[MechanoMan]

I have a task where I need to machine out a lot of light foam round-profile shapes on a Taig.

Easiest way seemed to set up the 4th axis and do side cutting. Which will work, but it's unnecessarily slow. My Sherline rotary table does something like 10rpm but the sanding cutter eats up the foam so fast it really could, and must, process faster. Like 1000 rpm would be great!

I will probably need to retain the indexable nature of the stepper for cutting some non-round features (think keyway). So I can't simply replace it with a DC motor and be done.

Given the very low torque and step-resolution needed, what came to mind is just mounting a big stepper here and direct-driving the whole thing, chuck, spindle, and foam. The foam's light but I probably want to use the Taig 3-jaw self-centering chuck and that does have mass that will never be perfectly on-center. I can slow way down the Acceleration in Mach3 to account for the chuck inertia.

In short I think I need some sort of pillow block capable of holding the stepper on one side and the chuck on the other. I looked at the pics of the Sherline tailstock but does that even have bearings inside, or is it just a point?

At this point I have only limited ability to make threads to mate with the rotary table. Hardware/software skill level and tooling limitation there. I do not have a lathe. I've got a tap and die set but that is probably larger than anything I have.

I also had some thoughts of using a portable drill chuck, the idea does have some merit.

Thoughts??

[jalessi]

MechanoMan

Use a 5C collet mount type chuck

http://tinyurl.com/cm4u2s

Add some bearings and a pulley to a 5C collet indexer and spin it with a stepper or servo motor.

http://tinyurl.com/bv3kq7

Jeff...

[MechanoMan]

OK I'm looking at those. How big is the spinner and chuck?
It says that's a 4" chuck... and esp given its depth, that must weight quite a bit. I'm concerned there about the stepper driving something THAT massive, esp if the spinner is also huge. The acceleration times may become unreasonable at least.

Also I don't see how to mount the spinner... although I'm sure I could find a way.

Could a Sherline headstock do the job? It's kinda lookin like a good idea. They have a pulley drive and I'd have to find some way to convert that to a stepper shaft. And it's meant to mount on lathe rails too not a Taig fixture plate. Now does that straight up mount the chucks that fit on my Sherline rotary table once I added the thread adapter between them?

[sansbury]

What about adding a pulley setup to multiply the RPMs delivered to the rotary table?

[ihavenofish]

What about adding a pulley setup to multiply the RPMs delivered to the rotary table?

the problem with that is the worm gear and bearings (or lack of) wont allow much of an inccrease. im sure it would get past 10rpm, but nowhere near 1000 likey. probably have issues before getting to 100rpm.

the indexer idea might work, but you could probably go even easier by finding a way to mount a chuck right onto a stepper motor that has quality bearings. if like positional accuracy is too critical the stepper will be 2000 microsteps - 0.18 degrees per step which is ok. obviously foam wont load the steppers bearings so it should run smooth. just need a chuck that can be attached to the shaft either with a set screw or compression ring and of course a bracket to mount to the table.

[rowbare]

Why not just buy a Taig lathe headstock you can spin that pretty fast...

[vlmarshall]

the problem with that is the worm gear and bearings (or lack of) wont allow much of an inccrease. im sure it would get past 10rpm, but nowhere near 1000 likey. probably have issues before getting to 100rpm.

Yes, of course the Sherline rotary table has bearings! Still, you're right, at the table's 72:1 gear reduction, you'll have issues getting a stepper to turn 72,000 RPM.

... I looked at the pics of the Sherline tailstock but does that even have bearings inside, or is it just a point?

Nope, tailstocks don't have bearings, that'd make drilling holes (with a free-spinning drill chuck) impossible. Look for a "Live Center", a tailstock attachment with bearings behing the point.
http://www.sherline.com/1191pg.htm

And, my 2 cents worth toward your problem, how about turning a spindle the Sherline way, with a stepper motor? http://www.sherline.com/6500pg.htm

Post pictures of your project, it sounds interesting, I enjoy 4th-axis work.