Fehlmann Picomax 50 CNC conversion/refurb

[Agathon]

I've already posted a few times regarding drivers and so on for this machine, but thought it might be worth just doing an over-view of the whole project.

This video is worth very many words:


https://youtu.be/0vZgQbFCj2Q

[Lee Roberts]

Welcome and nice to meet you David,

Thanks for sharing and the introduction, I've also sub'ed to your YT channel and look forward to following along. Will go and have a look now to see if i can help regarding drivers.

[Clive S]

David welcome to the forum. It looks like its going to be a nice project. Are you running this from the parallel port or with a motion controller? Have you also thought about Linucnc if you want in the future to use ATC ect and as many inputs and output as you want.

[Agathon]

Thanks for the welcome(s). I've already done a great deal of the groundwork to get this thing up and running, so it shouldn't be too difficult to get it actually doing some work.

I spent this afternoon looking at the ways and ball-screws of the X-Y table and after a little adjustment it's working much better. This thing is, like most Swiss stuff, beautifully made and really nice quality components have been used including dual-ball-nut screws allowing the micro-adjustment of the pre-load. I'm going to stick to the 2000mm/min rapid as this is reliable.

I'm running from the parallel port of a 10 year old Dell PC - two parallel ports actually (in anticipation of the many inputs required for the extra limit switches). I really like your suggestion of using LinuxCNC. I've only been using Mach3 up to now as I have a friend who's been building small CNC machines for the last 15 years and is very knowledgeable about Mach3. However, I've always used a Mac and am not overly keen on the MS operating systems so switching to another Unix based OS appeals to me.

Would I be better off using a motion controller rather than the parallel ports?

[Clive S]

Using a motion controller is night and day difference. I don't want to get into the Mach3 V Lcnc I use both. But If you say do a feed hold in Mach3 and it is in a cycle it won't stop until the cycle is finished with Lcnc it will stop immediately.

I you decide on the Lcnc route with steppers you would need a Mesa 5i25 or 6i25 (pci or picx) and a 7i76 bob that would give you at least 34 input and output, 5 axis 2 encoders. spindle control, 24V inputs differential signaling etc.

edit: You could also just use a 7i76e if you want an ethernet version without the 5i25 etc

Lcnc is a steep learning curve but it is a rock solid system. It will do what ever you want.

I think you said you had 4mm screw if so I don't think you can go much faster rapids with a nema34 I think the max motor speed would be 500-800 rpm.

[Agathon]

Using a motion controller is night and day difference. I don't want to get into the Mach3 V Lcnc I use both. But If you say do a feed hold in Mach3 and it is in a cycle it won't stop until the cycle is finished with Lcnc it will stop immediately.

I you decide on the Lcnc route with steppers you would need a Mesa 5i25 or 6i25 (pci or picx) and a 7i76 bob that would give you at least 34 input and output, 5 axis 2 encoders. spindle control, 24V inputs differential signaling etc.

Lcnc is a steep learning curve but it is a rock solid system. It will do what ever you want.

I think you said you had 4mm screw if so I don't think you can go much faster rapids with a nema34 I think the max motor speed would be 500-800 rpm.

Thanks once more Clive. Many things to look into and think about. I'm happy with the 2000mm/min rapids, I'm still somewhat incredulous that those old Superior steppers could run any faster.

Sorry about the cock-up with the video editing btw. Don't know how I managed to get two copies in one video.

[Agathon]

Here's the latest on the Fehlmann table. Sorry that it's a bit long - will try and be brief in future.


https://youtu.be/nwekbZpsq6Q

Making good progress on other stuff and will post more soon - watch this space!

[Clive S]

Coming along nicely I enjoyed the vid. Re the Nema34 they might run better with a higher voltage that 70v I think you can get 230v drives for them.

[Agathon]

Coming along nicely I enjoyed the vid. Re the Nema34 they might run better with a higher voltage that 70v I think you can get 230v drives for them.

Hi Clive, just come in from the workshop after more fun. More vids tomorrow...

Do you think it sounds like they're missing steps or is it a step-generation/processing issue? Difficult to answer without test I suppose. The quill has always made the same noise from time to time. I've was driving it with one of those crappy HY-DIV268 things and when running a repeating cycle of ten up an down movements it always returned to the same place with better than 0.01mm variation - which I was very impressed with.

I think after going to the effort of buying the highly recommended AM882 drivers, in the short term at least, I'd rather replace the motors - they only cost £27 for the pair including delivery so I can afford to replace them!

In the longer term I still favour going all-out for servos. Those Teknic Clearpath things look very impressive. If confidence in Sterling would just improve a little I'd be tempted to order.

[Agathon]

Motor operation and control issues:


https://youtu.be/EafSH0RX1Lk

[Clive S]

One problem using the PP is that until the pc is powered up the pins can be in any rambled state and they can also chatter as the pc is powering up causing all sorts of unexpected happenings. That is the beauty of a motion controller this behaviour does not happen with Lcnc and a Mesa card.

edit Having said that you might be able to use the charge pump in Mach3 so that the bobs are not enabled until the charge pump signal is seen.

[Agathon]

One problem using the PP is that until the pc is powered up the pins can be in any rambled state and they can also chatter as the pc is powering up causing all sorts of unexpected happenings. That is the beauty of a motion controller this behaviour does not happen with Lcnc and a Mesa card

Mmm.. yes, I understand that, but it's more of an issue with the BOB itself in that they've used the NC rather than the NO side of the relay - can't see the reasoning behind this or a way around it.

BTW I'd love to move over to LCNC, but my impression is that it's for people with an interest in programming and computing rather than just wanting to get on with using a machine. I've looked hard, but I can't find the equivalent of the Mach3 User's Guide. I find that I can't get to a position where I can understand what I need to do to use Mach3 - and I regard myself as being moderately savvy with PCs.

[m_c]

Without seeing the videos (my broadband is currently not working, so am limping along on mobile broadband), if you're using a parallel port, you really need to use a charge pump for safety, regardless of what software you're using. As Clive has already said, parallel port pins can act randomly during loading. If the BOB you are using has no charge pump, the easiest option is just not to power up the machine until the computer is fully loaded.

The Clear tecknic servos do seem good, however you have to remember as they need the step/dir signal directly, it adds in a lot of extra potential for interference and losing/missing steps. If I was to use them, I'd be looking at adding differential signal drivers to avoid potential noise issues.
Plus I think they're more closed loop stepper, than what's more commonly referred to as a servo. Good in the fact they're better for direct driving ballscrews, but does mean top speed is limited.

Performance wise, you're more likely to be better of with some good Nema23 motors, and adding a 2:1 drive ratio. Nema 34 really need high voltage drives to get the best performance from them.

[Agathon]

Without seeing the videos (my broadband is currently not working, so am limping along on mobile broadband), if you're using a parallel port, you really need to use a charge pump for safety, regardless of what software you're using. As Clive has already said, parallel port pins can act randomly during loading. If the BOB you are using has no charge pump, the easiest option is just not to power up the machine until the computer is fully loaded.

The Clear tecknic servos do seem good, however you have to remember as they need the step/dir signal directly, it adds in a lot of extra potential for interference and losing/missing steps. If I was to use them, I'd be looking at adding differential signal drivers to avoid potential noise issues.
Plus I think they're more closed loop stepper, than what's more commonly referred to as a servo. Good in the fact they're better for direct driving ballscrews, but does mean top speed is limited.

Performance wise, you're more likely to be better of with some good Nema23 motors, and adding a 2:1 drive ratio. Nema 34 really need high voltage drives to get the best performance from them.

