lead screw

[luther]

hello i was wondering the bigger the lead screw the more torque to turn it ? my Gantry weight is going to be about 100 lbs. i got some 300 in. oz. motors and i'm going to reduce them 1 to 6 ratio for my 48" x 48" router/ palasma table

[dertsap]

it depends upon the dia of the leadscrew ,if its within reason then the difference will not be noticable , my first build consited of 120 oz motors direct to a 3/4-6 acme screw , it worked great , i would never suggest using anything smaller ever though plenty of guys do ,

with the ratio your looking at you ll have more than enough torque
ive got 800oz motors connected direct and my 9 yr old boy can barly hold the gantry back if at all , most times he has to let go , and hes a big boy

[ger21]

You're acceleration will suffer due to the greater inertia.

Gearing steppers 6:1 is a bad idea for a router or plasma machine. Steppers lose torque quickly as rpm's increase. Spinning the motor 6 times faster could conceivably give you less than 1/6th the torque at higher speeds.

If you read through all the router threads here, you'll have a hard time finding one that used a gear reduction running leadscrews. I know of one, that actually got better performance by reversing the gearing, and spinning the motor slower.

[luther]

so i could go the other way are sould i hook directley to the end of the lead screw ?

[Regnar]

I have 2 48" 1/2 10 acme hooked up to 1 269oz stepper for my x axis. Every once in awhile I have stalling at 90 ipm but at lower speeds say 50 ipm I have none at all. This is cutting speed. For my y axis I have 1/2 10 hooked right up to the stepper motor with no stalling at no matter what speed I run it at within mach.

[luther]

hello regnar, how heavy is your Gantry? mine weigh about 100 lbs. and i have 2 pcs of 1/2" 10 acme screw would that be big enough for that much weight i have 305 in. oz. motor from hobbycnc.com and i was going to run one down the middle of the machine with a guard over the top of the screw do you think that would work

[dertsap]

1/2" rod pushing a 100 pound gantry would probably flex ,
take the rod put it upright so one end is on the floor and push down on the other end with your hand and you ll have an idea of what kind of flex your machine will be dealing with

[Regnar]

I dont know for sure but guestimating around 60lbs. You can have a look at the machine and a view videos of it moving here. http://cnczone.com/forums/showthread.php?t=37485 I wish I could tell you if it would work or not but I am still learning myself. I can just go off of what I have done. I know that having two leadscrews for the x axis makes it really easy for squaring up the machine. So you might want to put that into consideration.