I've built this machine 100 different times in my head!!!

[Jonathan]

I saw the 10mm pitch threads too but now I have the 1605 I'm sticking to my guns. The results dean gets from 1605 are plenty good enough for me and if I can get to anywhere close I'll be a happy man!

The thing is, it's not just a question of does the machine work well enough with 1605. If 1610 is used where appropriate, then you will get better acceleration and probably higher feedrates with the same motors. The maths to prove that is simple - moment of inertia (J) of 1610 and 1605 is pretty much identical, but to get the same acceleration 1605 needs to spin twice as fast. Torque is moment of inertia multiplied by angular acceleration (Newton's 2nd law), so since we require double the acceleration the torque is twice as great.
Now you may say that you don't need these benefits, since the 1605s are 'good enough', but the point is if you leave it at the same speed and acceleration as you get with 1605 and use 1610 the required torque from the motors is lower. That means you're running further from the limit, so are less likely to have problems since the system isn't being 'stressed' so much. That's not to say you should immediately sell the 1605 screws, since it's no loss to try it and see.

[Iwant1]

That's not to say you should immediately sell the 1605 screws, since it's no loss to try it and see.

That's exactly what I plan on doing, stick them on and try. If 1605 doesn't work well for me, a pair of 1610 at 1300mm will cost an extra £100 + p&p so its not too bad. What I'd like to clarify, is resolution regards pitch, and micro stepping, and pulley reduction. here's the situations:

1. stick to my 1605 and gear 1:2 to get effective 10mm pitch but, will my nema23 have the torque needed for this gearing? I got the option to gear 1:1 when I need resolution,

2. buy 1610 and gear down 2:1 for high resolution, and stick to my nema23

3. buy 1610 and use micro stepping when high resolution is needed.

Thanks

[Jonathan]

Microstepping helps with resolution, but not as much as it initially appears to. The datasheets for many stepper motors specify that the tolerance on the angular position for each step is 5%, for a 200step/rev motor. That means you can say with some confidence that if stopping on a full step, the motor will be accurate to 1/(5/100%)=1/20th of a step. That implies that down to around 1/20th microstepping you'll gain resolution, however when stopping on microsteps the tolerance is worse since the relationship between the reluctance of the rotor, and angular position, is not ideal. It's hard to say exactly how much resolution you can gain. My micro lathe has 4mm pitch ballscrews, geared 2.5:1, so the effective pitch is 1.6mm and with 1600step/rev (1600 is good number to use in general) that's 1um per microstep. If I put an indicator on it and try and measure this, the axes do appear to move about 1um per step, which is promising but bear in mind that's in a static situation. Whilst the motor is spinning continuously it will be less accurate. Arguably the main bonus from microstepping is it means the motors are exciting the system at a higher frequency, so problems with resonance are attenuated.

I can think of very few parts that would benefit from the 2* resolution gain got from using 5mm effective pitch instead of 10mm. There's only one part I've made where I decided to swap my pulleys round to get higher resolution, and that wasn't the Mayan calender. However there are numerous other reasons to use pulleys, so it's still a good idea to plan for the ability to swap them to get the higher resolution. If you stick with the 1605 screws then option 1 (1:2 to get 10mm effective pitch) will work substantially better than 1:1.

Unless you'

[JAZZCNC]

If you stick with the 1605 screws then option 1 (1:2 to get 10mm effective pitch) will work substantially better than 1:1.'

You can't say that without knowing what's being done with machine.? 1610 doesn't work better it just allows higher speeds and if those speeds aren't needed then there's no point.! . . . Infact it's wasted resolution/torque.

That said I didn't realise Adil bought 5mm pitch screws for all axis and believe he mainly wants to cut wood in which case 10mm pitch would have been better suited. But as we know it's not the end of the world and with belt gearing easy sorted.

Regards Micros stepping then Really you shouldn't consider micro stepping for resolution it's biggest help is with smoother operation of the motors at lower speeds and like Jon says it helps with resonance. Just remember the higher you set the resolution the harder the Parallel port has to work putting out more pulses's for the same movement so you'll need a good PP port other wise you could easily lose steps. More than 2000(10x) micros steps is pointless really has most of the Cheaper motors can't resolve to higher than that.