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Cheng Ki Turret Mill

C

cannuck

Active Member
Years ago my wife bought a dovetail mill/drill and Marvel 8 saw from a retiring/closing shop so I would have a bit of local history in my shop. Well, loading/working that mill let me know it is really not rigid enough for some operations.

So, have been looking at a Cheng Ki 1.5HP turret mill. Anyone know what tool holding system I should expect to find? Any idea if anyone still sells/supports these tools (guessing about 40 years old, but from pic looks in very good condition). Anyone care to suggest a value (no tooling included). Can I run the whole thing from a solid state phase converter (there are 120V motors for feed and coolant as well as a 230/460 3ph motor for spindle).

Any comments, suggestions or advice greatly welcome.
 
IIRC I'm pretty sure that is a mainland Chinese straight up series one variable speed bridgeport knock off. I'd say rate it like a well used and clapped out bridgeport $1000-1500. Because on the market that is the main alternative. If it were me I'd hold out for a actual bridgeport to be assured of parts compatibility and supply.

You should be able to run it from a VFD if the motor is a 230/460 3 phase. Go with a mist coolant system
 
R8 is pretty common for a smaller mill, I would start with something cheap r8 and see if that's what you have
 
TorontoBuilder said:
IIRC I'm pretty sure that is a mainland Chinese straight up series one variable speed bridgeport knock off. I'd say rate it like a well used and clapped out bridgeport $1000-1500. Because on the market that is the main alternative. If it were me I'd hold out for a actual bridgeport to be assured of parts compatibility and supply.

You should be able to run it from a VFD if the motor is a 230/460 3 phase. Go with a mist coolant system
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Everything I have read puts it from Taiwan and if you go back 40 years, China's borders were still closed. All of that early tooling came from Taiwan (I have a lathe and a power feed drill press from same era - and both Taiwanese - the drill a nice tool the lathe...uh...so/so).

My concern with solid state inverter is that I think this is wired 480 (460) with control and some other stuff (feed motors and coolant pump) running off of 115 (120). I can re-connect the spindle motor and transformer to 230 but I can't tell if there is some feedback from multiple induction coupled loads that might confuse the SSI (that is really a VSD).
 
phaxtris said:
R8 is pretty common for a smaller mill, I would start with something cheap r8 and see if that's what you have
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I went to have a peak today and it is indeed R8. I have some R8 tooling around so will get me started.

Toronto Builder: Forgot to mention your price range is smack on where I think/hoped it should be.
 
if your going to run it off a vfd you need to connect only the motor to the vfd, the vfd cannot run the whole system, you will have to go through all of the other items and wire them to their own power source if you plant to get your spindle power via vfd

if you want to run the whole setup as it is you would need a rotary phase converter to supply you with the 230 3ph, or with a transformer & rotary phase for 480 3ph
 
cannuck said:
Everything I have read puts it from Taiwan and if you go back 40 years, China's borders were still closed. All of that early tooling came from Taiwan (I have a lathe and a power feed drill press from same era - and both Taiwanese - the drill a nice tool the lathe...uh...so/so).

My concern with solid state inverter is that I think this is wired 480 (460) with control and some other stuff (feed motors and coolant pump) running off of 115 (120). I can re-connect the spindle motor and transformer to 230 but I can't tell if there is some feedback from multiple induction coupled loads that might confuse the SSI (that is really a VSD).
Click to expand...
Yeah I would happily stand corrected. The one I looked was over 5 years ago so I could easily misremember where I thought it was from. Especially since I dont read Chinese.

If you find it is taiwanese then I wouldn't hesitate to buy it if it looks decent. I'd say they likely have a lot closer to bridgeport clone and parts may be compatible.

