Re: [CAD_CAM_EDM_DRO] Re: Machine construction.

>> What is the most inherently accurate machine configuration?

5/6-axis gantry mills are usually used for high accuracy aerospace type
work.

Gantry mills are designed such that the absolute minimum amount of solid
machinery needs to move for a given operation. This means that they can
achieve very dynamic movements and be constructed in a very solid way.

From memory, industrial gantrys can now manage something like 40 - 60 metres
per minute. There are quicker VMCs using a standard XYZ configuration, but
they have limited table capacity for a fixed price - because the drives need
to push the work piece around as well.

Which way you go is quite dependant on what you're machining.

A gantry is useful for big heavy parts, where the part will weigh a lot more
than the moving surfaces. If you're only machining small model engines or
something similar, a standard XYZ configuration will be better in most
cases, since the work table's weight will be well within the realms of
normality.

If you want accuracy, hunting around on eBay for some linear ways with
recirculating carriages is a good way to go.

If you want to get super duper style on it, you could pick up some linear
motors from eBay. These things usually cost thousands new, but they appear
on eBay from time to time as lab surplus type gear. If you decide to go this
way, you'll most likely end up with a mix and match set of three, each from
a different auction, as opposed to three shiny matching motors.

Linear motors will be the new 'it' in machine design within the next ten
years. They are already gaining pace on servos. Other than cost, at the
moment, there is little about them that isn't better. A desktop mill powered
by a set of linear motors would seriously move!

A linear motor is a direct drive system. There aren't any belts, gears or
transfer mechanisms in the way. The actuator sits in a groove between a rare
earth magnet guide. A voltage is applied to the carriage and it rockets
away.

You should take a look at this guy's site -
http://www.5bears.com/cnc.htm

He is very accuracy orintated in his design for his own CNC mill.

Best wishes,
John