CF5135B-Z/CF5135C-Z Tachometer Display Box W/ Battery for Milling Machines/Lathes (+Mounting Options for OPTImill BF16 Vario Mill)

This tutorial will provide instructions on how to build a small box fitting a Tachometer Display with internal battery supply and an attached Hall sensor for inductively measuring Rotation speed as an upgrade to small-scale lathes and/or milling machines.

The box is sized to stand on a switch box and held down by two magnets fitted into its base to avoid being shaken loose by machine vibration.

1. One LED Digital RPM Meter Tachometer Speedometer & NPN Reverb Proximity Switch Kit (or equialent) consisting of:
2. A CF5135?-Z Tachometer Display box w/ cables
3. -A NJK-5002C Series Hall Sensor w/ nuts
4. -A (~6Ø x 1.5 mm <=> 1/4"Ø x 1/16") Neodymium Magnet
5. A KCD Series (15x21 mm) Power Rocker Switch
6. One 9V Battery Contact with Leads
7. 9V Block Battery
8. Two (18 x 3 mm <=> 3/4"Ø x 1/8") Neodymium Magnets w/ Glue pads
9. Approx. 10 cm (4 in.) of 1/2" Double Sided, Self-Gripping Velcro Strips
10. A Heat Shrink Tubing Kit
11. Tools:
12. Soldering iron w/ solder
13. Hot air gun
14. Stanley knife or X-Acto Blade
15. Access to a 3D-printer (recommended: Prusa MK4S)

The Power Rocker Switch and 9V Battery Contact should be available in every moderately well-stocked electronics store.

This type of switch is also one of the most commonly used ones in power supplies, so should you happen to have recently scrapped one, you could take it from there and save yourself the effort of having to solder wires onto the switch. Note that these recycled switches might have more pins than necessary for this Project (e.g. double-throw and/or ON-OFF-ON switches).

In this case, you will want to pull up the respective wiring datasheets on which contacts to solder the power leads and display the bus cable to. You may cut off the unneeded contacts or use them if you ever want to upgrade this device.

The large Neodymium disk magnets and 9V Block Battery were bought at a local hardware store.

The kit was purchased from a chinese Ebay shop. Note that there are many similar kits available which might have different display sizes, something we will come back to during the next step.

Check the label on the backside of your display. Depending on which version of Display you have bought, you will want to print different front covers for the box.

The "larger" cover is sized to fit a 72x39 mm display, corresponding to the CF5135C-Z Display variant, which is the one I've been using. The "standard" cover is sized to fit a 68x33 mm display, corresponding to the CF5135B-Z variant. I recommend measuring out the dimensions of the display anyway to make sure you won't misprint.

Next, select how you want to mount the Hall sensor.

I have devised two mounting options for this. You may either:

1. Replace the Cap cover (Part No. 219) with a 3d-printed Cap cover with an Opening for it to be glued into
2. Use the Clamping lever (Part No. 236) to attach a 3d-printed bracket to attach it onto

The former Option will likely be the more practical, as it cannot get in the way of your tools and will be protected from dust and debris.

To get the project files, visit the Printables project page here!

If you have a MK4S Prusa Printer, you can open up the Project files in PrusaSlicer, drop in the mounting Option of your choice and get right to printing. Or print the box first and the mounts later.

Should you not have a Prusa printer, you will need to recreate the Printer project in another slicer program of your choice using the original .stl files supplied there.

The original box was printed using the following Settings:

1. Filament: PLA
2. Nozzle: 0.6 mm High Flow Prusa MK4S
3. Layer Height: 0.4 mm (STRUCTURAL)
4. Infill: 100% rectilinear
5. Perimeters: 6
6. Supports: Paint-on Supports on box part and the Replacement cap cover part.

Do not forget to add supports! Especially the Replacement cap cover cannot be printed without them!

Your resulting slice should look like the supplied images.

Note that the Rocker switch does not yet fit into its cutout. Carefully clip away at the corners of the switch until it fits, testing every so often as to make sure that you have not clipped away too much as the fit will not be firm anymore. If you never intend to remove the switch again, then disregard this and just glue it into the cover cutout.

Put it in your preferred direction, this will not impede it from operating properly. Then slide appropriately sized shrink tubing over the battery contact leads and Power switch wires.

Now solder the Power switch, the 9V contacts and the power cables of the display bus together as shown. Pull the shrink tubing back over the soldered area and shrink it down by applying heat onto it from all sides.

Pull the dust covers off the Magnet's glue pads and glue them into the rounded recessions in the floor of the box. Note that the recessions have been designed so that the magnets may be pryed out of the plastic by inserting a knife below it though the opening beside it and applying leverage.

