Centroid Community CNC Support Forum

Hi Team, I have Acquired an old Bed Mill from my work place (in fact it was the first CNC I learnt to run 10 years ago).
It Must be about 25 years old, the controller no longer operates, and the servo motor drives have been used to keep another one of these machines up and running.
Since I have been given this for Free, I am looking to refit with an Acorn. Although not perfect, the machine has plenty of life to give mechanically and should be perfect for my little hobby jobs I do - since I no longer operate a CNC at my work place I don't get to use the machines as much these days (Now I am a Mechanical Design Engineer designing automated packaging machinery).
I am looking into my options in to getting this Mill back up and running.
The Machine has SEM MTS30M4-48 Dc Servos (I think all 3 are the same - But have not confirmed yet)
I would like to run the Machine on single phase, and will use a VFD for the Spindle Motor speed control and phase conversion.
Options I am Looking into:

Option 1: Acorn Board, NUC/PC, Pro License, and replace the servos with closed Loop steppers
(https://www.omc-stepperonline.com/ts-se ... -3-clts120)
From what I can tell these steppers seem to be a good replacement for the 29 in-lb dc servos.
My Only reservations are the non complete closed loop control (the steppers and drives are closed loop).
I understand that the control will loose positioning of the axis if they are moved mechanically during an estop or when drive power is free.
When the machine is energized, but not running a program, will the steppers hold their positions?
The Pros of this combination to me are the cost (I don't want to spend a fortune on an old machine) and that I can run it off single phase.

Option 2: Reuse the old dc servos, fit new encoders, use an Allin1DC board, and a NUC/PC
Pros - Superior Control, Don't have to mount new motors (But not really an issue)
Cons - Cost (Allin1DC + encoders + pro License) is quite a bit higher + the motors are already pretty old, and the existing transformer appears to be 3 phase.

I am happy to accept that the machine may not have as much power/torque as the original servos - after all any CNC is better than no CNC.
Would I be disappointed in the accuracy if I was to fit the steppers?

The machine currently has a variable speed belt drive, I would look to replace this with a fixed set of pulleys and use the VFD to control the spindle speed. If i were to fit an Encoder, would rigid tapping work with an induction motor or would it be a disaster?

Looking for some feed back from the experts.

Thanks, Luke.

I would use Acorn and 1500W JMC servos.
Open loop is no problem with powerful drives for high precision.

It is about 1000$ more than the 12Nm Steppers, but better performance than the old DC servos and very easy to install.

Uwe

Depends on your appetite and capability to do mechanical modifications. On my 1980s Shizuoka, I also have SEM brushed motors and didn't have any easy way to rework the drives, so I fitted 3 of the DG4S-16035 brushed controllers from cncdrive.com I was able to use the original encoders and leave all the mechanicals untouched.
https://www.cncdrive.com/DG4S_16035.html

This has been fine and hasn't caused any problems. The machine flies along with modern toolpaths in a way the original manufacturer would never have imagined. A modern servo would doubtless give better performance but having said that, we are talking fairly old machines here so it's all relative.

With high speed toolpaths and coolant, you need to think about enclosures too!

As for your question about spindle encoders, induction motors and rigid tapping, that machine of yours seems to have a Bridgeport head which is very difficult to fit an encoder to. For rigid tapping, you need the encoder to be geared 1:1 with the spindle which is pretty tricky. My machine head has a similar design, so I simply use a tension-compression head and the std threading cycles (which are variations on the std drilling cycles).


Unless you have an (arguably) overspecified spindle motor, you'd benefit from using the reduction gearing. Although many VFDs can operate down to zero speed, they are better suited to operation nearer their base speed which is typically 1500rpm or 1800rpm depending where you live. Even Uwe wouldn't try tapping near those speeds!

Muzzer wrote: ↑Sat Aug 20, 2022 6:46 am ......, they are better suited to operation nearer their base speed which is typically 1500rpm or 1800rpm depending where you live. Even Uwe wouldn't try tapping near those speeds!

sure I do , I set lowest speed for rigid tapping to 800, but most times I use 2000-3000rpm for small taps

Uwe

Thanks for your replies so far. The DG4S-16035 seems like it could be a good option if I want to retain the original servos.
I have since found out the original drives may not have been installed in another machine, and that they may be sitting sitting somewhere in our local CNC service techs workshop. However these are no use to me with the Acorn as they have the optical communications?

The Spindle Motor is 3.7kw - the New machine we have at work that replaced this mill (its just a new version of the same thing) appears to run a similar motor and that seems to have plenty of power only using a vfd to control the speed. Whether or not I choose to retain the current spindle drive is really not to important at this stage.

The Rigid tapping for me is not a big deal, I've used the compression tapping holders many times with great success. I found even on machine with full servo spindle control the compression holders helped increase the life span of the tap in the smaller diameters in 304ss.

For me the big thing is not wanting to over capitalize in an old machine - so really looking to get it operational as cheap as possible.
Is anyone running these AC servos from stepper online?
https://www.omc-stepperonline.com/t6-se ... 0h2a3-m17s
They appear to support 'pulse control" which is the same as Step and Direction? EDIT: It appears these are re branded leadshine servos and drives.

Also worth nothing I am in New Zealand, so 240vac or 415vac 3 phase is what we run here.

Luke.

No experience with those particular ones but I've got some LiChuan servos on my lathes (https://www.aliexpress.com/item/1005001 ... 1802S8fPX0). They aren't quite in Yaskawa territory and the setup is fairly basic but they take step/dir inputs and I've had no issues with them. The fans were noisy as hell but I changed them for some PAPST equivalents.

These servos run directly from single or three phase which makes the installation fairly simple and neat. Consequently, the motors have unisolated mains voltage in them, so the (unsealed) phase connections to the motors need to be kept clear of coolant and swarf - an RCD / GFCI would be sensible.

With these Chinese drives you get a lot of drive for the money but obvs there's the uncertainty of how they will perform and last and some question over what warranty cover if any you might expect. I believe JMC are another possible supplier of servos of a similar quality.

There seem to be many clones of the Leadshine product range on ebay and AliExpress, so it's not clear which are rebadged and which are bootlegs.

After reading the manual, I am sure they work with Acorn as axis drives. I also have had never a bad experience with Stepperonline.

The reason I am using JMC is the german distributor, and that the drives also have an analogue innput, so I can use them as spindle drive.

JMC needs some soldering, the ones from Stepperonline have screw terminals so very easy to connect.

Uwe

Thanks for you feedback Uwe and Muzzer.
When it comes to sizing, it seems to me that stepper online ones are equivalent to the original brushed dc servos (29in-lb/3.2nm). I havent really been able to find a torque curve for the dc motors, bit they are both about 1kw @ 3000rpm? Would that be a fair comparison?
The single phase installation is very appealing to me, and you bring up a great point about RCDs.
In an earlier post you recommended JMC 1500w, do you have a more specific model that you use?
Edit - found the jmc versions, having only viewed their website on my phone only showed their integrated servos - had to scroll across to find the std ones.

Luke.

lwiseman89 wrote: ↑Mon Aug 22, 2022 11:32 am ....
In an earlier post you recommended JMC 1500w, do you have a more specific model that you use?

Luke.

sure:

https://shop.cnc-technics.de/product-22-35-106.html

They are powerfull enough to drive the axis directly, 750W-1000W would be better to reduce 2:1 with HTD belt drive.

Uwe