Upgrade recommendations for X2 CNC open-loop steppers to prevent loss of position?

Hello- Several years back I purchases a Sieg type X2 Mini Mill and converted it to CNC. I haven’t run it in a long time, but became pretty frustrated when during longer cuts (1hr+) the machine would miss steps and ruin the parts (that had taken several other long cuts to get to this point). In researching this a bit, I thought that upgrading to adding rotary encoders would be helpful, but I’m open to all suggestions. Hoping to spend no more than $500-$1000 to get a more reliable machine. I'm looking for your guidance on what I could/should do please!

For reference my CNC upgrade was done using the following:
• X, Y, Z Ballscrews (CNC Fusion kit)
• NEMA23 270 and 381 oz/in steppers (X + Y/Z respectively from Automation Technology Inc.)
• Gecko Diver G540 4 Axis Driver (Automation Technology Inc.)
I’m not even sure the driver would accept encoder inputs.

Please provide me any suggestions!

Kelly

The Sieg X2 is a small mill with a 1/3 HP spindle motor so it's not intended to be too aggressive in the works requested of it. Some ideas of what you are cutting, how and the speeds and feeds along with the tooling being used would be useful.

First things might be to check if the machine holds position when doing air cuts over long periods, then perhaps to use lighter loads (lower travel speeds and lighter cuts).


Cheers,

HarryE.
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Hi,
I suspect you must be pushing the envelope of your steppers. You haven't specified what voltage power supply you are using for
the G540 stepper drivers? If its low, that is 24-36V you could try increasing it to the limit of the G540, 48V. That may improve the situation at speed
to avoid missing steps.

Even if you had encoders, the G540 can't handle all of the inputs. Even if it did, then what? You need some sort of smart driver to take advantage of the
feedback. And even if that were the case....they are still steppers, feedback DOES NOT MAKE THEM MORE POWERFUL, they are just as subject
to overload and losing steps as open loop steppers. You say 'but the smart drive will issue more pulses to keep up', but the only reason it lost steps in the
first place is overload, what make you think that extra pulses are going to have an effect when its already missing ordinary pulses?

To be honest, fitting encoders OR fitting closed loop steppers and drives does not offer enough advantages for the money invested. At best the steppers
will still miss steps as they do now but the smart drives would fault 'following error' when they do so.

I think you could really make a difference to your machine by fitting genuine AC servos.

https://store.dmm-tech.com/products/...ac-servo-motor
https://store.dmm-tech.com/products/...ac-servo-drive
https://store.dmm-tech.com/products/...-encoder-cable
https://store.dmm-tech.com/products/...-camp-hh-_-ssp

That is $321 per axis (60V,200W drive, servo and cables) which takes near to the top of your budget but it will achieve a result that steppers of any description
won't match. For an extra $10 a servo you could step up to 60V 400W servos. They will wipe the floor with any stepper!

Craig

Thank you Craig and Harry!

To be clear on my issue- I'm not concerned so much about speed or power, but want to be able to walk away from my machine and know it didn't screw the part up. Ideally even being able to stop and fault out would be better than having to babysit it the entire time, or having to break down the cut paths into many small paths and starting and stopping the machine over and over.

A bit more info:
I am supplying the steppers with 48 volts

Craig- I like your suggestion to go with AC servos and would like to learn more. Can you help me understand what I would need above and beyond those four items? I used a UC100 Parallel to USB motion controller for Mach3 in addition to the items I listed, but this is an area that I'm pretty confused. I'm running Mach3 on a dedicated cheap desktop and it seems to work fine.

Kelly

Quote:

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Originally Posted by he1957

The Sieg X2 is a small mill with a 1/3 HP spindle motor so it's not intended to be too aggressive in the works requested of it. Some ideas of what you are cutting, how and the speeds and feeds along with the tooling being used would be useful.

First things might be to check if the machine holds position when doing air cuts over long periods, then perhaps to use lighter loads (lower travel speeds and lighter cuts).


Cheers,

HarryE.
===

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Harry-
I'm not sure I remember exactly the background of if it was only with finish cuts or not, but I do remember it happened often on finish cuts. I think I would have been using a 1/4" ball end mill taking off .005"-.010" at pretty low speeds.

