Technique for dressing scratches/gouges in gasket flanges?

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Technique for dressing scratches/gouges in gasket flanges?

Postby ian_krase » Thu Mar 16, 2017 8:04 am

(Possibly FAQ bait?)

Ebay is a good source of vacuum valves, fittings, etc at low prices. However, it's common for such used parts to be beaten to hell and back on the flanges, which of course are often the most exposed part of any given component (especially in the case of KF flanges).


And it doesn't take much of a scratch to exceed the compliance of a fairly stiff viton o-ring and open a leak

I often see it recommended to somehow dress damaged flanges and restore them to annular-scratched perfection. However, I don't think anybody has ever said what exactly the technique is. Filing? Lapping? Stone or metal plate? What kind of grit? What do you do if your flange has one of those "protective" ridges around the periphery?

(Not talking about setting things up in the lathe, here).
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Re: Technique for dressing scratches/gouges in gasket flange

Postby Richard Hull » Thu Mar 16, 2017 8:19 am

For polishing sleeks and minor scratches a drill press might suffice. What grit? What is the scratch like? We can't do your thinking for you at range. Read up on grits and polishing methods. Without a lathe, significant problems just might be beyond effective repair. Again, we can't spoon feed blanket solutions to a multiplicity of mating surface, dings scratches and sleeks. You buy surplus or used gear, then you buy into whatever arrives and hopefully pack the gear needed to solve such problems on the fly.

For a totally probelm free scenario, purchase every single component brand new. No need to pack the problem solving gear then, just have a lot of money.

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Retired now...Doing only what I want and not what I should...every day is a saturday.
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Re: Technique for dressing scratches/gouges in gasket flange

Postby Peter Schmelcher » Thu Mar 16, 2017 4:44 pm

Ian this is an old post to get you started
viewtopic.php?f=10&t=4175

-Peter
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Re: Technique for dressing scratches/gouges in gasket flange

Postby Rex Allers » Thu Mar 16, 2017 9:04 pm

For cleaning up flat metal surfaces, lately I have become fond of diamond 'stones' for sharpening knives. They are flat metal plates having one side encrusted with a diamond grit. There are a lot of them on ebay, mostly from China. Here's the title of one multiple listing that I purchased from recently:
New Thin Diamond Square Knife Tool Sharpening Stone Whetstone 60 - 3000 Grit

They aren't too expensive and seem to last a long time if you don't abuse them. I wet them with water and as they start to accumulate metal (you can see the diamond surface start to darken) I clean them with a little soapy water and a tooth brush, rinsing them under a faucet.

I recommend three grits: around 240 (only for deep scratches), 500 or 600, and 800 or 1000. I think 800 is probably fine enough and could be finished off with a metal polish from there, but they do offer 1000 and even finer grits. I bought the biggest size I saw listed -- 170 x 75 mm.

There are also double sided options with two grits, but I think these are all just two of these metal plates glued to the opposite sides of a piece of plastic. Nothing wrong with that.

If you get yourself into the Sharpeners section of ebay and search for 'diamond stone' or 'diamond plate' you should see many options. I would only go for the ones with diamond across the whole surface; they have some with diamond only in spot patterns.

If you run out of flanges, you could even sharpen some knives.
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Re: Technique for dressing scratches/gouges in gasket flange

Postby ian_krase » Fri Mar 17, 2017 5:19 am

Cool! Thank you, everyone.

I have a diamond stone with the hole pattern but I'm not sure how flat it is.
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Re: Technique for dressing scratches/gouges in gasket flange

Postby prestonbarrows » Sat Mar 25, 2017 3:16 am

Elastomer seals just need a smooth surface to mate with. If this is specced during a standard manufacturing process, it typically means limiting the depth of the final lathe cut and/or the radius of the tool used on the final pass. ~10 micron will be a mirror finish, ~30 is good for elastomer seals, ~1000 micron is a bead blasted surface.

If you are touching up something that already has been machined, standard grinding, lapping, or scotch-briting methods are applicable depending on the depth of the feature to be removed.

For fusor work, where exceptional vacuum levels are not needed, slobbering some vacuum grease onto the elastomer from Corning or Apezion will take up fairly large gauge fuckups.
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