Stuck MK10 Piston cap (Scubapro)

[ams511]

Now the highest graded Micro-Mesh is 8000, equivalent to 3 "Micron" according to the conversion chart here. That gives "scratches" that are nearly invisible to the naked eyes, and way finer than a 400 grits sand paper.

I think you are right:

Three (3) Grades of Micro-Mesh are now available

•Micro-Mesh Regular (silicone carbide grit with standard backing) - The standard grade of Micro-Mesh used for the majority of operations on plastics, paints, wood and most metals and polymers. It is used to produce a uniformly smooth surface and bring the surface to a high gloss finish. Available in grades 1500 to 12000 (30 to 2 microns).

•Micro-Mesh MX (silicone carbide grit with heavier backing) - This grade of Micro-Mesh is similar the standard grade except that it has a slightly stiffer cloth backing and has several coarser grits available. Primarily used on metals to bring the surface to a micro finish. Using a combination of one or more of the MX series, a sub 1.0 micro-inch RA can be achieved. Available in grades 80MS to 1200MX 945 to 3 microns).

•Micro-Mesh Aluminum Oxide (aluminum oxide grit) - This grade of Micro-Mesh was designed specifically for finishing aluminum and other solid surfaces. Available in grades 1500 AO to 12000 AO (30 to 2 microns).

 

[Zung]

The difference might be that things like brake and engine pistons have a constantly renewed supply of fluid lubricant that recoats the sealing surfaces which is not the case with a regulator where the lube is more like a grease

Great point, as usual!
I actually did a search on cylinder sleeves and piston rings surface roughness, got some interesting numbers, but decided against hurting my head with this whole business.

 

[Couv]

......Something's wrong, there's a discrepancy that's 2 orders of magnitude, please educate me.

Brother Zung,

I'm not a math genius like Master Awap, so I must find tools to do the work. (You know this part already, but for the others.) Here is a handy tool to convert between micro-meters and micro-inches. Convert um to microinch - Conversion of Measurement Units

In the PH handbook, (see 5-5) for Dynamic O-Ring Sealing, "The most desirable surface roughness value is from 10 to 20 micro-inches."

To get a surface finish of 10micro-inches use 320 paper. See this chart http://www.microfinishusa.com/services/Microfinish Surface Finish Chart.pdf

Couv

 

[redacted]

You guys are making my head hurt. But I think I may have figured out what is going on here.

320 grit has an average particle size of 32 microns and produces a roughness measure (RA) of .3 microns.

http://www.massasoit.com/SurfaceMeasurements2.pdf

What about a material variable??

http://www.sunnen.com/graphics/assets/documents/e2e25e493b00.pdf

 

[halocline]

Couv, give it a try, and please let us know how it works out.

For us peons, is a micron a millionth of a meter, i.e. .001 mm? That's pretty small.

 

[Couv]

Yes, a micron is a millionth of a meter. 1 micro inch = 0.0254 micrometer / 1 micrometer = 39.37 micro inches

Give it a try?....What are you crazy? This is life support!

Actually, my primary regulator has been treated this way and has been for 2 years. I decided to experiment when my MK 10 was honking (more like wheezing) like a MK 7 scaring the fish away. Unfortunately, it's not a real test as the ambient chamber is packed with O2 lube......but at least I've cured it's bad cold.

Awap, I'm too tired to examine all those charts with much clarity, so please correct me if I'm wrong. Looking at the chart in the lower right hand corner: grit size 320 gives a surface roughness average of 6-15 micro inches-probably a better match than the 400 I chose. Ideally, the surface roughness is best produced by bead blasting to get a dimpling effect-like a golf ball. Next would probably be the correct stone and last sand paper.

When I performed this operation on my favorite reg, I was only guessing at the grit size. I compared it to a small cylinder hone I have but I bumped up the grit value in case I was making a mistake. 400 grit "felt" right so that's what I used. According to your chart, I could have gone a bit coarser (somehow that word doesn't seem right) but I felt happy with the finish.

It's just like me to experiment.....then do the research.

 

[halocline]

Well, are you sure that wasn't you wheezing?

Somewhere in the dark recesses of my feeble brain I remember something about the average limit of human eyesight being .1 mm. So you're talking about scratches something like 40 times smaller than that. I just don't see how 320 grit sandpaper can produce that. I've used 1500 grit micromesh dozens of times on acrylic (and brass) and it produces clearly visible and feel-able scratches. And that's the most coarse micromesh. I realize steel is a lot harder and consequently the scratches would (I guess) be smaller.

But, what do I know...I'm hardly anything like an aeronautics engineer.

 

[Couv]

....yeah.....something about these numbers doesn't understand me.

If 10 micro inches = 100 thousandths of an inch, it would be damn hard to feel or see even with my contact lenses in the correct eyes.