Kelly

I have an X3 running 381oz-in steppers on the X and Y and Nema 34 on the Z all driven by G203V Geckos @ 48volts. I have never missed a step that I know of. I have same question as others have mentioned about what voltage you are running at? Also why do you have different steppers on the X &Y? I looked at the automation technologies website and it looks like the 270 oz-in stepper has an inductance of 3.6 which means you could run that one at 60 volts except for the 50 volt limit of the G540. Where as the 381 oz-in one has an inductance of 2.8 and could be run at 53 volts so is a better fit for the G540 50 volt limit. What I would do would be to change the 270 stepper for a 381 and up your voltage to 48 volts if you are not already there. Then while waiting for parts check the gib adjustment and look for any mechanical binding. Also be sure that your PSU can supply the required amps.

Humm, for an X2 .010" is a quarter mm (0.25) - that's a fairly heavy load if it's mild steel, sticky for aluminium if not using coolant or compressed air and the right cutter. The Sieg range about 10 years ago were a bit notorious for inconsistent casting/mounting holes so your mod kit may not align as well as it could. Check the table moves smoothly, especially when changing direction and/or entering curves/corners. Belt tension (if fitted) or gibs too tight?

See what max travel speeds you get with no load and/or try setting the acceleration/braking curves lower or higher (at finishing cut rates inertia may be causing lost steps).

Try an air cut, whole-table coverage pattern with some "interesting moves" and see if it holds origin.


Cheers,

HarryE.
===

Hi,

Quote:

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To be clear on my issue- I'm not concerned so much about speed or power, but want to be able to walk away from my machine and know it didn't screw the part up

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That is EXACTLY what this is about, your existing stepper DOES NOT HAVE ENOUGH TORQUE at the speed you are driving them. The attached pic is a pretty typical
example of a 23 size stepper. Note how the torque is reduced to less than half by 500 rpm. Thus your machine doesn't have to be going very fast at all before
the torque reduces to the point where it misses steps.

A servo on the other hand has nearly constant torque right up to it max rpm. The 200W servos I linked too in the previous post have a torque of 0.64Nm or abut 80 oz.in
but maintain that up to 3000 rpm. Peak (short overload) torque is 1.9Nm or about 200 oz.in. The slightly more expensive 400W servo has cont. torque of 160 oz.in and a
peak torque of 480 oz.in

Unlike steppers, even closed loop steppers, when a servo lags behind the servo drive really ups the current and therefore torque. There is a limit to how long it can do
that before overheating but none the less it is VERY MUCH more likely to RECOVER ITS POSITION than a stepper.

Modern AC servo drives/servos are as easy to drive as a stepper.

Servos of this description would mean that you can go faster, despite that not being your primary objective, but more importantly it will move with MUCH more
AUTHORITY and if it does lag behind (by a programmable error) it fault and stops rather than bugger up your part.


You would replace your G540 with a cheap parallel port breakout board like a C10 ($23 fromCNC4PC) and run step and direction wires to each servo drive. You will
also probably run another wire common to all servo drives to enable them, and probably one wire common to all servo drives back to the breakout board
and therefore back to Mach as a fault signal.

Craig

Suggesting $960 for AC servos for an X2 mill is in my opinion a lot of overkill. You can buy a brand new X2 type machine for about $600 and it just seems extreme to spend 1-1/2 times that much on drive motors. Oh, and that price doesn't include the power supply you will need for the AC servo/drive setup.

There is also nothing wrong with an open loop stepper system that is set up properly. I have a open loop stepper system on my G0704 mill and it works just fine. Tormach machines use open loop steppers and they work just fine. There are tons of open loop stepper machines both factory and converted that operate just fine. The key is setting them up right.

To put it in perspective, I just bought three 1600 oz-in closed loop steppers with AC powered drives for an RF-45 size machine for less than the 200W servos linked. I have the X and Y axes under power and they can run better than 200 IPM without issue. I really don't know the top speed yet because I'm testing with Grbl which is limited to 30kHz step rate.

So, what is going on with the OP's machine? Some things we know:

1. Machine has ballscrews
2. G540 drive (50V, 3.5A max)
3. 270 ox-in on X and 381 oz-in on y and Z (Why the difference? )
4. Using Mach3 with UC100


What we don't know:
1. Power supply voltage
2. Max feedrate
3. acceleration setting
4. Backlash compensation turned on?

On that last one, I've never used mach3, but I seem to remember talk of the backlash compensation causing problems presumably because it tries to instantly accelerate the axis on direction reversals.

