Warco VMC mill conversion

[treb63]

I know this has been done before quite a few times however whilst I was doing research I found photos online useful so here goes, firstly the mechanical stuff.

All acme screws on the machine have been replaced with ball screws, 16mm on X and Y and 25mm on the Z(Knee) the Quill has been left alone so the machine could still have manual function besides the rack and pinion had far to much play. First comment would be buy the best you can afford the Z axis was from Zapp and appears to be a quality item the other two were from another supplier who advertised quality but once they were fitted and tested the backlash in the nut became obvious, lesson learnt. Easy enough to turn custom ends on the stock scews with the right tips.
All support bearings replaced with preassembled and preloaded ball screw support assembly's these were quite easy to set into a machined pocket in the original (yellow) bearing supports.

The Z axis on the Warco goes into a bearing assembly which is removable so with a little machining this support block was made to accept two taper roller bearings , the ball screw then passes through these bearings through the gear and terminates with a locknut as before, below the bearing assembly the ball screw was machined to accept a taper lock pulley so the motor could drive the ball screw direct without using the manual gear system as this has far to much backlash and potential for play.

Once completed this machines has been tested and calibrated using a Renishaw ball bar which showed the best I could achieve was a positional tolerance of 40 micron in a 8" circle and a best circularity of 35micron again on a 8" circle. For those that don't know the Renishaw ball bar is a device made to be able to test machine tools for accuracy and repeatability they cost lots (15K plus) and need training in order to use correctly fortunately due to my profession I am fortunate to have access to such goodies.

I will try and post up now some photos taken during the build and any questions ask away I will drop in here from time to time and am willing to help where I can......

[treb63]

Ok first thing to do is strip it down and see what wever got.... no going back now.

[treb63]

Z axis detail, hope this helps some.

[treb63]

Y axis detail,

[treb63]

The nearly finished machine, still some labels to add to the control panel and put some handles on the exposed ball screw ends, the Z axis (knee) lift has been removed for now to save weight on the Z screw/ motor, I may be fitting a gas spring later as I feel this combo with 1 to 2 gearing is still putting a little to much load on the motor when run at high speed and it can loose pulses (motor screams).
I may look at a different slide guarding system as even with the mods I did to the knee casting to increase the Y travel the guards restricts the y travel to much so I sometime3s struggle to machine much over 150mm wide.

[treb63]

Also the crappy lubrication system has had a complete overhaul and a proper pressurised system fitted although the pump has been retained the injectors now are all correctly graded restrictors thereby ensuring all lube points 'get a bit'.
 A couple of shots of the first two things machined, a little test piece and a exhaust anti vibe mount.

[Brass_Machine]

Hiya Treb!

First, welcome to the collective

2nd, that is a nicely done conversion. You can never have too many build logs on CNC conversions. I am always looking at them to see what I can do to mine (since mine isn't even close to complete and I am going to tear it down and start over)

Looks like it has a one shot style oil system? I see some tubing... Got any closer pictures?

Eric

[Brass_Machine]

Also the crappy lubrication system has had a complete overhaul and a proper pressurised system fitted although the pump has been retained the injectors now are all correctly graded restrictors thereby ensuring all lube points 'get a bit'.
 A couple of shots of the first two things machined, a little test piece and a exhaust anti vibe mount.

Looks like you were posting the same time as me... I have been trying to figure out how I want to do mine.

[treb63]

Now for the electrics, not my forte.

I have used these Nema 34's 4.6Nm for the X and Y at 1 to 1 and direct drive. http://www.cnc4you.co.uk/index.php?route=product/product&path=20_95&product_id=211
This motor for the Z axis Nema 34 8.7Nm firstly at 1 to 1 then now at 2 to 1 gearing http://www.cnc4you.co.uk/index.php?route=product/product&path=20_95&product_id=187
I have used these drives http://www.cnc4you.co.uk/index.php?route=product/product&path=82&product_id=29 rated at up to  but not exceeding 80V
The power supply was this one http://www.cnc4you.co.uk/index.php?route=product/product&path=81&product_id=33  48V 12A 600W

The interface to the pc running Mach3 was via a UC300 which I can wholeheartedly recommend, it will do everything you ever need for possibly more than 1 machine also via usb no old parallel port needed so My pc is a cheap net top style asus revo.

