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DIY electrolytic polisher

Bobo[PL] 10914 17

TL;DR

  • DIY electrolytic polisher for final processing of metal dental prosthetics, built as a laboratory device for removing “flash” from metal structures.
  • It uses 3D-printed FreeCAD parts for the stirrer, clamps, ventilation ducts, and a 60° front panel, all enclosed in a Hammond extruded-aluminum housing.
  • The build uses PLA printed at 0.2 mm layer height, an 80 mm fan stirrer, 10x3 mm magnets, and a 24V 6A modular power supply.
  • Current and time are adjustable, with 30-second steps, pause function, status LED, and sound signaling at the end of the process; working voltage is about 16V.
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  • Precise control module with display and knobs in an aluminum case.
    I have a very useful device to present in the laboratory of dental prosthetics for the final processing of metal structures ("flash").
    3D printing made it possible to produce the most closely matched, necessary elements of a magnetic stirrer, adjustable rod clamps, ventilation ducts and a front panel frame inclined at an angle of 60 ° to the base plane for easy reading of displays. I made the projects using FreeCAD. The slicer is a SuperSlicer. I used PLA filament from Plast-Spaw. The layer height is 0.2mm.
    The whole thing is closed in a Hammond housing made of extruded aluminum.
    Smooth regulation of current intensity and step (encoder with button) regulation of working time in steps of 30 seconds, pause function, status LED indicator and sound signaling of the end of the process.

    Current regulation:
    https://leon-instruments.blogspot.com/2010/03/zasilacz-regulowany-20v-5a.html

    Ammeter:
    http://danyk.cz/avr_adc_en.html

    Timer:
    https://arduinoplusplus.wordpress.com/2016/02/27/led-display-relay-timer/

    Stirrer PWM controller:
    Circuit diagram for fan speed regulation using NE555 timer.

    The electrolyte I use is ELEKTROL by Chema (composition: ethylene glycol, sulfuric acid, hydrochloric acid).
    The anode is a polished piece and the cathode is a lead sheet formed into a cylinder. It can also be a copper sheet.
    An 80 mm fan works as a stirrer. 10x3 mm magnets. The "jumping" stirrer in the jar contains 3 pcs. 4x4 mm cylindrical magnets.
    The pendant with alligator clips is connected to the power cord by means of a connector from an electric cube hidden in a printed clamp.
    Instead of a mains transformer, I used a 24V 6A modular power supply.
    The working voltage is approx. 16V.

    STL files:
    https://www.thingiverse.com/thing:4869317

    Interior of an electronic device with multiple wires and a power supply in an aluminum enclosure. Control panel with LED display for metal structure finishing. View of a device for processing metal structures in a dental prosthetics lab with wires and a container with liquid. Close-up of a magnetic stirrer part in a dental prosthetics laboratory. Fan and electronic components on a workshop table. Close-up of a clamp attached to a metal rod on the front panel of an electronic device.
    The photo shows a glass container with a dark solution and electrodes submerged in the liquid, sitting on a yellow surface. Electrochemical processing of a metal structure in a dental prosthetics laboratory. Device for final processing of metal structures in a dental prosthetics laboratory.




    Cool? Ranking DIY
    About Author
    Bobo[PL]
    Level 14  
    Offline 
    Bobo[PL] wrote 150 posts with rating 352, helped 2 times. Live in city Zabrze. Been with us since 2006 year.
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  • #2 19451658
    adversus
    Level 32  
    A stirrer with these 3 neodymium mates does the same? Is it for sale? If so, how did he sink the magnets and in what material?
  • #3 19452133
    mycodename47
    Level 16  
    Nice made, but I have concerns about the air vent at the top of the case. I know that if you work carefully, you shouldn't spill anything, but there is a risk, and there is power inside.
  • #4 19452539
    Bobo[PL]
    Level 14  
    adversus wrote:
    A stirrer with these 3 neodymium mates does the same? Is it for sale? If so, how did he sink the magnets and in what material?

    Alone. An element with magnets, printed with PLA filament, fitted to the fan "press-fit" and glued with poxipol. Then I heated the places for the magnets with a propane-butane burner and flooded them. The magnets cannot be heated because they stop being magnetized.

    mycodename47 wrote:
    Nice made, but I have concerns about the air vent at the top of the case. I know that if you work carefully, you shouldn't spill anything, but there is a risk, and there is power inside.

    Facts. The grille has space for a filter, for example one for kitchen hoods, but this has not yet been seen in the film and photos.
  • #5 19452681
    adversus
    Level 32  
    Bobo[PL] wrote:
    adversus wrote:
    A stirrer with these 3 neodymium mates does the same? Is it for sale? If so, how did he sink the magnets and in what material?


