Ping Morris Dovey re CNC wood Lathe

[Art Ransom]

Told that you were involved in CNC. I am close to building a CNC wood lathe with 24" swing and 10' between centers.

[Morris Dovey]

| Told that you were involved in CNC. I am close to building a CNC | wood lathe with 24" swing and 10' between centers.

You're a braver man than I! The CNC part doesn't strike me as being anywhere near as difficult as meeting the structural requirements for spinning a chunk of wood that size.

If I needed to build a machine to "turn" something that large, I think I'd opt to do the turning part with a gang of stepper motors and do longitudinal CNC routing - an approach that would allow for features like mortising, fluting (both straight and helical), and production of non-circular cross sections...

Sounds like an interesting project!

-- Morris Dovey DeSoto Solar DeSoto, Iowa USA

[mac davis]

Good point, Morris... Maybe a CNC version of that Legacy Milling Machine Bill Grumbine uses?

[Morris Dovey]

| Maybe a CNC version of that Legacy Milling Machine Bill Grumbine | uses? | |

comes fairly close. The legacy appears to be an x-y machine, with the y-axis at a fixed height, which might be a bit restrictive for an application like Art's.

Keep the long x-axis, dispose of the y-axis altogether, and add a (vertical) z-axis with just over a foot of travel. Replace the hand wheels and indexer mechanism with PC-controlled stepper motors; and you'll have something closer to what I'd imagined.

I think I'd weld up the machine from 4" square steel tubing - the Legacy's aluminum rails just aren't "beefy" enough to hold that much mass. The same (80/20?) rails and slides could probably be used if they were secured to the steel structure - but I'm not sure if they're available in 10+foot lengths. The ball-type lead screw could be used if precision isn't a significant factor, or a finer pitch Acme lead screw could be used if it is.

The challenge would be in arriving at a good balance of torque and precision to rotate that much mass. An "easy-button" solution would be a large ring gear driven by however many steppers it'd take (the larger the ring gear, the greater the available precision).

Like I said, an interesting project. :-)

-- Morris Dovey DeSoto Solar DeSoto, Iowa USA

[Morris Dovey]

| Like I said, an interesting project. :-)

I couldn't leave it alone. Last night I got to thinking more about this. The more I thought about it, the more the problem became one of dealing with the size and mass of the workpiece; and that the best solution would be one that required (precision) moving of the least mass.

By the time I was ready to call it a day, it appeared to me that the best solution would be to position the workpiece inside the machine and tell the machine where the "centers" were. A machine capable of rotating an x- and z-axis could use trig to displace all cut surfaces from the line connecting the those centers.

If an additional reference point were established at each end, the workpiece could be turned approximately 180 degrees and the second half machined with only a pair of "V" supports - and it would work for asymetrical and helical/spiral cutting as well!

The machine would then only need to be "beefy" enough to support itself and withstand cutting forces - a very different situation from trying to spin a heavy piece of wood at lathe turning speed; and a considerable improvement over turning a heavy workpiece even slowly with steppers.

The only workpiece movement needed could be done with a fork lift!

-- Morris Dovey DeSoto Solar DeSoto, Iowa USA

[CW]

The process you have just described is known as hemstitching. Commonly done on CNC mills.

[Morris Dovey]

| The process you have just described is known as hemstitching. | Commonly done on CNC mills.

I'd really like to see this. I struck out on my web searches. Can you point you point me at any photos?

-- Morris Dovey DeSoto Solar DeSoto, Iowa USA

[Morris Dovey]

| CW (in DlCQf.4791$ [e-mail]) said: | || The process you have just described is known as hemstitching. || Commonly done on CNC mills. | | I'd really like to see this. I struck out on my web searches. Can | you point you point me at any photos?

Oops! It's making the separately machined edges match up. I've done that with CNC routing but never knew it had a name.

Thanks!

-- Morris Dovey DeSoto Solar DeSoto, Iowa USA

[CW]

No, actually I can't. Never really looked. If you're in the Seattle area, I could arrange a live demonstration. Been running some parts for the last three weeks that a major feature on it is hemstitched.

[Morris Dovey]

| No, actually I can't. Never really looked. If you're in the Seattle | area, I could arrange a live demonstration. | Been running some parts for the last three weeks that a major | feature on it is hemstitched.

I'm halfway across the country from you - my loss. If I ever get out that way, I'll give you plenty of warning! :-)

-- Morris Dovey DeSoto Solar DeSoto, Iowa USA

[Morris Dovey]

|| Like I said, an interesting project. :-) | | I couldn't leave it alone.

I'm my own worst influence! I made a few drawings and think I'll need to build a scaled-down version of one of these things. A three-axis (x,r,theta) machine for turning not only round parts; but also for routing things like wood forms for watercraft hull and aircraft (fuselage and wing) molds...

-- Morris Dovey DeSoto Solar DeSoto, Iowa USA

[Tom Nie]

Stay in touch with your progress.

TomNie