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How to polish a small diameter punch to high degree surface finished to Ra 0.05

In my previous post on how to pierce small holes on a thin strip, I mentioned about polishing a 0.5mm diameter punch. Since these punches are very tiny and very hard to polish to such a high degree of surface finished, I felt a need for me to elaborate on how I did it.

polishFirst of all, you have to machine the small diameter punch carefully to ensure the surface is finished as smooth as possible. One should also try to maintain a good roundness and prevent dig marks remain on the surface. Any digging mark remaining on the surface are not removable away during the polishing process. Dent marks will be left on the part and would eventually creates problems during future usage.

In addition, you should also consider adding some allowances on the diameter to allow material removal for the polishing process. In this case, 0.03mm diameter allowance is sufficient for small parts. In this case, the diameter of the punch is 0.52 mm. Adding 0.03 mm will give it a total of 0.55mm in diameter.

I am using a 0.005mm grade Diamond polishing compound, an ultra-sonic polisher and a mini lathe machine to do the job.

polish small punchpolisher

1. Hold the tiny punch on the machine chuck. Adjust speed to 500 rpm.
2. Set the polisher to medium speed.
3. Apply diamond compound to the wooden polisher tip.
4. Move the polisher lip front and back along the punch diameter. Apply gentle force to the polisher, do not push too hard, or the punch may just give way.
5. Clean up the area and make measurement by a micrometre, make sure diameter is within the specification.

punching small hole
Polish small punch on the lathe machine with diamond compound and ultra-sonic polisher

 

 

 

 

To polish down the diameter and to obtain a good & smooth surface finished, it took only estimated 5 minus for one punch.

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