Superfinishing Stainless Steel

A. Hi Kim. You can buy #8/8K finished stainless steel if you wish. And there are dozens of youtube videos showing you how to do it yourself if you prefer, or where to buy machines if you want to do it in production.

But I think the thing that most people who are new to this don't realize is that it cannot be done in a single step, or even two or three steps. It takes four steps at best, and probably more.

Simply, you need to do a coarse grind until there are no scratches deeper or wider than the size of your grit; then you do it again with a finer grit and stop only when there are no scratches deeper or wider than that finer grit. Then you move to a finer grit and repeat, and a still finer grit and repeat. A trick that some people use is to do the coarse grind in one direction, the next step in the perpendicular direction, the third step back to the original direction, etc. -- the reason for this is that if at any point you see a scratch running perpendicular to the direction you're polishing, that step is not yet finished and you must not move on.

Luck & Regards,

Hi again. Sorry I am not familiar with that but we will leave your question on line and hope that a reader can help you,

Luck & Regards,

A. Maybe somebody can prove me wrong, but I really don't think it's possible to chemically etch your way to a smoother surface, i.e., with acid. Electropolishing, or acid with electric current, sure, because in that case it's the current doing the work and the acid is only there to carry the current. But acid on its own is going to remove material from the surface randomly, not selectively from the microscopic "peaks" as you would need to increase the smoothness. Sometimes acids are used as "brighteners" for metals, but in those cases you are not making a smooth, reflective surface, but rather an etched surface that scatters light more in the direction of the viewer. Sometimes etching makes the surface darker though, light is scattered more away from the viewer.

A. One very common reason for getting a scratch at late stages is that your cloth is contaminated. This is caused by a failure of cleanliness between stages and/or a failure of cleanliness in storage of the buffers/polishing cloths.

Between each stage of finishing, you must clean the surface of the sample well. Pay particular attention to small holes and crevices which tend to retain particles. Your working area, workholders, etc. should also be clean. Your cloth used for final polishing must only be used for that 0.3 µm media and be stored in a clean manner. If it is contaminated, just throw it out and replace it.

If you transfer any grit from earlier stages, you will very easily scratch your sample. Patience and cleanliness is the key.

A. It sounds as if someone is trying to give you mis-information. Wet polishing is normally referred to as burnishing media. This can be either steel or porcelain or an equally hard fine particle material which does not breakdown during processing. Therefore, this media works primarily via lapping and weight. Any material removal is caused by fracturing or fatigue of the materials being worked. Whoever told you lead is involved is incorrect. Normal composition of porcelain media is around 71% silicon oxide, 22% aluminum oxide, 4% potassium oxide and 3% other materials. No lead! Basically porcelain is inert and behaves like a glass container meaning chemicals will not normally effect this media even in a concentrated liquid. Any fumes encountered would be from a liquid additive or chemical accelerator used to speed up processing. This maybe what you are referring too. This involves a whole lot more than can be explained here.

A. Centerless grind followed by polishing with diamond paste on balsa wood.

A. This is a very stringent requirement that will take some effort to meet. My first piece of advice is that it will take more than one process step to attain Ry < 0.4, as you have already discovered, so be prepared for that. Second, Type 303 SS will not polish well, regardless if it is by electropolishing or conventional finishing techniques, so you may want to eliminate that from consideration and stick to Type 304.

With such a low surface roughness specification I am assuming that the shaft also requires excellent straightness and concentricity, with low runout. If so, you will likely need centerless grinding to start with, unless this shaft is relatively short. Based on this assumption, I would look into one of the following processes to improve the as-ground surface:

1. electropolishing
2. roller burnishing
3. automatic shaft polishing (through-feed process, sometimes called superfinishing)
4. media tumbling, possibly multiple steps, and/or Isotropic Super Finishing

A. Before attempting to recommend something please tell us what is the shape or geometry of the parts and what do you mean by huge volumes. G. Marrufo-Monterrey-Mexico