Thanks for the reply. What's a "charge pump"?

Re Clearpath - they are true servos rather than hybrid servo/steppers. I take your point about interference. I might pose the question to Teknic and see what they say - they've been really helpful so far.

There seem to be as many opinions about drives and motors as there are drives and motors. I did canvass this forum and others quite extensively before buying drives and the consensus seemed to be that Leadshine AM882s at 70v was the way to go. Still, the Z axis is fine, and the X&Y drives can be redeployed. If I do make some change to the X and Y drives it will be to servos - not poncing about with these poxy stepper things any more:wink:

[EddyCurrent]

Thanks for the reply. What's a "charge pump"?


if the bob does not see a continuous signal from the controlling PC it shuts down.
Also called a 'watchdog timer'

From my bob manual,

The charge pump uses the 12 kHz signal from the parallel port generated by the
CNC software to operate a logic circuit that gives an active low output. Any
piece of machinery that uses powerful motors can be dangerous if controlled
by a computer that can be in an unknown state while being powered up or in
a software crash condition. Using the charge pump circuit to disable power to
motors is a safety device in that it only operates when the software is running
correctly and under user control. The charge pump circuit is also used to
disable the output signals so even if your stepper boards do not have an
enable pin they will be disabled automatically when the charge pump signal
is not present.

[Clive S]

Thanks for the reply. What's a "charge pump"?Mach3 generates a 12.5Kc/s pulse onto one of the pins of the PP This is used to enable the bob. When Mach3 starts up. It is used in case there is a software problem or e stop situation the pulse disappears and basically switches the bob off.

Re the drives is is usual for us to have a two to one reduction with a belt drive. I use these AM882 on my mill.
Your mill though is in a league of its own.

[Agathon]

Mach3 generates a 12.5Kc/s pulse onto one of the pins of the PP This is used to enable the bob. When Mach3 starts up. It is used in case there is a software problem or e stop situation the pulse disappears and basically switches the bob off.

Re the drives is is usual for us to have a two to one reduction with a belt drive. I use these AM882 on my mill.
Your mill though is in a league of its own.

I'll do some research on charge pumps.

I have been puzzling about using Nema 23s with a reduction drive, but can't see how this will help in my situation. If I wanted to achieve 1000 rpm at the feedscrew the motors would have to run at twice that speed with the inevitable massive drop-off in torque. Even if the torque itself is multiplied by 2:1 (which it won't due to losses in the drive belts etc) the torque of the motor is likely to have dropped way below any mechanical gain. I can see how it helps with gaining torque at lower speeds, but looking at the torque curves of even the lowest induction and rotor inertia steppers it looks like less than a zero-sum game to me since their torque drops down to less than a third of their maximum. By the time any motor gets to having nearly 7000 steps a second they're going to have no torque at all. These topsy-turvy stepper things do my head in!

22119

[Agathon]

How do you get rid of attachments? Realised that the axes on the blue graph don't make any sense.

[m_c]

Thanks for the reply. What's a "charge pump"?

Re Clearpath - they are true servos rather than hybrid servo/steppers. I take your point about interference. I might pose the question to Teknic and see what they say - they've been really helpful so far.

There seem to be as many opinions about drives and motors as there are drives and motors. I did canvass this forum and others quite extensively before buying drives and the consensus seemed to be that Leadshine AM882s at 70v was the way to go. Still, the Z axis is fine, and the X&Y drives can be redeployed. If I do make some change to the X and Y drives it will be to servos - not poncing about with these poxy stepper things any more:wink:

I'd like to get my hands on one to see, but the torque curves look more akin to those of a stepper system, than a servo system. Stepper and brushless motors are very similar, it's just stepper motors are synchronous (which is what gives them the detents), while servos are a/non-synchronous, which means you don't lose power/torque overcoming the detents.

Regarding the Nema 23 v 34 argument. Compare them running similar voltages. You'll generally find Nema 34 graphs are using a high voltage driver, while Nema 23 are done using a relatively low voltage driver.
I've just had a quick look to see if I could find a couple graphs to do a comparison, but the Nema 34 graphs I found were mostly using a 110VAC supply (about 155VDC), while the Nema 23 ones were using 30-40VDC supplies. At those low voltage, torque drop of is very noticeable, and crippling Nema 34s with only 70VDC also makes for a very similar torque drop-off. You need voltage to over come the back EMF at speed. Without that voltage, torque at speed is very limited.

[Agathon]

I'd like to get my hands on one to see, but the torque curves look more akin to those of a stepper system, than a servo system. Stepper and brushless motors are very similar, it's just stepper motors are synchronous (which is what gives them the detents), while servos are a/non-synchronous, which means you don't lose power/torque overcoming the detents.

Regarding the Nema 23 v 34 argument. Compare them running similar voltages. You'll generally find Nema 34 graphs are using a high voltage driver, while Nema 23 are done using a relatively low voltage driver.
I've just had a quick look to see if I could find a couple graphs to do a comparison, but the Nema 34 graphs I found were mostly using a 110VAC supply (about 155VDC), while the Nema 23 ones were using 30-40VDC supplies. At those low voltage, torque drop of is very noticeable, and crippling Nema 34s with only 70VDC also makes for a very similar torque drop-off. You need voltage to over come the back EMF at speed. Without that voltage, torque at speed is very limited.

I have to say all this stepper and servo stuff is new to me. I'm very familiar with squirrel cage motors and vfds, but steppers, and now servos are a very steep learning curve. I know what you mean about the Clearpath graphs, but Teknic have stated that they are servos and not steppers. Their torque curves are certainly much more healthy at speed than any stepper graph I've seen (which admittedly isn't that many). Certainly when you compare the torque/speed graph of the Clearpath 2.04 Nm (rms) (CPM-SDSK-3421S-RLN) servo I was thinking of buying to that of the Astrosyn 4.8 Nm (holding torque), there's no competition. Where the Clearpath has no problem producing its nominal rms torque at 1000rpm the Astrosyn has fallen to something in the region of 0.9 Nm at around 3000 steps/s (900rpm).

2212022121

Just as an aside, if the Astrosyns were geared 2:1 they'd only be producing 0.4Nm

Having looked at the torque curve more carefully I see now that with my table axes running at 2000mm/min that the motors should be producing something in the region of 1.7Nm - which should be fine and indeed seems to be so. I can also see why increasing the speed by 50% causes them to lose steps as they've lost 0.5Nm in torque:grumpy:

[Agathon]

Moving off steppers and on to the spindle motor:

I spent this afternoon setting up the inverter and its control in Mach. I found that by fiddling with the PWM base frequency that I could get 100% on Mach spindle control to correspond to 100hz on the inverter (which previously it would not).

Having sorted this out I turned to pulleys and defined the four motor speeds as pulleys. I then calibrated the spindle speed to a range that I thought would work without me having to move the mechanical variator (Reeves type drive) or even replace it with a single fixed ratio poly-v-belt drive. I reasoned I needed speeds between 150rpm and 4000rpm. However, having run the slowest speed of the motor at the lowest reasonable frequency I quickly concluded that the motor has insufficient torque at this speed.

So I've decided to use be able to use the variator in two positions giving tops speeds of 2000rpm and 4000rpm with plenty of low-down torque in the lower range setting. I'll be mostly machining cast iron and steel so the lower range will be deployed most of the time.

As I understand it Mach3 while it's possible to tell Mach3 the spindle speed it cannot change the pulley setting automatically. It would have been nice if one of the four motor speed control relays could have been linked and operated by this feature of the software, but I guess I'm hoping for too much! In any case I'll have to set the variator manually.