Press the front cover firmly into the front side of the box, the side of the switch being closer to the magnets than the screen. Note: The front side is the one with the hook shaped cable retainers pointing away from them. Bend the cables sideways until each one of the switch cables and the bus cables have been secured in the cable retainers.

This should look similar to the image. Keeping the cables fixed like this will make pressing in the rear cover far less tedious.

Clip the contacts onto the 9V Block battery and put into the fixture. Pull the Double Sided, Self-Gripping Velcro Strips through the Slots in the rear cover and around the battery and strap it in. Press the rear cover into the rear side of the box, battery-side facing up as to avoid getting in the way of various wires.

Take all remaining bus wires and pull them through the round hole in the front cover. Take the sensor and slide a large shrink tube over the multi-wire cable, smaller pieces of shrink tube on each strand, then take the insulation off the single strands.

Now all there is left to do is to solder each of these wires to their corresponding Colors, apply the smaller shrink tubes, then shift the larger shrink tube above them and apply it as well to bunch the cables up nicely.

The box should now be all done. It should now look as below. You can now place it onto your device switch box.

1. Using the Replacement Cap Cover Mount:

Align the front of the sensor with the inside Surface of the RCCM. Leave of of the nuts on the sensor in case you ever need to force the sensor out of the mount. Glue it into the RCCM like so. Trim any excess glue that the sensor may have pushed into the center cavity of the sensor mount. Take off the original Cap Cover and plug in the replacement.

Attach the small Neodymium Magnet to the Tool bar with two layers of transparent adhesive tape matching the height of the sensor.

1. Using the Clamping Lever Bracket:

Screw off the Clamping Lever and screw a M6 Nut onto it, followed by the bracket. Put it back on and use the Nut to press the bracket firmly against the Surface of the Milling head. The ramp-like feature on the bracket will align it with the lower Edge of the Milling head and keep it from swinging out in any direction. Attach the small Neodymium Magnet to the Tool holder with two layers of transparent adhesive tape. Screw the sensor onto the bracket and adjust distance the tool head with the nuts until a good detection distance is reached.

All you need to do now is test if everything works and you are good to go!

Safe to say that I was in no way fan of using an inductive sensor for measuring the RPM of a mill like this due to the real possibility of the glue holding the magnet in place being degraded by excess heat and the strong vibration it would ultimately Encounter during operation. In this case the magnet would likely be shattered from being tossed against the wall, and the sensors, the machine or the operator may suffer large damage.

To preemtively remediate this issue I have attempted replacing the original sensor with an E18-B03P1 IR Optical sensor in an reflective mark setup.

I intended on marking the tool bar with a White marker pen so that the sensor would count every pass of the White line just like the Hall sensor would count every pass of the magnet, but could not find any marker that would change IR reflectivity enough for the sensor to detect. The Markers I tried out were Edding-brand markers 750, 8055 and 8200. I should have tried an IR marker as well, but was unable to find any in local stores.

Utilizing a notched disk like those used in optical encoders would likely have worked better, but due to the difficulties of attaching a notched disk onto the tool bar without getting in the way of either the tool itself or the tool changing Opening, ultimately gave up on this side Project.

Still not satisfied with the precarious mounting Situation, I attempted to instead replace the small Neodymium Magnet with flexible Adhesive Magnetic Tapes instead. These tapes have increased adhesion and would smoothly conform to the surface of the tool bar, reducing the risk of the magnet scratching up the sensor if it ever came loose. An additional benefit is that by attaching a long strip of tape along the top of the bar, the Tachometer would still return accurate values during boring operations, while the solid magnet would be moved to far away from the sensor to work.

I purchased 10 mm wide Sticky Ferrite Magnetic Tape (t=1.5 mm) and a 19 mm wide Adhesive Magnetic Tape (t=0.35 mm) from local magnet retailer store www.supermagnete.at to run some Tests with. To my disappointment, the Hall sensor did not even pick up any flux from the thinner tape.

The thick ferrite tape was picked up by the sensor, but so weakly it could never be used practically as the clearance between the tape was less than a milimeter (<1/32"). Additionally, the tape was magnetized along its length, so the sensor would Count every pass of the tape as three or four passes instead of one, making readout of the Tachometer confusing.

I hope I will soon be able to repeat testing with a strip of stronger Neodymium Magnet Tape instead. I am however worried that the Magnetism of the Neodymium will significantly degrade if exposed to the high Levels of heat the Tool bar will encounter during Operation.

The machine exterior may very well reach 40 C° or more after a while of running and I can only guess the inside temperatures. Long-term testing will be required to evaluate the viability of using this type of tape.

(Coming soon, hopefully!)