Re: [CAD_CAM_EDM_DRO] Homing position

On 03/14/2012 09:30 AM, Roland Jollivet wrote:

> I'm busy converting a conventional lathe to cnc, and wanting to know where
> people generally place the home position.
>
> On the Z, if I put it right at the far end, the tailstock might get in the
> way if it was set up supporting a short rod. On the other hand, I don't
> want to drive the tooling into the chuck to home. Similar with the X. If
> tools are mounted, I might not be able to retract the X far enough, or
> maybe tools are set up for turning with spindle reversed
>
> Do I presume the 0,0 home is set up at about 1/3 of the Z, and X, at about
> 1/2 way?
>
> Regards
> Roland

Roland,

First of all, a tailstock is probably not needed on a full featured CNC
lathe, unless it is powered and the carriage movement on the ways
(Z-axis) is interlocked with the tailstock.

In most cases, tooling will be mounted so it passes through the center
of the workpiece and gang tooling is pretty simple. Add a tailstock?
How will it be actuated and what will it be used for? Clearly the two
or three axes needed are expensive (bringing you to at least 4 axes plus
spindle.) Then there is the limit switching to prevent the tooling from
crashing into it.

The tailstock will need to be moved along the ways, will need to extend
and retract, and will need to be offset. If offsetting is ignored (it
can be simulated by setting the X-Z motion to cut a taper), you still
have two extra axes. One axis moves the tailstock to position, one
moves the ram (for example drilling or support with a center), and the
carriage must "know" where the tailstock is, or it can run into it.

This is like the problem of a compound, it needs 2 axes (rotation and
translation) and may not be needed for common operations where the tool
can be mounted at an angle and the carriage can be programmed to move
diagonally.

Making home too far from the chuck has problems with accuracy as the bed
expands and contracts with temperature, but chucking the work so it is
machined to a reference surface cut by the tooling will fix that.

Dave 8{)

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