[m_c]

I quickly concluded that the motor has insufficient torque at this speed.
[pedant mode] The motor should have the same torque at any speed provided the VFD is not limiting current. It's the lack of gearing that means there is insufficient torque at the spindle[/pedant mode]


As I understand it Mach3 while it's possible to tell Mach3 the spindle speed it cannot change the pulley setting automatically. It would have been nice if one of the four motor speed control relays could have been linked and operated by this feature of the software, but I guess I'm hoping for too much! In any case I'll have to set the variator manually.

Mach 3 can via Macros. I've never done it, however you can use a Macro that takes the requested spindle speed, and changes gears accordingly. Probably worth having a search for gear change over on the Mach forum.

[EddyCurrent]

I hadn't understood the four contactors for speed were operating a mechanical device, I thought you were using the inverter digital inputs to select four preset speeds.

[Robin Hewitt]

I feel your pain. I got the notion that everyone was getting better performance out of stepper motors than me and I now have 3.4's which I drive at 220 Volts. Problem is they run hot and I don't trust them at full tilt which is strangely self defeating. You can't win. I keep thinking servo motors are the way to go but I have always been just one rebuild away from wonderful so I am not convinced. Do you really need mega speeds? What is the max delay, end to end on the table? Is it really a problem?

I suspect the reason we can't have nice stepper motors is that someone has decided they must all be 200 full steps per rev. I got a Roland mill which had 400 full step/rev motors and it is freakin' amazing.

You are blessed to have that quick tool release, but I am not so sure about driving the Z through the quill rack. I put a ball screw to drive the Z, a ball screw that has to be released every time I hammer out taper tooling. It's only one M8 cap head but I've already had to helicoil the thread.

[EddyCurrent]

You should have a look at Mach3 Brains, watch this video to get an overview; https://www.youtube.com/watch?v=O8V7dZy02og

[Agathon]

[pedant mode] The motor should have the same torque at any speed provided the VFD is not limiting current. It's the lack of gearing that means there is insufficient torque at the spindle[/pedant mode]

While I don't claim any expertise on inverter drives, I've been using them for the last 20 years and my understanding and experience is that torque falls off either side of the nameplate frequency. Modern motors designed for inverters and "vector control" improve the flatness of the torque curve but the reason machine tool manufacturers using this type of drive specify such huge motors is due to the drop-off in torque. As an example, one of the Swiss firms I represent in the UK make a plain lathe of 70mm centre height designed for instrument making and horological work. The spindle is belt driven at 1:1 by a inverter controlled 1.1kW motor. In the past this machine was made with multi-pulley drive with a fixed speed motor of 300W!!!

[QUOTE=EddyCurrent;92791]I hadn't understood the four contactors for speed were operating a mechanical device, I thought you were using the inverter digital inputs to select four preset speeds.

You may have provoked me into boring you all with another video! The contactors just control the 4 motor speeds nothing mechanical. The variator (Reedes drive) gives the mechanical variation.

[EddyCurrent]

Is that Reedes or Reeves, the one where the pulley opens and closes so the belt rides up and down ?

[Agathon]

Is that Reedes or Reeves, the one where the pulley opens and closes so the belt rides up and down ?

Sorry, yes Reeves.

[Agathon]

I feel your pain. I got the notion that everyone was getting better performance out of stepper motors than me and I now have 3.4's which I drive at 220 Volts. Problem is they run hot and I don't trust them at full tilt which is strangely self defeating. You can't win. I keep thinking servo motors are the way to go but I have always been just one rebuild away from wonderful so I am not convinced. Do you really need mega speeds? What is the max delay, end to end on the table? Is it really a problem?

I suspect the reason we can't have nice stepper motors is that someone has decided they must all be 200 full steps per rev. I got a Roland mill which had 400 full step/rev motors and it is freakin' amazing.

You are blessed to have that quick tool release, but I am not so sure about driving the Z through the quill rack. I put a ball screw to drive the Z, a ball screw that has to be released every time I hammer out taper tooling. It's only one M8 cap head but I've already had to helicoil the thread.

Thanks for the empathy - much needed! I think the thing is that most people are building routers with very low friction linear rails and low mass tables/gantries. What I've got here is a beast compared to a CNC router. In fact it's probably one of the lightest and smallest pro CNCs that was built. Since owning this machine I've been looking at other high quality, but old, CNCs with a view to doing the same thing, but these are all massive for the same envelope that the Fehlmann has. A couple of good Deckel CNCs have sold on eBay recently for just over a grand but you're talking about 2-4 tonnes of iron, which I don't have the space or the heart to be involved with. Maybe I'll eventually replace my manual Aciera F4 with a bigger CNC, but for now I'll sit tight.

You are quite right about the traverse speed. The afore-mentioned Aciera F4 has a rapid of 1800mm/min which has never made me feel like I need to pop the kettle on while it does its stuff. So 2000mm/min is fine on the Fehlmann - if it can do it reliably.

Having been involved with very high-quality manual machine-tools for a very long time I tend to want a professional solution to a problem. It's been a steep learning curve, but as I see it stepper motors for machine tools are now really an amateur thing. I want this machine to perform as an industrial machine should and I will be using it to produce high precision stuff for my own amusement and for my business (I say business, it's Halcyon-days are behind it and with things as they are at the moment it's a paying hobby, which isn't such a problem as I have another job too). Hence, I am drawn to servo motors. The only problem is I know sweet FA about them!

I'll see how driving the rack goes. As I said in the vid, this thing is a very high precision thing and I can detect no backlash in the rack. There must be some of course, but it's certainly less than 0.01mm. Fehlmann developed this machine into a 3-axis a year or two later and drove the rack with a servo motor - they seemed to have sold quite a few of these machines and they are still sought after in Switzerland.

Hammering-out taper tooling is always bad news. Have you thought about making a captivated draw-bar so that it pushes the tooling out as you unscrew it?

[EddyCurrent]

At the end of the day I would be looking to convert an S value in gcode to a combination of inverter speed and contactor selection, does that sound correct ?

So what is the relationship regarding gcode S value, inverter frequency, contactor selection, spindle output speed equal to gcode S value ?

If that can be determined then it looks like a Mach3 Brain can be used. If you watch the video linked to above you will see that their example has similarities to your own requirement

[Agathon]

At the end of the day I would be looking to convert an S value in gcode to a combination of inverter speed and contactor selection, does that sound correct ?

So what is the relationship regarding gcode S value, inverter frequency, contactor selection, spindle output speed equal to gcode S value ?

If that can be determined then it looks like a Mach3 Brain can be used. If you watch the video linked to above you will see that their example has similarities to your own requirement

You've lost me a bit there, but I'll take a look at the video.

[Agathon]

You've lost me a bit there, but I'll take a look at the video.

Took a look at the Brains video - that looks very promising. I'll do some research.

I did make a little video on the spindle speeds - probably redundant now, but here it is:


https://youtu.be/hncxZvUoy1g

[m_c]

While I don't claim any expertise on inverter drives, I've been using them for the last 20 years and my understanding and experience is that torque falls off either side of the nameplate frequency. Modern motors designed for inverters and "vector control" improve the flatness of the torque curve but the reason machine tool manufacturers using this type of drive specify such huge motors is due to the drop-off in torque. As an example, one of the Swiss firms I represent in the UK make a plain lathe of 70mm centre height designed for instrument making and horological work. The spindle is belt driven at 1:1 by a inverter controlled 1.1kW motor. In the past this machine was made with multi-pulley drive with a fixed speed motor of 300W!!!


