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I’ve been talking a lot to a friend who is trying to create a bar-fed milling machine. He’s been so successful with his bar-fed lathes that he wants to be able to do the same on the mill. I know he’ll eventually get there, as he’s very creative. Talking to him has caused me to keep eyes peeled for this sort of thing and that’s how I discovered “Inverted Spindle Lathes”. First I saw mention of one on eBay and wondered what it was, then I came across a Hardinge brochure on their VL series lathes, and finally an MMSOnline article. Eventually, I was looking at diagrams of these machines and somehow or other, they just looked like they have more in common with a mill than a lathe, which got me to thinking (always a dangerous thing!).
CNC mills are out there with nice big tables and good sized spindles. There are any number of hobbyists that keep trying to use their mills as lathes by rigging up gang tooling on the table. It’s easy to do but the problem is no bar feeding–so it’s slow. Enter the Inverted Spindle Lathe idea.
In this scenario, we use a portion of the table for incoming slugs to be machined, a portion of the table for gang tooling, and a portion of the table for outgoing finished parts. Table layout might be something like this:
We mount a hydraulic chuck in the mill spindle, and essentially we have not just a gang lathe, but a pick-and-place capability. For slugs, we can mount hydraulic chucks to the table. The main thing is that we can locate a slug well enough to position the spindle over the center, drop down, clamp it in the spindle chuck, release the slug chuck and now we’ve loaded a slug for machining. Hydraulic or air-operated 3 jaw chucks seem ideal for this purpose, although any fixture that would locate the slugs and allow them to be locked or unlocked individually would work.
Once a slug is loaded in the spindle chuck, we head over to the gang tooling area. The middle of the table is ideal for this, and we machine the part. When finished, position the finished part over the appropriate catcher bin and let it drop in from a minimal height so it isn’t scratched or damaged. The bins could be made removable, or, a simple inclined ramp would let the parts roll down into a bin sitting on a cart in front of the table.
Given that we’ll be spinning good sized slugs and have a heavy chuck in the spindle, it’s a good bet we want an enclosure for a machine like this. It does make you wonder whether that old mill sitting in the corner can’t be put to good use though, doesn’t it? With some ingenuity, it should be possible to run some live tooling in this kind of setup too.