Best tool for grinding, sanding or blending metal to a flat surface?

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Looking for a better tool to get the metal to a flat surface.If there are big welds and high spots to bring down I just use the angle grinder and a sanding disc.  Sometimes, if they are only small imperfections, I will go straight to the air powered sander (rotary only) 6" (150mm) using 80 grit paper.  This sands and blends down the high spots quite well because of the velcro backing pad.  It allows for a flat surface across the entire diameter of the sanding paper, where as the angle grinder has the nut in the middle that holds both the paper and backing pad on so you can not get a really flat surface. The angle grinder has heaps more power to turn the sanding discs but will not make a very flat surface.  Where as the pneumatic rotary (only) palm sander makes a nice flat surface but needs more spinning power.There are air sanders 7" etc that will spin at around 4500rpm, maybe I need one of these (if they have a velcro backing pad).  I really like the mobility of the palm type sander and how easy it is to handle compared to the angle grinder or even the other DA sander.  Having said that, I see you can get geared sanders also known as mudhogs, which spin much slower at 900rpm and will not stall out.  They have gears in them where the normal air sanders do not.What would be the best tool for the job here.  Those photos show some parts of what I do, but also I also need to do other blending of butt joints etc, where a perfect seamless transition is required.  Especially for the jobs that have metallic paint going on after.
Reply:Psst... You forgot the picts....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:Get some flap discs for the angle grinder. Then you have the power to turn them as opposed to the air grinder, and the control to blend in the surfaces. You really need more than one angle grinder anyway, so you can have several, each equipped with a different wheel for different uses. Like DSW said, add pictures.
Reply:I use a grinder with a flap disk then follow up with a 7" sander if needed. Mine has the retaining nut recessed so that i can lay it flat like a DA. I've also used a DA for blending where i wanted a really flat surface. Takes a lot of patience sometimes.GravelThe difference between theory and practice is that in theory there is no difference.
Reply:If you take a 4-1/2" or larger angle grinder and put on a backing disc and a flat paper disc on it, it will allow you to hold it totally flat if the spindle doesn't protude. When it is used totally flat it will only take off spatter and high spots, it will barely scratch areas that are already flat.
Reply:Whoops, here are the pictures!
Reply:Yeah you want a 4.5inch angle grinder with flap disk.Maybe an angle die grinder with paint and light rust remover pad.old Miller spectrum 625 Lincoln SP-135 T, CO2+0.025 wireMiller model 250 and WP-18V torchCraftsman 100amp AC/DC and WP-17V torchCentury 115-004 HF arc stabilizerHome made 4 transformer spot welderHome made alternator welder
Reply:I probably use cloth back rolok style sanding discs.  I have a 4 inch Dynabrade pneumatic that I use a lot for this type of thing.  I have 2 inch and 3 inch Dynabrade pneumatics as well, but use them much less often.
Reply:Depending on the size of the weld, I would use a 4.5 inch grinder with a flap disk, or a small angle air die grinder (20,000 rpm or so)  with 2 inch roloc sanding disks.  Some folks prefer 3 inch roloc; I think it depends on the scale of what you are working on, I tend to work small.I tend to start grinding welds with 36 grit or 60 grit, and keep going to finer grit until I get the surface that I want.None of these things are very expensive if you don't buy top of the line stuff.   Why not try each and see what works for you?  It sounds like you have most of the tools, maybe you just need to try different kinds of abrasives.   If I want the surface really flat, with a uniform finish, I use an air random orbit (dual action) sander.  I have a six inch and a two inch,  but that it not what I would choose to grind out welds.Sculptures in copper and other metalshttp://www.fergusonsculpture.comSyncrowave 200 Millermatic 211Readywelder spoolgunHypertherm 600 plasma cutterThermal Arc GMS300 Victor OA torchHomemade Blacksmith propane forge
Reply:Car guys use DA sanders a lot to blend flat areas. I've also seen belt sanders used.
Reply:A good flap disk without a doubt. You can finish it with a higher grit DA but I would start with the flap.
Reply:For the record, I was talking high speed rotary pneumatic, not DA.