Polishing Stainless Flatbar

[calderp]

I have a one-off job with some 3/8" thick parts. I needed a lot less than a sheet of 316 L and all I was able to source was bar stock so I'm going to have to deal with the cupping and mill finish. End parts need to be fairly close to a mirror polish and fairly flat, say +-.004. I've got about .013 cupping to deal with.

Any tips on best process for this using typical sanding tools? I can't take it anywhere with a timesaver because I can't contaminate it and it's not worth paying for a whole belt for a couple parts and obviously electropolishing won't fix my flatness issue.

I was thinking start with 80 grit on either a belt sander or fiber discs on an angle grinder and then move to a random orbital once I get them flat. Open to any tips or suggestions, I have done this before and it's really a pain.

All in it's about 40" of 6" stock to do. Should I start with a flycutter? I'm concerned that getting out the tooling marks will be more work than the time it saves me.

 

[GregSY]

.013 is a lot to remove without a serious grinder or cutter...but a belt sander would do the trick as long as your .004" tolerance is in play.

Regardless, if you need to end up with a mirror finish...IMO, you're nuts not to start with some polished SS no matter what it costs. Life's too short.

 

[plastikdreams]

Sounds like a lot of work...hope yer getting paid well for it.

 

[calderp]

.013 is a lot to remove without a serious grinder or cutter...but a belt sander would do the trick as long as your .004" tolerance is in play.

Regardless, if you need to end up with a mirror finish...IMO, you're nuts not to start with some polished SS no matter what it costs. Life's too short.

Agreed, I would love to start with polished but I called every shop and supplier I know and everyone had the same answer- the only way to get polished plate that thick is to buy it by the sheet. If anyone has a source I'd love to hear it.

 

[604Pook]

Try and get a good finish with your fly cutter. Depending on the size of the parts its going to be hard to get them flat just by grinding and sanding without gouging them up.

 

[guythatbrews]

If you can flycut flat with reasonable finish a bumper plating shop can polish them slick as hell.

 

[Ultradog MN]

I built bathrooms for a living.
Had to do some creative things in some of them. A couple of times I had to use a 3/8"x4"x 8' stainless flat bar as an exposed structural member. I put a bunch of hours on my Bosch 4x24 belt sander polishing those pieces of stainless.
You can't get a mirror finish on it and flatness or thickness wasn't an issue as long as any cupping or divots weren't visible but it did look polished and matched the polished stainless fixtures in the rest of the room quite well.

 

[BT Fabrication]

how big are the parts? just going to be a ton of manual labor any way you cut it.

 

[rons]

how big are the parts? just going to be a ton of manual labor any way you cut it.

Is the idea to flatten out a larger piece and then make parts?
Or cut up the warped stock into part-size pieces first. And then flatten less material?

This shinny business is the best, but I prefer brushed finishes in some cases.

 

[Ries]

MIrror finish is a big pain. Belt sander, at maybe 4 different grits, is a first step, but after that, I usually go to 3 or 4 descending grits on a random orbit, then buffing with descending grits of compounds. Real mirror you need to end up at 3000 to 5000 grit. I turn those jobs down and send simpler things out to the electropolishers. If ireally had to do a lot of it i would buy one of these https://www.csunitec.com/metal-surf...near-grinding-blending-and-polishing-machines

 

[petersen]

" if anyone has a source" ?
Have you heard of a little company called McMaster Carr ?
Page 4246

 

[Rocketdc]

First of all, what a pain in the dick.

I would take a light pass with a face mill on both sides to cut through the mill scale. Should give you a better surface to start the belt grinding sequence. Buy extra belts of each grit for whatever grinder you'll be using and make sure to swap them out the second they start to dull. Let the abrasive do the cutting and don't use too much pressure.

Look into unitized discs or wheels, they make discs for fillet weld grinders and wheels for angle grinders and they are phenomenal for removing scratches in the polishing sequence! They leave a very smooth surface for the next polishing step.

 

[GregSY]

" if anyone has a source" ?
Have you heard of a little company called McMaster Carr ?
Page 4246

I didn't see any mirror finish 3/8" SS...post a link or screenshot

 

[petersen]

"Tight tolerance sheets" precision ground 63rms
flat , square,parallel 8896k4

Not mirror finish, but much closer starting than HR .013cupped.

Sorry, I don't do links, reading from paper catalog page (official geezer status)

 

[Mike Henry]

McMaster link:

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

The listing only goes to 3/16 but they can often source specials pretty quickly and for a fair price. Call the number listed on the web page for the quickest result.

 

[Garwood]

Sounds like a 5 minute Blanchard job then polish