SainSmart Z-Axis Touch Probe

What that changes on the bench:

• Consistent depth. A V-carve at 0.5 mm deep is 0.5 mm on every sign, not 0.3 mm on one and 0.8 mm on the next.
• Safe bit changes. Roughing with a flat end mill and finishing with a V-bit needs Z reset between them; the probe does it in seconds.
• Fewer broken bits. A 0.1 mm engraving tip is easy to snap when lowering it by eye onto the stock.
• Repeatable routines. The same probe command runs the same way on every job, with no judgement call.

The puck is 30 to 35 mm across and 14 to 20 mm thick by SainSmart's figures, with a 25 mm contact surface on top. It sits on the stock under the bit, a clip goes onto the bit or collet, and a single command lowers the spindle slowly until contact.

Walnut and MDF both work the same way, because the puck sits on top of the stock. The wood itself never needs to conduct, only the bit and the puck.

Cases that need a little care:

• Warped plywood. The probe measures one spot. A cupped sheet can be a millimetre higher at the centre than at the corner where the puck sat, so probe near the area being cut.
• Painted or coated bits. The clip must reach bare metal. Clip onto the collet nut or the shank above any coating.
• Chips under the puck. A single MDF chip lifts the puck and every depth in the file with it. Wipe the spot before each probe.
• Copper-clad board. Isolation milling wants the copper surface itself, not a puck on top of it. GRBL senders such as Candle can build a height map by probing a grid across the copper when it is wired as the contact surface.

It sets Z only. X and Y still come from jogging to a corner or a mark, unless a separate corner probe joins the kit later.

1. Power the machine down and plug the probe into the board's probe port.
2. Place the puck on the stock under the bit and attach the clip to the bit shank or collet nut.
3. Test the circuit first: tap the clip against the puck and check that the sender's probe indicator changes.
4. Jog the bit to 10–15 mm above the puck.
5. Run the probe routine, then remove the puck and clip before starting the spindle.

A typical two-stage routine, fast then slow, for a 20 mm puck:

G21 G91
G38.2 Z-30 F100
G0 Z1
G38.2 Z-2 F10
G92 Z20
G0 Z5

The last number in G92 is the puck's thickness. Measure your own puck with calipers and use that figure; a tenth of a millimetre here shows up in every cut. Candle stores a routine like this behind its Z-probe button, and Mach3 users set the same values in its probing script.

The slow second touch at 10 mm/min is the step that makes the zero precise; the fast first move only finds the puck quickly.

More on senders and GRBL settings is on the 3018 software page.

The 2-pin probe's missing light is the one real trade-off. With an indicator, a glance confirms the clip is making contact before the spindle starts to descend. Without one, the sender's probe status is the check, so keep that field visible in Candle or UGS and look at it each time.

Worth confirming on the board and sender:

• The board has a free probe input; on a 3018-PRO board it is a labelled 2-pin header.
• The sender can run a probe routine, which Candle, UGS and most other GRBL senders can.
• The 1.1 m cable reaches every corner of the bed from the board.

A probe is the first add-on for most 3018 owners, ahead of clamps and a spoilboard, because it prevents the most common early mistake: a bit driven too deep on the first pass. The full order is on 3018 upgrades by payoff, and the 3018-PRO kit can be ordered with this probe already in the box.

Store the puck face-down on a clean cloth, not loose in a drawer of bits. A scratched or dented top face changes the contact height by a hair, and that error lands in every job afterwards.