Probe Z Axis Construction - VikOlliver/RepRapMicron GitHub Wiki
Probe Z Axis
These instructions are for PIKA, and MAUS V0.05. The V0.04 instructions are here.
The printed part plates for the Probe Assembly are found in the 3D print file (maus_probe.stl or pika_probe.stl) which is derived from maus_probe.scad or pika_probe.scad.
Two additional constraining flexures need to be fitted to the Z Axis Driver, and these are in maus_complementary_plate_C.stl. The flexures are derived from maus_complementary.scad by setting the "plate" variable at the end of the file.
Pre-built STLs are on Printables here.
The Probe Assembly consists of a blade with a vertical slot referred to as the Probe Beam, a U-shaped sliding bracket providing a grounded mounting position for the Probe Tip assembly called the Probe Shuttle, and the Probe Arm itself which is a carrier for the etched Probe Tip. The joints are articulated such that the Probe Tip can be positioned with 5 degrees of freedom anywhere in the printer's working volume. Two identical Probe Arms are supplied, one for making a coarse tip, and one for a fine tip.
Additionally, a Probe Jig is provided on the sheet, which is used to hold the Probe Tip in alignment when fitting it and to subsequently protect it during integration with the Probe Assembly.
Part Preparation
Axis Driver
You will need to construct one Axis Driver for use with the Probe Z Axis.
Probe Tip Points
Electrochemically etched point (left) compared to a 0.5mm diameter hypodermic needle point
The Probe Tip requires a fine, conductive point. Suitable ready-made points for coarse tips include 0.5mm or finer hypodermic needles, and 40mm+ acupuncture needles. Be careful with it, 007. If using a hypodermic needle, carefully crush the plastic connector on it with pliers or a vise and rotate the needle to remove it from the crushed remains. Remove all the fragments from the needle shaft (scraping with the back of a scalpel blade works well) so that its base will have good electrical contact when attached to the Probe Arm.
Coarse tips are recommended while familiarity is developed with the μRepRap system. Instructions on how to fabricate a fine, electrochemically etched point can be found here.
Insert Captive Nut
Probe Beam captive nut insertion
Insert an M3 nut into the captive nut slot in the Probe Beam with the nut's sides parallel to the sides of the slot. Drive smartly home with a small screwdriver. Test by inserting a screw into the round hole and temporarily engaging it with the nut.
Z Touch Wire
This simplifies the removal of the Probe Assembly when changing probes. Strip 12mm or so of the end a 50mm wire with a Dupont connector or similar on it (here an insulated 0.1" pin is used). Put a mating connector on the lead you will use for the return wire on your CNC's Z Touch input. Put the bare end of the Z Touch Wire half way through an M3 spring washer, fold the bare wire, and twist firmly together to secure the washer. Try to secure it in the middle of the unsplit part.
Removing centre nut from Axis Driver
Carefully remove the central nut from the driving end of the Axis Driver. It would interfere with Probe Assembly attachment.
Assembly
Inserting Probe Beam into Probe Shuttle along with two washers
Hold two M3 7mm x 0.6mm washers on the end of the Probe Beam as shown - up to 10mm diameter is fine. They should rest in partially circular depressions, one each side the Beam. Slide this into the Beam Shuttle (pinching the Shuttle slightly will help hold them in place) using the depressions to help guide the washers into place. Ensure you have the Shuttle in the correct orientation as per image above.
Joining Probe Beam and Probe Shuttle, with additional washers. Note that the nut is on the right-hand side
Slide one M3 washer onto a 16mm M3 screw. Insert a convenient pointed object through the Beam and Shuttle, lining up the washer holes. Put the screw through the washers. Note: There is a slotted protrusion near the round hole on the end of the Probe Shuttle. This is a wire via. Make sure that you insert the screw from the other side, ending up with the nut on the same side as the wire via.
Onto the end of the screw, add another M3 washer, an M3 spring washer, and an M3 nut. Slide the Shuttle back and forth on the Beam a few times to clear any print imperfections before finger-tightening the nut. The Shuttle should still be able to slide on the Beam if moderate force is used. Adjust nut torque accordingly.
Securing Z Touch Wire in Probe Shuttle
Temporarily secure the Z Touch Wire washer in the circular depression in the Probe Shuttle with an M3 screw, M3 washer and M3 nut. This will prevent glue getting on the spring washer. Fix the Z Touch Wire into the wire via on the Probe Shuttle with a flexible adhesive that you can remove if/when the Z Touch Wire breaks. Remove temporary fasteners.
Aligned end of Axis Driver
By rotating the Axis Driver either electrically or by manually rotating the Flexure Coupling, align the driving end of the Axis Driver with the base of the driver's frame as shown in the image above. This is the driver's neutral position. This is necessary as the two Z Flexures are not interchangeable and it is otherwise possible to align them incorrectly.
Try-fitting a Z Flexure
Try-fit a Z Flexure to the Axis Driver using two 25mm M3 screws in the central two holes of the Z Flexure. Ensure that the forward plate on the flexure (with four holes in it) is resting flat on the top of the driven end of the Axis Driver. If it does not lay flat, try the other Z Flexure to see if you have the right one.
Also check the protrusion of the M3 screw into the frame. If it looks likely to interfere with the driver's flexure mechanism, remember to add sufficient M3 washers under the screw heads during assembly to prevent them from interfering with the flexure mechanism. In this case it was determined one M3 washer was required.
Secured Z Flexure
Put one M3 nut on each of the two 25mm screws, finger tight (this will require tweezers or a strip of duct tape). The inside of the frame has a captive nut cavity. Carefully tighten the screws, causing the nut to be drawn into the cavities. Loosen the screws.
The 25mm M3 screws and their washers can now be removed, and replaced with 20mm M3 screws if desired. These will not protrude into the flexure mechanism. Do not fully tighten them yet though.
With two 10mm M3 screws, loosely attach the outer two holes on the Z Flexure to the driving end of the Axis Driver.
Repeat the process on the other side of the Axis Driver with the second Z Flexure.
Tighten all screws, taking care not to stress the flexures.
Probe Tip
Probe Tip in a Probe Jig
The process for fabricating a Probe an the use of the Probe Jig are found here.
Completed Probe Z Axis with Probe Assembly fitted
The Probe Z Axis Assembly is now complete.
Testing
Secure a Probe Tip in the Probe Assembly with washer and M3 nut. Secure the Probe Assembly to the central hole in the driven end of the Axis Driver using a 12mm M3 screw fitted with an M3 spring washer and an M3 flat washer. The intention is that this will allow limited rotation of the Probe Assembly without accidentally unscrewing it.
Check conductivity between the Z Touch probe wire and the Probe Tip. You may wisely choose to remove the Probe Assembly again at this point to avoid stabbing yourself in the next steps.
Integration
The Probe Z Axis Assembly is now ready to be integrated with the support structure. Note that in use the Z Axis is homed towards the maximum limit of motion, not towards zero. This prevents the Probe from being driven into the XY Table when homing, and causes positive Z values to be above the XY Table. Arrange your CNC or 3D printer software accordingly.