For induction motors, torque remains pretty constant over the rated speed range up to the rated speed, and is a result of the amount of current flowing through the windings. Although frequency controls the speed, as speed drops, the voltage required to drive that current through the windings also drops proportionally I.e. for a 3000rpm 240V motor, peak voltage will be around 120V when running at half speed.
Now because voltage is reduced, so is the power output, so if the above motor was rated at 1KW, at 1500RPM it would only be producing 500W. You could increase current (which some inverters can do to give a low speed torque boost), however you risk overheating the windings due to the extra current.

Above the rated speed/power, current becomes limited. So taking the above example motor, and trying to double it's speed to 6000RPM, you can do so by doubling the frequency, however unless you double the supply voltage, 240V will only be able to force half the current needed to get full torque through the windings, with the result you will only get half the rated torque.
The result is above the rating, the motor becomes power limited. You can have double the speed, but only half the torque, so even though the motor is spinning faster, you still only have 1KW of power.

This is why when fixed speed motors with gearing get replaced, they're often replaced with far bigger motors.
With gearing, say you take a 2Nm 3000RPM (probably about 600W), you gear it down 4:1 and get 8Nm at 750RPM.
To get that same torque at the same speed using direct drive, and still retain 3000RPM, you now need a motor capable of 8Nm and 3000RPM, so you need a motor with 4 times the power. (realistically you'd compromise with some gearing, a bit less torque, and running the motor so higher speeds are above the motor rated speed and into the derated/reduced current area).
That's the reason why most modern CNC machines come with such big spindles. For most end users, it not because they're going to be managing to use upwards of 10KW hogging metal with endmills, it's so they still have enough torque to drive a big facemill at a couple hundred RPM while still taking a decent depth of cut.

[Agathon]

For induction motors, torque remains pretty constant over the rated speed range up to the rated speed, and is a result of the amount of current flowing through the windings. Although frequency controls the speed, as speed drops, the voltage required to drive that current through the windings also drops proportionally I.e. for a 3000rpm 240V motor, peak voltage will be around 120V when running at half speed.
Now because voltage is reduced, so is the power output, so if the above motor was rated at 1KW, at 1500RPM it would only be producing 500W. You could increase current (which some inverters can do to give a low speed torque boost), however you risk overheating the windings due to the extra current.

Above the rated speed/power, current becomes limited. So taking the above example motor, and trying to double it's speed to 6000RPM, you can do so by doubling the frequency, however unless you double the supply voltage, 240V will only be able to force half the current needed to get full torque through the windings, with the result you will only get half the rated torque.
The result is above the rating, the motor becomes power limited. You can have double the speed, but only half the torque, so even though the motor is spinning faster, you still only have 1KW of power.

This is why when fixed speed motors with gearing get replaced, they're often replaced with far bigger motors.
With gearing, say you take a 2Nm 3000RPM (probably about 600W), you gear it down 4:1 and get 8Nm at 750RPM.
To get that same torque at the same speed using direct drive, and still retain 3000RPM, you now need a motor capable of 8Nm and 3000RPM, so you need a motor with 4 times the power. (realistically you'd compromise with some gearing, a bit less torque, and running the motor so higher speeds are above the motor rated speed and into the derated/reduced current area).
That's the reason why most modern CNC machines come with such big spindles. For most end users, it not because they're going to be managing to use upwards of 10KW hogging metal with endmills, it's so they still have enough torque to drive a big facemill at a couple hundred RPM while still taking a decent depth of cut.

Very nicely and clearly explained. I was aware of the frequency voltage relationship, but hadn't really twigged the issue of running higher than the name-plate frequency and the consequent lack of volts. As the video shows, I don't really think that torque is going to be so much of an issue as far as the spindle goes, so I'm fairly hopeful about my plan to use the higher mechanical speed setting most of the time. We shall see.

Having looked into Brains more I understand your previous post and think that it all looks doable even for a novice like myself.

[Agathon]

I've done more fiddling with the table and found that at 2500mm/min the table is repeating position over 200mm for the x and 150mm for the y better than 0.01mm (in fact pretty consistently within 0.003mm) which I am extremely pleased with. I tested fairly extensively with 10 or 20 repeat cycles.

I am still getting the grunting noises from time to time, so I suppose this is down to the latency of the processor generating the pulses?

[Robin Hewitt]

repeating position over 200mm for the x and 150mm for the y better than 0.01mm (in fact pretty consistently within 0.003mm)

3 microns is an interesting number BUT what about the backlash?

[Agathon]

3 microns is an interesting number BUT what about the backlash?

What backlash? This thing is Swiss! I would think that the 3 microns is simply down to vibration in the mechanical loop between the digital dti and the mount. If you're not careful you might provoke another mind numbing video!

[EddyCurrent]

Try the attached spreadsheet (I use LibreOffice if you don't have excel)

Just enter the desired spindle speed in cell A4 and it will calculate the inverter frequency and contactor to energise.

That logic needs put into a Brain using Mach3 DRO 169-Cmd SpindleRPM as the desired frequency.

It uses an inverter frequency up to 100 hz and assumes the manual adjuster is set to 1.5 * motor speed, so for the 1400 speed it's set to 2100 RPM then the inverter will take it to 4200 RPM

[Agathon]

Try the attached spreadsheet (I use LibreOffice if you don't have excel)

Just enter the desired spindle speed in cell A4 and it will calculate the inverter frequency and contactor to energise.

That logic needs put into a Brain using Mach3 DRO 169-Cmd SpindleRPM as the desired frequency.

It uses an inverter frequency up to 100 hz and assumes the manual adjuster is set to 1.5 * motor speed, so for the 1400 speed it's set to 2100 RPM then the inverter will take it to 4200 RPM

Thanks, that's really kind of you. I do have Excel so I'll take a look.

Can anyone tell me what G0 code will make the x axis move +100 back to zero and then +100 repeatedly - say 10 times? I'm looking around for a simple answer but can't seem to find one.

[Agathon]

Ignore that last request I worked out how to do it - probably in a very labourious way but none-the-less it worked.

[Neale]

3 microns is an interesting number BUT what about the backlash?

when I was testing the touchplate setup on my router, I was getting repeatability to within +-0.003mm. Quick back-of-envelope sums showed that this was equivalent to one microstep. Might this be why this magic number is there? Mind you, my backlash is a bit more than that..

[Agathon]

As it happens Neal I've just run some more tests. Prepare to fall asleep! Contrary what the fool in the vid says, the Y does seven cycles!

Despite all the grunting (not mine) the steppers don't appear to be losing steps at 2500mm/min.


https://youtu.be/pyuFoJNj5cI

Actually, I don't know what the backlash is yet. I would think it was small but I need to set-up a proper test.

[Agathon]

Just measured the back-lash at 0.03mm on each axis. I'm a little surprised by this since I can't push/pull either axis by more than 0.01mm. The motors are coupled to the screws with flexible star-type couplings (see pic) - which are original and in good condition, but I have to say I've always been suspicious of. Now they are robbing me of precious microns!

Seriously though I can live with 0.03mm.

22152

[Robin Hewitt]

Seriously though I can live with 0.03mm.

I used to tell myself that I could live with a slight backlash but deep in my heart of hearts I knew it wasn't true.

I move 5um per step. Could I watch it step 6 times without moving the table then sleep at night?

Difficult question...

[Agathon]

I used to tell myself that I could live with a slight backlash but deep in my heart of hearts I knew it wasn't true.

I move 5um per step. Could I watch it step 6 times without moving the table then sleep at night?