However my question to you stepper motor experts out there would be that with these motors I was hoping to be 'over the top' with the power available but I have found that I am a little prone to loosing steps and the motors start to scream and stall. This usually happens when the motors are trying to set of from rest into a rapid move of more than one axis at once or I am rapid jogging one axis and I also select another axis via a joystick control to also rapid jog this starts at least one of the motors screaming and loosing position.

I suspect that the power supply is not up to the job and at 48v is dipping under the load of two motors running in rapid (1500mm/min) it could also be uprated as the drives could take up to 80v max so would this help in delivering more torque out of the motors?  Any thoughts in this matter would be gratefully received..

[treb63]

Mr Brass,

The lube pump supplied is ok to use however the design of the system is crap, in order for the system to work correctly all lube points must receive the oil pressure for the same amount of time in order for the lube to find its way to the necessary points correctly.
The original system has pipes with no restriction's so what can and does happen is the lube will always find its way out of the biggest gap or least restriction first.

What needs to be done is fit restrictors to each of the lube point as close as is possible so the pump develops the pressure and holds the pressure in the pipes feeding these points, these points then leak out at a predetermined amount (more needed for cast iron slides than ballnuts) there by ensuring all points receive oil.

The system is not cheap but I think Arc euro trade stocks all the items individually so it can be built up sequentially and when driving these soft cast iron slides faster than they were designed for I think it is essential.
A system like this design is what I've acheived
http://www.arceurotrade.co.uk/Catalogue/Machine-Spares/One-Shot-Lubrication-System#One-Shot-Lubrication-Parts-for-Myford-ML7
regards

[9fingers]

Hi Treb, Welcome to the forum.

I'm still experimenting with steppers and still learning but I have found that you have to ramp up the stepper speed from zero to the desired step speed gradually otherwise steps will be lost.
I *think* this is done by mach3 when in CNC mode but not sure.
If your manual jog inputs are being routed direct to the motor drivers, then this could be your problem.

There will be more knowledgeable people here who will possibly know.

Bob

[treb63]

Hi,
I've tried tweaking the velocity response in motor tuning and when jogging only one motor all is usually fine, to be on the safe side I've reduced the velocity parameter down until the motor response is noticeably slow to accelerate.
Just don't want to fork out for increased power supplies unless I'm sure were on the right path.

[kstrauss]

As others have mentioned you do need to ramp the stepper speeds to avoid losing steps. Why not check the power supply voltage while running all three motors? I would use an analogue meter (rather than digital) because it is easier to see flucuations.

[9fingers]

OK - just looked at the spec of your power supply and it soiund like it is rated at sufficient current but it depends on what the transient response is like.

You might get some idea by attaching a multimeter set to AC volts and then provoke the fault situation and see what the meter reads. The result will depend on the quality of your meter (true RMS types are best)
A perfect PSU will read next to nothing and I would not worry at a volt or so but it should give you an idea if the psu is sagging badly.

Bob

[treb63]

Hi Bob,

Will give this a try later today, so connect my Fluke meter set to AC volts across the 48v DC rail supply to the Drives and make the machine fault out. Then see if there is or has been any fluctuation in the AC reading.
Thanks will report back asap.

Rob

[9fingers]

That's right Rob.
On a dc supply there should be no ac present but there tends to be a small amount plus some induced 50hz in the leads. Twist the leads for as much of the length as is practical to reduce this effect.
If your meter has a peak hold feature then that can be useful.

I've looked at the diagrams the supplier suggests for wiring up the power supply and drivers and am surprised to see no big capacitors shown to be fitted close to the drivers. The power supply will have some inside but they will be designed to reject the internal switching frequency of the PSU at around 100kHz.
Maybe they are not shown for a good reason or maybe a genuine omission?
When I get round to it I'll be making my own PSU as I prefer linear supplies and can experiment then.

Bob

[philf]

Hi treb63,

I assume that you've set the current on the drivers and that you've wired the motors correctly? Mine is a smaller machine with Nema 23 3.1Nm motors wired parallel and I use much less than the rated current without stalling. I'm using switched mode supplies at around 42V with no extra capacitors.

Also - are you using microsteps? Full stepping can have resonance problems where, at certain speeds, the torque almost disappears. I run mine at 8 microsteps.

Phil.

[AbrahamLom]

Looks like a nice mill. Solid appearing from the very limited views. Went for cheap if under 300 bucks. Hope it was you.