what thread size to use for threaded drive system

Hi,

i'm making a repstrap with threaded drives and am having trouble figuring out what size thread i should use.

I remember reading about .5mm accuracy, does this mean i should go with M3?

I'd avoid using threaded drives, as they're usually pretty slow for a Reprap. We shoot for 0.1 mm / step resolution, which is pretty easy with a belt drive and 200 step steppers. If you were to use an M3 threaded drive with a 200 step stepper, you'd get 0.0025 steps per mm, and a top speed of around 2 mm/s (rough estimation). My Darwin runs at 16 mm/s, and takes a full week of extrusion time to build a complete set of parts; an M3 bot would take over two months of extrusion time to do that.

Also, m3 is pretty spindly, you'd want to go up to atleast m5, maybe.

As Wade said, belt or rack and pinion is probably better.

hmm Ok thanks guys. I will abandon the threaded drive, i assumed using a belt was just to save space, didn't think about speed. Time to learn about belts!

thanks again

actually i am going to go ahead with the threaded drive...

in the past i constructed one for manually controlled stop-motion camera moves,if i go this way after i have printed mendel parts i can't make, i can use the cartesian bot as a motion control system with openMoco (i'm an animator)

so if i make it with m5 thread, with a pitch of .8mm, does that mean my 3d designs would come out larger? Or does the reprap software compensate for this and they are just less detailed?

my X axis is going to be around 800mm (for the motion control unit) so i guess i will have to put the opto stops much further in while reprapping.

M6 is a nice round 1mm pitch.

as far as I know, there should be somewhere in the firmware configuration to set steps per mm, which totally glosses over drive methods and such.

cool i will go with m6. thankyou all for your help

> as far as I know, there should be somewhere in the
> firmware configuration to set steps per mm, which
> totally glosses over drive methods and such.

ReplicatorG uses a file: machines.xml. In there you will add your machine and its attributes. There you can tell it the number of steps per mm for the X, Y and Z axis.

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