Probe Profiles

The Probe Library

To open the Probe Library, choose "Probe Library" from the application menu. It lists every probe profile available to the current machine profile, with each one's type and tip diameter on its second line.

The "Create New Probe Profile" button at the bottom of the list opens an empty profile. The two buttons at the top import and export profiles, and the "Sort by" control changes the order the list is shown in.

Probe Types

The type is the first thing a profile records, and it decides everything else the profile asks for. TouchDRO supports four.

Type	What it is
"Touch probe"	Triggers on contact; compensates for stylus diameter
"Edge finder (2D)"	Mechanical or electronic; compensates for tip diameter
"Tool height setter"	Sets Z from a known setter height
"Camera / microscope"	The crosshair is the reference; no compensation

The four types don't support the same functions, and it's worth knowing the differences before you buy rather than after.

Function	Touch probe	Edge finder (2D)	Tool height setter	Camera / microscope
Edge finding, including bore and boss centering	Yes	Yes	No	Yes
Setting a Z reference	Yes	No	Yes	No
Tip diameter calibration	Yes	Yes	No	No

Only a touch probe does both edge finding and Z reference, which is the practical argument for owning one. Bore and boss centering is not a separate function: it is done inside the Edge Finder dialog by touching opposed edges and taking the midpoint, so any type that can find an edge can center a bore.

Creating a Probe Profile

The type decides the drawing and the fields that follow it, so set it first. A touch probe is asked for a tip diameter and three offsets; an edge finder for a tip diameter and two; a tool height setter for its height; and a camera for two offsets and nothing else.

Name and Units

The name is what the probing functions will offer you, so it's worth naming the instrument rather than the type: "6 mm edge finder" tells you which one it is when there are three in the drawer.

The units belong to the profile rather than to the machine, so a metric probe can keep metric numbers on a machine you work in inches.

Trigger Source

The trigger source is the port on the adapter the probe is wired to. The choices are "Port P", "Port Q", and "None".

"None" is for an instrument that doesn't signal at all: a wiggler you line up by feel, or a setter you jog down onto by eye. You touch off and set the value yourself. Everything else about the profile still applies.

Tip diameter calibration needs a trigger port. A profile set to "None" can hold a tip diameter you typed in, but the calibration button (the ruler icon) will not be available, since the wizard has no way to tell when the tip has touched.

Tip Diameter

This is the diameter of the stylus or the edge finder tip, on the two types that have one. Enter the nominal figure, the one marked on the tool. It isn't something to go and measure: calibration replaces it later with a measured effective diameter.

The calibration button beside the field, the one with the ruler icon, runs the tip diameter calibration wizard covered below. The rest of this page calls it the ruler button.

Touches to Average and Max. Touch Spread

These two describe the instrument's repeatability, and they belong to the probe rather than to the machine. A kinematic touch probe repeats well enough to trust a single touch. A budget probe does better averaged over three, with a wider ceiling on how far apart those touches may land before TouchDRO objects.

Left blank, both fall back to a default, and the hint in the field names the figure actually in force. After a calibration run the spread hint reads "measured" instead of "default", because the run has established what this probe's own scatter really is.

Offsets

The offsets describe where the tip sits relative to the spindle axis. They are what allow the instrument to be mounted off-axis in the first place: a probe can sit on a bracket of its own, and TouchDRO will still report positions as though the measurement had been taken at the spindle.

How you arrive at the offsets depends on where the instrument is mounted, and there are two quite different cases. An instrument on a bracket of its own is meant to be off-axis, so the offsets are measured and entered. A probe held in the spindle is meant to be on-axis, and the work goes into making it so rather than into measuring how far off it is.

A Probe Held in the Spindle

A probe in the spindle should be adjusted until it is as close to concentric as you can get it, and its offsets left at zero. Most probes have adjustment screws on the head for exactly this, and the probe's own manual will describe how to use them.

What has to be centered is the point at which the probe triggers, and an indicator won't find it. An indicator reads the surface of the stylus ball under a fraction of an ounce of pressure. The trigger point is where the stylus has deflected far enough to open the switch, which takes real force and doesn't necessarily sit where the ball's surface says it should. A probe that indicates beautifully can still trigger off-center.

The probe itself is the instrument that can measure this, since it is the only one that applies the right force:

1. With the probe clocked the way you normally use it, indicate an edge on a workpiece and set the absolute origin there.
2. Rotate the probe 180 degrees in the spindle.
3. Indicate the same edge again.
4. Read the difference. If it is zero, the trigger point is on the spindle axis.

Any difference is twice the error, because turning the probe around moves the trigger point across the axis rather than to it. Adjust the tip by the procedure in the probe's manual and run the check again. A few rounds of this is normal.

An Instrument on Its Own Mount

A probe on a bracket is measured rather than adjusted. The offset is found by locating the same edge twice, once with the instrument and once with a tool you trust, and the difference between the two readings is how far the instrument sits from the spindle axis.

The same measurement gives a camera or microscope its offset, which is the figure to allow for when you read a position through the crosshair.

