G penny Spindle?

[joeavaerage]

Cl=750/12000/3=0.021mm that's a small chip thickness for aluminium? nearly a rub. Most data says run at 0.08 to 0.12mm? even 0.15mm have you tried less edges and faster? Peter a 1% cut is 0.06mm and that's light for 6mm tool. Just looking at a guhring chart and for a 6mm 1F they quote a mm/z of 0.04mm at a surface speed of 300m/min....Peter

Hi peteeng,
with my small (800W) spindle I use predominantly small tools, 1/8" and smaller. Ocassionly I use a larger 6mm tool, although its less about increased metal removal but decreased number of passes
and therefore cycle time, the wee spindle has such low torque that trying to take thicker chips will stall it.

If the job warrants it then I swap over to my other spindle (1.8kW) and run 12mm and 16mm tools....then the chips fly off.

Craig

[planebuilder]

I ordered the spindle kit
https://go.skimresources.com/?id=119...lick%20%5B2%5D
I got no responses to my questions directly to G-Penny, but ordered due to recommendations about their quality.
I didn't see any reference to a cable being included to connect the spindle to the VFD, do I need anything special or just wire?

[ardenum2]

Hi peteeng,
with my small (800W) spindle I use predominantly small tools, 1/8" and smaller. Ocassionly I use a larger 6mm tool, although its less about increased metal removal but decreased number of passes
and therefore cycle time, the wee spindle has such low torque that trying to take thicker chips will stall it.

If the job warrants it then I swap over to my other spindle (1.8kW) and run 12mm and 16mm tools....then the chips fly off.

Craig

When are we going to see this vmc of yours you've been hinting at since forever? I wanna see that frame and what those delta servos can do with it...pretty please?

[joeavaerage]

Hi,
I have posted a few pictures of it....I assure you it sounds way more dramatic than its reality!.

I don't have any video of it operating, and really that's the only way to get a true impression of its speed. I very seldom have out to max speed, 25m/min, because it files around
all over the place and scares me!

Referring to the attached pics, you can see just the very top of the 32mm steel frame sides just poking out above the Z axis servo. Note the Z axis servo has an electromagnetic
brake and it about 75mm longer than the standard 750 W Delta servos. The X axis bed is cast iron, 700mmx 250mm and weighing about 115kg. Its not easy to see but the Z axis
is mounted in another identical cast iron bed (inverted as we see it) as is the Y axis that is obscured by the way covers.

I've also attached a pic of my near new fourth axis. Its fitted with a standard 750W servo. It has a chuck at the moment but in the near future the chuck will be replaced with a
trunnion table, and another servo reducer from the same company (Atlanta Drives) for a fifth axis. The fifth axis gearbox is pictured and has arrived in the country (New Zealand) from the US,
and I expect to have it this week.

Craig

[TMToronto]

Thank you for sharing the pictures and some more details of your CNC build. Is the drive for the 4th axis one of the high-torque (HT) low angular backlash models? From the description it looks to be a good match for your CNC for milling metal.

[joeavaerage]

Hi,
the gearbox for the fourth axis I bought some years ago, and after turning up here in New Zealand I realized that it was just too big for my then mini-mill.
It is however a perfect size for my new mill, and so I pursued the fourth axis with the result pictured.

The gearbox is the Atlanta Drives 58 series which is heavy duty and < 2 arc min lash, but not the higher spec 98 series. This particular one is 63mm, that is to say the distance between the
center of the worm gear and the driven gear is 63mm. It has a max output torque of 400Nm, which is near the strength limit of the gear teeth and a rated output torque of 125Nm and
4000rpm input. If the gearbox has any lash I can't feel it by hand or is it detectable in the parts I've made with it.. It would have been nice to use either a harmonic drive or a cycloidal drive,
but they are just beyond my means. As it is, when I bought this gearbox the cost was $130USD and the shipping to New Zealand about the same, so about $260USD.

The servo cost $1000NZD and the chuck another $150NZD and I had my employee turn up the shaft, him being a much better turner than I. So overall the fourth axis was not cheap
on the other hand I'm very happy with its rigidity and accuracy.

The drive I have just bought for the fifth axis is a new (old stock) Atlanta Drives 98 series gearbox, that is the high torque, low lash (<1 arc min) version. It cost $180USD and international shipping and
NZ tax cost about the same, say $360USD. It's arrived in New Zealand and already through customs, should see it tomorrow or the day after. The servo mount is detachable and I plan to remove it
and have a servo drive it through a gear set that reduces the external dimension so that the trunnion can have full +90 deg and -90 deg movement.

It would have been nice to use something like a low profile NSK torque drive, but the cost stopped me cold. I am extremely happy with the previous (lower spec) Atlanta gearbox and have reason
to hope that this new (higher spec) gearbox will every bit as good as a fifth axis. The reduction of the new gearbox is 6.75:1, so with a 3000rpm servo will result in about 440rpm output
which is fast enough to do a little straight turning!

You might now see the reason that the steel frame extends well above the current height of the Z axis. By the time I get a trunnion table and fifth axis underneath the spindle I'm going to start to run out of Z travel.
The whole idea of mounting the Z axis in a cast iron bed is that when (or if) I get around to a trunnion and fifth axis I can just drill four new holes in the steel frame and raise the Z axis thereby reclaiming
the Z travel that I would otherwise lose.

Craig

[TMToronto]

I appreciate you taking the time to share these details. It is useful information for when I look to add a 4th axis in the future. I now have a new source to look at for the gearbox. I know what you mean about pricing for other brands, and for harmonic drives - even on used machine sites these require quite the financial investment, and I imagine for most are not worth the extra expense.

[joeavaerage]

Hi,
just an update, my new servo reducer for a fifth axis was waiting for me at work this morning. NZPost handled the international shipping and while I was surprised at the cost (higher than I hoped!)
I have gotten very prompt service....so you get what you pay for. The servo reducer looks perfect for my purposes. I've just ordered another 750W Delta servo to drive it.

Craig

[ardenum2]

Hi,
just an update, my new servo reducer for a fifth axis was waiting for me at work this morning. NZPost handled the international shipping and while I was surprised at the cost (higher than I hoped!)
I have gotten very prompt service....so you get what you pay for. The servo reducer looks perfect for my purposes. I've just ordered another 750W Delta servo to drive it.

Craig

are the delta motors pmsm's? what control modes are available on the drives?

[joeavaerage]

Hi,
Delta are genuine AC servos, so permanent magnet rotor with three phase stator excited by a sinusoidal three phase current.

The entry level ones like I buy, and pictured above, have all the regular modes, that is Step/Dir, CCW/CW, Quadrature, analog velocity and analog torque modes.
You can have dual modes. For example the primary mode might be Step/Dir and the secondary mode analog velocity. You can change modes by asserting/de-asserting
one digital input.

There are eight programmable digital inputs, six independent programmable digital outputs, two programmable analog outputs, an A/B/Z auxilliary encoder output.....so
all the bells and whistles you'd expect of a modern servo. There are EtherCat, CANBus, DCNet models as well.

Craig