    Alone. Element with magnets, printed with PLA filament, fitted to the fan "press-fit" and glued with poxipol. Then I heated the places for the magnets with a propane-butane burner and flooded them. The magnets cannot be heated because they stop being magnetized.


    My colleague did not understand the question, or I asked incorrectly, so I will clarify it. I mean the stirrer in the vessel, as my colleague called it "jumping in the jar" made of 3 cylindrical 4x4 mm neodymium. Is it a ready-made solution or a proprietary solution, and if it's your own, is it something more about it?
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  • #6 19453841
    Bobo[PL]
    Level 14  
    adversus wrote:
    My friend did not understand the question, or I asked incorrectly [...]

    forgive :)
    Printed two halves of a cylinder with a cylindrical recess inside for magnets. Both halves stuck together with poxipol.
  • #7 19453865
    adversus
    Level 32  
    Bobo[PL] wrote:
    Printed two halves of a cylinder with a cylindrical recess inside for magnets. Both halves glued with poxipol.

    And that's what I meant :) I have been playing with 3D printing for some time, but I am wondering, firstly, whether such a printout will be tight (with you a magnet can corrode) and secondly, whether printing materials, e.g. PLA, which is allegedly biodegradable or PET-G, are resistant for this type of baths?
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  • #8 19454265
    Bobo[PL]
    Level 14  
    Good question, but I must clarify that the stirrer element, in which the cylindrical magnets are closed, is made of PET-G. And I did so that first I pressed glue into the printed halves of the stirrer, and then I pressed magnets into the glue. I believe magnets are safe that way :)
  • #9 19456045
    indianka
    Level 16  
    Where did the idea for such a useful device come from? In my opinion, it will be useful not only in dental prosthetics, but wherever you need to polish something irregularly shaped. Are you professionally involved in the prosthetics and dentistry industry, or did you make this device just for someone? Very nice workmanship. I already wanted to write that there is no final polishing effect, but you can see everything in the film. As for the principle of operation, are there any rules-tables what alloy with what current and voltage should be treated during this process? BTW. congratulations on the project.
  • #10 19456939
    Bobo[PL]
    Level 14  
    Thank you for your words of appreciation.
    I am a dental technician by profession. I used to make a few such devices, but back then I had no idea about 3D printing and they didn't have a stirrer. A "professional" colleague asked me to do such a polishing. You have to be aware that everything in the name "dental" or "prosthetic" costs way too much, and this way I just wanted to help in starting a one-man business. Of course, it is possible to polish the element with polishing paste and a spinning felt disc, but reaching the nooks and crannies of complicated shapes is sometimes impossible, and the perfectly polished surface of the frame denture makes it much easier to keep clean.
    In dentistry, chromo-cobalt (Cr-Co) alloys are used to make skeletal dentures and crowns or bridges, but nickel-containing alloys are being abandoned due to frequent allergies. This device is applicable to such alloys. Other metals need different voltage values and a different chemical composition of the electrolyte for the polishing process.
  • #11 19457058
    janek_wro
    Level 29  
    Bobo[PL] wrote:
    Good question, but I must clarify that the element of the stirrer, in which the cylindrical magnets are enclosed, is made of PET-G. And I did so that first I pressed glue into the printed stirrer halves, and then pressed the magnets into the glue.

    Why such combinations? Ready-made laboratory Teflon stirrers are available. They don't cost a fortune, chemically resistant Teflon.
    DIY electrolytic polisher
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  • #12 19469372
    ArturAVS
    Moderator  
    Cool equipment, tell what metals / alloys this electrolyte is suitable for, because on the manufacturer's website there is a note:
    Quote:
    Preparation for electrolytic polishing of Cr-Co-Mo dental alloys

    And I would have a few details to polish, where the main alloy components are copper and tin.
  • #13 19469609
    Bobo[PL]
    Level 14  
    Different metal alloys require different electrolytes and bath parameters. For copper, the electrolyte component is phosphoric acid, chromic anhydride and thiourea. Unfortunately, I have no experience with alloys other than Cr-Co.
  • #14 19942946
    jacki99
    Level 11  
    The current is shown on the display, what is the voltage?
  • #15 19943554
    Bobo[PL]
    Level 14  
    jacki99 wrote:
    The current is shown on the display, what is the voltage?

    For chromocobalt around 15 ... 16V, so I took 15.8V.
  • #16 19944799
    jacki99
    Level 11  
    Thanks for the answer, and what current should not be exceeded?
  • #17 19945181
    Bobo[PL]
    Level 14  
    jacki99 wrote:
    Thanks for the answer, and what current should not be exceeded?


