My Present Stage
The XZ stage is the most critical (and most expensive) part of the hardware. If you scrounge on eBay, you can often find an appropriate stage. However, be prepared to overhaul the stage -- there is a reason why the prices are cheap on eBay! Another source for used stages is Powell's Surplus.
The stage must be extremely rigid and repeatable. Absolute accuracy is less important, but will usually accompany a stage with good repeatability.
When talking to manufacturers (or looking for used ones on eBay) you will see people referring to these as an "XY stage". That's the orientation of the axes for a milling machine and many other applications where Z means the up/down direction. Don't get confused. I'll continue to refer to it as an XZ stage because that's how we will use it on the lathe.
My stage is a Parker Motion Series 300AT stage that I bought on eBay for $150. The grease on the lead screws was like old chewing gum. That was a great deal and I've never seen another like it for anywhere near that price. New price on this unit is about $6500. You can download the data sheet and look at the detailed specs for a "standard grade" #310062AT.
There are many other stages that would also be good. Here are some important things to look for in a stage:
- Total travel: 6" is adequate for most work. 4" would not be enough in my opinion.
- Lead screw pitch: 10TPI is about ideal in my opinion. 5TPI (or 5mm) would probably be OK too. 2TPI is definitely NOT adequate from my experience.
- Having two bearings or rails is important -- the further apart the better. The 12" separation on the 300AT series gives extremely good rigidity.
- No backlash in the lead screw. (You can never get zero -- you want as small a number as possible).
- Repeatability -- The lower the number the better. Mine is +-12 micron, which seems OK but smaller would be better.
- Motor Mount -- A NEMA 23 motor mount will allow a broad range of choices for the motor. The shaft from the lead screw should be 1/4" diameter, and have a flexible coupler between the lead screw and the motor. (You can buy these separate on eBay if needed). Couplers can be hard rubber (what I started with), helical (what I have now), oldham, or bellows (the most accurate).
- Limit sensors on both axes are a MUST. You may cause severe damage if you don't prevent the stage from crashing into the ends. Limit switches used to be mechanical (metallic switches). Now, you are most likely to see optical sensors or magnetic (Hall effect) sensors.
- "Home" sensors aren't really needed in my experience. I have them on mine, but have never used them.
The one thing I really dislike about my stage is that the linear bearings are open to collect wood dust. I've had my wife sew up a spandex "skirt" to attach around the stage and attach it with velcro.
