ER11A Zero Probe

prusaprinters

A simple to assemble version of the ER11A Z axis probe that screws onto an ER11A spindle. It has indicator LEDs and can be used to measure and compensate for a bed that isn't flat when engraving, for example a PCB or a curved surface. I use it for my Stepcraft CNC. This design uses "Pogo" type pins to retain the sense tip and make contact with the stationary part of the switch. The front guide section just screws on and can be opened for cleaning if anything doesn't work.It is very sensitive and repeatable. I measured the spring force to activate the switch to be about 55g. Repeatability is 4um (0.00015") on a sample of 11 measurements taken at the same spot but that's really down to the repeatability of my Z axis, readings were just changing between 2 values.Pogo pins I used are 16mm long, 1mm diameter and the end is rounded so it can slide on the washer. They were called P75-J1Print SettingsPrinter Brand:CrealityPrinter: Ender 3Rafts:NoSupports: NoResolution:0.12Infill: 35%Filament: Amz PLA Purple Notes: Fine threads, use high resolution.Print with 4 wallsIn Cura, set "Experimental", "Splicing Tolerance" set toExclusive or threads will be too tight to easily assemble.Use a brim.Total print time is about 2 hrsThe guide section is conical and on my print the one side had a rougher surface because the cooloing is reduced in that direction, another material may print better than PLA which needs lots of cooling. You can try reducing the temperature otherwise just sand it afterwards and add some clear nail varnish.Post-PrintingAssemblyRead the Z axis probe thing for some hints and background. Pictures below. Make sure all surfaces are clean to ensure good electrical contact.ScrewAdjust the screw used for the probe tip so that it slides smoothly in the guide section.Remove the drive slot or cross from the screw, the Pogo pin presses down on this area and needs a good surface to make proper electrical contactSleeveClean out the single (layer printed to help the step inside the ER11A threaded nut section).It may help to solder a wire onto the back of the side pin but to enable the side spring pin to fit in the hole the solder will have to be a butt joint. If you're careful you can solder the red LED directly onto the pin when it is installed.Insert the 2 Pogo pins so that only the thinner sprung part is showing. The pin it may be loose in the hole so use epoxy where their back ends protrude into the wiring cavity to fix them in place. You can also apply some solder to fatten the pin a bit.GuideUse a small round file to smooth the inside of the guide, printing can leave bumps.For the stationary contact I used a brass washer, 11mm OD and the ID has to be larger than the screw shank that becomes the probe tip. Clean both surfaces and make sure they're flat. Glue it in the recess with epoxy or CA glue using the probe to hold it while it sets. Don't glue the screw, it needs to move. Make sure there is no glue on the top surface to interfere with electrical contact.Screw the guide into the sleeve and check that it makes contact by using a multimeter on the Pogo pins.LEDsYour probe input may not be able to use the probe if you add the LEDs and they don't really add any functionality. If you don't know that your controller hardware will work with them, don't add them. My CNC works fine with the autoleveller plugin but not if I use the probe as zero probe.Wire the LEDs (if you're using them) and the cable to the CNC probe input. Before you close everything up check polarity and that the LEDs work as expected. If you only use one LED, use the blue or white (or 2 reds etc) in parallel with the switch that indicate the swith is open. It is much harder to see the red led flash OFF than the white LED flash ON.When you've done the wiring and secured the wires so they don't pull out, add the cover to hide the wiring and keep dirt out (the spindle can be quite dusty). This is a loose fit and will need some glue to keep it in place.Pictures:Washer glued into recess with small amount of CA or epoxy. Use probe to position it.Insert pins, bottom viewEpoxy in the bottom to make sure everything stays putReady for wiring, check electrical continuitySchematicWire up the diodesAdd a cover to hide and protect the wiringAssembled. Front can still be screwed off.    Category: Machine Tools