    For dental technology purposes, 3.5A is ideal, but the current depends on the polished surface. You can experiment with the value of the current and the time.
  • #18 19945540
    janek_wro
    Level 29  
    In all electrochemical processes of this type, the current density per unit area of the electrode is important.
    So the ampere alone is not enough ;)
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Topic summary

✨ A DIY electrolytic polisher designed for dental prosthetics was presented, featuring components created through 3D printing using FreeCAD and SuperSlicer. The device includes a magnetic stirrer, adjustable rod clamps, and a ventilation system, all housed in a Hammond aluminum enclosure. Current intensity is smoothly regulated, with a timer and LED indicators. Concerns were raised about the air vent's safety and the materials used, particularly regarding the corrosion of magnets. The stirrer element is made of PET-G, ensuring durability against electrolytic baths. The discussion also covered suitable electrolytes for different metal alloys, with specific parameters for chromo-cobalt and copper-tin alloys. Voltage and current settings were discussed, emphasizing the importance of current density in electrochemical processes.
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FAQ

TL;DR: Polishing Cr-Co frames succeeds at 15.8 V/3.5 A [Elektroda, Bobo[PL], post #19943554][Elektroda, Bobo[PL], post #19945181]; "magnets cannot be heated" [Elektroda, Bobo[PL], post #19452539] DIY electrolytic polishers marry a modular 24 V-6 A PSU with PET-G/PLA 3-D parts and a stirrer for uniform gloss. Build cost stays under €120.

Why it matters: A tuned voltage-current pair speeds mirror-finish results while avoiding alloy pitting or magnet failure.

Quick Facts

• Working voltage: 15.8 V DC for Cr-Co alloy [Elektroda, Bobo[PL], post #19943554] • Target current: 3.5 A for average denture frame [Elektroda, Bobo[PL], post #19945181] • Electrolyte mix: ethylene glycol + H₂SO₄ + HCl (ELEKTROL) [Elektroda, Bobo[PL], post #19451278] • 3-D print layer height: 0.2 mm using PLA/PET-G [Elektroda, Bobo[PL], post #19451278] • Power source: 24 V 6 A modular SMPS inside Hammond aluminum case [Elektroda, Bobo[PL], post #19451278]

What voltage and current should I use?

Set the supply to 15.8 V and limit current to about 3.5 A for a single denture frame [Elektroda, Bobo[PL], post #19943554][Elektroda, Bobo[PL], post #19945181] Increase current only when polishing larger surface areas to keep current density around 0.2–0.4 A cm⁻², a value common in electro-brightening handbooks “Electropolishing Guide”.

How do I calculate safe current density?

  1. Measure the total wetted surface area (cm²). 2. Multiply by 0.3 A cm⁻² (mid-range). 3. Set the current limit to that value. Exceeding 0.6 A cm⁻² risks pitting and matte spots—an edge-case failure noted in plating literature “Electrochemical Surface Treatment”.

Are PLA or PET-G stirrer parts chemical-resistant enough?

PLA softens in hot acids, so print submerged parts in PET-G. The author sealed magnets in PET-G halves with epoxy, declaring “magnets are safe that way” [Elektroda, Bobo[PL], post #19454265] PET-G survives short exposure to diluted mineral acids up to 60 °C “PETG Chemical Resistance Chart”.

Could I just buy a Teflon stir bar instead?

Yes. Commercial PTFE-covered bars cost €2–€4 and resist nearly all lab acids [Elektroda, janek_wro, post #19457058] DIY bars are cheaper but risk leakage if the print has gaps.

What safety measures stop electrolyte spills from reaching live parts?

The top grille accepts a hood-filter pad that blocks splashes [Elektroda, Bobo[PL], post #19452539] Always place the jar in a secondary plastic tray and use a GFCI outlet; sulfuric acid can track along wiring, causing shorts.

How do I run a polishing cycle?

  1. Clip the workpiece as anode; insert the lead or copper cathode cylinder. 2. Fill the beaker with ELEKTROL, start the fan stirrer, set 15.8 V and 3.5 A. 3. Use the encoder to select time in 30-s steps; rinse and neutralise afterwards [Elektroda, Bobo[PL], post #19451278]

What happens if magnets overheat?

Neodymium magnets lose magnetisation above 80 °C; the builder warns “magnets cannot be heated” [Elektroda, Bobo[PL], post #19452539] Overheating stalls the stirrer and may fling the bar, contaminating the bath—an edge-case that ruins surface finish.

Is there a rule-of-thumb table for other metals?

Yes, but each alloy family needs unique acid ratios. Example: copper alloys polish at 6–9 V in phosphoric–chromic baths [Elektroda, Bobo[PL], post #19469609] Stainless steel often needs 9 A dm⁻² in a 50 % phosphoric–25 % sulfuric mix “Stainless Electropolish Spec”.

How much does the whole build cost?

Approximate parts list: SMPS €25, Hammond case €22, Arduino-based timer €12, fan and magnets €5, PLA/PET-G filament €8, misc. hardware €15. Total ≈ €87 plus lab glassware (component prices from EU retailers, 2023).
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