[nikel]

First, I know this is a subject that has been beat to death, so I apologize for bringing it up again.

I have a BP clone, new, and will be converting to CNC this year. I have most of everything figured out, but have a question about servos.

I have seen DC and AC servos used. I have seen the AC servos used on bigger more expensive machines. Is that the way to go?

Second question I would like to throw in is who provides a good quality ball screw set for a BP clone.

I have gone threw several threads on this site, but most are pretty old.. and with the crappy economy it seems that a lot of these retailers have gone under.

Thanks,
Nik

[dreammstr6]

not sure if they would work for ya but i have a set of 3 new panasonic servo motors and drivers. the drivers are 208-230 3 phase and the motors are 116v 3 phase with 2500ppr encoders. they are 750 watt. they accept torque mode velocity mode and step & direction mode. if ya inteterested i will accept a resonable offer they are brand new with cables.

[nikel]

not sure if they would work for ya but i have a set of 3 new panasonic servo motors and drivers. the drivers are 208-230 3 phase and the motors are 116v 3 phase with 2500ppr encoders. they are 750 watt. they accept torque mode velocity mode and step & direction mode. if ya inteterested i will accept a resonable offer they are brand new with cables.

Can you reply with model numbers so I can look up the specs. I am assuming the drivers would supply the 116v 3ph power? I can feed the drivers with 230v 3ph with out a problem.

I am still trying to get an answer on the AC vs DC servo question. I can see that the AC motors are more expensive, and that a lot of the VMCs use them, I just can't see why.

At this time I plan on driving the mill with EMC or Mach3. I can really customize a linux setup; which would be preferred.

EDIT:
I was just reading up on what I think is the Panasonic drivers you have. How familiar are you with them? This Full-Closed loop option has peaked my interest. My mill already has a good DRO on it and it seems to me in this mode the drive would be able to determine its position off the scale? This is intriguing, since my mill is new and the ACME lead screws in it are very good with little back lash. This will deteriorate over time, but would allow me to get the setup running before tearing it all down to install the ball screws. It would also remove any back lash issues, although minuscule, in the ball screws.

[dreammstr6]

yes the drivers supply it. driver panasonic model MSDA083A1A51 MOTOR PANASONIC MSMA082A1E they have 2.4nm of cont. torque. one thing on dc servos is the brushes. i have 2 ez-trak mills with dc servos. odd thing is the encoders on them is 250ppr. i thought it would have been higher.

[ichudov]

AC servo motors have greater performance and better cooling. They are, however, more expensive and need to be matched to the drives correctly.

They also do not have brushes to wear.

i

[nikel]

Thank you ichudov. This is what I was looking for.

Now does anyone have a trusted source for a ground ball screw setup for a BP clone?

[ichudov]

Thank you ichudov. This is what I was looking for.

Now does anyone have a trusted source for a ground ball screw setup for a BP clone?

I personally highly do NOT recommend converting a manual milling machine to CNC. A huge effort, relatively expensive, and I think not the best use of resources. It does not even increase the value of the machine. And in the end, the machine y ou will have was not originally built to be a CNC workhorse.

Just the small issues like lubrication, can really be a huge drag.

i

[nikel]

I have considered this.. and still am, but my mill is damn new brand new. And I went through a lot of trouble to get it here and installed. I don't have access to heavy moving equipment.

I don't plan on performing big production runs.. it is a hobby for now. If I were ever in the position to make it more I would got with a VMC.

So, given that information, do you still offer the same opinion?

[ichudov]

Yes, I have the same opinions. I also do not do production runs. When I bought my CNC Bridgeport, I sold my manual mill. I had to restore my CNC mill, as its control was obsolete and broken.

Having seen a manual and a CNC Bridgeport mill, I formed an opinion that retrofitting a manual mill is a very troublesome approach.

i

[mactec54]

nikel

If you want to use servo's you should look at Dmm Technology They have AC servo's system that is a great price, & are very easy to set up

http://www.dmm-tech.com/

[nikel]

Yes, I have the same opinions. I also do not do production runs. When I bought my CNC Bridgeport, I sold my manual mill. I had to restore my CNC mill, as its control was obsolete and broken.

Having seen a manual and a CNC Bridgeport mill, I formed an opinion that retrofitting a manual mill is a very troublesome approach.

i

Ok, so this got me thinking. What is the real difference? A CNC Bridgeport is just a bridgeport with the CNC stuff added at the factory? no? You have the mill, the servos, the controller? The most difficult fabrication is the quill drive. In my case I would be adding the hardware rather than the factory.

If I am over simplifying this please take a moment to correct me. I have seen about a thousand posts thus far across this the Internet debating this issue, and I am still stuck on why.

[mactec54]

nikel

The Bridgeport CNC like the Boss series Is Very different to a manual, Some of the parts in the head are the same, but the rest of the machine is different

There is nothing wrong with converting a manual machine to CNC, a set of Ballscrews that fit your machine, & you are on your way, Try Hiwin they have a good kit for most Bridgeports

[nikel]

Yeah, I think I am really stuck going this route. I would really like to pick a CNC ready machine... and actually I should have waited. My mill is only a year old, and purchased new. Given the economy, I am not sure if I could find a buyer. I am in central florida, and I don't see too many mills available locally, but if I would prefer new over used.

