Maximum step size for a stepper motor on a reprap?

I am working on making a reprap rostock using mainly parts I have lying around. The only stepper motors beefy enough to run the printer have a step angle of 7.2 degrees, which means it is 48 steps per revolution. Will this resolution, given microstepping, be able to give me reasonable print quality?

I am using the a4988 driver for reference.

Your best bet is to ask on a 3d printing forum, those guys might not deal with the code as much, but they'll know the motors required. http://3dprintboard.com/forum.php is the one I frequent.

Steppers are not so precise or as powerful when using microsteps because the in-between steps are achieved by using the coils to oppose each other.

AFAIK most 3D printers use 200 step motors. The RepRap forum is another possible source of advice.

...R Stepper Motor Basics

I thought of another idea - what if I just 3D printed some gears that would make the motor essentially 1.8 degrees, or 200 steps? I have a 20 tooth gear already on the stepper, so I would make a 80 tooth gear. Therefore, when the stepper turns 7.2 degrees, the gear would only turn 1.8 degrees.

I could even go a step further an make it 160 teeth, making the step size 0.9. I know these motors do exist, but why aren’t they used? It seems as though they should make higher quality prints.

Because there's a maximum number of steps per second. Using tiny steps means your printer will be slow.

Speed is not an issue - I would much rather have a slow and accurate machine than a fast an inaccurate.

Let me know the next time you have a 10-hour print time. I've printed things with print-time measured in days. They weren't even especially big. A few percent improvement is nice. Making the whole printer run at worse than half speed is really a bad idea.

electricviolin: I thought of another idea - what if I just 3D printed some gears that would make the motor essentially 1.8 degrees, or 200 steps? I have a 20 tooth gear already on the stepper, so I would make a 80 tooth gear. Therefore, when the stepper turns 7.2 degrees, the gear would only turn 1.8 degrees.

Wouldn't it be much easier just to get a 200 step motor and eliminate all the corner questions that are going to arise with a bodge. For example, gears introduce backlash.

Of course it is possible that the main purpose of your project is just to explore possibilities rather than to get printing asap.

...R

MorganS: Let me know the next time you have a 10-hour print time. I've printed things with print-time measured in days. They weren't even especially big. A few percent improvement is nice. Making the whole printer run at worse than half speed is really a bad idea.

This. When you start getting down to .1, .2 mm layers and high infills...... In a discussion now about a guy who wants to print a 1:1 t-rex skull. That's an object that's roughly 2m x 2m x 2m , on a printer that only does 200mm^3 at a time. Now we're talking months.

Also, speed can affect temperature, and that can have devastating effects.

Of course it is possible that the main purpose of your project is just to explore possibilities rather than to get printing asap.

This is exactly the point here. I am not trying to make the best machine ever. I have access to a makerbot. This is just something I am making so that I can say it is possible and just to get a better understanding of 3D printing. For this reason, I am not interested in spending a lot of money to get the best parts, as long as it works.

electricviolin: This is exactly the point here. I am not trying to make the best machine ever. I have access to a makerbot.

Then you certainly have a big advantage over me. Why not just try it and see what happens and report your results.

If you can get reasonable results with a significantly cheaper machine I'm sure there will be lots of interest.

...R

I'll try it out and see what happens. The stepper is getting hot with no load (although there is no current limiting either). I will add current limiting to try to keep the temperature under control, but will this decrease the speed of the motor much? I know it will decrease the torque, but with the gearing I'm sure it won't be TOO hard to find a good current limit to torque ratio.

electricviolin: I will add current limiting to try to keep the temperature under control, but will this decrease the speed of the motor much?

You will have to suck it and see.

...R

I ordered some a4988 stepper drivers so I can do current limiting... they will be here in a 2 weeks :(

electricviolin: they will be here in a 2 weeks :(

I admire your patience. 2 or 3 days is about my limit.

...R