Grit for pre-blue polish. - Page 2

Dixie Gunsmithing · January 9, 2015, 10:45 AM

If you blast them, you get a non-shiny dull or mat surface, similar to Parkerising. Polishing can be used for several types of finishes, from brushed to mirror. It is according to what the customer wants, or to match a factory finish.

**Unclenick** · January 10, 2015, 03:38 PM

I think what Scorch said is key. Note that whether he stopped at 220 grit or 440 grit, it was followed by buffing. Buffing and polishing compounds work a bit differently than abrasive cutting compounds. Where abrasives in the coarser grades remove a lot of metal, polishes remove amounts disproportionately smaller than their particle size and also smear surfaces smooth microscopically. I recall reading how, even with something as hard as glass, electron microscopes found small particles of polishing compound under the polished surface of glass lenses, due to the glass having smeared over top of it.

If you apply buffing to a surface that was first abraded by something much coarser, it will remove the microscopic surface variation except down in pits, and that will look much more polished than the raw product of the abrasive grit did.

It's also the case that the choice of abrasive affects this. The sharp shards of silicone carbide wet/dry paper will cut faster but leave a duller, more gray surface than the rounder particles of aluminum oxide do. If you want to see this for yourself, go to a Woodcraft store where they sell the white (aluminum oxide) Norton sand paper from 80 down to 400 grit. You can run the 220 grit wet/dry, wipe the surface with alcohol to get the traces out, then repeat with the aluminum oxide 220 over a portion of the surface to see the difference. You can even buff them both to see the difference.

tobnpr · January 10, 2015, 08:17 PM

I use two-stage currently- 120 mesh aluminum oxide (matte) followed by 70-100 glass bead that provides a satin finish.

I'm getting ready to try good 'ol walnut shells in fine 18/40- supposedly will provide a polished finish (sure does it to our brass) without peening the surface.

**Unclenick** · January 12, 2015, 10:09 PM

Let us know how that goes. I've used wood to card rust off steel before, but it hadn't occurred to be to polish with it by direct impingement. Sounds like a good idea.

Dufus · January 19, 2015, 07:45 PM

What I do: if the owner wants a deep blue black finish, then I final polish the barrel with crocus cloth and or a buffer wheel impregnated with jewelers rouge.

The action and other smaller parts will get a light bead blast followed by a day or two in the vibratory tumbler for a mirror finish. My tumbler will hold 45 lbs of media & parts.

For a matte finish I polish with glass beads in the 90-150 micron range, then wash thoroughly with solvent to remove the beads in all the crevices and blow dry with compressed air.

January 10, 2015, 03:38 PM	#27
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,063	I think what Scorch said is key. Note that whether he stopped at 220 grit or 440 grit, it was followed by buffing. Buffing and polishing compounds work a bit differently than abrasive cutting compounds. Where abrasives in the coarser grades remove a lot of metal, polishes remove amounts disproportionately smaller than their particle size and also smear surfaces smooth microscopically. I recall reading how, even with something as hard as glass, electron microscopes found small particles of polishing compound under the polished surface of glass lenses, due to the glass having smeared over top of it. If you apply buffing to a surface that was first abraded by something much coarser, it will remove the microscopic surface variation except down in pits, and that will look much more polished than the raw product of the abrasive grit did. It's also the case that the choice of abrasive affects this. The sharp shards of silicone carbide wet/dry paper will cut faster but leave a duller, more gray surface than the rounder particles of aluminum oxide do. If you want to see this for yourself, go to a Woodcraft store where they sell the white (aluminum oxide) Norton sand paper from 80 down to 400 grit. You can run the 220 grit wet/dry, wipe the surface with alcohol to get the traces out, then repeat with the aluminum oxide 220 over a portion of the surface to see the difference. You can even buff them both to see the difference. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

January 10, 2015, 08:17 PM	#28
tobnpr Senior Member Join Date: August 1, 2010 Location: Tampa Bay Posts: 4,556	I use two-stage currently- 120 mesh aluminum oxide (matte) followed by 70-100 glass bead that provides a satin finish. I'm getting ready to try good 'ol walnut shells in fine 18/40- supposedly will provide a polished finish (sure does it to our brass) without peening the surface. __________________ Remington 700/Savage Rebarreling /Action Blueprinting 07 FFL /Mosin-Nagant Custom Shop/Bent Bolts Genuine Cerakote Applicator www.biggorillagunworks.com

January 12, 2015, 10:09 PM	#29
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,063	Let us know how that goes. I've used wood to card rust off steel before, but it hadn't occurred to be to polish with it by direct impingement. Sounds like a good idea. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

January 9, 2015, 10:45 AM	#26
Dixie Gunsmithing Moderator Emeritus Join Date: April 27, 2013 Location: Ohio Posts: 1,923	If you blast them, you get a non-shiny dull or mat surface, similar to Parkerising. Polishing can be used for several types of finishes, from brushed to mirror. It is according to what the customer wants, or to match a factory finish.

January 19, 2015, 07:45 PM	#30
Dufus Senior Member Join Date: December 10, 2014 Posts: 1,965	What I do: if the owner wants a deep blue black finish, then I final polish the barrel with crocus cloth and or a buffer wheel impregnated with jewelers rouge. The action and other smaller parts will get a light bead blast followed by a day or two in the vibratory tumbler for a mirror finish. My tumbler will hold 45 lbs of media & parts. For a matte finish I polish with glass beads in the 90-150 micron range, then wash thoroughly with solvent to remove the beads in all the crevices and blow dry with compressed air.