Best method for zeroing in on the top of part

M

Maplehead

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Hi All
Edges are easy for finding zero, just wobble them, but how do I find the top?
Currently I use a thin gauge strip that lays on the top of the part. As I slowly bring down the bit I slide the gauge back and forth until the bit presses into it and forces the strip to stop. Once I tighten my Z axis the bit slightly rises and allows me to remove the gauge strip.
Is there a more accurate way to find the exact top?
Some things I know that make my method less accurate are:
Gauge strip is .015”
Bit slightly dents into strip
Tightening z axis raises bit

Just curious as I try to perfect my accuracy on all things milling.
 
One thing would be to use ordinary paper, instead of the gauge strip. Depending on the thickness of the paper, you will feel resistance at about .003” off, and the paper will bind at .002”, or so.
 
dpb said:
One thing would be to use ordinary paper, instead of the gauge strip. Depending on the thickness of the paper, you will feel resistance at about .003” off, and the paper will bind at .002”, or so.
Click to expand...
Oddly, I never thought of that. Thank you
 
It probably depends on your mill. I position the knee about right, set the dial to zero, or just stop on zero when adjusting the knee. Then bring the tool down to touch the part, lock the quill, and back off knee by 20 or 30 thou. Move the tool away from the work in x or y, then raise knee back to zero, plus the desired depth of cut and mill away.
 
For basic tool height setting, using a piece of paper works. Having a polished surface helps with consistent measurements. Old timers used cigarette papers; probably because they were readily available.

You can use a piece of shim stock as you do or a piece of steel of known thickness such as a gage block. I prefer not to do this as I am concerned about dulling my cutting edges.

If the surface that I am contacting is to be further machined, I will sometimes just slowly lower the tool until it just begins to cut the surface as I rotate the spindle manually. For operations where the tool height isn't critical, I will bring the tool down until it touches the surface and set my zero. I use this mostly for drilling.

Another method is to use a tool setter. They come as either a mechanical or electronic device which will indicate when your tool is a defined distance above the work surface. These work best with a DRO as you can zero the tool on the tool setter and offset the tool by the height of the tool setter and rezero.
https://www.mscdirect.com/browse/tn...-Tools/Tool-Setters-Presetters?navid=12107796

A big step further is to use a tool holding system like the Tormach TTS. It permits tools to be removed and replaced in the spindle without losing the tool height. I use that system on my Tormach and on my old mill/drill. My method of zeroing involves using a digital indicator as a reference and zeroing it and my z axis with it. My tool offsets are all referenced to the indicator in a tool table so I can change tools at will by simply changing to the DRO subdatum for that tool or, in the case of the Tormach, changing to the proper the tool number.
 
Thanks for the suggestions. I wonder if the following would work: For chucks or collets, what if I leave the drill bits or end mills in them loosely, lower the z-axis until the tool is resting on top of the work piece, tighten my z-axis and then tightened the chuck or collet?
 
For ordinary work, a friend of mine took a phone book, tightly clamped it between two pieces of scrap plywood, and then sawed it into strips 1" or a little wider across the width of the pages. That leaves you with strips of paper the width of the phone book long, still bound together by a portion of the spine. Open the short but wide book up in the middle, and use a string or light wire wrapped and tied around the binding to hang it on or near the machine. Measure the thickness of a page carefully with a mic or caliper under a light load and use that as a thickness starting point. I came up with .003" and that number has proven repeatable in use. It is easily used one handed and without going for a walk, and the strips are long enough to be quite safe to use, no fingers close to the spinning cutter. My one slice of the big city phone book is likely a lifetime supply. Do it soon, while there is still such a thing as a phone book... ;)
 
Maple: your method is fine, I do pretty much the same thing, with a feeler gauge.
I believe someone sells a fancy-shmancy electronic gadget that uses electrical contact, but it seems like more work to me
Mark
 
I use Winegrowers method, crank the knee up until the tool is close, advance the quill until the tool touches the part, then lock the quill. Zero out the Z-axis on the DRO, back the table down to clear the part and move off the part. Move the table up to my DOC and have at it.

Bruce
 
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For me, as in a lot of things, it depends... Sometimes, I just touch off, take a cut (not to full depth), measure and then make adjustments for the finishing cut. Sometimes, like others, I just use a piece of plain paper. If I want something very close and can't take a first cut not to depth to measure (like when setting a slitting saw to the center of a shaft) I'll use paper to get close and then add some dye or marker on top of the piece and raise the table little by little taking small pass cuts on the top until I just remove the dye. It helps with this method if you have a DRO when you get close so you can take tiny steps.

YMMV,
Ted
 
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