First Time Advice?

[CR250Greg]

I will be converting an X3 to CNC in the next couple of weeks. I have already made the nescessary conversion kit purchase, now all that is left is the electronics.

Initially I have planned on keeping to a strict budget, but now I have come to realize there is no sense in nickle and diming and inadvertently cutting corners in the process.

At the moment the budget is means for debate... I am looking for some direction as far as spending the extra for a servo/G340 setup as opposed to a stepper/G203V setup.

Essentially I would like to get as much from the X3 as possible, while still weighing precision and speed equally. With the little knowledge I have about either type of setup, I have gathered the complexity of a servo setup is greater. As a first shot at doing a conversion, It may or may not be the best route.

Also, is there any place where I can purchase all required parts and have them setup, this way to make sure I do not over look anything?

Thanks

[CJL5585]

I presently have one of each, a stepper system CNC which I built, and a factory assembled servo CNC which uses the Gecko 340's.

As for the difference between the speed and accuracy between the two; there is none that I can see.

The stepper system utilizes adjustable microstep drives which I operate in the 10 microstep mode. Power supply voltage is 48 volts DC. I use precision ballscrews which are 10 turns per inch on the X and Y axis, and an 8 turns per inch leadscrew on the Z axis.

The servoed system utilizes Pittman servos and 250 count per revolution Pittman encoders. The power supply is 36 volts DC. The leadscrews are 8 turns per inch on all axis.

Both systems will easily operate at 60+ inches per minute. Somewhere above that, the servo system will sometimes get a following error and fault the drives due to endplay on the X leadscrew due to the method used by the manufacturer to control that parameter. (vibration over time allows the endplay nut to loosen.) No problems at 60 IPM and below.

I have had the stepper system 3 years, and the Servo system 1 1/2 years. There is not any difference in accuracy between the two systems.

With my experience with these two systems, if I were to build or purchase another CNC system, I would go with steppers if cost was a factor. I would go with servos, if noise was a factor. The servos run cool and are very quiet. The only sound is from the spindle. The steppers run extremely hot at 48 Volts DC, and the steppers whine at high transverse speeds.

I have only used my systems on wood, thin aluminum, and laminates, and use a Porter Cable laminate trimmer (30,000 rpm) for the spindle. (I also found it necessary to purchase an electronic speed control in order to reduce the spindle speed, especially on the metal and laminates.) Most of my cutting occurs at 30-60 inches per minute.

You have the right idea on purchasing the best components one can afford. The quality of components, and quality workmanship is the key to a quality machine. One cannot have both very high accuracy and repeatability using cheap components and / or shade tree engineering.

Just thought I would share my experience with you. Hope it helps you come to your own decision.

Jerry

[CR250Greg]

Hi Jerry, Great info, this should be helpful in determining my plan of action.

A friend of mine always used to say "do not step over dollars while chasing pennies". I believe this holds true here.

Many times I have chosen the cheaper or more readily available alternative only to come to regret my decision down the road. Even cheap electronics are too costly to warrant having to upgrade later on if I find my initial component choices to be inadequate. This is a one shot deal, I would like to do this right the first time.

I could have made due with regular ballscrews, however I opted to upgrade to precision zero backlash rolled ballscrews, as I feared it would be an inevitable upgrade down the road. Likewise with servo's as opposed to steppers.

Noise and heat both represent some concern. I am guessing the life expectancy of a stepper motor is reduced compared to a servo due to higher operating temps?

Is there any rule of thumb for choosing a power supply?

Also, I will be needing a breakout board, start and limit switches, any reccomendations?

-Greg

[CJL5585]

Greg,
The choice of a power supply is based upon whether you use servos or steppers, and also upon the voltage and current ratings of those motors.

Factors which come into play in determining motor size are:

1. Ballscrews, leadscrews, threaded rod?
2. Rails with ball bearings, Handmade rails, V-groove type rails?
3. CNC or Mill frame fabrication of wood, aluminum, or other?
4. Torque in in/oz to move the various axis after fabrication.

Only after this is accomplished can one define the required motors, and then the power supply requirements.

In my opinion, unless one is building a hobby desktop model CNC or Mill, one should utilize drives which can supply over 6 amps of current for steppers, or about 20 amps of current for servos. These ratings are standard, and will suffice for the majority of CNC's and Mills manufactured by homebuilders. The voltage range of these drives should be 24 thru 80 volts. Many kits are limited to 30 or 35 volts DC and 2 or 3 amps of current. The kits are strictly for the desktop model units.

For quality units and factory service, I recommend the G203V stepper drives for steppers, and the G-340 drives for the servos.

There are many breakout boards on the market. A quality product is the CNC4PC line of products which are sold at http://www.cnc4pc.com.

Many vendors can supply the Emergency stop, start, and limit switches. They are also available on e-bay.

