Marlin Motion Related Configuration.h Settings for MakerFarm i3v

[printbus]

ACME LEADSCREW CLARIFICATIONS

Some of my earlier information about leadscrews was misleading since I didn't know enough about them. I've corrected the earlier post(s), but this should help others from being similarly confused when starting to look at lead screws as a possible upgrade.

My misunderstanding was in assuming that an 8mm diameter leadscrew with a 2mm pitch would provide 2mm linear travel for each rotation of the rod. Turns out that's not likely.

A standard screw or threaded rod has a single thread. In that case, the linear travel possible per turn, or lead, is the same as the distance between ridges of the thread, or pitch. On an ACME type lead screw, there are usually multiple threads essentially operating in parallel. A "four start" has four threads machined into the rod. A "two start" has two. Pitch is still the distance between ridges on the thread, but it's now the distance between adjacent threads, not the same one. Here, the linear travel per turn, or lead, is the pitch multiplied by the number of thread starts. Although the thread pitch is 2mm for both, a four start 8mm diameter leadscrew will provide a lead of 8mm per turn, and a two start leadscrew will provide a lead of 4mm per turn. The amount of torque required goes up with the lead value. I've read about people having problems driving 4-start leadscrews on the Z-axis due to inadequate torque from their stepper motors.

REFERENCES:

I found this to be helpful - http://www.protoparadigm.com/news-up...n-3d-printers/, including links to other info.

Info on decoding the Tr8*8(P2) kind of label some suppliers use on their lead screw is available at - http://www.shapeoko.com/forum/viewto...=1554&start=10