Difficult question...

I'm not sure I can either! After I posted I took another look and the back-lash is at the feedscrew. I think I slackened the pre-load on the X too much and need to tighten up the Y. Watch this space....

[Agathon]

Decided to strip the ball-screws and repack with new balls:


https://youtu.be/MVdal0BjrpU

[Clive S]

Decided to strip the ball-screws and repack with new balls:Very nice vid. Would you mind giving a link to where you purchased the balls from. Tnx

[Robin Hewitt]

I have my nuts sprung together one quarter ton. I hold the X screw in tension, Y and Z I crush angular contact bearings together. Everything is one quarter ton and feels glorious.

I sprung my Roland mini-mill to 200 lbf, I don't have a magic formula, I just use whatever seems right.

Do you have a way to inject oil in to the nuts or do you depend on that grease? I started fitting narrow bore nylon tube to carry oil but one of the push fit connectors didn't fit and I wanted to play cutting stuff so I left it out. I think I have to strip back and finish the job. Gravity feed is traditional but would that need wider bore piping? Such fun.

For a moment I was worried that I might have put you off with talk of backlash. Glad to see you back.

[Agathon]

Very nice vid. Would you mind giving a link to where you purchased the balls from. Tnx

Hi Clive, I just ordered them through my local branch of Brammer - 1/8" Chrome steel balls, Grade 100 £10.08 for 500. These nuts have about 0.004" clearance, so I did look into getting balls at 0.127" - but they were very expensive ranging from £58 - £82. As I say in the vid, I realised this wasn't the right way to go with this type of nut.


I have my nuts sprung together one quarter ton. I hold the X screw in tension, Y and Z I crush angular contact bearings together. Everything is one quarter ton and feels glorious.

I sprung my Roland mini-mill to 200 lbf, I don't have a magic formula, I just use whatever seems right.

Do you have a way to inject oil in to the nuts or do you depend on that grease? I started fitting narrow bore nylon tube to carry oil but one of the push fit connectors didn't fit and I wanted to play cutting stuff so I left it out. I think I have to strip back and finish the job. Gravity feed is traditional but would that need wider bore piping? Such fun.

For a moment I was worried that I might have put you off with talk of backlash. Glad to see you back.

The machine's central lubrication system is very comprehensive and delivers oil to the ball-nuts and ball screw in a couple of places.

I'll put the x-axis back together later today and see if there's any improvement on the backlash.

[hanermo2]

Fwiw...
I think You have one of the best manual tools of this type (c frame small mills) ever produced.

Your explorations/experiences/results are similar to mine, on a decent-rigidity heavy chicom 12x" lathe.
Except that mine is about 10x worse in terms of fit, finish, quality in general, of course.

I would opine, while never having seen a Fehlmann in person (is a tour available if I happen to be in Your country ..?),
- repeatability to about 1 micron is very achievable
- resolution to much better than 1 micron is available to You, and probably relatively easy to do

My experience for 0.03 € (I need to make a profit, You know..):
I made treadmill-dc motor-servos with geckos (320) about 2005.
So-so, at 10.000 counts, accurate but noisy, sparks, ozone, some jitter, heating.

I used the treadmill servos (DC motor 180V/6000 rpm, at 68 V dc, so too many amps and not enough volts, but I never need speed anyway)..
and at 1:3 via HTD, 5/15 mm, 1:3 or 16:48 teeth, could reliably index, or incremental-move, 1 micron at a time.

The basic accuracy and stiction and smoothness of the chicom 12x is probably 2x-4x worse than Your mill.
(But it is more rigid. Lathes always are, especially heavier ones, like mine. 350 kg/24" == 2000 KG on a 1.2 m long bed.Maybe not more rigid than a Fehlmann, one of the best ever made.Imho.)

So I built very heavy supports, mounts, belts, using HTD8-30, taperlocks, 17 mm shafts on 220V ac brushless servos, of 750 W, 10.000 counts, at 1:2.
Results are weak in accuracy.
Pulleys are poor, relatively, and belts may or may not be poor, relatively.

But..
Using these relatively-expensive servos, 700€ landed, I do get 1 micron indexing or relative movement.
But it is not smooth, consistent, steady, and no-way no-how a dial-to-size solution.
But..
Theoretical resolution is 0.2 microns, and the fact is, the screw itself *will* move by 0.2 - 0.n micron increments, every single time. Increments, not accuracy.
Screw will always move in angular terms. Some waviness from belts/pulleys., ie it is not perfectly linear/smooth/accurate, transmitted to saddle x axis, with "some" bounces of uncertain size, perhaps 1-2-10-20 microns, depending on gibs, tension, position, oiling.

With light (typical manual) gibs, oiled, imho, about 0.5 microns resolution is perfectly reliable for me. I cannot measure this, yet.
I will, and may put in 0.1 micron glass scales (thats the plan, anyway).
I opine You can easily get 0.5 microns, or better, resolution from one of the best mechanical mills ever made, via servos.

Once pre-loaded on an axis,
Led readouts, on the servos, show errors, which are always zero, at position, because the servo has == 10 Nm / 10.000 counts / rev, or 20 Nm at screw, about 10x more than any possible resistance.
At 20 Nm the push force == 2000-3000 kgf.

The saddle bounces because of these mechanical errors, none of which relate to stepper or servo as such,
- the x mount is not rigid-enough and not mounted in-plane with the screw thrust
- sticktion
- gibs
- poor screw (I knew this)
- yoke connection to saddle is poor re:rigidity. Much worse than I thought, just saw this 2 days ago.
With a heavy load/stiff gibs, everything bends noticeably on the x axis.

Everything bends always, I/one just did not see it well enough in the past.

I got great results with soft gibs, semi-heavy x axis lock, like manual turning, since 2005 or so.
The current ballscrew on x is 14x more rigid than the original 16-17 mm acme screw (fixed-fixed mount, in tension, rigid for 2x, half free length for 4x, thicker for == 2x).
So I expected 6x more rigid belt drives to do better.
They did worse, or same, with much better servos, and more rigid/tighter gibs.

Probably, softer gibs==manual, would deliver better results in resolution. I now think.
All this is related.
I got 20x, perhaps better, higher mrr or Material Removal Rates, than I have ever had, last week.
Industrial level results.

2.5" 63 mm ISO30 face mill, 4 inserts. Cutting thick tool steel, full width.
3.9 mm deep, !!! 63 mm woc ie full face, 45 mm/min speed, 550 rpm.
That is a relatively 63 mm thick end mill, 3.9 mm deep !! for milling terms, full width.

The machine was worked hard, but quite happy, when I achieved balance.
Balance was hard / impossible to maintain.

New face mill, axxx something, new inserts, I just hold the facemill front in the 12" 4-jaw chuck, clocked to 0.01 mm or better tir.


- gibs are now too tight, after adjusting
X-axis Screw is now 0.750 " roton, rolled.
The new x axis screw is TBI taiwan, 32 mm, 5 mm, with a 60 mm thick yoke.
I need major work before it is in, ..
new saddle plate (ends are now milled, hooray !), yoke all 6 faces, yoke bored, supports of no particular accuracy.

My opinion(s);
1. Go to servos.
2. Go direct drive. There must be a reason all manufacturers use direct drive.
3. Use a bigger coupler.
4. Make anything used in the motion-control train very very heavy in steel.
5. Use highest-resolution servos you can, while being relatively economical, and having sufficient speed in khz/mhz for your controller.
Mine is a csmio-ip-s, 4 MHz.
A 3000 rpm/10.000 count servo, is 50 revs/sec, = 500 kHz.

