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How To Find “Edge” on Z Axis

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Maplehead

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#1
Hi All
I use my wobbler all the time to find the edge of material.
However, let’s say I am milling a series of non-through holes along the top of a bar. The holes are shallow but I want them all to have the precise depth.
How do I set the mill at the exact same start depth for each hole?
Right now I watch closely as I slowly bring down the mill until I see the very start of material being removed and then I stop and lock my Z axis and switch to using the fine feed that is already set at zero.
 

Cadillac

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#2
You can take a know thickness like a piece of paper. Put on top your part. Bring spindle/cutter down to touch paper. Then you know the distance to your part. You could have hen use a dial indicator mount and zero to table and then you can see what you move on the z axis. They do sell z height gauges but many ways to get around it.
 

Canus

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#3
Maplehead, you state "Right now I watch closely as I slowly bring down the mill until I see the very start of material being removed and then I stop and lock my Z axis and switch to using the fine feed that is already set at zero." Do you mean that you are raising the table until you get contact then lock the Z axis? If so you are good to go. I am assuming you have a DRO on the quill. The method Cadillac covers is also acceptable and widely used.
 

Maplehead

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#4
I wish I were raising the table but my mill is the lowering the head style. But yeah, that’s what I do. I still get size differences in the holes however. No DRO for Z.
 

markba633csi

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#5
Assuming your fine feed has enough travel to do the hole depth + a little more I would keep the z locked and do it all with the fine feed and touch off with paper or a probe
Your mill is a square column correct?
mark
 

Maplehead

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#6
Yup, square column.
 

Cadillac

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#7
The fine feed screw is probably not precise enough to hold accurate movements. Get yourself a 2” travel dial indicator. Figure out a way to mount to machine to read spindle travel. That’s your cheapest route. Even a 6” dro just a little more mounting involved but I wouldn’t rely on the screw for depth readings. That’s just me though.
 
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