[86turbodsl]

Perhaps someone here can give me advise.

I am an engineer for a company in the automotive business. I have been managing at the floor level of a small machine shop with 2 machinists/fabricators. My boss has an interest in expanding capability of our machines, and in the last year or so we have added a VMC. Right now we have only one lathe, the Clausing Colchester. It's a 15" variable speed engine lathe.

My boss wants to add CNC lathe capability to the shop. We don't have ANY more room to add a machine and so a purpose built CNC lathe is out. We can't expand and we can't get rid of anything. Partly political, partly logistics. What i've got is what i've got.

I've got a very good handle on the controls and servo side of the business, but don't have any experience in what it takes to convert a lathe. I've convinced my boss that conversion is about the only way to get what he wants and he agreed. I've found some nice packages in our price range. So the controls are handled i think. We'd use Mach3 and the package.

What I DON'T understand well and need your input on is HOW this lathe can be converted and MAINTAIN the manual lathe capability. We really need to be able to keep capability to operate the lathe manually, as we have occasional techs who come in the shop to quickly lathe a part for their work.

Is such a task even possible?

The apron of the lathe looks to be fairly complicated internally. I don't think it would be required to keep threading capability manually, but certainly the power feed would need to be maintained. The feed speeds and spindle speeds are controlled at the gearbox, and there's a VFD with rheostat for speed control in that range.

Do i need to re-engineer the apron? Or come up with a way to engage the feeds somehow? I suspect this is a very very difficult task i've signed up for.

School me please.

[pippin88]

You can use CNC stuff "manually" via jogging and MDI - are you familiar with this control side of things?

You could fit MPGs where the old hand wheels are.

Threading via CNC simple macros - LinuxCNC and Mach3 both have these, though LinuxCNC is more customisable if you can code a little and should produce better threads because it uses multiple pulses per revolution for spindle encoders.

Some people fit hand wheels to the back of steppers. I think this is a bad solution as you don't gain the benefits of semi manual turning and the feel is affected. You'll want ballscrews as well which will further change things

[jalessi]

86turbodsl,


CNC4PC has a ready made lathe MPG panel.

CNC4PC

Many commercial CNC lathes have similar controls mounted to the apron that would provide the hand control you require.

Jeff...

[86turbodsl]

How well do these jog controls work relative to the feel of the manual hand wheels?

And secondly, how does one "engage feed" with these sorts of systems? IE, now we engage the feed on the apron, and
the apron or crossfeed moves depending on whatever gear ratio vs rpm the spindle is rotating. If they are disconnected due to the cnc conversion,
is there some way to get a fixed speed out of the cnc movement? The quality of the surface finish doesn't really get there unless the feed is
a fixed speed, something a guy turning a jog wheel will be hard pressed to do consistently.

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[jalessi]

The wheels have 100 detents per revolution (clicks)

The resolution per click is adjustable depending on the rotary switch setting.

The tactile feel is not the same as a wheel attached to a acme lead screw however it is not difficult to become acclimated.

Jeff...

[86turbodsl]

I think that still the surface finish depends on how smoothly the machinist can turn the knob. What would make sense in this case, is a switch you can flip that turns feed on in a direction and the feed rate would be controlled by a knob. Set the knob where you want it and it just feeds till you turn the switch off.

[jalessi]

I think that still the surface finish depends on how smoothly the machinist can turn the knob. What would make sense in this case, is a switch you can flip that turns feed on in a direction and the feed rate would be controlled by a knob. Set the knob where you want it and it just feeds till you turn the switch off.

Adding a joystick for jogging and a potentiometer for feed rate speed would be very simple, the sky's the limit with Mach3.

Jeff...

[proengines]

If you set the lathe up running Mach3, one of the shuttle express controllers may be the go. There's buttons you can program to choose the axis, you can set the step resolution with another button and it has a spring loaded wheel you can use which varies the jogging feed rate fairly cleanly. My Tormach mill came with one and I thought it was a toy at first but they're a very capable little device that makes manual machining very do-able on a CNC machine. There's a plugin available for download on the Mach3 website and you can configure the 5 buttons to do whatever you want them to. They also cost well under $100 and just plug into a USB port on the computer.



Harrison 280 cnc manual with mach3, touchscreen, Shuttlexpress and usb camera - YouTube

[hanermo]

First..
1. The current Mach3 lathe has several weaknesses that will go away with the new Mach4 sw. This is imminent. Ie the sw exists, and the motion control plugins are coming.

2. Its very feasible to maintain full manual operation.
I did that to my 12x light-industrial lathe, with 0.1/0.2 micron step size, and 1 micron real world resolution.
This needs drives that are easily disabled.
Std ac servos will work.

Put the second ballscrew behind the lathe (Haas does the TL lathes like this).
Have a bolt/yoke/bracket of your choice, to either have the ballscrew engaged or not.

3. Use servos of your choice.
Make sure that they dont engage when back-fed, ie back-emf does not turn them on.
Most modern drives are like this, I think.

4. Use high resolution servos.

5. The real MPGs are very very good, much better than any power feeds on a lathe.
I have x and z power feeds, but the cnc feeds are much better.
Also, you can use a z/x joystick and a feed override. This is very easy.

6. You really, really, really need to use a good motion-control card.
THE CSMIO is my choice, and its very much better than anythign else I have tried.
From CSLABS, in Poland.
I have about 10 different cards/solutions/drives.

7. Part 6 is critical.
None of the USB solutions are any good, ime (pokeys is an exception, but too slow/light for your use, ar 125 kHz and 4 axis. You need 250 kHz and threading ie encoder support).
All the USB stuff implement a mismatch of crap differently.)
Only consider ethernet based boards, with *good sw support.*
So homing, slaving, step/dir spindles/, speed/rev, CSS, threading either;
-dont work, dont exist, or work differently to a PP, with the USB boxes.

The CSMIO has excellent plugins and is an industrial quality solution in hardware.Lots of IO, 24V, protection, isolated. It also has/will have Mach4 support.

Use a big ballscrew.
Two sizes bigger than you think. 40 mm or 50 mm in D if long.
Rigidity is critical. A thick screw is rigid.
You dont need a ground screw (imo), but it needs to be rigid.
A 40 mm screw is 20x more rigid than a small one (like 16-18 mm).

Make rigid z-axis screw mounts with good bearings. Or buy stock mounts and swap the AC bearings for good P4 quality ones.

I favour belts and 1:3 transmissions from servo to screw.
Threading needs high acceleration (for the pullout).

I am one of the more experienced Mach3 lathe users, and my stuff and interest is in the industrial quality area, seems to be about what you want.
I am currently doing a project with the Mach people and software, for a lathe with industrial quality, more info will come soon.
I will be glad to help in detail.
I am in Barcelona, Spain.

[86turbodsl]

What an excellent and informative post. Thank you and I will try to ask more questions as they come up.

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