Re: [Emc-users] Auto center finding?

[Gene H. <ghe...@wd...>]

On Sunday 31 March 2013 03:31:47 Gregg Eshelman did opine:

> I've seen some vertical milling setups that have a touch block for
> automatically setting the tool length. I assume the surface of the
> block is insulated from the machine and has a wire to a controller
> input to sense when it's grounded by the tool.
> 
> Easy, hands off tool length setting, no need for a measuring fixture and
> tedious manual entry of lengths and keeping them updated when changing
> tools in their holders.
> 
> For a lathe you'd want a block set perpendicular to the spindle with its
> face a measured distance out towards the operator, mounted somewhere
> fixed and always accessible. Having it dead on center would get in the
> way of turning between centers, unless mounted to a removable base
> machined to fit the V ways.
> 
> Select the auto center function, slide retracts fully, carriage zips
> over to the touch block, slide advances until making contact and the
> control knows exactly where the tip of the cutter is.
> 
> With a removable center block, just place it next to the saddle (it'd
> need to be wide enough to extend over the cross slide), hit the auto
> center command and the cross slide advances until it grounds the touch
> block or hits its limit and displays a "No calibration device found."
> error.
> 
> This could also be used to set a Z axis offset, would need to measure
> from a known point such as the center of the cross slide screw. That
> touch block would need to be in a fixed location.
> 
Actually, I use a touch block to zero mine for both x & z, z first, then x.  
It sets on the ways, and is backed left up against the workpiece mounted in 
the chuck, so it establishes the Z zero by using an offset such that I 
write code that runs in the -Z range, very repeatable, a thou or so.  The x 
is somewhat less accurate because I need to rig a single point rest where 
it sits on the flat back rail of the bed now, with so much area sitting on 
the bed that I can wipe the vactra off & move the x home 1 to 3 thou.  A 
single point rear contact should help with that.  Oh, and be sure to blow 
the swarf off the cutter tip. Don't ask how I know. :)

I made this one with another flip down bar so I can reach inside it and set 
it for boring bars too.  But that takes a restart on a different .ini 
because the x search direction is reversed.

> With the cutter tip point's location in the work envelope known exactly*
> in X and Z, setting parameters like diameter to cut to would be very
> easy.
> 
> *Assuming vertical mill axis convention where Z is in line with the
> spindle, X is crosswise to the spindle/head support, Y perpendicular to
> the spindle/head support.
> 
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Cheers, Gene
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