4' X 8' CnC router table can't run faster then 35ipm ??? Please help???

[tomp]

I use Gecko stepper driver G203v, Nema34 (Pittman) holding torque 1076 oz/inc and operated under Mach3. I have bought a used 4' X 8' Phoenix cnc router it's a heavy duty one with 1" X 48" lead ball screw in Y-Axis and 2" X 96" lead ball screw in X-Axis. Y-Axis running & jogging fine but X-Axis can't go faster than 35ipm when I try to air cut the part and motor also lose step, it's ratio 2:1 1 pulley 5" diameter 40 teeth and 1 pulley 2 1/2" diameter 20 teeth. I am thinking of changing that set of timing pulley into 5:1 ratio to increase the motor's torque or replace the nema42 with higher torque to make machine runs better. I hope somebody in the forum can help me with this matter with your thought.
Tom,

[pkirby]

I'm not the most skilled with diagnostics, but I can give you a couple of things to do that will narrow down your problem.

1) Swap the x and y motors. Try running it and if your y axis is now messed up then you know it's the motor. If it runs the same as before swapping the motors are probably fine.

2) Swap the x and y drivers. If the problem goes from the x axis to the y axis then you know the driver is bad. If not, it's probably fine

3) If neither of these things work, try reinstalling your software.

4) If that doesn't work try using a different computer to run the cnc.

Now, I'm out of ideas so good luck

[dana_swift]

There are folks in North Carolina who have a solution. It will be painted blue, and will cut at a minimum of 300 inches per minute and as much as 600 inches per minute and never lose a step.

Not that I don't make scrap occasionally, but at least I get to make my operator mistakes at 450 inches per minute. And the scrap is never created by lost counts on the alpha machines.

Lost marbles maybe..

D

[srwtlc]

Check your motor tuning in Config/Motor tuning. You may have the acceleration set too high on the X. Velocity settings, kernel speed, mechanical issues...

Might have better luck asking here...http://www.machsupport.com/forum/index.php?PHPSESSID=06dsuafhfp9afm8d2oktcl7q05;www

[richards]

I'll need more information before being able to help.

What is the model number of the Pittman motors? Do you have electrical specifications for the motors?

How much weight are you trying to move? The Phoenix routers that I found on Youtube are "big iron" (heavy) machines.

What is the specifications of the ball screws? How far does the nut travel per revolution?

Let's plug in some numbers. On the Thompson Ball Screw site, they list two specs for 3/4" screws, 0.200" per revolution and 0.500" per revolution. You have a 2:1 drive attached to the ball screw. If you had a ball screw that moved 0.200" per revolution with a 2:1 drive, then the screw would move 0.100" per revolution, or 0.100 / 2000 = 0.00005" per step. At 30,000 pulses per second, the axis would move 1.5" per second or 90" per minute.

Using a ball screw that moved 0.500" per revolution with a 2:1 drive, you would move 0.250 per revolution or 0.000125 per step. At 30,000 pulses per second, the axis would move 3.75" per second or 225" per minute.

When a stepper motor misses steps, it usually means that you're driving it too fast for the load that it can handle. Typically, the bigger the motor, the slower its top speed. In other words, you need to match the motor to the stepper driver. I've had extremely good results with the Oriental Motor PK299-F4.5 wired parallel. I have no trouble driving that motor at 1,350 RPM with Mach3 running at 45,000 pulses per second (45,000 / 2,000 * 60). The secret to that speed is proper ramping.

I also have some older PH299 stepper motors that will hardly run at all with the Gecko G203v stepper drivers. Those older PH299 motors have very high inductance. To get "snappy" performance from those motors would require a stepper driver that could handle 275 VDC. The G203v can only handle 80VDC. Those PH299 motors are not suited for use with the G203v. I'm suspecting that ONE of your problems is a mismatch between motor and driver.

On the Geckodrive.com site, in the support section, you'll find a document titled, "Choosing A Drive". They give this formula to calculate the watts needed: (Heaviest object * IPM) / 531 = Watts. If the Watts = 100 or lower, a stepper motor is recommended. If the Watts > 100, they recommend using a servo motor.

For instance a 100-lb gantry moving at 500 inches per minute would require (100 X 500) / 531 = 94 Watts, so a PK299-F4.5 motor would work, but a 500-lb gantry moving at 250-ipm would require 235 Watts, which means that most steppers would loose steps. You would need a servo to handle that amount of mass at that speed.

[danhamm]

You would get a better response at CNCZone as shopbots dont do ball screws or Mach3 software...

