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Speed up my cnc machine
« on: September 10, 2017, 10:55:34 AM »
Hello,

I purchased the hardware to build my own cnc back in 2014 or 2015. I want my cnc to move quicker. I want to update my lead screws on all 3 axis (X,Y and Z). The lead screws that came with the hardware of my cnc move slow and to do any project is time consuming. I researched lead screws and I found one that is 1/2" 5 start and 10 TPI ACME precision lead screw, which translates to 2 turns per inch. Will this make my cnc move quicker.  Let me know.

Thx Vince
Re: Speed up my cnc machine
« Reply #1 on: September 10, 2017, 11:27:29 AM »
I believe that is way to fast a pitch. You will need much larger motors to get enough torque. The full step size will be 0.0025 which even with micrstepping will be very coarse, so you'll need gear reduction which defeats what you are trying to do. A pitch of 0.200" or 5mm per revolution would be better.
Re: Speed up my cnc machine
« Reply #2 on: September 10, 2017, 02:53:28 PM »
Hi,
what are your existing lead screws?

If you are serious about CNC and making fast and accurate machines then consider ballscrews. Rolled ballscrews are reasonably cheap and
have an accuracy of 50um per 300mm. Ground ballscrews are way WAY more expensive, C5, the entry level ground grade is 18um per 300mm
right up to C1 grade for semiconductor machines made to special order.

garylucas is correct a pitch of 0.2 inch or 5mm is about right, you still get good mechanical advantage obviating the need for gearboxes  without
having to spin them at blinding speeds to get useful rapids.

Craig
My wife left with my best friend...
     and I miss him!

Offline ger21

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Re: Speed up my cnc machine
« Reply #3 on: September 11, 2017, 09:47:59 AM »
What motors, drives, and screws are you currently using?
It's possible that3 /- 5 start screws will be much faster. But if your other components aren't up to the task, they may not work well.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html
Re: Speed up my cnc machine
« Reply #4 on: September 11, 2017, 07:45:18 PM »
I have: 
(3) NEMA 24 425 oz-in stepping motors
(3) Drivers (3.0Amp 24-40 Volts, 1-1/64 microstepping)
(1) 36v 8.8a Power Supply
Re: Speed up my cnc machine
« Reply #5 on: September 11, 2017, 08:45:10 PM »
Hi,
those units should do 500 rpm if you don't load them too much, may be as much as 1000 rpm.
With a 5mm pitch  screw that's 2500-5000mm/min...100-200ipm, probably pretty reasonable for
a hobby machine.

Half inch lead screws that you are proposing certainly would go fast but I don't think your steppers
have the grunt to drive them.

Craig
My wife left with my best friend...
     and I miss him!
Re: Speed up my cnc machine
« Reply #6 on: September 12, 2017, 01:37:49 PM »
In the real world machines with high acceleration and deceleration run rings around ones with low accel/decel. Machining is a drag race not going around a track. Unless you doing very long cuts, or lots of air cutting you seldom see the top speed. So for most parts working at getting a really high top speed at the expense of acceleration is counter productive.

Offline ger21

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Re: Speed up my cnc machine
« Reply #7 on: September 12, 2017, 08:23:13 PM »
Those motors should get you more speed with 5 start screws, but to get the most performance from those motors, they need better drives and 72 volts.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html