I am going to contact Hiwin regarding prices since they don't really post any.

Thanks,

[probinson]

Hey Nikel,

My opinion on the Bridgeport CNC conversion is quite different. A CNC mill makes a lousy hand operated mill but a hand opperated mill converted to CNC does both quite well. If you have ever tried to do a quick machining job using the jog wheel on a CNC you know what I mean so be sure to have an easy way to disengage the CNC for hand operattion.

Although putting a ball screw on the quill is a real pain in the butt, the rest of the conversion is very simple.

The accuracy of the ball screw in meaningless. Your glass scales are already more accurate then a precision ball screw so just use the scale outputs instead of rotary encoders on the screws.

As long as you don't go with a really small ball screw, backlash is the only issue you need to worry about. You want double ball nuts on each screw so that you can pre-load them for zero backlash.

Pete

[nikel]

Thank you for the input. I was coming from this point of view myself. Although, very good info on the ball screws.

I took the other input to heart and went on a serious search of CNC mills. Depressing, most used equipment in the 10k budget is pretty old and would more than likely require too much work.

This all however brings up another question. I was planing on using AC servos, but I am now wondering if that might be simple over kill?

Hey Nikel,

My opinion on the Bridgeport CNC conversion is quite different. A CNC mill makes a lousy hand operated mill but a hand opperated mill converted to CNC does both quite well. If you have ever tried to do a quick machining job using the jog wheel on a CNC you know what I mean so be sure to have an easy way to disengage the CNC for hand operattion.

Although putting a ball screw on the quill is a real pain in the butt, the rest of the conversion is very simple.

The accuracy of the ball screw in meaningless. Your glass scales are already more accurate then a precision ball screw so just use the scale outputs instead of rotary encoders on the screws.

As long as you don't go with a really small ball screw, backlash is the only issue you need to worry about. You want double ball nuts on each screw so that you can pre-load them for zero backlash.

Pete

[probinson]

The difference between AC and DC servos is just electronic commutation. Some power is lost in brushes, they wear out, and they take up space in the motor which means that an all electronic motor can be a more powerful than the same size DC motor and be virtually maintenance free.

AC servos are cheaper to build but they are newer technology, higher power density, and maintenance free so they can fetch a higher price. Your best bang for the buck, however, will probably be a DC servo system, especially if you are shopping the surplus market.

If you were building a CNC that had to run 24/7, needed maximum power in a small space, or needed really massive motors then AC servos would be the only way to go. For hobby or small business applications, the bushes will never need replacing and you won't see any difference in performance between the two. You are shopping for power per dollar in your servo system, not power per cubic inch or bragging rights.

I think I went over my 2 cents worth. Oh well, inflation..

Pete

[ichudov]

The difference between AC and DC servos is just electronic commutation. Some power is lost in brushes, they wear out, and they take up space in the motor which means that an all electronic motor can be a more powerful than the same size DC motor and be virtually maintenance free.

AC servos are cheaper to build but they are newer technology, higher power density, and maintenance free so they can fetch a higher price. Your best bang for the buck, however, will probably be a DC servo system, especially if you are shopping the surplus market.

If you were building a CNC that had to run 24/7, needed maximum power in a small space, or needed really massive motors then AC servos would be the only way to go. For hobby or small business applications, the bushes will never need replacing and you won't see any difference in performance between the two. You are shopping for power per dollar in your servo system, not power per cubic inch or bragging rights.

I think I went over my 2 cents worth. Oh well, inflation..

Pete

Another advantage of AC servos is that current goes into the stator (outside), not the rotor (inside), and so AC servos are easier to cool.

[probinson]

Another advantage of AC servos is that current goes into the stator (outside), not the rotor (inside), and so AC servos are easier to cool.

Yes, thank you. That is definitely the most important selling point for the AC servo and I should not have left that out.

For an application where the machine does a lot of rapid moves, motor heating is a critical issue. With the Bridgeport conversion, however, we are loading the work piece manually and doing manual tool changes so, unless your motors are seriously undersized, motor heating won't be an issue.

[nikel]

@probinson

This concept of using the dro scales got me doing some research. Thus far I have not found much information, which leads me to think I am not searching for the right subject. Do you (anyone really) know where I could find more information on how this kind of setup would be wired?

If I go the DC route I have some Gecko drivers that might be used: G320's I think. If I go the AC route I will purchase a driver/servo set.

[nikel]

For anyone else interested; I just found a nice tutorial on dual closed loop & improved dual closed loop systems here: http://www.galilmc.com/checkreg.php?...sation-methods

@probinson

This concept of using the dro scales got me doing some research. Thus far I have not found much information, which leads me to think I am not searching for the right subject. Do you (anyone really) know where I could find more information on how this kind of setup would be wired?

If I go the DC route I have some Gecko drivers that might be used: G320's I think. If I go the AC route I will purchase a driver/servo set.