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DIY electrolytic polisher

Bobo[PL]  17 10917 Cool? (+30)
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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.



About Author
Bobo[PL] wrote 150 posts with rating 352 , helped 2 times. Live in city Zabrze. Been with us since 2006 year.

Comments

adversus 26 May 2021 09:23

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? [Read more]

mycodename47 26 May 2021 14:31

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. [Read more]

Bobo[PL] 26 May 2021 18:08

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.... [Read more]

adversus 26 May 2021 20:02

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... [Read more]

Bobo[PL] 27 May 2021 16:01

forgive :) Printed two halves of a cylinder with a cylindrical recess inside for magnets. Both halves stuck together with poxipol. [Read more]

adversus 27 May 2021 16:22

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... [Read more]

Bobo[PL] 27 May 2021 21:25

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,... [Read more]

indianka 29 May 2021 12:26

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... [Read more]

Bobo[PL] 29 May 2021 22:19

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... [Read more]

janek_wro 30 May 2021 00:33

Why such combinations? Ready-made laboratory Teflon stirrers are available. They don't cost a fortune, chemically resistant Teflon. https://obrazki.elektroda.pl/3051506100_1622327451_thumb.jpg [Read more]

ArturAVS 07 Jun 2021 15:26

Cool equipment, tell what metals / alloys this electrolyte is suitable for, because on the manufacturer's website there is a note: And I would have a few details to polish, where the main alloy... [Read more]

Bobo[PL] 07 Jun 2021 18:28

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... [Read more]

jacki99 22 Mar 2022 09:47

The current is shown on the display, what is the voltage? [Read more]

Bobo[PL] 22 Mar 2022 17:30

For chromocobalt around 15 ... 16V, so I took 15.8V. [Read more]

jacki99 23 Mar 2022 13:38

Thanks for the answer, and what current should not be exceeded? [Read more]

Bobo[PL] 23 Mar 2022 18:23

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. [Read more]

janek_wro 23 Mar 2022 21:46

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 ;) [Read more]

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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