My own bridgeport is run off of a VFD, directly connected to the motor. Any accessories you should run separately. Easy Peasey conversion
 
Found the original seller = Akhurst Machine (a chain in the West) and they still bring stuff in from Taiwan. Believe the design and most parts are still produced with dozens of different brand names - but best I can tell they all originated with Cheng Ki. Will hit my top auction budget price (with fees) of $2k and also picked up a really nice, beefy dividing head (came in with the mill but auction house separated them) for $250. Think I will dump the transformer (as is 3 phase) and run a box splitting of 120 from 240 (neutral back to panel) and run a 3HP VFD to the motor. I had all of the reasons explained to me why you can run the whole thing on VFD particularly if other motors have to start and stop (as a feed motor certainly would).
 
Have also been contemplating rotary phase converter. I had a 5HP for many years but had stopped using it so gave it away. No big tears as it was pretty crude and very unbalanced voltage on one leg.
 
cannuck said:
I had all of the reasons explained to me why you can run the whole thing on VFD particularly if other motors have to start and stop (as a feed motor certainly would).
Click to expand...

Unless I don't understand what you claim, I do NOT believe this is correct. If you had someone tell you that, I believe they were mistaken.

You will need one separate VFD for each 3phase motor you plan to run. 3 motors need 3 VFDS. If you need more detail I can provide it and there are dozens of forum members here who can also help.

That is not a vote against using a VFD. I love VFDs and prefer them over other methods. I have Four 3phase motors running off 4 VFDs (one for each) in my shop. And I won't hesitate to get another one if I get another machine that needs it.
 
3 vfds in my "shop", they are the cat's a$$

i would do the vfd over a rotary phase converter in a heart beat
 
Susquatch said:
Unless I don't understand what you claim, I do NOT believe this is correct. If you had someone tell you that, I believe they were mistaken.
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What is swaying me towards RPC is leaving the current wiring as is. There is one transformer that shares feed with the spindle motor and taps off control voltage and run power for the feed motor and coolant pump. I can easily rewire to accommodate a VFD on spindle circuit, but that means I would have to change back if and when I move that tool into a 3ph shop. Seems simplest to just build another RPC and leave this (and some other tools) wired as they are.
 
cannuck said:
Seems simplest to just build another RPC and leave this (and some other tools) wired as they are.
Click to expand...

I can see that.

It isn't what I would do, but I'm as comfy wiring as I am having a good nap. And VFDs give you easy peasy variable speed.

But ya, with that many machines and your longer term concerns, I can see your point.
 
Susquatch said:
I can see that.

It isn't what I would do, but I'm as comfy wiring as I am having a good nap. And VFDs give you easy peasy variable speed.

But ya, with that many machines and your longer term concerns, I can see your point.
Click to expand...
dragged it out to farm on a very low trailer frame so IF it comes in at right weight I can turn spreader bar upside down and use 2 shop cranes to pick it onto floor (only 9' under hooks). Wanted to weigh it but the keys to mobile crane were taken out of key drawer to make copies...but got lost in the process. Had to take lock switch to locksmith so can weigh it in AM. Removed coolant pump and tank only to find out the motor is 230V 3ph. Suspect I will find same in feed circuit - so no question I will need to go rotary.

What I really need now is a 3HP or preferably 5HP reasonably new 3ph motor located SK or North AB. Anyone got a spare?
 
I believe some vfd's will convert single phase to 3 phase, we were doing it at work with a number of different pumps. No other phase converters needed. This handles the 3 phase and variable speed. All in 1 box.
Are the coolant pump etc. also 3 phase? As I believe using one leg of in coming power will give you 120 volt if it is 220/240 single phase incoming.
I am not up to date on what the various VFD's can do now a days. It is my understanding that in hand with motor speed control, and phase conversion, some are also able to change voltages. I think this was/is about a 1to 2 change up. And programmable for odd voltages!!! This was what my friend was doing with the milling machine I had given him, as it was 460or 480 volt on the main drive.
As he was not feeling so good the day I seen him, and there was so much to see that he had been doing, some things got lost/ mixed.
Perhaps, others could chime in and confirm or otherwise on this as I am not an "sparky". Yes, I do make sparks, welding or to be followed by a "oh, sh@$%t" as the smoke is not catchable.
 
cannuck said:
Removed coolant pump and tank only to find out the motor is 230V 3ph. Suspect I will find same in feed circuit - so no question I will need to go rotary.
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I don't see why you say "no question". 3ph 230 can be handled either way (rotary or VFD).

