Magnetically levitated bed/table

[rollover_contem]

Anyone done this? I am in the process of designing a CNC mill 3 translational axis, with a moving bed/table, and a spindle/cutting tool which only moves up and down, and is stationary. Does anyone know of anyone who has done anything like this?

[Palerider]

Do you mean a Lathe or Strange Mill where you are using an non rotating milling tool which moves in Axis Z while the table rotates around Axis A, and simultaneously moves in Axis X, and Axis Y?

[rollover_contem]

Originally Posted by Palerider Do you mean a Lathe or Strange Mill where you are using an non rotating milling tool which moves in Axis Z while the table rotates around Axis A, and simultaneously moves in Axis X, and Axis Y?

no, the cutting tool moves, however it is fixed relative to x and y directions.

[Palerider]

I have a friend who make a mill which does what you are describing.
Its' a gantry style that moves it's table in X and Y, but where the spindle only moves in Z.

How about the Magnetic Levitation?

[rollover_contem]

Originally Posted by Palerider I have a friend who make a mill which does what you are describing. Its' a gantry style that moves it's table in X and Y, but where the spindle only moves in Z. How about the Magnetic Levitation?

the magnetic levitation would be to possibly eliminate the presence of any guide rails or the such, and to hopefully completely remove any sort of vibration of the work piece itself. I am still trying to figure out how to move the table with ball screws, or by some other means.

[Palerider]

What do you plan on cutting, how fast. and how much do you plan on spending on the project?

[rollover_contem]

I plan on cutting nearly anything probably not much wood, lots of aluminum, steel, polymer, I was going to base everything around a 4'x4' table, I am not sure on how much I will spend yet, I am sure in the end a few thousand dollars. I am a graduate student right now, and despite having no social life or time to do anything other than school, I have convinced myself to try and figure out this project in my "spare time" and to try and manufacture as much stuff as I can before I graduate and loose access to the wonderful lab facilities at my disposal.

[Palerider]

My thought is you won't have a mag lev table for even many thousands of dollars. Unless you spens months on it (might be an option.) Linear motors are really expensive, and the control schema is dense to say the least. I cut all those materials you mentioned, performance is what drives cost. Six months ago we spend $150,000 on an Okuma mill with 30 HP roughly. I have cut 2-4 wide @ 6500 RPM & 400 IPM With a .200 inch depth of cut.

Since you are looking to do a project mill what are you parameters?

[Palerider]

Oh, That was 6061-T6 by the way.

Have Cut with a 1.25 insert mill .06 deep @ 1900 RPM @ 160 IPM.

[Palerider]

Sorry again, that was in 304 Stainless (Its' the wine.)

[ahren]

You need more than just low friction motion -- you need some sort of system to constrain motion that would otherwise be caused by cutting forces on your part. Just levitating the table won't help you with this.

Linear motors are just another drive mechanism -- they are still typically coupled to some sort of guide mechanism.

I would say that while they are a cool idea in principle, magnetic bearings have some really significant challenges. If you want to use them to constrain motion in multiple directions against even moderate cutting forces, you'll need to have super strong magnets, which may require extreme forces to assemble. You'll also have to come up with an interesting way to mount the magnets to get counter opposing forces for each degree of freedom you want to constrain.

That being said, things like this have been done. Some reading material for you:

http://en.wikipedia.org/wiki/Magnetic_bearing

http://ieeexplore.ieee.org/Xplore/lo...number=1532334

If what you're looking for is a fun an interesting project, this could be it. If you're looking to have a useable machine at the end of it, there are definitely more practical options.

Ahren
www.cncrouterparts.com

[mc-motorsports]

Siemens did it. Unreal transverse speeds, well beyond what a ballscrew would ever be capable of. Saw one at IMTS years ago, they are now in service at Ford.

Thier rep explained it as cutting a stator open and laying it flat, the unrolling the rotor. They are the fastest machines available.

MC