From reading I also understand that the UCCNC software from the UC100 maker is very good software, most users saying it is better than Mach3, so you may want to consider switching to it.

The first things I would personally do is make sure you have a 48V power supply and that the G540 is properly set up for the motors. (ie proper current set resistors installed). If the current set resistors are wrong then you could have shorted your motors due to too much current. You may also want to get a third 381 oz-in motor, but should be able to experiment some first. Also make sure the gibs are properly adjusted and not too tight. Also turn off backlash compensation if on.

For setting up steppers, I generally do something like this:

1. Set acceleration low, like 3 in/sec^2 and make moves of increasing speed until the motor stalls. Do this several times to get the lowest speed at which stall happens.
2. set the max feedrate to 80% of the result of #1
3. now increase the accel gradually until the motor stalls trying to accelerate. Again, do this several times to find the lowest accel that causes a stall.
4. set accel to 80% of this value.
5. repeat the above for all axes.

I like to set all 3 axes to the lowest value for any single axis, but it really shouldn't matter. That should give reliable accel and max feed settings.

Now you can run some torture tests to see if you are still losing steps.

Quote:

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Originally Posted by 109jb

Suggesting $960 for AC servos for an X2 mill is in my opinion a lot of overkill. You can buy a brand new X2 type machine for about $600 and it just seems extreme to spend 1-1/2 times that much on drive motors. Oh, and that price doesn't include the power supply you will need for the AC servo/drive setup.

There is also nothing wrong with an open loop stepper system that is set up properly. I have a open loop stepper system on my G0704 mill and it works just fine. Tormach machines use open loop steppers and they work just fine. There are tons of open loop stepper machines both factory and converted that operate just fine. The key is setting them up right.

To put it in perspective, I just bought three 1600 oz-in closed loop steppers with AC powered drives for an RF-45 size machine for less than the 200W servos linked. I have the X and Y axes under power and they can run better than 200 IPM without issue. I really don't know the top speed yet because I'm testing with Grbl which is limited to 30kHz step rate.

So, what is going on with the OP's machine? Some things we know:

1. Machine has ballscrews
2. G540 drive (50V, 3.5A max)
3. 270 ox-in on X and 381 oz-in on y and Z (Why the difference? )
4. Using Mach3 with UC100


What we don't know:
1. Power supply voltage
2. Max feedrate
3. acceleration setting
4. Backlash compensation turned on?

On that last one, I've never used mach3, but I seem to remember talk of the backlash compensation causing problems presumably because it tries to instantly accelerate the axis on direction reversals.

From reading I also understand that the UCCNC software from the UC100 maker is very good software, most users saying it is better than Mach3, so you may want to consider switching to it.

The first things I would personally do is make sure you have a 48V power supply and that the G540 is properly set up for the motors. (ie proper current set resistors installed). If the current set resistors are wrong then you could have shorted your motors due to too much current. You may also want to get a third 381 oz-in motor, but should be able to experiment some first. Also make sure the gibs are properly adjusted and not too tight. Also turn off backlash compensation if on.

For setting up steppers, I generally do something like this:

1. Set acceleration low, like 3 in/sec^2 and make moves of increasing speed until the motor stalls. Do this several times to get the lowest speed at which stall happens.
2. set the max feedrate to 80% of the result of #1
3. now increase the accel gradually until the motor stalls trying to accelerate. Again, do this several times to find the lowest accel that causes a stall.
4. set accel to 80% of this value.
5. repeat the above for all axes.

I like to set all 3 axes to the lowest value for any single axis, but it really shouldn't matter. That should give reliable accel and max feed settings.

Now you can run some torture tests to see if you are still losing steps.

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Thank you to everyone for the good feedback. It sounds like I have a good amount of checking and testing to do. I'll give some of these things a try and see if I'm still having the issue. I very much appreciate the quick responses and useful feedback!

Quote:

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Several years back

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Bit of a long shot here but the earliest run of G540's included some duds. If 'several' means many it's an outside possibility. The revision # is stamped on the board.

Hybrid closed loop steppers do some cool tricks. If they're of any interest I'd encourage you to do a bit of research.

And a good comparison of the options in this video.

https://www.youtube.com/watch?v=OrEwKZ8JWAU
The action starts around the 20:00 mark