1. ## question: dual lead screw single motor

i have looked at alot of threads over several years,and racking seems to be a problem on single lead screw machines. has any one built a machine with a single lead screw that does not have racking issues? if not, how big is the machine? and how much racking do you have?

i would like to use a machine somewhere in the area of 2 foot (wide) by 3 foot (long) and moving gantry with a bosch colt size router. and rapid at a max of about 200 to 300 inches per minute (this is not exact but just for reference)

the logical fix is dual lead screw ,but then the problem of two drive nuts (if using delrin or other plastics) causes the stepper motor to loose torque .now , i am no engineer so i dont know how much torque is actually lost by using one motor to drive dual lead screws on one axis to eliminate the dreaded racking issue .so frictional coefficient formulas are available

i have been looking at a single motor and using a rack and pinion with a shaft with gears on each end meshing with the rack on each side of the gantry sounds complicated but should work (and i am just stubborn enough to avoid using two motors on one axis to MAKE it work) but as for now my main question involves this...

exactly how much torque is lost in the delrin nut on say a steel lead screw? now how much is lost on two lead screws? ok then ...since ((X)) amount of torque is lost, we need a bigger motor to make up the difference. how big of a motor would be needed?

am i missing something why not just do this, instead of using two motors on a single axis? (i really dont wanna use two motors on one axis) as it seem like, if one will do it, why use two? or if two are not still strong enough , do you then use 3,4 or 5 till it moves the way you require? sounds silly but you get the idea

not stepping on any toes ,as i have built nothing , and look forward to input from some people who have "been there dont that,here is why it wont work...."

thanks in advance for any input

2. There is no reason you cant use a single screw in the middle of a 2 foot wide gantry.
Jidleroy