Lathe Bed Discussion Pros and Cons

We've discussed several options for the lathe bed. Here's a list of the options that I can recall, and maybe some pros and cons.

Box Bed Style

Pros

Inexpensive material costs
Easy to assemble

Cons

Stock size variations for CRS +/- .007 tolerance
Many holes to drill and tap
Scraping is necessary for truing bed

Steel Shaft Bed / Ways

Pros

Built in precision
No Bed grinding necessary
Rigid
Stable
Design can be downsized or increased to fit lathe size
TGP material is finish ground
Easy to assemble
Cost Moderate
Future length expansion possible
Short assembly time
Can easily be adapted to any lathe size
Can be used with EG castings to eliminate precision boring

Cons

Precise tail and headstock boring is necessary
Precise boring of tail support and carriage necessary
Boring requires a long boring bar, easily deflected unless substantially mounted
Boring requires a long quill or table movement for a carriage or headstock of 12 inch length
All of the examples cited use a substantial cast iron base to constrain movement of the round ways
Cost Moderate

Rectangular Tube / Concrete

Pros

Very rigid
Commonly found in many sizes
components can be attached easily

Cons

concrete need inside for vibration damping

Granite

Pros

Comparatively the most inexpensive
rigid
stable
good damping

Cons

We're metal workers.
May have unforseen defects particular to each piece
anchors may damage the piece if too close to edges
untappable (requires anchors for any attachments)

Epoxy Granite

Pros

Hard
Smooth
Best Damping properties
Potentially very economical
rigid
supplies readily available
No subsequent machining necessary
Can be cast to tight tolerances
Self leveling
Can be lapped and polished

Cons

We're metal workers.
Many unknowns
Engineered mixes are expensive
Ways need to be cast in, or bolted on.
Bolting might cause warping of the ways
Vibration could be necessary to eliminate voids
Personal protection required for handling epoxy, e.g. Gloves, mask

Cast Iron

Pros

Good Damping
secondary machining necessary
easy to machine
minimal material waste
Can be made to any size

Cons

Expensive for small quantity ($1000+)
Cast Iron requires long seasoning time (1 year?)
Not many people have the skill or the equipment
scraping of ways necessary for accuracy

Stock Cast Iron (Durabar)

Pros

Dimensionally stable
pre-aged
easily machined

Cons

Expensive
stock bar in bed size would be impractical for home shop
substantial material waste

Aluminum

Pros

Easy to work
Easy to ship/transport

Cons

Poor Damping

TAPR Open Hardware License (OHL) and the GNU GPL