Some vendors are:
Future electronics
Digi-Key
Radio Shack
Jameco Electronics
Newark Electronics
numerous others which I cannot recall at this time.

Hope this helps.
Jerry

[CR250Greg]

Hi Jerry,

Im going to spend the extra and go for servos.

What are you thoughts as far as adequacy of these servo's?
http://www.homeshopcnc.com/page4.html

Could I get away with running them from a single 60V power supply? I doubt I will ever find a use for their peak RPM. How many amp supply would you say is required? I read somewhere to purchase a supply which equals 60% the combined continous amperes of all drives, is this correct?

My primary concern is I would like to be able to add a 4th axis eventually and not have to replace the power supply.

Ive been searching around for servo's with no avail, most online retailers seem to be selling pretty much the same products.

[CJL5585]

Hi Jerry,

Im going to spend the extra and go for servos.

What are you thoughts as far as adequacy of these servo's?
http://www.homeshopcnc.com/page4.html

Could I get away with running them from a single 60V power supply? I doubt I will ever find a use for their peak RPM. How many amp supply would you say is required? I read somewhere to purchase a supply which equals 60% the combined continous amperes of all drives, is this correct?

My primary concern is I would like to be able to add a 4th axis eventually and not have to replace the power supply.

Ive been searching around for servo's with no avail, most online retailers seem to be selling pretty much the same products.

Q: What are you thoughts as far as adequacy of these servo's?
A: The servos are a good choice. Which one? Depends upon your intended machine table size and weight. Router or Mill? Moving or fixed gantry?

Q: Could I get away with running them from a single 60V power supply?
A: Yes. You probably would have to build the power supply. I can design a supply for you and specify all the parts, if you can assemble the various components into a working unit. (Or have someone do it for you.)

I need more info on your CNC that you are building, or plan on building, in order to determine which model of the servos you will need. The power supply would be designed to handle 4 of the servos.
Jerry

[CR250Greg]

My apologies, I should have been more specific.

The mill is a Sieg X3 clone, not sure if you are familiar with this particular model, It is one of the larger benchtop mills.

The stock lead screws will be replaced with precision ball screws.

The Z motor is a Nema 34 mount, the X,Y utilize Nema 23 size motors, so both motors listed in that link will be used in conjunction.

Unfortunatly, I do not have the time/tools/experience to tackle an original design. This is a learning experience for the most part. Optimistically, I would like to have the machine up and running in the next two weeks.

I appreciate your offering to assist in design/building of a powersupply to suit my application. Honestly, I have no business working with expensive electronic devices. The only electrical experience I have is in audio and computers, which holds almost no pertinence to this. Since I am short of time I would like to see what is commercially available first and go from there. However, If it comes down to it, I will gladly take you up on the offer. I will provide just compensation for your time and efforts.

[CJL5585]

Greg,

You need to contact Torchead who is a member on this site. He sells complete commercial and hobbiest systems for Plasma, Mills, and routers. His systems are based around the Gecko drives. He offers complete packages including the power supply. It is plug and play. Just let him know the size servos you need. Below is his business web site. Scroll down at the screen that appears to see the servo systems, and at the end he offers several size servos with his systems.

Here is his website: http://www.candcnc.com/RouterPakPriceChart.htm

Jerry

[CR250Greg]

The 3 axis servo system is far above my price range, infact none of the systems he offers are even remotely affordable. If I have to pay someone twice as much to deliver a plug and play unit, its just not worth pursuing this at all.

Ok, perhaps I understated my electrical aptitude. The only part I am unsure of is the correct voltage/amperage to supply to the servos and how my power requirements/distribution will be affected when adding a 4th axis. I am not completely entirely inept when it comes to things of mechanical nature but do need some assistance from time to time, this is one of those times.

Once I have the parts in front of me it should be fairly easy to figure out what goes where.

[GaryCorlew]

Here is another site you may want to check out:
http://www.kelinginc.net/index.html

[CR250Greg]

I priced the drives/motors/encoders at both homeshop CNC and Kelinginc.

With 500 line encoders and G340 drives, Keling comes to 903, Homeshopcnc is 914 and everything is in stock.

[CJL5585]

I priced the drives/motors/encoders at both homeshop CNC and Kelinginc.

With 500 line encoders and G340 drives, Keling comes to 903, Homeshopcnc is 914 and everything is in stock.

Greg,
If you purchase the servo's from Homeshopcnc (per the specs on the servo motors at their site), you can use the Keling power supply part #KL5413. It is rated at 54 volts at 13 Amps. This supply will be able to handle 4 servos.

The servo specs were 72 volts DC for the 34 frame servo and the voltage for the 23 frame servo is 60 volts DC. The 54 volt supply will work with both of these motors, and also the Gecko drives. Cost for the supply is $139.00.