I could not care less about top speed, and may use something near top acceleration, in the future, or not.
Today I use about 1/5 top speed and top acceleration, and both greatly exceed the best stepper systems I used in the past.

"Good" steppers as in fast nema 23 steppers, 68 v, gecko 203v, centipede hw pulser/controller (excellent hw and timing).
At that, the stepper made in tests 10.000 rpm, over 4-6 secs acceleration, with no torque, no-load.
Geckos fault 380 kHz-400 kHz+ or so.
In use, best-optimum std nema 23 steppers make about 600-700 rpm, in == 0.2 secs (lathe, needs acceleration, as much as possible).

Small nema 23 servos, and the bigger nema 34 servos on the lathe, deliver;
== 0.02-0.04 secs to 3000 rpm, at load.
About 10-50x better in acceleration, real-world.
About 5x more accurate.

Imho, accuracy is very important.
Acceleration is very important, or important.
Top speed is totally irrelevant.

what happens is that servos are excellent at many small tiny moves, like 3-d contouring, or modern high-speed milling toolpaths.
Or very,very accurate tiny moves, that steppers cannot do directly.

A stepper at 1/10 microstep (2000 steps/r) has about 1/10 rated torque iirc (gecko, Mariss).
So a 3 Nm stepper has 0.3 Nm at 0 rpm (best case) at 1&10 microsteps. It is, in essence, a spring.

A servo at 10.000 steps has 3x rated torque, from 1 step at 0 rpm to 1 step at max rpm, say 3000 rpm (for the 3 secs max peak torque).
The servo of 1.3 Nm (400 W, similar cost 290€ / axis), 68V DC/AC, has 1.27 Nm cont, == 4Nm peak.
So the small servo has approx 4 Nm vs 0.3 Nm stepper torque of a similar size, about 13 times more, and over 50-100x more torque over 1000 rpm vs a stepper.

All this with a cheap small economical Nema 23 400 W servo, of course.
If comparing to more industrial-type stuff, ... well...

My 750W - 220V ac driven servos .. are exactly the same in use.
Just 10.000 counts vs 5000 counts,
220V vs 68 V,
3.x /10 Nm vs 1.27 Nm.

My 0.2 micron (now) step size lathe has 10.000 x 2 / 5 mm = 0.25 micron resolution, theorical/electronic.
= 7.5 m / minute, 0.125 m second.
Typical free length is less than 100 mm = 10 cm, on z. 24" minus 12" chuck 180 mm, minus ts, == 220 mm, == 400 mm.
About 250 mm free length between 12" chuck and ts at shortest extension.
And plenty length for me, never needed to remove the gap from the bed, or the ts maybe once, minor stuff.

I don´t usually do e. gunstuff, or long spindles, and when I do, easy mounts exist.
My lathe is a technology demonstrator, mostly.


When cutting anything, clearances are usually 2-3-5 mm, for me, now, and less when everything is dialed in.


The absolutely only need for high acceleration /speed in lathes, for me, has always been leaving threading, at the end.
And it is extremely important to be very, very, very consistent, of very high torque, at very high speed in both start-time and pullout-time, in ms, when pulling out.

E.typical.
Threading at 500-800 rpm towards hs, steel, about 1-1.5" D workpiece.
Typical, maybe 8 passes.
Every pass makes the end bit divot deeper, and the pullout point is always deeper, and more rigid, each pass.

Any tiny error or delay, makes the threading tool dig-in, if there is any bend (there is always bend), slop, backlash in the whole x axis drivetrain.
Any tiny dig-in, exponentially increases the error until failure of something, unless the tool is pulled out fast enough, strong enough, to avoid failure.

In this scenario the great benefit of servos is,
-vastly faster acceleration for pullout
-vastly higher force of pullout
-vastly more accurate/repeatable pullout point and action
The relevant part of the pullout is perhaps 0.1 - 0.5mm in length, aka most of the thread depth, and takes maybe 0.1 secs with a stepper, and maybe 0.05-0.01 secs with a servo.
But the servo exerts 10-50x the force, at 10-50x the acceleration, and 5x or more accuracy.

It is of note that a very tiny 0.01 - 0.02 mm mechanical slop with steppers, or machine error, can snap the tooltip, as the dig-in is exponential and mechanical and increases exponentially.
This does not usually happen with servos, because no matter what most of the tooltip is already out of the workpiece, with the same mechanical error condition, simply leading to a slightly rounded pullout edge.


E.
I used 50 mm / 2" thick tool steel for the mount plate for the Z axis ballscrew.
About 140x200x50 mm.
Not because it is "stronger" but because it is very much stiffer, and will repeat better.
I think 10x more rigid than "typical", don´t really know, and it only cost == 20-30€, maybe 15 kg in mass for the mount plate alone.

My z axis screw is 32 mm.
Yours will be similar, I think.
32 mm screw == 1600 kgf push force, rated, static (weakest rating).

Example/anecdote.
This push force is == equivalent to lifting a SUV with the screw.
And You want to try to bend as few microns as possible, while lifting the suv.
A typical 32 mm screw has 54 kgf/um or 540 N/micron rigidity.

I am by no means a "servo zealot".
Steppers are very easy and can provide excellent repeatability, accuracy, force, positioning, of relatively low rpm, very reliably and cheaply.
But they have low dynamic range.
This means either accuracy, or speed/power, but not both.

So the ideal apps for steppers are
e.g.
telescope mounts of low rpm and very high geared resolution/repeatability,
cutter grinders, similar,
saw accessories,
microscope accessories,
cnc mills of typical hobby shops needs, some jobshop uses,
cnc jewellery stuff,
etc.

E.
I have made all my x-axis mounts/stuff behind the lathe .. so it looks stock from the front, and can be used manually.
New screw connects to yoke of 60x120x120 mm.
It will be about 100x more stiff than now (because I use a temp. crap lashup to bolt to the current saddle plate, (was better in the past, pre new servos) of temporary/test use).

With direct drive, I will get 0.4 microns/step vs 0.2, but no wind/spring/bounce from belts, and vastly less from winding error / screw, and much less bend from yoke.
And no pulley error, belt error.

Belt drives with small belts are great for steppers - but the wrong choice for servos. Imho, Imhe.

[hanermo2]

I have a comment.
I have seen credible comments from guys with experience, that the grease used in milling spindles, had great effect.

Re: heating at higher rpms, power used, etc.
Like 30-50% of the power went to heat, vs 5%, with better grease.
And noise decreased 50% or so, by tfar method.
(That Feels About Right).

Kluber Isoflex 15 is the gold std, for high end machine tool industrial spindles.
It is very expensive.
You need very little, about 1.5 cm3 for a big spindle bearing.

I bought a 50 gm tube, for 1 micron spindles I am making, 4 of, experimental/commercial test samples, with real abec 9/iso 2, bearings in 25 and 40 mm D.
I will make 4 test spindles, 2 of 25 mm and 2 of 40 mm, with both bearings, and see how they work.
Yes, the spindle at 40 mm is now hardened, ground, polished, has 2 microns tir (in spec, just) but I will use a soft lap and diamond paste to reduce the error a bit.

Anyway, better grease has reportedly made a major difference on spindles.
If You want some, I am happy to mail some Kluber "unicorn snot value" grease to You, free.
I doubt the grease has any major effect on accuracy .. but ..

I think it quite probable, perhaps, the grease can/will point out the next error in the chain.
Contact me any way You want, if You want to try some.
One email is greystoneprecision at the google mail dot com.

