GH1440 Lathe Bed Conversion

[m_c]

Komatiad, my understanding is the spindle would become an A axis, with a separate milling head bolted on elsewhere.

My thoughts were to use 2 separate motors, and couple them both to the spindle: one geared up and the other geared down. But only one would be powered on and running at a given time. At the same given time, the other one would still be rotating, but driven by the spindle (as it won't be powered) - the spindle would rotate due to the other one.

That wouldn't work. Say you have the low speed with a 10:1 ratio, and the high speed direct drive, that would mean at high speed the low speed motor will be getting driven with a 1:10 ratio, so at 3000rpm, it would be doing 30'000rpm.

I would create a lathe profile (in Mach3 for instance) and run the machinery in lathe mode, with the high RPM / low torque servo power on (and the other servo off).

When milling is needed, I would shut down everything, create another profile (mill profile) and run the machinery in milling mode only, but this time with the low RPM / high torque servo powered on (and the lathe spindle servo off, which would still be rotating due to the other motor), configured for the 4th axis role.

The lathe and mill would share the X and Y axis steppers.

There is a Swapaxis function within Mach3 that you probably want to look at.
If you've not already seen it, you may want to have a read of this thread - http://www.machsupport.com/forum/ind...c,11422.0.html

A possible option, depending on if you don't need the 4th axis to move while machining, is to add a brake, as then you don't need lots of torque to hold the spindle. You just need enough torque to locate the spindle, then use the brake to hold the spindle.

[Valfar]

Morning!

The only major compromises I'm making is the compact size of the machinery, and the lathe + 4th axis mill combo. Have already gotten the bed + headsock + tailstock. From here, will definitely won't go cheap. It will be used mainly for hobby, not production, but you never know. I need to bring to life a few design ideas I have.

M_c is right, the lathe's spindle won't be used as a milling spindle. The lathe's spindle will be used as a 4th axis when in milling mode. Another spindle (perhaps an ordinary 3kW water cooled spindle off ebay or a better one - no idea yet) will do the XYZ operations, similar to what a conventional milling machine does. But it will all be much clearer when I'll have a 3D model ready to show you.

I'm not yet familiar with Mach3 and with the low level programming. At work I'm using an industrial 3 axis router, and software like Vectric / ArtCAM (you get the idea). Will definitely look into the 'Swapaxis' function, thank you for bringing it into discussion.

I was aware of the brake system design for a 4th axis. But my thoughts were to use the 4th axis simultaneously. The brake could be added as an option though, when only one face would need machining. But it adds to the complexity, and I'm trying to keep it as simple as possible. Wouldn't a geared 12Nm Nema34 do the job without a break? I don't need high speed & feeds. I will consider a brake if it doesn't.

Also, good point m_c about the low speed motor driven by the other one at extremely high RPM. Haven't thought about it. That means the lathe motor (the 2.2kW low RPM komatias has been suggested) can be permanently attached to the spindle, and a servo (hybrid) stepper would need somehow to be detached when in lathe mode.

I see this guy nailed it. He made a lathe and a 4th axis mill run simultaneously. I'm sure you are well aware about his project.
https://www.youtube.com/watch?v=b2-Kdud7eiA

And with a single motor attached to the spindle. What's the catch?

Plenty of homework for the week-end.
Thank you for your time. You guys are great!

[hanermo2]

I am perhaps the only one with experience, who has done this, so...

At this time, after 3-4 trials, I have a 2.5 kW AC brushless servo as the spindle drive, at 1:3 belt drive, via HTD 8-30 belts, on a very strong, sturdy, rigid frame of approx 60 kg mass.
So I get 0-1000 rpm, with a C axis or "live cnc spindle".

Servo is 10.000 counts at 1:3 belt drive for 1:30.000 counts at spindle.
This is not rigid enough for milling.
And my 600€ belt drive 30 mm wide, 8 mm profile, taperlock pulleys, 24:72 teeth at spindle, setup is very, very industrial, so...

The setup is excellent for turning and lathe use.
I get 90 Nm at spindle.
Spindle motor is 10 Nm cont, 30 Nm peak (3 secs) x 1:3 = 90 Nm at all rpm.

I will use it as-is, until I switch to a secondary, likely a (double) worm drive or planetary at 1:10, at some point.

My experiences, working at this for 10+ years.
Steppers are no-where near accurate enough.
Even the best belt drives are not accurate enough.

HAAS uses a gear on the spindle, for C axis use.
But they use a class 9 ultra-precision gear for the C axis, only, switch it in-out, and the gear grinder cost 9M$, I have met the guy who sold it.

So my system is better/similar to simpson of cubestudio, and not good enough in rigidity for C axis.
I use a bigger/more accurate servo, and similar/bigger belts (his are also HTD-8, I think mine were wider).
And my lathe is a 12x, fwiw..
Hth.

[m_c]

I am perhaps the only one with experience, who has done this, so...

Yet nobody has ever seen any prove that you have, despite being asked numerous times...

[hanermo2]

I try to provide data.
Any data that seems incorrect, please comment on.

I have numerous pics, data, stuff from numerous clients, and none of it may be shared without prior approval from clients, and usually client they do not want to.
I try to help people, thats all.

Yet nobody has ever seen any prove that you have, despite being asked numerous times...

[m_c]

I try to provide data.
Any data that seems incorrect, please comment on.

I have numerous pics, data, stuff from numerous clients, and none of it may be shared without prior approval from clients, and usually they never do not want to.
I am not engaged in a popularity contest, and if/when I want to show publicity stuff I will do so.

