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Microfinish comparator finishes, visual roughness guide

[editor appended this entry to this thread which already addresses it in lieu of spawning a duplicative thread]
Q. Hello everyone,

I am a graduate student in computer graphics, and we're doing a study to comparing real surface roughnesses to the models we use in graphics.

I need to procure 5-7 sample of varying roughness using the same process, ranging from about the roughness of a MacBook to a complete mirror finish. The problem is that I do not know anything about real surface finishes and I am looking for advice on how to get the finishes we need.

My first thought is to get a smooth surface through lapping and/or polishing, and then anodizing it to different roughnesses. Is this something that could work, and is there a finishing shop that can get this done for us in a cost effective way?


Matthew Avolio
- Waterloo, Ontario
April 24, 2024
    privately respond to this RFQ   ^
Ed. note: As always, gentle readers: technical replies in public and commercial replies in private please (huh? why?)

Surface Finish Comparators
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A. Hi Matthew,
We've posted your contact info in case a shop wishes to help you, but actual samples of finishes created by different technologies are readily available -- they are called "comparators" or "surface finish comparators".

The need for such is extensive enough that they are mass produced -- a master copy is produced using the actual tool in question (lathe, casting machine, grinder, etc.) then multiple copies are made by electroplating/electroforming copies from the master.
Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey

RFQ: Thanks for the response.

I stumbled upon these earlier, but unfortunately every comparator I've found is too small for our purposes. It seems that these are made to be pocketable, with every sample only being a few cm^2.

I should have specified this earlier, but we need each sample to be a plate roughly 5x5 inches.

Matthew Avolio [returning]
- Waterloo, Ontario
April 25, 2024
    privately respond to this RFQ   ^
Ed. note: As always, gentle readers: technical replies in public and commercial replies in private please (huh? why?)

⇩ Related postings, oldest first ⇩

Q. We as a company are getting into exterior grade high end automotive parts. I am looking for scale that will tell me what degree of polish I need in order to achieve a mirror finish all the way to say 50 grit finish.

I know there are polish scales but I just need to find them.


David McCulloch
- Troy, Michigan, USA

A. Just type "surface finish comparators" in your preferred conventional search engine. It will give you dozens of alternatives from sophisticated digital equipment to commercial inexpensive pocket size visual and tactile plates.

Guillermo Marrufo
Monterrey, NL, Mexico

Q. I work for an airline and we just got some new microfinish comparators. When there is small damage to our planes we usually 'blend' the damage to a smooth contour using a rotary disc. Most of the paperwork we use to authorize these types of repairs calls for a surface finish of 125 RHR or better. On the comparators we have there are 6 different categories of finishes; lapped, ground, blanchard, shape-turned, mille, and profiled. My question is which one of these finishes corresponds to the situation I have where material was blended away using a rotary disc.

Chris Riggs
airline - Atlanta, Georgia

simultaneous replies
Profilometer: Mahr Pocket-Surf
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A. Milling as well as turning and profiling are performed by single point cutting tools. Lapping uses loose abrasive particles. Grinding, although performed with fixed abrasive particles similar to a disc, leaves a straight pattern. So, I would say blanchard best approaches a rotary disc finish. Depth of cut or roughness value is a physical measurement not related to the above. It would be useful for you to make some coupons and smooth 'em as you would normally do. Then have them measured with a profilometer for your reference. Visual comparators are just a guide but can sometimes be misleading.

Guillermo Marrufo
Monterrey, NL, Mexico

A. The method by which the surface was finished is immaterial. 125 Ra is a measure of the roughness, regardless of the method. For example, you could have a coarse grind finish at 125 Ra, or a very fine grind at 8 Ra. Use the comparator to estimate roughness without reference to the method or pattern.

jeffrey holmes
Jeffrey Holmes, CEF
Spartanburg, South Carolina

Multiple threads merged: please forgive chronology errors :-)

Q. I am looking for a visual comparison chart for Ra surface finish values.

Gary Merkel
tool & die - Richfield, Wisconsin

A. You will find comparator metallic plates. They can be either manufactured to your specs or according to vendor's standards in stainless steel, vacuum or galvanoformed.

Guillermo Marrufo
Monterrey, NL, Mexico

on eBay or


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A. A visual "Ra" chart is going to be terribly subjective. Light reflection can be seriously different between straight line sanding and single point machining, grinding and dual action sanding, and blanchard grinding.

James Watts
- Navarre, Florida

A. McMaster-Carr will sell you a comparator sample plate, or any good tool supply company.

jeffrey holmes
Jeffrey Holmes, CEF
Spartanburg, South Carolina

A. I agree with James from Florida. Your best bet is to just break down and buy either a surface gauge or profilometer. Way too many variables.

Brandt Hinton
- Elk River, Minnesota

Multiple threads merged: please forgive chronology errors :-)

Q. I am a Mechanical Engineer. I have the task of specifying surface finishes for mating parts and thermal contact. A colleague of mine, who has left the company, had a metal plate with various surface finishes. Each example surface finish was labeled appropriately as to the kind of finish it was. It was very handy because you could actually rub your finger across the particular finish or roughness and get a visual of what it was and felt like. Does anybody know where I could get one of these things? It would also help the young guys no what to put on their drawings without it costing a fortune.

Troy Allen Garcia
- Madison, Alabama

A. I think what you're looking for, Troy, is called a "comparator" [on eBay or Amazon (adv.)] .

Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey

Q. I was wondering what the numbers on the, S-22 Microfinishes comparator, mean? Such as 2L, 4L, 8L, 8G, 16G, 16BL, etc.
If someone could let me know?

- chino, California U.S.A.
April 18, 2012

A. Hi M. The L means lapped, the G means ground, the BL means blanchard.


pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey

Q. I am looking for a 16Ra finish on mild steel. What would be comparable on the S-22 microfinish comparator. EXAMPLE 16G 8G. I would really appreciate some guidance.

Daniel LaComb
- Rayne, Louisiana
October 20, 2015

A. Hi Daniel. 16G would be equivalent to 16Ra. 8G would be equivalent to 8Ra. Mechanical finishes applied by different machinery can look a bit different to the eye even if they are the same Ra value, so the comparator may show you, for example, a 16G (ground) and a 16BL (blanchard) finish, and an 8G (ground) and an 8L (lapped) finish.


pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey

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