GH1440 Lathe Bed Conversion

[Valfar]

Thank you for the reply m_c. Good points.

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.

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.

I hope it makes sense.

Do you think I'm going on the right track, or talking bananas?

[komatias]

Hi Valfar

Bananas for sure.

Get a mill for milling and a lathe for turning. Even a small benchtop mill is better than what you are trying to do.

Also, for a lathe , there is no need for a servo spindle, just install a indexing pulse to tie every thing together. Then with a nice 3phase motor on a VFD you can do all you need to do.

Regards

[Valfar]

Hi Komatias, thank you for the input.

I'm sure there are lots of things better than what I'm trying to achieve, but in my view it all goes down to what one's able to compromise, like every single bit in this life. I think everybody agree a lathe/mill combo is not a new concept. That being said, I don's see a problem with the design idea. The challenge would be how it's implemented. I now need to understand what's wrong with my approach.

I understand a VFD + 3 phase motor would work similar say to a 3kW spindle found on the ebay, but also add an indexing pulse into the equation. Is that correct? Is there any VFD/motor you would recommend for a DIY application, or does any reasonable priced ones bought over the ebay would do the job?

Cheers!

[komatias]

Valfar,

Are you looking to make money from your machine or are you just doing it for a hobby? If you are planning to make money, do not be cheap.

Any lathe has been designed to take cutting forces in the direction that causes the saddle to compress against the bed ways. Even the machines that have a milling head on the top of them take forces in that direction. Using the lathe spindle to mill causes a torque which compresses the one side of the saddle while lifting the other side. Not very good for the saddle clamps and will undoubtedly make milling a pain in the rectum.

Myford users get away with it because they only take light cuts. With the 1440, it would be a waste really.

Yes, you are correct in the watercooled spindle comparison, only difference is that the lathe spindle motor can be 2.2kw and have lower RPM, thus higher torque ;)

[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 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.