Sanding/Smoothing steel and welds

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Hi,Today I came across this picture http://1.bp.blogspot.com/_1XF-wsEQ6h...new+r+2+17.jpg  and it got me wondering how I could achieve a similar smooth finish on steel like this? Until now I have just been grinding my welds down with an angle grinder and grinding wheel however after painting the grinding wheel leaves deep marks that can still be visible.Any ideas on how to create an "invisible joint" like this? Would I use a flapper wheel or just a regular sanding technique using gradually finer sandpaper?Any ideas would be welcome! Thanks!
Reply:Get a couple flappers with different grits.  60 to start and 80 or 125 to finish with a soft touch.  Looks to me like the piece you linked may have been sand blasted.
Reply:Knock off the big stuff with an abrasive wheel, then finish it out with a flap wheel (or 2 using finer grits). The flap wheels are great but expensive and I burn them up pretty quick for full time usage.If you don't want to stand behind our Troops, feel free to stand in front of them.
Reply:I too am a fan of flap disks.   That said, I switch to sanding disks for the finer grits, like 120.A lot is in the technique.  I spoke to one guy who worked at a high end aluminum furniture manufacturer.  He said when they hire a new person, they spend a week grinding welds on practice pieces before they are considered good enough to work on real product.  When he saw me work, he said that I was not too bad, he figured that I could be trained to grind welds.......What he suggested is when you switch grits, change direction at the same time.   Let's say that you were grinding with 60 grit, and the sanding marks were going east-west.   When you switch to 120 grit, you change your position such that the sanding marks are going north-south.   You grind with 120 grit until all the 60 grit marks are gone.  Then you switch to 220 grit and do it again.There are some high end tools that leave linear marks on the work, rather than the circular marks left by sanding disks or flap disks.   But most of us can't justify spending $900 for a machine to sand welds.A couple of other tips:   A light touch, and never let the tool stop on the work.  Start the tool off the work, and bring it down with the tool moving.Due to the nature of my work, I often end up trying to grind out welds to the undetectable point, with some success.  The example shown is certainly a very good example of what is possible.Practice Practice Practice.RichardSculptures in copper and other metalshttp://www.fergusonsculpture.comSyncrowave 200 Millermatic 211Readywelder spoolgunHypertherm 600 plasma cutterThermal Arc GMS300 Victor OA torchHomemade Blacksmith propane forge
Reply:Good info from ggarner, Swells and raferguson.  I'm just finishing a dining room table, and have spent a LOT of time grinding/sanding.  Legs are 4"x4"x.125", and cross pieces are 2"x2"x.125" - mild steel (I'll shoot it with clear coat later).  Much like Richard advised, I began with 50 grit flap disks on 4 1/2" and 7" grinders.  Then 80 grit flap disks, then 80 grit sanding disks.  This leaves a lot of the circular swirls in the steel.  I then spent a lot of time with a 3x18" belt sander - 80 grit (with occasional returns to a 50 grit belt) - and all the same direction.  Then 100 grit by hand with a block, and 120 grit belt sander.  Finally, 120 by hand with a padded block.  I budgeted WAY to little time for the sanding and too little money for sandpaper.  I'll know next time.  Also, I have found that the better quality sandpaper is worth it (the blue stuff) AND that while I have a few Harbor Freight tools, their Chinese made sanding belts are worthless (though the stuff labeled "Russia" is pretty good.  I also wore a mask the whole time - lots of dust.  Good luck!  CJMiller 211 MIGMiller 375 Extreme Plasma CutterMiller Maxstar 150 STL TIGOxy-Acetylene torch
Reply:If you are going to paint it, why not do it the way you have been doing it and smooth it with bondo.  Works on cars.
