"Finishing" a bumper

[sandman]

So I've built a few bumpers, roll cages, and "what not" now and I'm looking for some advice on the finishing part. Mainly for a bumper. I think the bumper here I just built turned out good but it's the little details that get to me. The corners and edges for example, what grit and tool do you use to get nice evenly rounded corners. I'm using a flapper wheel but I think it's too course. Is a grinder the wrong tool for this? Should I be doing it by hand with a file or what? Also, if you look at the bumper you can see I welded 3 pieces together. I ended up rounding the area where it starts to taper back. How do you get a nice sharp edge here? Once again I used a flapper and I couldn't get a straight sharp line. It's all about the details. Any advice from some master fabricators?
http://www.imagehosting.com/out.php/i225017_TABLE.JPG (http://www.imagehosting.com)
http://www.imagehosting.com/out.php/i225016_frontbronco.JPG (http://www.imagehosting.com)

[Aces'n'8s]

I can't see the bumper....can you make the pics bigger?

Flap wheels are fine for roughing in a weld, joint, etc. but after that process is completed, I would go over it with a orbital sander 80grit, 120 or 180 grit, then 220 grit. If you want durability, I would epoxy prime, 2K prime, then paint it with the appropriate paint. Or you could spring for a high $$$ powercoat finish.

[MT4Runner]

If you want a perfect finish, it's a lot of fill welding and grinding.

Or get it flat, and then Bondo after the 80 grit with the random orbital sander. Porter Cable makes a great ROS for about $40. Square orbital sanders sucketh.

[sandman]

[QUOTE=Aces'n'8s;6489786]I can't see the bumper....can you make the pics bigger?

I figure from all your years of welding your eye sight is starting to go. Just wanted you to be able to see the pic:D I'll dig out the orbital, wipe the dust off of it and give that a try. Thanks for the advice. MT4Runner, you aren't kidding about the fill welding. You think you have it, grind it, and more pits appear.

[YJTypeR]

I use a rubber backing disc type thing behind some 4.5" sanding discs on my angle grinder. You can get them down to pretty fine grits and they work very well. The backing disc was from DeWalt for, IIRC, around $12. You can get the sanding discs anywhere. I use 60 grit all the time, almost as much as my grinding wheel.

It also helps to run the entire length of the joint with the disc back and forth to avoid high and low spots.

[FFRubicon]

For long edges I have had success with a Straight Line Sander like this (http://www.mytoolstore.com/ir/ir315.html) (just used the link for a picture, may be cheaper elsewhere). It really makes it easier to keep waves out of the long edges.

[urjb]

Dont grind across the joint, go paralel (sp) to the weld...

the "grain" should be paralel to the joint. I use a 60 grit sanding disc thats a little worn down on either a air or electric grinder.

[Gummi Bear]

I use the sandpaper discs with the rubber back and 40-60 grit to knock down the bigger stuff.

For final finish I use a flap disc, 120 grit, take your time, and use a very light touch.

I've gotten to where I don't use a regular grinding wheel nearly as much as I used to.

[Wicked_S10]

I use a grinding disc to knock the welds down, a 40 grit flap wheel to level it out and shape it, and get it reasonably close to what I am after, then hit it with a 120 grit flap wheel and smooth it out. The 120 will take most of the lines out that the 40 grit and grinding wheel leaves behind, but it will still leave light grinding marks in the metal. If you are concerned with getting a mirror finish, after using the 120 grit flap disc, finish up with DA or random orbit sander with progressively lighter grits. Then if it still isn't smooth enough for you, switch to a buffing wheel and buffing compound. It all depends on how far you want to take it. I find for most of the stuff that is getting primmer and then paint, the 120 grit wheel is more than sufficient.

Later,
Jason

[sandman]

For long edges I have had success with a Straight Line Sander like this (http://www.mytoolstore.com/ir/ir315.html) (just used the link for a picture, may be cheaper elsewhere). It really makes it easier to keep waves out of the long edges.


That definitely looks like a handy tool to have around.

[sandman]

I use a grinding disc to knock the welds down, a 40 grit flap wheel to level it out and shape it, and get it reasonably close to what I am after, then hit it with a 120 grit flap wheel and smooth it out. The 120 will take most of the lines out that the 40 grit and grinding wheel leaves behind, but it will still leave light grinding marks in the metal. If you are concerned with getting a mirror finish, after using the 120 grit flap disc, finish up with DA or random orbit sander with progressively lighter grits. Then if it still isn't smooth enough for you, switch to a buffing wheel and buffing compound. It all depends on how far you want to take it. I find for most of the stuff that is getting primmer and then paint, the 120 grit wheel is more than sufficient.

Later,
Jason


Good point. Most of these bumpers are going to rubbed up against a tree or rock at some point.

[pickupmn172000]

I use a 4.5 angle grinder with a backing pad as previously stated with a 36 grit. Keep pad as flat as possible and use as much pad as you can (keeps from gouging) Start on edges and blend them first that will give a sharp uniform corner. Then soften the radius as desired. I personally dont use flappers (too slow and inconsistant especially on long edges) Use a DA 50-80grit on whole piece for (adhesion powder or liquid):D

[MCgiver4x4]

I use a grinding disc to knock the welds down, a 40 grit flap wheel to level it out and shape it, and get it reasonably close to what I am after, then hit it with a 120 grit flap wheel and smooth it out. The 120 will take most of the lines out that the 40 grit and grinding wheel leaves behind, but it will still leave light grinding marks in the metal.
Jason


x 2 i have do the same with the previous bumpers i have done

[Brad]

Sharp corners are a pet peeve of mine, EVERYTHING I do gets radius'd

[Wicked_S10]

I personally dont use flappers (too slow and inconsistant especially on long edges)

Try out some higher quality flap wheels. I use norton zirconia alumina's and they are neither slow, or inconsistent. They also last far longer than most of the garbage you can pick up out there at hardware stores and what not.

Later,
Jason

[AthlonAJ]

Pretty much the same as Jason does, knock down the weld just above the level of the surrounding metal. Then flatten it out with a 60grit zircon abrasive disc on a flexible backer. Give it a quick once over with 80 grit flap and done deal. Any marks from there are small enough to be filled with primer. Pretty quick but I do this everyday. Like what people have said, keep it moving back and forth along the weld, never across it to keep it nice and straight. Let the abrasives do the work and not bear down on it too hard. Having good light helps too.

The welds that are on the outside are easy to get to like this one...
http://ajsoffroadarmor.com/cgi-bin/upload/Custom%20Work/xjn3.jpg

But when they get in the nook and crannies that blending brings the SUCK!
http://ajsoffroadarmor.com/cgi-bin/upload/Custom%20Work/jerryb2.jpg

[sandman]

AthlonAJ, nice work. I also use the discs with the backing pad and love those. I pulled out the orbital last night with 120 grit and and the corners turned very good. Seems like common sense, should've done it awhile ago but I had the mentality the orbital was for wood:shaking: I've bought flapper discs at home depot and lowes and wasn't real impressed with them. Then my Father-in-Law brought me some from the Refinery he works at and it was like night and day. Must be a much better quality. I have one which I beliece is called a Big Cat and that sucker grinds like no tomorrow. Thing just won't die.

[64rovr]

I have had a lot of problems in this area as well, but I solved the problem instead by becoming a better welder and now i just prep everything and paint it ;)

Any fool can make an ugly weld and grind it smooth.