Your ball screws are are reduction, you have 2 to 1 drive reduction, your probably getting up there in communication steps..

Turn your mach software down to its lowest level of 25k, check your power supply voltages, and check your ball screws to see if they are free..

[tomp]

Carl,
Yes, you are correct. Y-Axis have 1" diameter lead screw and I use the same motor for all axises but the only X-Axis got an issue because of that big heavy load of lead ball.

[carlcnc]

TOm
from your description, you have a major issue with
A those are BIG ballscrews,lots of power to start and accelerate them.
whats the pitch? I bet it is more like 1" per rev
if so it takes about 350 oz in to get 100lbs "thrust" ,
add in the inertia of screw, load of object ,friction and probably it's more
like 600 oz in just to start moving,

B; unclear, you bought NEW size 42 motors or are they existing?
either way, size 42 steppers are DOGS, I repeat DOGS
Mike Richards could probably explain the theory , all I know is they are DOGS

C; I have found that Gecko 203v are happy with about 1200 ox in size 34 ,the square type. but I always have to put in about a 300K resistor
without a resistor [don't know why] drive will often fault under even modest acceleration, adding the resistor cured that problem

D; did I mention size 42 steppers are DOGS ??

[tomp]

Mike,
I would like to input all information about it as what I know.

All axises use the same motor Nema34 Pittman N203451035A http://www.clickautomation.com/PDF/items/MAE%20Express%20NEMA%2034%20Step%20Motors.pdf

Gecko Driver G203V current set @ 3.5A Bipolar parallel connection

Power Supply KL-7220 Unregulated Power Supply 1440W, 72VDC/20A ,120VAC or 230VAC http://www.kelinginc.net/SwitchingPowerSupply.html

1 1/2" X 96" Lead ball screw 3 thread per inch

Machine was manufactured by Phoenix GS48 Cad/Cam CNC router. It's use to Dayton servo motor mount on. I would send pictures if you need to figure out.
Y-Axis included Z-Axis I guess it's weight about 200lbs.

Please let me know if anything else you need.
Tom,

[carlcnc]

Tom
OK, size 34 is good,having 72v is good, but aren't those motors rated 5 amp?? in parallel?
can't guarantee I can will be available exactly when you call
but,you're welcome to
36-zero- 2-zero-4- 5-six-7-six
I am up the road ways in Bremerton Wa, so at least we are in the same time zone.

Carl

[richards]

Tom, Carl is correct; the motors, when wired bipolar parallel can handle 5A (SQRT(2) X 3.5 = 4.9A). A 72 VDC power supply is okay (32 x SQRT(8.5 mH) = 92, but the G203v is limited to 80VDC). Verify that you have at least 22,000 uF of capacitance on the power supply to filter out the AC ripple (80,000 X 5A / 72VDC = 5555 uF per motor). You'll need to use 120K 1/4W current limiting resistors on terminals 11 and 12 on the G203v. (117K is ideal, but 100K to 120K will work just fine.)

The torque chart indicates that the motor should be able to run at 500 RPM with excellent torque.

Does the ball screw have a single thread, or are there multiple starts? The easy way to figure that out is to mark the ball screw and then measure how far the ball nut travels per revolution of the ball screw.

The G203v requires 2,000 pulses per revolution. If the ball screw actually moves .333 inches per revolution, each pulse would move the ball nut 0.0001665" (0.333 / 2000 = 0.0001665"). If the ball screw moves 1" per revolution, each pulse would move the ball nut 0.0005".

By comparison, the Shopbot PRS-Alpha with a 7.2:1 gearbox moves an axis about 0.000327" per pulse.

Round stepper motors are much less desirable than square stepper motors, but I would not like to recommend that you spend $850 to buy four new Oriental Motor PK299-F4.5 motors unless you can verify that there is no binding and that all parts are well lubricated.

Verify that the acceleration is slow in Mach 3. Set the rate to allow 1 second for the ramp time. You can always increase the acceleration after you verify that the axis will move fast enough to do the job.

You have two motors on the X-axis, so if the gantry weighs 200 lbs, each motor is responsible for 100 lbs. Using Mariss's formula on the Geckodrive web site, that size motor should be adequate for jogging speeds up to about 500" per minute.

I'm guessing that something is either binding, Mach3 is not properly configured, or that you're moving much more mass than you think.

A friend in Boise, Idaho, built a machine that had a much heavier gantry that ran just fine with PK299-F4.5 stepper motors. He replaced those motors with the PK2913-F4 model. (He also used the G203v stepper drivers and a 65VDC power supply.) His machine has ball screws and linear guides.