Reply:Hey, HakbotLike others have said, technique and finer grits are key. Blending out the sanded area a ways helps prevent an obvious "dip" in the surface. Once down to 120 sanding disks or flap wheels, I use these round scotch-brite pads that stick to a hook and loop( velcro-like) backer pad. They are the cats arse for blending out to practically invisible. Get them at the LWS. I don't like the Walter brand of backer. I didn't hold the pad for love or money and was too stiff. Got a black, no name one that works great. I think one could convert a regular sanding disk backer with some stick on velcro and you could buy the green scrubby pads at the local super market and just cut them round. I think they'd probably stick to the hook velcro pretty good. Haven't had the need to try this myself, but seems do-able. Difference being that the "real" pads seem to have been impregnated with some sort of polishing compound. Guess one could try smearing some tooth paste into the homemade pad and letting it dry. Again, just shoot from the hip here And, yeah, that piece in the pic has been blasted.Good luck,Bert200amp Air Liquide MIG, Hypertherm Plasma, Harris torches, Optrel helmet, Makita angle grinders, Pre-China Delta chop saw and belt sander, Miller leathers, shop made jigs etc, North- welders backpack.
Reply:Thanks for the ideas guys. I will try using flappers next time around and see how it comes out. I dont have the ability to sand blast yet so this looks to be about my best option.Thanks!
Reply:When I am grinding welds flush, I never use scotchbrite pads, or flap wheels, because they are soft.  They tend to grind both the low and the high spots, which is not what you want.  A hard sanding disk grinds the high spot without touching the low spots.   I am assuming that your goal is for the weld to disappear.I have a big collection of 2 inch roloc scotchbrite pads, but I don't use them for grinding welds smooth.  I use them to take off oxides or paint, or put on a uniform finish, after I have the welds flush.I should say that I am talking about butt joints, not fillet joints.RichardSculptures in copper and other metalshttp://www.fergusonsculpture.comSyncrowave 200 Millermatic 211Readywelder spoolgunHypertherm 600 plasma cutterThermal Arc GMS300 Victor OA torchHomemade Blacksmith propane forge
Reply:Most of the guys have covered the finishing well. One thing not mentioned is the welds themselves. Good prep and skills will limit the amount of weld you need to remove. I often see people just jam the two pieces together and then glop weld on top, only to have to grind it down. A  bevel or "V" ground in the pieces or a bit of a gap will give the weld material somplace to go rather than just piling on top.  One other problem is that often they turn the heat down when they jam things tight and try to limit the material that gets placed on top they will need to grind down. Unfortunately that cuts down the weld penetration and after grinding there is often very little material left holding the two pieces together, as all the weld was ground away. The other thing I often notice is that people will go too fast and have a lot of undercut on the edges. Then they try to sand everything smooth, and have to dig into the original material to remove the undercut..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:Getting smooth finishes starts with the weld. No undercutting is acceptable. The next key is to remove only the material necessary. Use a hard grinding disc to remove any material that protrudes above the desired finished surface. Do not let the hard disc come into contact with anything that does not protrude. Then switch to a sanding disc to blend in the surface. Then switch to a flapper to remove the sanding discs marks. For opaque paint an 80 grit flapper should be smooth enough. If a finer finish is desired switch to an orbital sander with the best quality wet sanding paper you can get.The piece in your picture wasn't blasted, it was sanded with an orbital sander.Ian TannerKawasaki KX450 and many other fine tools
Reply:Originally Posted by fortyonethirtyGetting smooth finishes starts with the weld. No undercutting is acceptable. The next key is to remove only the material necessary. Use a hard grinding disc to remove any material that protrudes above the desired finished surface. Do not let the hard disc come into contact with anything that does not protrude. Then switch to a sanding disc to blend in the surface. Then switch to a flapper to remove the sanding discs marks. For opaque paint an 80 grit flapper should be smooth enough. If a finer finish is desired switch to an orbital sander with the best quality wet sanding paper you can get.The piece in your picture wasn't blasted, it was sanded with an orbital sander.