I do know for a fact, that modern cnc lathes (tools) use P4 bearings or better, since the packaging on mine says so.
And my factory training.
And these bearings do very much benefit from rgw better grease, mostly at higher speeds 2-5k and up.

Personally, I doubt it matters at low speeds, but think I might well be wrong.
CNC machining is often about corner cases, and stuff works different to what one might expect.

The tiny balls in bs supports and nuts actually run really fast at their surface speed.
Anyway, You want a bit, You can have some.
No conditions at all.



Decided to strip the ball-screws and repack with new balls:

[Agathon]

Hi Hanermo2 and thanks for your very comprehensive and convincing post on your experience of servos. I'm coming to the same conclusion. Steppers are fine for hobby machines, but for anything a bit more industrial a servo is the way to go. Fehlmann certainly dropped steppers within a couple of years and went to servos.

The Fehlmann is a slightly odd machine in that it's a drilling machine with milling capability - so despite it's industrial specification in terms of mass, the design is a compromise, with milling, and then CNC, as an afterthought. With that said they sold well in their home market. The latest generation of Fehlmann machining centres are built round a conventional square slide-way for the Z axis, but they still produce a manual and semi-cnc/manual version of the Picomax: http://www.fehlmann.com/en/products/milling-drilling-machines/picomaxr-21-m/

I was interested in what you mentioned about direct drive. When Fehlmann switched to servos (see pic) they mounted the motors remotely - not sure if it's a belt or gear drive, but suspect belt. The latest semi-cnc/manual of the drill mill that I have also has remote servos - I'm not sure about their machining centres.

22222

Having reassembled the ball-screw, replacing it proved interesting since the nuts, or rather the keys in the nuts, didn't want to go into the key-way. The key-way or the keys were obviously minutely out of line with each other. A rub over a stone got them to slide in, but the results from the screw were disappointing - still not sure why. It could be an alignment issue - which seems strange given the precision nature of the table and the screw, but it's the sort of thing I've regularly encountered with precision machine tools - a lot of fettling takes place when these things are built. Anyway, I decide to but the nuts on the in the original orientation which seems better, but I can't get the backlash better than 0.01 without sacrificing the smoothness of the screw. I will tinker some more today.

I've had 20 years experience rebuilding machine tools and generally I've found that even if a bearing's tracks look good through a loupe they may well be slightly rough when under load. This is sometimes due to poor fitting (hammering the inner) and tiny imperfections are left on the bearing tracks which will only show up under a microscope. I suspect that the ball-screw and nut assembly have similar issues. I'm not about to replace them so will live with the 10 microns of backlash.

Thanks for your offer of the Kluber Isoflex. This is a product I'm familiar which since it's specified by some of the manufacturers I deal with. I actually use an SKF LGMT2 which has a similar specification and was more readily available at the time I needed it. In fact the Fehlmann's central lubrication system covers everything from the spindle bearings through to the ball-screws and everything in-between. The Vaseline used was just to get the balls to stick to the nut during assembly - it will soon wash out.

If you're ever in my "neck of the woods" you'd be more than welcome to visit.

[Agathon]

I forgot to say that it would be nice to see a photo or even a video of you CNC machine(s).

David

[Agathon]

I will, and may put in 0.1 micron glass scales (thats the plan, anyway).

I forgot to ask about the above which intrigued me. What control system are you using? Are you planning on linking the scales back to the controller in a closed loop? Can this be done?

[Agathon]

Spent the evening trying different permutations of the ball-nut assembly and the best I can achieve on both axes is 10 microns. If this were a conventional manual machine I'd be overjoyed with 4 tenths of a thou! In fact the very expensive Swiss machines that I sell have a backlash from new of around 0.01-0.02 mm.

Anyway, the machine is running very nicely and the back-lash compensation on Mach3 is working well.

As I frequently say to my customers "it's a metal cutting machine not a grinding machine" so I don't expect nor want to machine to tolerances better than +/- 0.005. I certainly don't think it will be a problem in respect of climb milling.

More soon...

[hanermo2]

Yes, the scales can feed back to the controller, at least thats what the makers say.
CSMIO-IP-S on lathe, from cslabs.

Somewhat expensive, very good, very good value for money.
Even if I only got dros from the scales, it would be good enough for my use via sw macros.

I am aiming for extreme resolution, repeatability, and fairly well willing to spend money.


I forgot to ask about the above which intrigued me. What control system are you using? Are you planning on linking the scales back to the controller in a closed loop? Can this be done?

[hanermo2]

Swiss backlash 0.01 mm new ??

I would have expected your picomax to have zero to 0-1-2 microns backlash.
I suspect the bs fixed end bearings are not properly adjusted/preloaded, or ..
.. your ballnut is loose/failed somehow and has no preload.

Easy enough to test.
Dti screw end, while loading back/forth with a prybar of some type, separately on screw end and on nut end/assy.
One should have a major deviation vs the other.



Spent the evening trying different permutations of the ball-nut assembly and the best I can achieve on both axes is 10 microns. If this were a conventional manual machine I'd be overjoyed with 4 tenths of a thou! In fact the very expensive Swiss machines that I sell have a backlash from new of around 0.01-0.02 mm.

Anyway, the machine is running very nicely and the back-lash compensation on Mach3 is working well.

As I frequently say to my customers "it's a metal cutting machine not a grinding machine" so I don't expect nor want to machine to tolerances better than +/- 0.005. I certainly don't think it will be a problem in respect of climb milling.

More soon...

[Agathon]

I've checked everything and it's all correctly adjusted - first thing I thought of was movement in the pillow-block bearings but there's no movement here. If I take the ball-nut preload one increment higher on the vernier the screws become notchy. It's probably just down to wear and tear. We'll see what the performance is like in practice.

[Robin Hewitt]

You are being very vague, is this sprung or a simple crush?

[Agathon]

You are being very vague, is this sprung or a simple crush?

Crush.

[Robin Hewitt]

It was a bit of a bodge springing mine, I added a spacer and 2 Belleville washers. Well 6 spacers and 12 washers to do all the bearings and nuts. But the reward was out of all proportion to the effort.

22229

[Agathon]

It was a bit of a bodge springing mine, I added a spacer and 2 Belleville washers. Well 6 spacers and 12 washers to do all the bearings and nuts. But the reward was out of all proportion to the effort.

22229

So, if I'm interpreting that correctly, you have a double ball-nut set-up like my machine?

I could do something like this although it would mean making a new retaining flange. I have to say that apart from grinding spindles, I'm not a fan of spring-loaded solutions. I'm also not convinced that backlash of 0.01 is much of an issue. My conventional mill has about 0.25 backlash and it's only a problem with heavy climb-milling or slot milling and then it can be overcome by reducing the feed rate and the depth of cut. Mind you the table and slide alone must way 200kg - mass helps, as do well adjusted gibs.

I meant to have asked what the rest of you mill consists of Robin - got any pics?

[Robin Hewitt]

I don't have a recent pic, here's an old one...

22230

[Agathon]

I don't have a recent pic, here's an old one...

22230

Very neat, especially the Z axis. Wouldn't mind seeing some details of this as I'm sure I'm going to have to go down this route eventually.

What sort of backlash have you achieved on the x and y?

[Robin Hewitt]

There's a build log from many years ago, I will try and link it...
http://www.mycncuk.com/threads/651-Warco-Major-CNC-build-log?highlight=Warco+Major
I fitted zero backlash double nuts, big disappointment, so I sprung them and it was like magic.
The springs mean that I have no backlash up to 1/4 ton but if I ever pass that loading presumably everything will go horribly wrong.
I do get some sideways slop in the quill if I forget to pack it out with thick, icky grease. Open to suggestions.

