Stepper Sizing for CNC conversion

M

Merlin123

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Hi All,
I haven't posted in a while as I am currently working on a kitchen Remodel that my life depends on!!
I am planning on adding CNC functions my PM-45m to improve it's skill set. My question concerns sizing the Stepper motors that will drive the X-Y feed screws. I expect I will need to use stepper gearmotors to achieve the required torque.
Any suggestions as to suppliers of the needed equipment? I figured that a NEMA 34 would be adequate to drive a 10 to 1 gear unit for the feeds. Let me know if I'm in left field or on the right track!
Thanks in advance,
Merlin123
 
NEMA 34 motors are an excellent choice. The 1288 oz/in (80 in/lbs or 9.12 N-m) may not require any reduction on a small machine like a PM45. I am running a 48 x 96 CNC router with these motors at 1.5:1 reduction and have never decoupled under normal load conditions. The motors that these replaced were 29 in/lb DC servo motors. The only time these have decoupled is under insane acceleration or speed tests. Like instantly trying to ramp up to 600 IPM or something crazy. I am running these at 20,000 steps per revolution, that equates to about 0.000002 inches per step with 5 pitch ball screws.

My favorite vendor is Automation Direct. Are they the least expensive? No. But their products are good, prices are competitive, and their documentation and customer service is excellent. Can you buy direct from China off of Ebay for less money?. Yes, you get what what you pay for. I'm sure there will be some additional comments on this subject.

http://www.automationdirect.com/adc/Shopping/Catalog/Motion_Control

I am using the STP-MTRH-34127 step motors, with the Sure-Step STP-DRV-80100 drive, powered with the STP-PWR-7005 power supply. Only one power supply is required for a 3 or 4 axis machine. With the Sure-Step drives you can run from 200 to 20,000 steps / revolution, which means that you can run directly from Mach3 or have the option of using a more sophisticated controller.

adxrouter.jpg


This is the power supply, drive and step motor that is going into my Z-axis drive for my mill. Setting it up on the bench before the install.
zaxisdrive.jpg
 
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Wow,
I seriously appreciate the effort you guys put into your suggestions. I especially appreciate the links to sites with products that will help me automate my PM-45. I have been using Automation Direct for years when purchasing electrical components for panel building.
I would love to be able to change the current lead screws over to ball screws to reduce the amount of drive torque. Do you recommend doing this or leave the feeds as they are?
Thanks again for your help,
Merlin123
 
Merlin123 said:
Wow,
I seriously appreciate the effort you guys put into your suggestions. I especially appreciate the links to sites with products that will help me automate my PM-45. I have been using Automation Direct for years when purchasing electrical components for panel building.
I would love to be able to change the current lead screws over to ball screws to reduce the amount of drive torque. Do you recommend doing this or leave the feeds as they are?
Thanks again for your help,
Merlin123
Click to expand...

It is my pleasure to help out.

If you want maximum accuracy changing to ball screws is the best idea, not to mention the reduced torque requirement. With zero backlash you could get away with not putting scales on the table and the quill. It is still my preference to use scales on the axis. I am using Renishaw LM10 1uM magnetic scales on both my mill and on the pictured router, glass scales work very well also. This compensates for any errors generated by leadscrew windup, backlash, and any other errors that may be introduced into the system since you are reading actual table position.

I purchased my scales off of Ebay, there are a lot of them available right now because they were being used in the now defunct solar manufacturing plants.

My scale installation can be seen here:
http://www.hobby-machinist.com/showthread.php?t=21060&highlight=z-axis+cnc+conversion
 
The story is ball screws run much smoother and require less effort. http://www.hobby-machinist.com/showthread.php?t=18812 post #14 shows one set for an upcoming conversion. The 1605 will easily fit in the X and Y space. The 2005, I will use on the Z with the zero backlash double ball nut measures 1.410 in diameter. The flange is 1.715 across the flats If you want to check if your mill has room for the larger ball screws in X and Y. I contacted the seller (Chai) at http://stores.ebay.com/linearmotionbearings and told him exactly what I was looking for. He immediately quoted it and shipped it well packed.