Reply:Originally Posted by fortyonethirtyGetting smooth finishes starts with the weld. No undercutting is acceptable. The next key is to remove only the material necessary. Use a hard grinding disc to remove any material that protrudes above the desired finished surface. Do not let the hard disc come into contact with anything that does not protrude. Then switch to a sanding disc to blend in the surface. Then switch to a flapper to remove the sanding discs marks. For opaque paint an 80 grit flapper should be smooth enough. If a finer finish is desired switch to an orbital sander with the best quality wet sanding paper you can get.The piece in your picture wasn't blasted, it was sanded with an orbital sander.
Reply:ZTFab,Quote: Don't forget to use plenty of High Frequency to pre-heat your parts or you won't get any silent beam flow! I've always suspected there was some "dark magic" used in your work.  Mr. McCormick (The Sith TIG Lord) accidently let the cat out of the bag.
Reply:Originally Posted by joedirt1966Mr. McCormick (The Sith TIG Lord) accidently let the cat out of the bag.
Reply:Originally Posted by joedirt1966ZTFab,Quote: Don't forget to use plenty of High Frequency to pre-heat your parts or you won't get any silent beam flow! I've always suspected there was some "dark magic" used in your work.  Mr. McCormick (The Sith TIG Lord) accidently let the cat out of the bag.
Reply:In my last gig, I spent a lot of time grinding welds to smooth for gloss powder coat.  Shows ALL surface imperfections.  I used a thick, square shouldered 120grit flapper wheel on a 4.5" angle grinder.  The trick is to lay the tool basically flat on the part.  The disc should be FLAT.  Both sides on the part and DON'T dig.  Rough down the weld to .060" then start with the flapper.  Its possible to get it perfect, like glass.
Reply:what about fillet welds?  how do you grind those down?  die grinder?
Reply:I've got some sanding rolls and cones for the die grinder in various grits thats great for inside corners and fillets. I picked the original kit up years ago for polishing the ports on an intake and heads. I'd have to dig and see where I got the sand paper rolls from last since I don't use them as much as I did years ago and I bought them bulk when I did..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:http://www.jegs.com/i/JEGS/555/80900...oductId=758018http://www.competitionproducts.com/S...ductinfo/8090/http://www.competitionproducts.com/H.../products/171/
Reply:Originally Posted by T-Birdhttp://www.jegs.com/i/JEGS/555/80900...oductId=758018http://www.competitionproducts.com/S...ductinfo/8090/http://www.competitionproducts.com/H.../products/171/
Reply:Originally Posted by T-Birdhttp://www.jegs.com/i/JEGS/555/80900...oductId=758018http://www.competitionproducts.com/S...ductinfo/8090/http://www.competitionproducts.com/H.../products/171/
Reply:I noticed last night that Harbor Freight sells something similar.  I have no idea of the quality, just thought I would share. Attached Images
Reply:Originally Posted by T-BirdI noticed last night that Harbor Freight sells something similar.  I have no idea of the quality, just thought I would share.
Reply:Just saw these in the latest issue of "Practical Welding Today" Magazine.They're flap discs that are designed to grind fillet welds!http://pferdusa.com/products/206/20610/2061006P.htmlhttp://all-a-cart.comWelding Cart Kits and accessoriesI see that your using CLECO's, I really like the way they work, and work.......Bruce The Welding ChefLincoln Weld-Pack 3200 NORWELD StickStanford Hill Farm
Reply:Hope this isn't a stupid question but is undercut caused by the metal not being heated enough?  ZTFab, what are open coat discs?  Thanks
Reply:Originally Posted by ponch37300Hope this isn't a stupid question but is undercut caused by the metal not being heated enough?  ZTFab, what are open coat discs?  Thanks
Reply:Under cutting can be caused by several things. You'll need to be more specific to get any useful advice. Preheating the metal can help in some situations like welding thick material. But, too much heat directed in the wrong way is a more likely cause of undercuttingLast edited by fortyonethirty; 07-30-2010 at 01:16 PM.Ian TannerKawasaki KX450 and many other fine tools
Reply:Originally Posted by fortyonethirtyUnder cutting can be caused by several things. You'll need to be more specific to get any useful advice. Preheating the metal can help in some situations like welding thick material. But, too much heat directed in the wrong way is a more likely cause of undercutting