Hi All,

I purchased a 2nd hand lathe from a good friend of mine many years ago now and always intended to convert it to CNC.

My profession is in the field of custom automated equipment design and build hence I started with a good idea of the fundamentals, however the mindset was a bit of a hinderance since I approached things as though it was a professional machine build and I didn't have the time or funding to match !

So eventually I revised my plans to be more pragmatic, since 13months ago we had a new baby daughter and live on a 12acre hobby farm hence my time is a little 'stretched'....

Architecture as follows :

CZ300 Chinese lathe as staring point
Spindle: Kollmorgen S614 Servostar Servo amplifier + Kollmorgen Goldline M-407-B-A3 motor  (good for 3200RPM, 50Nm peak torque)
X axis : Delta 400W Servo amplifier ASDA-AB, with Delta 400W servomotor : ECMA-C30604ES  60mm frame, 400W and 3000RPM, 10000 count/rev enc
Z axis : Delta 750W Servo amplifier ASDA-A+, with Delta 750W servomotor : ASMT07L250AK  80mm frame, 400W and 3000RPM, 10000 count/rev enc
PC: Embedded pico ATX ATOM core duo running XP embedded
Controller :  MACH3 (of course)
Interface : ESS + CM126 breakout board

Since I have a big strong servo for the spindle, I decided that it should be setup to run in position mode ie step&dir or similar so that it can be switched between being a spindle and a rotary axis.
This meant I am driving it with a timing belt to ensure no slippage.

X axis screw is a 5mm pitch 12mm OD ballscrew. This was a big challenge to fit within the crosslide and required significant modifications.

Z axis screw is a 5mm pitch 20mm unit with rather odd multi contact bearing arrangement. This was donated to the project by a good friend and came out of a large printing machine. It seems to work fine at this time but I suspect it will need to be 'upgraded' to a proper ballscrew in time.

Current performance numbers are :

Z axis : 0.5um resolution, accuracy not measured, max speed : 125mm/s or 7.5m/min, acceleration set to 0.5G
X axis : 0.427um resolution, accuracy not measured, max speed 208mm/s or 12.48m/min, acceleration 1G
Spindle/A axis : 11878.4 counts per rev, 2200RPM, 72Nm peak torque

Some pics attached (still not sure how to insert them inline)

Will post some images of the build process and video of it running shortly.

CS

Some more pictures of the build process :

Cross Slide modifications were significant and tricky since there was barely enough room to fit the ball nut (cylindrical).

A 5200 bearing (back to back angular contact) was chosen as the bidirectional thrust and radial load bearing. Since this was large in OD than the original bore would handle and I needed room for locknuts etc, the crosslide base/carriage top needed to be bored out. Since the original cast iron material was lacking on the bottom side, I had to weld some material in place prior to boring. This ended up being a block of mild steel and welded in place using some high nickel content 'weldall' rods after heating the whole assembly to about 200degC.

Unfortunately there was a little warpage of the carriage top surface (approx 100um) and this needed to be flattened out. In the end I did this with some stones and an aluminium block and lapping paste.

There is also a radial support "anti-whip" bearing on the far end of the screw since I do spin it up to 3000 RPM or so.

After all that, the cross slide works a treat with low clearance (gib done up nice and snug) and the axis seems to repeat within a few micron or less under servo control so couldn't be happier.

Unfortunately I'm still pondering where to put the limit switches which is the next task for this part of the machine.

CS

Nice work CS - please keep posting the pictures and info on you progress. 

Tweakie.

Great work. I am doing a similar project on a Pakistani lathe. x-axis ball screw installation is in progress right now. It would be exciting to see your lathe in action. Post it's videos whenever you put it in work.

Zafar

A few videos of it running although it is still not quite finished :

Running in 'indexer' mode ie spindle running as A-Axis and pretending there is a spindle mounted on the toolpost.

http://youtu.be/fLNduamJI2s

First run under CNC, note spindle speed & feedrates are all wrong

http://youtu.be/DhYdeFltGbU

Very early video of servo spindle under direct control of the amplifier ie not under Mach3 control.

http://youtu.be/BHnfT_Vr-9M

CS

Nice videos. I like your spindle servo. It's almost 10 hp. Isn't it too big for a machine this size. The spindle in position mode should be called C-axis, I guess.

Zafar

Hi Zafar

Yes in terms of power the motor is oversized but in terms of torque and inertia match it is about right.

If the servo was only for turning and not indexing then I guess a 3hp motor would be more suitable.

Even so the main reason I'm using it is because I already had it 

Regarding it being C axis, you're absolutely correct, not sure how I screwed that up !

CS

Coming along nicely
Servo spindles are great, even put one on my manual lathe
Hood

I was making a part today out of steel in this lathe and was drilling a 16mm hole at about 300RPM and noticed how much better it was with this setup than the old open loop induction motor.

I also tried cutting a thread for the first time with this lathe afte CNC conversion under MACH3 and it was great !

http://youtu.be/PrUnIrXUnOM

Pitch and diameter were spot on, however I may have made a mistake in setting the infeed angle to zero since as the cuts got deeper the surface finish suffered a little since it was cutting symmetrically on both sides of the tool. Anyway it worked as hoped and I'm very happy with how easy it was in the end.
I used the built in 'simple threading' wizard.

CS

You are right. Low speed cutting torque needs a big motor like yours. An open loop induction motor would have stalled even with step down pulleys.

Enjoyed seeing your threading video. Let's see how good threads I get with my setup of C300 and Delta VFD-E series inverter.

Zafar