Dave
 
Jim! Dave! You're the best! The info you have provided me will definitely get me through this project. I promise to keep in touch as I progress. There is a ton of work involved but I expect it'll be fun.
I already setup a geardrive Z axis control for my PM45 as I was tired of running that hand crank every time I changed to different cutters and Collets. I got the gearmotor on Ebay for about $40. It had a clutch and brake circuit on it but with an output of 60 rpm and toothed belt drive pulley, I removed the brake circuit and used the clutch to engage the drive. It's a great setup and I'd like to be able to use it for the Z axis drive when the CNC conversion is complete.
Keep your fingers crossed!!
Thanks,
Merlin123
 
Merlin123 said:
Jim! Dave! You're the best! The info you have provided me will definitely get me through this project. I promise to keep in touch as I progress. There is a ton of work involved but I expect it'll be fun.
I already setup a geardrive Z axis control for my PM45 as I was tired of running that hand crank every time I changed to different cutters and Collets. I got the gearmotor on Ebay for about $40. It had a clutch and brake circuit on it but with an output of 60 rpm and toothed belt drive pulley, I removed the brake circuit and used the clutch to engage the drive. It's a great setup and I'd like to be able to use it for the Z axis drive when the CNC conversion is complete.
Keep your fingers crossed!!
Thanks,
Merlin123
Click to expand...

If it is not a stepper or servo I don't think Mach or other software can use it. Generally they control measurements down in the few ten thousands range. Keep us updated.
Dave
 
I'm currently doing a CNC conversion on a PM-932, http://www.hobby-machinist.com/showthread.php?t=21442 , same basic machine as the PM-45. I'm using 2005 ball screws all around. The slot in the machine base requires some modification to keep full travel of the y-axis and the x-axis is a close fit so it requires some planning to make it fit and still get the table on.

I'm using the same basic steppers that Jumps4 used on his ZX45 conversion. 1600oz on the x,y and 4200oz on the z. Last I checked, the stepper, driver and power supply package was about $800 on ebay. I got mine from another forum member who decided not to do his conversion so the cost to me was reduced.

Jay
 
Merlin123 said:
Jim! Dave! You're the best! The info you have provided me will definitely get me through this project. I promise to keep in touch as I progress. There is a ton of work involved but I expect it'll be fun.
I already setup a geardrive Z axis control for my PM45 as I was tired of running that hand crank every time I changed to different cutters and Collets. I got the gearmotor on Ebay for about $40. It had a clutch and brake circuit on it but with an output of 60 rpm and toothed belt drive pulley, I removed the brake circuit and used the clutch to engage the drive. It's a great setup and I'd like to be able to use it for the Z axis drive when the CNC conversion is complete.
Keep your fingers crossed!!
Thanks,
Merlin123
Click to expand...


Theoretically you could make a servo motor out of almost any DC motor but it may be more trouble than it's worth. The control is all in the drive and the motion controller. There are a number of PWM DC drives available, some will accept a pulsed (stepper type) input, some will accept an analog input. Trying to control them with out purpose designed software/hardware might be a bit tricky. For instance, you could use Mach3 with a K-flop controller to achieve the desired result but I have not have had good luck with this setup.(It could just be me also)

Mach3 does not directly provide an analog output (+/- 10 volt is the industry standard) to control a drive so you need an interface like the K-flop that will. I did run a DC motor as a servo with Mach3 directly by building a charge pump circuit to provide a 0 to 5 volt analog signal drive the motor, it worked pretty well but required about 2 months of R&D to get it right.

My mill came equipped with Baldor DC motors on the X and Y axis and Fenner SFD-1525-12 drives. I have no idea what these cost but they work very well. I am also setting up a step motor on the Z-axis, but will be running it in velocity mode so to my controller it looks just like a servo motor. I am controlling the whole setup with software that I wrote, DC CNC, and am using a 4-axis Galil DMC-1846 motion control card to handle the real work. However this is not an inexpensive setup, and my software will only work with the Galil family of products, for now anyway. I am using the 4th axis to control the spindle speed from the computer. I wish I would have purchased a 5-axis card to allow a rotary axis on my mill, maybe I'll do that if I really need it, or just throw in a single axis card to run the spindle.

Having rambled on for a bit here, the bottom line is I would recommend installing a stepper motor on the z-axis when you get to that point.
 
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