1. Clamp a square reference against the table, such as a 1-2-3 block or the fixed jaw of a milling vise, and check that it really is square to the travel.
2. Locate an edge on it with the instrument, and mark the spot. The trusted tool has to reach the same spot, not just the same edge.
3. Zero the readout on that edge.
4. Swap the instrument for a reliable edge finder.
5. Find the same edge again, at the mark.
6. The readout now shows the offset. Enter it into the profile's X or Y field, or press the button at the end of that row to fill the field from the current reading.

Repeat the same sequence for the other axis.

The Z Offset

The Z offset is a separate quantity and isn't found by either procedure above. On a touch probe it is a genuine height offset. On a tool height setter it is the setter's own height, entered as a plain positive number. 2D edge finders don't use Z at all, and the field is switched off for them.

Standard Tips

TouchDRO ships with a set of ready-made edge finder profiles in common sizes, marked "Standard tip (read-only)". They can't be edited, because every machine profile sees the same ones. To work in a size they don't cover, or to change anything about one, create your own profile instead.

Deleting a Probe Profile

To delete a profile, press the delete icon on its row. TouchDRO will confirm first, and the confirmation says what goes with it: any function currently using that profile loses its probe selection.

Deleting one of your own profiles removes it from the machine profile it belongs to. Deleting a standard tip removes it everywhere, as described above.

Importing and Exporting Profiles

The two buttons at the top of the Probe Library move profiles between machine profiles and between tablets. They work on a TouchDRO probe profile file, which carries the extension ".tdprb".

Exporting

The export button writes every profile belonging to the current machine profile to one file, and TouchDRO confirms the name it saved under. The name carries the machine profile and the date, so several exports can live in the same folder without becoming a guessing game.

The standard tips aren't exported. They are the same on every install and arrive with the application rather than with a file, so writing them out would only import them back on the far side as a second set of duplicates. Everything you created is exported, and nothing you didn't.

An empty library still produces a file. That a machine profile has no probes is a true thing to record, and it restores to the same nothing.

Importing

The import button asks for a file and then shows you what it would do before it does any of it. Nothing is written until you press the import button at the bottom of the preview.

The line above the tabs says which machine profile the file came from and when it was exported. The "Operation" control decides how the file meets the library you have now:

• "Add as new records" adds every profile in the file, leaving what you already have alone. A profile that came from this same library will arrive as a second copy.
• "Update matching records" writes the file's version over profiles it recognizes, and adds the rest.
• "Replace all existing records" deletes the machine profile's current probes and puts the file's in their place. TouchDRO asks for confirmation first and says how many profiles it is about to remove. The standard tips are not affected.

The "Profiles" tab lists what is in the file, one row each, with the type, the tip diameter, and what will happen to it. A check mark beside the diameter means that probe arrives with a calibration behind it rather than a typed figure.

The "Warnings" tab is worth reading before importing rather than after. A warning is not a failure, and most of what appears there describes a profile that comes across usable with one piece missing. The two to act on are a probe whose trigger port doesn't exist on this adapter, which arrives without an input and needs one assigned in the Library, and a calibration history TouchDRO could not verify, which is left behind while the probe and its measured diameter come across normally.

Importing into a different machine profile than the file came from is allowed, and TouchDRO says so in the warnings rather than stopping you. It is a reasonable thing to do when two machines share a probe. It is also an easy thing to do by accident, which is why the warning calls it out.

Tip Diameter Calibration

The nominal diameter marked on a 2D edge finder or a kinematic touch probe is a starting point. During probing, the forces acting on the stylus cause the trigger point to be offset from the true center of the stylus, and depending on the probe model the difference can range from negligible to tens of microns. TouchDRO measures the effective diameter based on the actual trigger point, which gives more accurate measurements.

Before calibrating the tip diameter, make sure your probe is centered as described in the "Offsets" section. The calibration process does not account for any misalignment of the probe, and if the probe is not centered, the calibration will yield inaccurate results.

You will need a ring gauge, or any accurate bore of known diameter. The inner race of a precision ball bearing works and costs a lot less than a gauge. Keep it on the small side: something in the 1 to 2 inch range is the most convenient to work in.

Mount the gauge on the table and move the stylus roughly to the center of the bore. It doesn't have to be precise; within a few millimeters of the center is fine.

Keep the stylus at the same Z height throughout. Moving up or down between touches lets any tram error in the head feed straight into the result, and the wizard has no way to tell that apart from a tip that isn't round.

The wizard will ask you to touch the ring gauge several times at each of four clock positions, taken in opposed pairs: 9 o'clock, then 3, then 12, then 6. This does a few different things under the hood. Besides calculating the effective diameter, it also measures how repeatable the touches are and how many it took to get there.

At each position, TouchDRO needs at least three touches to calculate the effective diameter, but doing more will give you a better result.

Once the third touch is in, the bar turns green and you can move on whenever you like. More touches make a better figure, since the extras are what turn a single reading into a repeatability number, but stopping anywhere in the green is fine. The bar reads full at ten touches; that is not a limit, and the wizard keeps recording any touches you take past it.

