z-axis problem

[nikbrewer]

well, i am nearing completeion of my cnc. My last hurdle is my z axis. Its got about 6" of traves. i used all the parts from cncrouterpart.com. i used a 9" 1 start 1/2" acme thread screw. I am using a 240 ox stepper and probotic controlers.

At first the z was binding, and it acted like the lead screw was slightly bent. I had a scrap od 5 start, 2 turn acme thread laying around, and tested it. it moved better, but once i installed my router, it could not lift it up. I ordered a new piece of 1 start acme thread, but my real questions are

can a 240 oz motor lift my 3.25 hp router with the 10 turn per inch screw?
how much will adding a assist spring help?
Do i need to fork out 70$ more for the 400 oz stepper like i am using on my y and x?

thanks

[ger21]

can a 240 oz motor lift my 3.25 hp router with the 10 turn per inch screw?

Depends on how fast you want to lift it.
According to Nooks catalog, a 1/2-10 acme screw with a plastic nut needs .624 oz-in of torque to lift one pound. 240/.624 = 384 pounds. That's how much weight you can lift, but very slowly. As speed increases, torque drops off, possibly very rapidly. Also, if the screw is binding, it can drastically reduce the force. Disconnect the motor, and you should be able to fairly easily lift the Z axis by turning the screw with your fingers. If you can't, something is binding somewhere.

[nikbrewer]

sso, should i be lifting with full steps, half steps, ect? how many inches per minute?

the delrin nuts from cncrouterparts are pretty tight. i am guessing they will break in if i run them back and forth alot. do i need to lube the screw? Should i just suck it up and order the bigger motor?

[ger21]

I'd try 1/8 step.

How fast? Start slow and work your way up to see how fast you can actually go.

Yes, lube the screw, it'll turn a LOT easier.

[Khalid]

I think your motors are strong enough... You tell us How many voltage and current u running at them..

[nikbrewer]

PUSHING 30V, ABOUT 2.25 AMPS