Techniques for getting best finish from flap discs?

[pendragon1998]

As an experiment, I am trying to get a mirror finish on an old rusty axe head. I started with a 40 grit flap disc and went up to a 80 grit disc, and now I am wet sanding with 120 grit paper on a block. I still have a bunch of deep scratches from the lower grits that aren't coming out with the 120 paper. It's like the flap disc had a grain or two of very coarse grit that put deeper scratches on the workpiece than the rest of the disc did. I am new to grinders, so I wondered if I could tweak my flap disc technique to get the best finish prior to working the piece by hand?

In the pic below, the vertical scratches are from the disc, and the horizontal ones are from the 120 hand sanding.

 

[jeepinerdeep]

I would think you would get closer to the results of what you are describing using a stripper disc and some non woven flap wheels. A 40 grit flap disc will remove almost the same amount of material on the flat as a hard rock.

I have used Norton and Benchmark stripper discs. The Nortons are nice, but 6x the price.

I have not used the non woven flap discs yet, but want to.

https://benchmarkabrasives.com/collections/surface-conditioning

 

[Shootinok]

40, 80 to 120 wet is a couple big steps.
Spend a little more time with 80 then 100 to get out deep scratches.
You might need to go to hand sanding both.

 

[tarmy]

Look into a burnishing tool...

I finally got tired of sloppy finishing of my work...got a Metabo, pricey, but you can get different types of rolls for it and make a pro type finish. There are some knock off cheaper versions...look into the tool...go from there...



This is from my tool...it shows some other handy metal working tools I got...like that file sander...and that long neck grinder...

 

[NORDFORD]

You need to get a unitized wheel. Google it. Clean it up with a flap disc, use the unitized wheel and you’ll be good to go. They are gray and have the same look as a pumice stone.

 

[kkroger]

Smooth strokes not back and forth with random direction changes the disk will dig a divot if you do that every time you change direction it will leave a mark. if you make a smooth movement from one side to the other it will leave a smooth finish, just make sure you are moving fast enough to not overheat and slow enough to get a smooth finish.

 

[LXCam]

Figure 8's

 

[quadrcr87]

You can also try a 120 flap disk before going to the manual wet sand. I’ve never tried a mirror finish but I like the results of the 120 grit flap I have.

 

[arrowhead]

Your not going to get far with 120 by hand, as mentioned go up to 120 with the flap disc. For finish sanding, I used these 2" hook and loop disks. Yea, about as cheap a quality as you can get, but I got two packs and it was plenty to polish up the stainless exhaust I made. I found the sweet spot was 180, 240, 600, 800 then buff. Not sure how they will work on carbon steel though.

https://www.amazon.com/gp/product/B077JXWN9M/?tag=atomicindus08-20

All of these joints were mig welded with stainless wire, ground and polished.

 

[BD1]

Don't waste money on cheap ones. Buy name brand ones and consult with supplier I what you want to achieve. A representative is your friend and should help. Navy manufacturers have contact emails where you can submit a picture too. It does help.

 

[Ole Slewfoot]

hold the disc flatter with teh material and along the direction of motion for more polish, steeper and across for more cutting. a new disc will be more prone to cutting hard at the edge.

 

[mike_dmt]

I'm in the camp with different tool with a finer grit medium. A flap wheel on a grinder is more intended for removing material in grits 120 and less..

They make a cool rubber flat wheel for grinders. The key word is flat. Throw it up on its edge and it will dig in to the material like anything else. Even a DA or palm sander would work too. You'll likely be moving to 240,600,800 maybe even finer, then buff..