Between the pairs the wizard asks you to come back to the middle, showing a marker to crank against. After the 9 and 3 o'clock touches the bore's center in X is known exactly, and the stylus needs to be near it to reach the top and bottom of the bore cleanly without fouling the bore wall.

When all four positions are done, TouchDRO reports the effective tip diameter, how repeatable the touches were, how many it used, and the gauge size it worked from. "Apply" writes the diameter into the profile; "Discard" leaves the profile as it was.

The result can carry one more paragraph, giving the diameter measured across X and the diameter measured across Y separately. It appears when the two differ by more than the run's own scatter, or by more than 10 µm, whichever is larger, on a clean result and a warned one alike. See "Across X and Across Y" for what to make of it. The refusals described below never carry it, since there is no result to describe.

Calibration Failure Scenarios

TouchDRO checks the finished measurement before offering to save it, and there are four ways the check can come back other than clean. Three of them refuse the result, because the number can't be right. The fourth is a warning and only asks you to look again.

Cannot Fit a Circle

"Cannot Fit a Circle" means the four touches don't describe one. Points that fall in a line, or two touches taken at the same place, leave nothing for the arithmetic to work with. Take them again, one at each clock position.

Tip Has No Size

"Tip Has No Size" means the circle the touches describe came out no smaller than the ring gauge you entered, which should be physically impossible with a properly functioning probe. The usual causes are a gauge diameter typed in wrong, and probing around the outside of something instead of inside a bore.

Unlikely Tip Size

"Unlikely Tip Size" means the arithmetic worked but the answer isn't a stylus. This one almost always comes back to the ring gauge figure as well, most often a metric size typed into an imperial profile, or a decimal point in the wrong place.

Retry and Cancel

All three refusals offer "Retry" and "Cancel". Retry throws the four touches away and starts the capture over at the first clock position, keeping the gauge diameter you entered, so a run spoiled by one bad touch-off costs you the touches and nothing else. Cancel abandons the run and leaves the profile as it was.

The Diameter Mismatch Warning

The fourth outcome is a warning rather than a refusal. If the measured diameter is a plausible stylus size but lands more than a quarter away from the diameter entered on the profile, TouchDRO says what it measured, says what the profile claims, and asks you to check the ring gauge. If the gauge figure is right, the measurement stands, and you can save it.

A quarter is a deliberately loose threshold. Pre-travel on a mechanical probe genuinely runs into hundreds of microns, so a measured diameter well away from the marked one is normal rather than alarming. The check is there to catch a wrong gauge number, not to tell you how accurate your probe is. It's also skipped entirely on a profile with no tip diameter entered, since there is nothing to compare against.

Applying the Result

When you apply the result, TouchDRO writes the measured effective diameter into the profile's tip diameter field, and it also keeps the run itself with the profile, with the date, the gauge size, and the measured diameter. A profile keeps one run, the most recent one applied to it, and calibrating again replaces it. The run is included in the export file for troubleshooting, so you can send it to TouchDRO support if you need help.

The Calibration Record

A profile keeps the run it came from. The information button beside "Max. touch spread" opens it.

Alongside the figures from the result, the record holds two things you can't get anywhere else once the averaged diameter has been stored. "Across X" and "Across Y" are the effective diameters measured along each axis, and the per-position list gives the touch count and spread at each of the four clock positions.

Interpreting the Result

The run is telling you about two separate things, and they have different causes. One is whether the tip measures the same in every direction. The other is whether it measures the same thing twice.

Across X and Across Y

A mechanical touch probe carries its stylus on a three-point kinematic seat, commonly three rods resting in pairs of balls at 120 degrees to each other. How far the stylus deflects before the probe triggers depends on which way it is pushed, because the stylus doesn't pivot against those three points the same way in every direction. The four touches sample that variation, and the difference between "Across X" and "Across Y" is what it came to.

A small difference is in the nature of the instrument and not worth chasing. A large one is worth a look at the probe itself: a stylus that has worked loose, or grit in the seat, will exaggerate it.

This has nothing to do with runout. Nothing is spinning during calibration, so a probe that measures differently across X and Y is telling you about its seat, not about how it is clocked in the spindle.

Repeatability

The plus-or-minus figure is how closely repeated touches at the same place agreed. Two things make it large.

The first is technique. Approaching the wall too fast registers the touch late, and on a manual machine the approach speed is whatever your hands did, so uneven cranking turns up directly as scatter. Slow, even approaches are worth more here than any setting.

The second is the probe. If the stylus doesn't return to exactly the same rest position after each touch, it triggers in a slightly different place every time. A worn or dirty kinematic seat does this, and so does a stylus that isn't properly tight.

What Counts as Good

There is no perfect probe. Probes costing several thousand still show some jitter on a manual machine, because the repeatability they are sold on assumes a controlled approach speed that hand feed can't deliver. The number is a judgment call rather than a pass or a fail.

As a rule of thumb, the best probes repeat inside a single encoder count, and a good hobby or prosumer probe should manage about one count either way. Judge it against your own scales rather than against a figure quoted elsewhere: one count is a micron on a 1-micron scale and five microns on a 5-micron scale, so the same probe looks very different depending on what it is measured with.