Titanium Grinding vs. Tumbling

May 1, 2008

Harbor Freight bench shear

I’ve tried a few different methods over the the years to reduce my hands-on time in getting rid of those razor-sharp fresh-cut titanium edges. I started doing this with essentially no tools or money to buy any. I first bought tin snips, and then a small bench shear something like the one pictured.

Polishing MotorThe merciless edges on fresh cut titanium encouraged me to buy leather gloves. To remove those edges, I first used emery paper (wet/dry sand paper) to smooth them. But the tedium soon urged me to learn that a motor, a couple of taper spindles, and Cratex wheels (rubberized carbide) were much faster and spit few sparks. I put my grinder/polisher together from a salvaged ΒΌ horse motor and parts from a mail-order catalog (this was around 1980). Now there is website: www.RioGrande.com and you can get everything there. But grinding small parts ended up using up finger tips; both gloves and my own.

Harbor Freight Cheap Rock TumblerOn a whim, I tried out my childhood rock tumbler. I just cut up a bunch of pieces, and threw them in with some rocks, and let them go for a week, then three weeks. There was some rounding of the sharp edges, but not much nor fast. I then ordered abrasive ceramic media from RioGrande, and tried that in place of the rocks. After a couple of weeks, nice, smooth edges. The ceramic media lasts for many uses (I have yet to reorder). You can also get it cheaply from HarborFreight, here or at your local Harbor Freight shop. You can also try rock shops, craft stores, or online.

Lightweight vibratory cleaner/polisherBut, c’mon! Weeks? So (many years later) I went to eBay to find a vibratory polisher. I wasn’t ready to spend $500 on a name-brand one at RioGrande. So I found one specified to clean shotgun shell casings for about $60 delivered. It has a clear top, so I could watch the pieces and media do their thing. It reduced the time to about 4 days. I ran it with a dry load, with no water or agents. Amusingly, the dust that grinds off from the media is hydophobic! Water runs right off of it, like mercury on glass. I found that adding tap water at the end and vibrating for another hour suspended the dust in the water and didn’t darken the titanium too much. Anyway, I etch after I tumble.

But I never did manage to get a shine with this machine. I tried ceramic media and porcelain media, I used polishing compounds, ran it wet, ran it dry, and still my best was a matte finish. My worst was that the titanium turns almost black in water with porcelain.

Harbor Freight Vibratory PolisherSo I thought I’d try another type of vibrator. I got it from eBay, and then found that I could have driven across town to HarborFreight and gotten the exact same unit for about $25 less. I first tried running it wet with porcelain. Blackish titanium, eww. I etched the titanium clean, and then tried dry with ceramic media: Shine! Trumpets and doves and a beam of light from above. The gray ceramic media turned dark and shiny in 24 hours, as the titanium deburred and gleamed.

Had this not worked, I would have finally bought a professional (expensive) circulating fluid vibrator assembly (Raytech). But I’ll hold off on those.

Advertisements

Uneven results from dimmer switch anodizer

March 18, 2008

Here’s another question I frequently get:

I followed your instructions on building an anodizer and I would like to say that you have made a great job illustrating it. My anodizer is the dimmer and light bulb type it delivers a maximum of 160 Volts.I prepared a solution of TSP in distilled water placed the cathode (aluminum foil) and the Ti at the anode ran the circuit. The voltage keeps rising slowly and I get shades instead of definite colors (mostly violet, golden and pale blue). I can’t hold the voltage at a definite value. What should I do to get smooth colors? I tried adjusting the voltage first then immersing the piece but the voltage after immersing is lower than what I’ve just set it to. Please help me out here and thanks in advance.
David S.

First of all, the dimmer based voltage control is going to be a bit temperamental and unstable. But I used one myself for years before replacing the dimmer with a Variac.

Aluminum should work for a cathode, but should be lightly sanded to remove the invisible insulating oxide layer that spontaneously forms. I usually use titanium, but have been told by many that stainless steel works well.

When you have a large capacitor smoothing a the choppy dimmer voltage, the top end will be a bit mushy. The lower voltages are the worst for this effect. The tan, violet and blues are at the low end of the voltage scale.

Another issue in getting smooth colors is getting the voltage everywhere simultaneously. You should have the piece to be anodized immersed in the solution before completing the circuit to the leads. That is, you need a switch to turn the leads on and off, while the anodizer is running at the voltage you want.

Cleaning and chemically etching the metal before anodizing also helps assure a uniform color, and is generally considered necessary for getting the higher voltage colors.

The voltage measured on the leads or capacitor will drop when you start anodizing, and should rise back to your preset voltage in a minute or so. The time depends on how big a piece you are anodizing, how big your cathode is, and on the efficiency of your electrolyte.

Another possible problem might be the material of your attachment to the anode piece. Only titanium or niobium should touch the electrolyte at the positive side. Never use copper wire or regular (galvanized or tinned) alligator clips to immerse your piece. The current will just go though that, and little will be applied to your piece.