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Help: How To Chemical polish stainless steel tube ID

Hi folks,

I have a question I am hoping the users of this group can help me answer. I post to rec.guns as well because there are probably some common overlaps, but my apology if it seems off-topic.

I would like to chemically polish the inside diameter of a 0.030" ID stainless steel tube, about 2-3" long. This piece of tubing will be used to make a length of microwave "waveguide", and so I would like to have a very smooth, clean surface with a well known initial ID.

Electro-polishing is out of the question. We've tried it with poor results because of the very small wire diameter and more complicated mechanics required. I've also tried mechanical polishing with dental floss and abrasive, and besides being tedious it didn't work so well either.

Others have suggested in the past that I purchase pre-polished hypodermic grade tubing to begin with, but it is difficult to obtain small quantities of steel tubing with a 0.030" ID to begin with. I am lucky to have what I have.

What I would like to do is find an appropriate solution or solutions that can be pumped through the tube using a tubing pump. I need an actual chemical *polish* that will remove surface irregularities in addition to scale, rust and debris inside the tube.

I know there are some companies that do this, but generally they don't want small quantities of stuff, and it would be very much more convenient to do this in-house, as we have a reasonably equipped chem lab. Furthermore, lots of commerical places use proprietary chemicals, so it will be impossible to know exactly what they did in the future if I need to repeat the process.

So, I am hoping someone can suggest some chemistries to chemically (electrolessly) polish steel that I can try in-house, OR recommend a shop that will do small jobs with a relatively sane turnaround time.

Thanks in advance for any suggestions.

Dan Koller ( snipped-for-privacy@earthlink.net)

Reply to
danube
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You would probably be better off starting with a solid piece of 303 stainless rod of the appropriate OD and drilling it to slightly under the final dimension and then reaming to the required ID.

cheers T.Alan

Reply to
T.Alan Kraus

If you only want one, you might try chatting up your doctor: they probably have some torturous device with such a tube in it. You might be able to get a replacement part from a surgical supply place.

Reply to
David R Brooks

What's wrong with mechanical polishing with a series of brass laps charged with grease and abrasive dust?

This lap may be slightly too large, but it can probably be reduced, or another brand found.

Joe Gwinn

Reply to
Joseph Gwinn

For reference, you can buy hypodermic SS tubing in small quantities at

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Part# HTX-18H has an 0.030" ID

To polish the bore, check with

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Don't know if the price is reasonable, but they can internally polish just about anything.

Randy

Reply to
Randal O'Brian

Stainless is difficult to polish; there are surface oxides that are very hard, and when it's done, you might want to worry about chemically passivating the surface. It also has magnetic properties and low conductivity so isn't a perfect waveguide candidate; have you considered silver instead? Or even copper?

Torque on a hone would be excessive, but if you thread a wire through the middle and reciprocate (like sliding a bead on a wire) it could work. I'd bend the hone wire into a spiral, so the slight spiral 'kink' will apply force on the inner surface, and just paint metal polish on the wire while sliding the tube back and forth. If you want 2", polish a 4" length, and cut both ends away.

As others have noted, 18 G tubing can be had from Small Parts.

If you are very careful, it might be possible to run a silver-plated wire down the bore and apply current to evaporate the silver (and that will flash the interior with a nice conductor).

Reply to
whit3rd

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