10 IPM, am I doing something wrong?

[jupdyke]

Hello all,

I am just about to get my cnc router up and running for the first time. It has been a long process of building it. I have a questions about my feed speed, and I will start with giving you some general specs on my set up.

I have a 200 step per revolution motor with 150 oz inches. I directly couple them to my precision acme thread using a spider coupler (LoveJoy). The acme screw is a 0.5"-10 screw (10 turns per inch). And I am driving my motors with a home built stepper motor controller, which is using half-stepping. I connect everything to Mach3 to run it.

that being said I believe that I should have 4000 steps per inch of travel. When I test everything out it runs fine at around 10 inches per minute. But this seems very slow compared to what I am reading about cutting speed.

Am I doing something wrong? Have I picked parts which were poor choices for a first time cnc router? any advice is appreciated.

Josh

[kawazuki]

The acme screw is a 0.5"-10 screw

What you are quoting is actually a 20 turn per inch screw! If it is then changing the steps per to 8000 should show an improvement!

[jupdyke]

Kawazuki,

Thanks for the response. However I do not see how it is a 20 turn per inch screw. Here is a link to the mcmaster page for the screw.

http://www.mcmaster.com/#99030a005/=3n0ynb

0.5"-10 is a half inch diameter screw with 10 turns per inch.

Could you explain further?

Also, I have increased the speed in Mach3 and I lose torque. This means I can not just turn up the speed much further because I will not have enough torque to move the screw. If I understand Mach3 correctly, increasing the number of steps per inch, would be about the same as increasing the speed. both result in a higher frequency of steps per second, however if you don't have the steps per inch set correctly you would not be accurate.

Josh

[rowbare]

Are you using microstepping drives? Then you need to multiply your step per inch by the number of microsteps.

[ger21]

4000 steps/inch is correct. The problem is the motor is too small, and 10 turns/inch is really just to many. The motor has to spin too fast, and steppers lose torque the faster they spin.


I don't know how big the machine is, but for more speed, you'll need bigger motors and higher pitch screws, like 1/2-8 2 start, or even 1/2-10 5 start.

[Mariss Freimanis]

Your motor speed is 1.67 revs per second at 10 IPM using a 10 TPI screw. That is very slow. A reasonable speed would be 100+ IPM with that TPI screw. You must be using a very low power supply voltage and/or a high inductance motor (low rated phase current). My guess is 12VDC supply and a 1A per phase motor to get such results.

Mariss

[kawazuki]

Originally Posted by jupdyke Kawazuki, Thanks for the response. However I do not see how it is a 20 turn per inch screw. Here is a link to the mcmaster page for the screw. http://www.mcmaster.com/#99030a005/=3n0ynb 0.5"-10 is a half inch diameter screw with 10 turns per inch. Josh

Sorry - just me being half asleep! Didn't even consider 0.5" was the diameter - apologies for any confusion DOH!

[jupdyke]

Thanks everyone for the input. I will be investing in different lead screw and more powerful motors as one of my first upgrades. It is a lot easier to upgrade once you get the dang thing running for the first time.

Josh

[ger21]

Your homebuilt drives may also be a factor, and may not get the full advantage out of larger motors. Drives, motors, power supply and screws all need to work together as a system for best performance.