VFDs add up cost wise and in the process rotary becomes more economically viable. But it doesn't mean "no question". I'd get VFD even if it cost me more just so I got the speed and control where I wanted it. About the only thing that would convince me to go rotary at all would be a half dozen little things where adjustment and smooth operation didn't matter. But I'd still go VFD for the big stuff.

In other words, it's VFD to start, then VFD AND ROTARY. But for me, I'd never go rotary only. Others might disagree, and perhaps some might also lean toward more rotary and less VFD.

At the extreme risk of offending someone, I'd say that anyone who thinks Rotary only is the way to go, never really gave a modern VFD a decent try.

I have NEVER forgotten the day @Dabbler convinced me to try a VFD. Up till then I'd been a full 3ph service, or rotary for 3ph, or single ph. VFDs were not an option. He convinced me to give one a try. I was blown away. I had no idea what I'd been missing till then. Now they are my first choice. That doesn't mean I wouldn't have a rotary converter, just that in most situations I'd prefer a VFD. They are not just one way to get 3ph power. They are also a way to get variable speed, motor smoothness (especially startup and shutdown), control, and protection.
 
The process of rewiring a lathe for a VFD is more intricate than for a milling machine, but is doable for anyone with basic+ electrical skills.... The 'lazy advantage' for using a Rotary converter, is that no rewiring at all is needed. For someone shy about changing things, such as rewiring the control buttons, or has mechanical/electrical links like my Leblond, it might be discouraging to install a VFD. The last tradeoff is having multiple motors, such as 3 or 4 to deal with. If you need to run a variety of motors each with different current draws, and the need to run them independently, then multiple VFDs might be required, and adds to the negative side because of additional costs.

How to mitigate the above in favour of VFD:

Only allow the secondary motor to run if the largest motor is running already. Yes this is a rewire, but is less complicated than you might imagine. Thus the coolant pump has a feed from the main motor, and is switched from that side. this means that at slow speeds of the main motor, the coolant pump is delivering less volume and may cease to deliver any flow at very low speeds.

--How is this possible? Because the main motor will experience a variety of current draws, depending on the running conditions - such as start up, and taking a large chip. If the secondary motor is a fraction of the main motor, perhaps 1/6 or 1/8 the current draw, the VFD just responds as if the main motor has some additional load.

---------

So the bottom line is: If you hate wiring, or won't rewire anything, go rotary, and you are done, perhaps at double to triple the cost. If you can tolerate some rewiring, you can fully integrate the VFD, or minimally add a VFD, save money, and get added speed control over your lathe.
 
Here is the reply from one of my electronics/electrical resources (with a lot of VSD experience):

"Motors should not be switched on and off with the power side of a VFD, only the control side.

The reason is because when switching off, the arc on the switch contacts will backfeed high voltage spikes into the output transistors and literally blow very small holes in the semiconductor. Eventually, the transistors will fail. The failures will occur more quickly on larger units and ones that run close to their current limit.

There are microswitches available for disconnect switches that can be connected to the VFDs controls that will stop the output current before the contacts open. This will ensure that no arcs will be present when the contacts open and thus, no miniature holes blown in the transistors.

Starting a motor on a running VFD is just the opposite.

A motor has basically 3 currents;

1) Magnetizing current. This occurs from when the motor is first energized and lasts roughly 1/60th of a second. It is very high current limited only by the available fault current (maximum possible current) of the source and the resistance of the motor windings.

2) Locked-rotor current. This is the current drawn by a motor after the magnetizing current all the way up to about 80% of normal speed. It's usually about 6 - 10X the full-load current of the motor.

3) Running current. This is the current drawn after the speed has stabilized.

The problem with switching a motor onto a running VFD is the magnetizing current is way more than the output transistors can handle but since it's a short time, it doesn't burn them up right away, it just takes longer."
 
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