Why different style mills?

[PaulH]

Maybe someone can clear this up for me: What is the difference between the various types of mills? I have seen models with an X/Y table that has a head that only moves in the Z-axis. Most of the home-brew plans here are for gantry style mills where the surface is still and the head moves in all three axes. I have even seen one, I think on Cranky's site, that the table moved in the X-axis, but the head moved in the Y and Z axes.

Help!

What makes one design more favorable than the others, and why?

I plan to build a CNC mostly for cutting balsa for airplanes and possibly hardwood for signs.

[musicmkr]

The type of mill you build depends on a few things.
1) How much are you willing to spend?
2) How much space are you willing to give up for your machine?
3) What resources do you have available for fabrication of your new machine.

The nice thing about the moving gantry style, where the spindle moves in all three directions and the part stays still, is that it takes less space. In order to get 24" of machinable area on one axis the machine needs only to be slightly larger than 24". In comparison in order to get 24" of machineable area on a machine where the part moves, you would need to have over 48" of floor space available to the machine. The problem with the moving gantry system is that you often required a larger motor to drive the gantry itself.

I think most first timers build a machine where the spindle moves in the Z and X directions, while the object to be milled moves in the Y direction. There are a few reasons for this. I think it's the simplest to build since you can align the X and Y much easier. Also you get some of the space saving benefits of the gantry type system, with out the need for a larger Y axis motor.

[andy_ck87028]

I have gone for a movable y gantry with movable z axis with all drive gear above the cutting table for the following reasons:

• if the table is movable with a static gantry, the mill is limited to material to a specified weight limit whereas a movable y makes for a machine where heavyweight material can be cut without having to make design modifications
• if the drive gear is under the cutting table, it makes for a more complex gantry with additional and unecessary weight
• I wish to be able to introduce long material to be fed into the mill which I could not easily do with a movable table
• the closer the cutting plane can be achieved to the x and y axis the better as it reduces the chance of vibration; allows for a more rigid system and reduces the chance of mill inaccuracy (not really relevant to movable table issue but thrown in anyway)

Cheers

Andy