[Agathon]

There's a build log from many years ago, I will try and link it...
http://www.mycncuk.com/threads/651-Warco-Major-CNC-build-log?highlight=Warco+Major
I fitted zero backlash double nuts, big disappointment, so I sprung them and it was like magic.
The springs mean that I have no backlash up to 1/4 ton but if I ever pass that loading presumably everything will go horribly wrong.
I do get some sideways slop in the quill if I forget to pack it out with thick, icky grease. Open to suggestions.

I might give the belleville washer thing a go. The Fehlmann's vernier adjustment is clever, but I think a grub screw lock would be better as it would allow finer adjustment. Quality manufacturers have a nice trick of fitting a pressed-in brass plug in the adjustment nut before threading it so that you have a formed locking piece that doesn't damage the thread and needs little pressure to lock.

Regarding your quill slop, there isn't really a satisfactory solution. The fit of a cylinder into a bore is something that requires a degree of precision and careful fitting at the point of manufacture - surface finish is critical. Any fool with a cylindrical grinder and enough patience can make a cylinder to size and parallel to a micron or two, but getting the bore honed for a perfect transition fit is another issue altogether. Most of the Chinese machines fall at this point, although I have to say that Myford's VMC (Taiwanese) had a pretty decent fitting quill - though not to Swiss, German or the best US and GB standards (has to be said though that most of the machine tools produced in the UK were not of a particularly outstanding fit in this respect).

You could split the casting and put a clamp in place, but this is a pretty crappy solution as you're going to get lots of point contact at the clamp position (the bore will be an oval) and you'll still have the original clearance further up. Alternatively you could get the quill hard-chromed and ground to a nominal size slightly larger than the clearance, but then you have the difficult honing issue mentioned above. Not worth doing either of these, better to start again with a higher-grade machine and transfer your clever CNC additions to it.

If you've got space there's been some fantastic 1980s CNC machines on eBay recently including a couple of Deckel FP3/4s for about £1500! Fab things with superb ball-screws and servos (probably old brush types though).

[Agathon]

Very neat, especially the Z axis. Wouldn't mind seeing some details of this as I'm sure I'm going to have to go down this route eventually.

What sort of backlash have you achieved on the x and y?

I meant to have complimented you on the really super job you've done on the casings for the drives - very professional.

[Robin Hewitt]

Most kind. This is the magic of CNC, it frees you from straight lines and you enter a wonder land of flowing curves. If I only had 2 more axes I could do blobs.

[C1Geoff2020]

Hi Hanermo2 and thanks for your very comprehensive and convincing post on your experience of servos. I'm coming to the same conclusion. Steppers are fine for hobby machines, but for anything a bit more industrial a servo is the way to go. Fehlmann certainly dropped steppers within a couple of years and went to servos.

The Fehlmann is a slightly odd machine in that it's a drilling machine with milling capability - so despite it's industrial specification in terms of mass, the design is a compromise, with milling, and then CNC, as an afterthought. With that said they sold well in their home market. The latest generation of Fehlmann machining centres are built round a conventional square slide-way for the Z axis, but they still produce a manual and semi-cnc/manual version of the Picomax: http://www.fehlmann.com/en/products/milling-drilling-machines/picomaxr-21-m/

I was interested in what you mentioned about direct drive. When Fehlmann switched to servos (see pic) they mounted the motors remotely - not sure if it's a belt or gear drive, but suspect belt. The latest semi-cnc/manual of the drill mill that I have also has remote servos - I'm not sure about their machining centres.

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Having reassembled the ball-screw, replacing it proved interesting since the nuts, or rather the keys in the nuts, didn't want to go into the key-way. The key-way or the keys were obviously minutely out of line with each other. A rub over a stone got them to slide in, but the results from the screw were disappointing - still not sure why. It could be an alignment issue - which seems strange given the precision nature of the table and the screw, but it's the sort of thing I've regularly encountered with precision machine tools - a lot of fettling takes place when these things are built. Anyway, I decide to but the nuts on the in the original orientation which seems better, but I can't get the backlash better than 0.01 without sacrificing the smoothness of the screw. I will tinker some more today.

I've had 20 years experience rebuilding machine tools and generally I've found that even if a bearing's tracks look good through a loupe they may well be slightly rough when under load. This is sometimes due to poor fitting (hammering the inner) and tiny imperfections are left on the bearing tracks which will only show up under a microscope. I suspect that the ball-screw and nut assembly have similar issues. I'm not about to replace them so will live with the 10 microns of backlash.

Thanks for your offer of the Kluber Isoflex. This is a product I'm familiar which since it's specified by some of the manufacturers I deal with. I actually use an SKF LGMT2 which has a similar specification and was more readily available at the time I needed it. In fact the Fehlmann's central lubrication system covers everything from the spindle bearings through to the ball-screws and everything in-between. The Vaseline used was just to get the balls to stick to the nut during assembly - it will soon wash out.

If you're ever in my "neck of the woods" you'd be more than welcome to visit.

I have some parts from an older machine looks like PICOMAX100 that was being disposed of by a machinery dealer .
It used sevo motors and timing belts to drive the ball screws .
when I arrived the controls had been chucked in a skip , the sevos removed and the intention was to strip the rest to get rid of the 3000 K that was in the way .
I still have the sevos , the SF 32 spindle , some SF30 tooling , the roller slides , massive leadscrews ( maybe 30mm ) with ball nuts and bearings .
So true sevos when others used steppers ! - well as you say , it IS Swiss.

[Agathon]

I have some parts from an older machine looks like PICOMAX100 that was being disposed of by a machinery dealer .
It used sevo motors and timing belts to drive the ball screws .
when I arrived the controls had been chucked in a skip , the sevos removed and the intention was to strip the rest to get rid of the 3000 K that was in the way .
I still have the sevos , the SF 32 spindle , some SF30 tooling , the roller slides , massive leadscrews ( maybe 30mm ) with ball nuts and bearings .
So true sevos when others used steppers ! - well as you say , it IS Swiss.

What a shame it was scrapped - I would have considered buying it.

I've only just started working on the old Fehlmann again after a couple of years of inactivity. My machine is a pain as it was originally only two axis. The Picomax 100 was a three axis machine that used the quill rack and pinion driven from a worm and wheel belt driven from a servo as the Z axis. It sounds like a terrible idea when one thinks about the average drilling machine rack and pinion, but being Swiss there's virually no backlash. As I mentioned earlier in this thread, the extremely clever engineer I bought the machine from had made a worm and wheel drive (the aluminium housing seen on the right hand side) to drive the pinion. However, I have found that because he used a fully throated worm wheel it has been almost impossible to remove the backlash.
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I will probably end up using a ball-screw to move the quill, but I have recently reinstated the machine's original worm and wheel drive (which employs a gashed bronze worm wheel) and have backlash of about 0.01mm - not bad. I shall see how it works in practice once I have mounted the stepper motor to the original 90º cross-helix gear drive to the worm shaft. There is significant backlash in this gear, but it will be unimportant in terms of the ability of the quill to remain in position because of the worm and wheel - the backlash is constant so it can be accounted for in the software. As I say, this is almost identical to how it was originally done on the three axis machines, however, it has proved difficult to employ a belt drive to the worm shaft due to differences in the head castings - see drawings.

[Agathon]

I should have said Geoff, if you want to sell any of the Fehlmann bit - especially the SF32 - tooling let me know. I've PMed you.

David