Smoother Than a Baby’s Bottom – Measuring Surface Finish

So just how smooth is a baby’s bottom? A verbal description would only be subjective. In machining though, a more definitive rule of measure is a mandate. In the United States, surface finish is usually specified using the ASME Y14.36M standard. The other common standard is International Organization for Standardization (ISO) 1302.

Surface texture is measured by three components:

  • Lay – where the machining marks are parallel typical of grinding and sanding operations.
  • Surface Roughness – where surface irregularities and finely spaced. They can be radial, cross hatched, or random.
  • Waviness – is the measure of irregularities with a spacing greater than surface roughness. This can be caused by tool chatter or warping.

The most common method to measure surface roughness is to use a diamond stylus Profilometer. For those of us old enough to remember the days of vinyl recordings, it uses the same concept as a record player. As the stylus is dragged across the surface it produces a frequency. This is deciphered by the instruments electronics producing a digital readout. The disadvantage of a Profilometer is that it is not accurate when the size of the features of the surface are close to the same size as the stylus.

Non-contact surface measurements are more accurate but more complicated. Here are some links if you want to read up on them:  interferometry, confocal microscopy, focus variation, structured light, electrical capacitance, electron microscopy, and photogrametry. For most manufacturing operations contact measurement are the norm.

A third “quick and dirty”  method is to use a surface finish scale. This is a flat piece of plastic with various micro finishes. Measurement is by a tactual comparison. You run your finger over the piece you are inspecting and then find the finish on the board that feels the same.

 Back in my machining days this was a source of many heated debates. My callused fingers could not detect with the same resolution as a female inspector with soft supple hands.

I hope you found this article informative. If  you need assistance with your application where you think compressed air products would be of benefit, feel welcomed to give me a call.

Joe Panfalone
Application Engineer

Phone (513) 671-3322
Fax   (513) 671-3363
Web: www.exair.com 
Twitter: www.twitter.com/exair_jp
Facebook: http://www.facebook.com/exair

Autum Leaves, Winter Blues, and Leaping Arcs of Energy

I spent the weekend enjoying the crisp autumn air raking leaves. Rover and I had a great time together. I did all the work and he playfully spread them out again. During one of my breaks, which in each passing year has become more frequent, the thought of winter came to mind. Not just the snow shoveling but the static electricity.

Around the office I am referred to as Mr. Static. I don’t know why it is, but I generate an inordinate amount of static electricity during the winter months. The sound of snap and crackle can be heard as I rush about the office. It may be humorous but it stops being funny when I blow out equipment; 3 cordless phones, 1 cell phone, and my desk phone. Rover won’t even come near me during the winter months. Some man’s best friend he is.

Co-workers are always there for you. It’s been suggested that I wrap my shoes in aluminum foil, wear a drag line, shower myself with Bounce ®, someone even went through the trouble of making me a tin foil hat! What I found to really do the trick is to carry with me a LED key chain discharger. The LED’s slowly allow the stored charges to go to ground eliminating my pain and ensuring the integrity of whatever I touch.

Static electricity is not only a personal issue. It rears its ugly head in manufacturing too. I’ve seen a bottle filling application   where the static charge was enough to divert the flow of liquid so it missed the bottle. EXAIR has a cool video on static electricity. Need help controlling your static. Fill out your application form and an application engineer will evaluate your needs and make the appropriate recommendations.

Joe Panfalone
Application Engineer

Phone (513) 671-3322
Fax   (513) 671-3363
Web: www.exair.com 
Twitter: www.twitter.com/exair_jp
Facebook: http://www.facebook.com/exair