

If you use microstepping it effectively reduces the power/torque available per step (by roughly the ratio of the size of the microsteps, 16 is 1/16th the torque of a 1 full step.

So like I said before... it depends. On what feed rates you NEED (versus want), size/power of your steppers, your choice for using microstepping (and how aggressively), whether you use a geared stepper or not, etc.

Personally I like to use spreadsheets when getting into this to keep my head from exploding with the minuchia of the mechanical design.

And you well might want a 5 start on X, 3 start on Y, and 1 start on Z, but in building YOU are responsible for what comes out. The good and the otherwise ... Lots of folks have good rules of thumb, but designing it to do what YOU want makes sense to me rather than using their guess about what is 'good enough' in their opinion.

And we haven't even gotten into the resolution/accuracy/repeatability discussion. Before asking about that, I suggest doing some reading of LOTS of forum posts.

Part of the joy of learning CNC is the learning, then the doing.

Enjoy the process.

[mike_Kilroy]

Jcoates hit it on the head. number of starts is TOTALLY IRRELEVANT AND NOT YOUR CONCERN.

find what PITCH screw you need for your app and buy that. whether it is built as 1 start, 2 startm, 4 start is of no concern to you; simply the final pitch. How the mfgr gets that is irrelevant.

Did I mention it does not matter? You got enough other worries than to worry about something totally irellevant like no of starts. We sell thomson and ballscrews.com screws. no of starts has no bearing on accuracy either. just ignore this. find the pitch you need and buy the accuracy per foot you need.

if you want help, download our free motioneering program and stick your machine parameters, weights, speeds, etc., into it and find what you need. avail free here:

http://www.kollmorgen.com/en-us/supp.../motioneering/