Lead screw choice dilemma

Lead screw choice dilemma

Postby cwolfs69 » Fri Dec 02, 2016 1:17 pm

i am replacing the lead screws on my small cnc router. the old screws are 10mm-2mm, 2 lead acme screws, (0.160"/ rev±) and work okay. i am replacing with 1/2-10 acme screws and was debating whether to use single start (0.100"/rev) or 2 start (0.200"/rev) threads. my first thought was single so the it would require less torque to move the axis around the table. but then i thought the stepper motor would have to rotate twice as fast and that can cause problems as well. of course the 2 start would have the closest pitch to the original. does anyone have any thoughts about my choices.
i am also upgrading the stepper motors to higher torque as well, going to 296oz/in vs whatever those that came on my chinese router are, very weak

any thoughts or advice would be helpful. i have been unable to find whether its better with fast travel or less torque when installing lead screws on a cnc.
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Re: LEAD SCREW CHOICE DELEMA

Postby calgrdnr » Fri Dec 02, 2016 3:58 pm

when I built my Joes2006 in 2007 I used 1/2- 2 start went to a 1/2- 5 start what a difference faster and smoother .
CNCzone.com would be the place I would look for answers to your question :)

http://www.cnczone.com/forums/woodworking-machines/?s=b6886eb2aeb807d3f95c92e90ab9a756
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Re: Lead screw choice dilemma

Postby Mogal » Fri Dec 02, 2016 7:04 pm

Hello,

Thought I'd chime in as I have the 1/2-10 dual start acme threads on my machine.
For a quick reference, I get a max of 160ipm on my machine which makes for a resolution of nearly 0.0002"
Problem with my machine though, is that I have a bad choice of steppers with a high impedance of 6.8mH (36v)
This makes the motors fairly slow (max of about 285rpm)
With better motors, maybe 300ipm would be doable. (500rpm steppers)
My machine is about 24"x30" and even at my 160ipm isn't too bad for this size of machine.

Chris
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Re: Lead screw choice dilemma

Postby ger21 » Sat Dec 03, 2016 3:06 am

160ipm with a 1/2-10 2 start screw is 800rpm, not 285rpm.

At 285rpm, even a 5 start screw would only give you 142ipm.
Gerry - http://www.thecncwoodworker.com
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