I try to help people, thats all.

But I thought you had built this as a personal machine?
At least that's what you seem to claim until anybody asks you for prove.

And just so you know Valfar, Hanu has posted about this mythical machine for many years on various forums/email lists, and although his theory is reasonable, nobody has ever seen any kind of prove that such a machine actually exists. Whenever pushed for evidence, the excuses I've seen are he has no camera, he can't because of confidentiality, or the toys simply get launched out the pram, so make up your own mind.

[Valfar]

Thank you Hanermo2 for the valued information.

I read your concentrated post at least 10x times to understand what's in there, but I think I got there in the end.

I understand steppers driven by belts are not accurate enough, and steppers driven by gears are rigid, suitable for the application, but the problem with these is the backlash. Is that correct? It does make sense, as the belt at the end of the day is made out of flexible material, unlike gears which are made out of steel.

When you say you'll be switching to secondary, do you mean you'll add another servo stepper for the C axis, but driven by a worm gear or a gearbox?

In my headstock I still got there a secondary spindle with spur gears all over it. There's also a clutch mechanism on the front panel which can engage the secondary spindle with the main spindle. So I might be able to direct connect a servo stepper for the C axis to that secondary spindle. But the trouble would be the backlash between the spur gears, and probably less accurate than a belt drive.

Today I grabbed a 2.2kW motor (that was quick!), but don't know many details about it yet. It was free of charge and it's blue :) . Next I'll need to invest in some VFD and play with it to understand the process.

I'll keep reading here in there.

Cheers!

LE Have found this 'CNC Lathe Spindle Encoder' design http://ve7it.cowlug.org/spindle-encoder.html

[m_c]

I was aware of the brake system design for a 4th axis. But my thoughts were to use the 4th axis simultaneously. The brake could be added as an option though, when only one face would need machining. But it adds to the complexity, and I'm trying to keep it as simple as possible. Wouldn't a geared 12Nm Nema34 do the job without a break? I don't need high speed & feeds. I will consider a brake if it doesn't.

You would need to run some figures using the torque your milling spindle could produce, and the diameter of your work piece, to calculate the torque required at the 4th axis.
I.e. using some random figures, say your milling spindle can produce 1Nm, and you have a 5mm radius (10mm diameter) cutter.
At the very edge of that cutter, you potentially have 200N of force (1Nm/(0.005m/2)).
Now apply that 200N to the edge of a 25mm radius work piece, you get 5Nm of torque produced (200N*0.025).

That means under perfect transfer of torque conditions (very unlikely), you need 5Nm to hold the spindle. You're not likely to get perfect transfer of torque, however the torque applied isn't constant, and that is compounded by should the cutter snag, you have the inertia of the spindle/cutter which will produce peaks far higher than 5Nm.
However that is assuming you're using some form of side cutting cutter, cutting at a tangent to the workpiece, and at 90deg to the 4th axis axis. Things like drilling holes around the circumference, will result in minimal rotational torque being applied to the 4th axis.

If you want to run figures, most of this can be worked out to a reasonable accuracy.

Also, good point m_c about the low speed motor driven by the other one at extremely high RPM. Haven't thought about it. That means the lathe motor (the 2.2kW low RPM komatias has been suggested) can be permanently attached to the spindle, and a servo (hybrid) stepper would need somehow to be detached when in lathe mode.

I see this guy nailed it. He made a lathe and a 4th axis mill run simultaneously. I'm sure you are well aware about his project.
https://www.youtube.com/watch?v=b2-Kdud7eiA

That is a video of the original design from that thread I posted. It's worth having a read of that thread, as Simpson explained quite a lot about how he designed and built the inturn's.

And with a single motor attached to the spindle. What's the catch?

Getting the required torque.

Plenty of homework for the week-end.
Thank you for your time. You guys are great!

Spreadsheets are your friend for working out some ball park figures for the required torque.

[Valfar]

Thank you m_c! It does make sense, and I've also found some spreadsheets for calculating stepper torque values. I also believe they are a good start before deciding to buy.

Also, an excellent tutorial (from my point of view) can be found bellow:
http://www.mycncuk.com/threads/1524-...otor-do-I-need

But now Hanermo2 wrote:

My experiences, working at this for 10+ years.
Steppers are no-where near accurate enough.
Even the best belt drives are not accurate enough.

Now from my understanding that means stepper motors driven by belts are not accurate enough (what's the exact value of this? 10 thou? 100?), and the way to go would be either a worm gear or a gear box. But the problem with these is the backlash they introduce, and a good quality one is out of the question for a DIY budget. Is that correct?

That leads me to believe is the belt itself causing the problems, being flexible, and not the stepper. Is that correct?

And of course, a brake system applied on the C axis would work, but that means the same issues are encountered on the other axis (XYZ) as well?

Getting the required torque.

I understand the torque value, but this contradicts with the high RPM value needed for the lathe operations?

Cheers!

[Valfar]

This is the AC motor I have, similar to the one in the link bellow.

http://www.brookcrompton.com/upload/...E_W_CI_IE2.pdf

Brook Crompton
kW: 2.2
V: 380-415
A: 5.0-4.8
RPM: 1415
Phase: 3

I shall use it for the lathe operations.

Is there a good VFD you would recommend, or should I just go for a reasonable one over the e-bay?

I will have to also design a lathe spindle encoder similar to the one in the link bellow, is that right?

http://ve7it.cowlug.org/spindle-encoder.html

Cheers!