Mirror Polishing

Posted by Joe Amick on February 15, 2023

What do you need to know when it comes to automating mirror polishing?

Mirror polishing is one of the tasks that is first on the list for automation. It is a hyper dirty job with a fair amount of personal safety issues. Getting someone to do hand polishing is not easy and getting them to do it long term is near impossible so turn over is insane normally. This makes it a prime candidate for automation. 

Like when talking about painting, Prep is vital. If you do not remove scratches, machining lines, orange peel or any of the other defects polishing is going to make it obvious. To get that clear mirror polish you have to go through the preparation phase. This will vary to a major degree depending on your parts. Cast vs forged or stainless vs Brass each aspect makes a difference. Brass is a softer material and tends to take to sanding well but there are limits. If you get it to hot the porosity can show  itself and you will enjoy a sea of tiny pin holes. Use the wrong tool and you can get a wave effect to the surface and good luck getting it flat again. This is a situation where an ounce of prevention is worth ten pounds of cure.


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You can see the reflection of the soda can in the polished part above. Its brass and was sanded and polished by automation to the finish shown. This part was fully processed from raw to mirror in under 3 min. So you can have quality and speed but it starts with the correct process and tools. Experience is a great teacher and it can put you ahead right up front.


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Forged aluminum can have a lot of the same pit falls as brass. You can get the same amazing finish that starts to look like a tinted chrome in aluminum. But again it is the prep and how you handle the parts. A super clear polished finish with no waves in the surface is not easy but is 100% possible. Respect the limitations of the material and choose your process carefully.


Do not skip the prep work and separate your processes. Don't try to sand and polish in the same place. You did all the right prep work but you end up with random scratches in the polished finish. Its the debris from the sanding contaminating your parts or buffing operations. When you sand that dust will be in the holes, joints and voids of the part. When you spin up a buff any where near the part the wind created will stir up that hidden dust fouling the polishing.  Separate the prep from the polishing and you will avoid much of that heartache.



Another aspect to keep in mind is quality. As odd as it may sound don't go too far. In the picture above you are looking at a replacement grill for a commercial truck. The factory has two categories of parts with the replacements being a bit lower in quality of finish. They process them faster than the parts for the assembly line to try and control the cost. The original tests had the quality too high and we had to speed things up to dial it back some. Be careful where you set the bar as you have to live in that space going forward. Having the ability to make a jewelry quality finish is great, but that higher level of finish might need to be on a higher level of product or come at a premium.

Knowing your material and where things tend to go sideways is valuable information. Share that information and more. Your experience with the material and parts is invaluable and can not be over stated. Go ahead and look into automating polishing applications as you can get that super fine finish.

AM Machinery Sales

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