What its all about

What its all about

Tuesday, March 4, 2008

Bumping metal


Beginners guide to body hammers.

So you’ve got a dent and want to work it out instead of filling it up with a half a can of bondo, but don’t know where to start. I’ve been there, and still need a little bit of filler now and again!

Go pick up a set of cheapo body hammers from Harbor Freight or any of the other fine Chinese junk retailers. You want a few smooth face hammers, and a few pick ends looking bit on the end, one with a small square point, and one with a square head (Shrinker/bumping hammer.) Along with the hammers grab an assortment of dollys. They come in all shapes and sizes, get as many different ones as you can. A slapper is a plus, as well a few good pieces of wood. A small vice with an anvil back, as well as a seam making pliers are good for flattening out small parts after the hammering is done.

The key is to go slow, no big swings. Let the weight of the hammer do the work, and choke on it as you get started. Big hits leave dents, and that’s what we are trying to remove. Hit only hard enough to see a very slight change in the metal, its like eating an elephant a lot of small bites and then the dent is gone.

This is the splash pan off the bus, I already beat the dents out of the front... oops.

Keep the piece clean, knock off as much paint, dirt and undercoating as you can. Keep the hammer faces and dollys free of pits and rust. Don’t use brake cleaner if you are going to do any welding, as it makes phosgene gas… nasty stuff. I like a twisted wire welding brush for knocking off the dirt, a can of carb cleaner and a razor blade for scraping paint off windows to take off the undercoating.

Start with the easiest, flattest part of the problem area. The flatter you can get the surrounding metal, the easier the big creases disappear. When you first start out flattening the metal, keep the sharpest curve of the dolly under the dent or ding. Work the metal with a small face hammer in concentric circles around the center of the ding… while holding the dolly directly under the lowest point. This gives the metal somewhere to go while it shrinks.

Start here:



#1 is pictured above. Then go to two, three and four.

How To:
Stretching: Hammering with a metal hammer, on sheetmetal backed up by metal. This makes the sheet metal thinner.
Shrinking. Hammer on metal backed up by wood. Any hammer, any wood and the metal sucks towards the hammer blows making it thicker.
Shrinker, a tool that makes shrinking faster. It leaves little pits in the metal however.

This is how it all starts out. This is the section marked #1 above. When you hammer, the dolly will be under the piece held firmly. Hit gently and work up and down along the x's while moving the dolly either not at all, or evenly with the hammer. Not moving, shapes metal faster... so long as the hammer doesn't get far enough into unsupported metal that the metal starts bouncing back. Moving evenly gives more control.
Choke up on the hammer as you start, to see how little force is needed to move the metal.

With picks, do not hit hard or the tip may go through the piece. Don’t hit the center of dents as when you roll the top inside out it makes a hard spot, that takes forever to shrink down. They are good for smoothing out the sides of “mole hills” on the sheet metal.


After picking, the dents will have a flat spot around the sides. Now switch to a small headed hammer and a steel dolly and work around in circles till they flatten out. When they look like pancakes, go to a larger hammer, when almost flat switch out and shrink them with a block of wood or a shrinking hammer. They will disappear like the picture below.




The crease is a tough one, as once a hard line forms and the metal has "Bent" it becomes hard to hammer. It is like trying to flatten out an angle iron, go slow to avoid this. Once the crease is flat switch over to the next detail.





Finished:


The beginning:

3 comments:

Jose said...

Very cool...will have to try this myself on some bent parts!

Avon said...

Great stuff!
Thank you for the info very well presented!
I will be book marking this page.

Pratik said...
This comment has been removed by a blog administrator.

The VW Bus

The VW bus as a daily driver.
Forget... forever onward what you consider the definition of transportation.

You are about to journey down the path of enlightenment, and learn the curious nature and language of a mechanical being. The Volkswagen is a peculiar beast, fed a steady diet of oil and gasoline it will move slowly from place to place.

Buses mark their spot. They pee on you when you least expect it. Like a foreign customs agent, it takes time to figure out where they want the grease. They take a little tweak here and there, when something not quite right they tell you if you listen.

When you hop behind the wheel of a bus you've got the best seat, as you'll soon experience she's a low flying slow air plane. Flying high enough off the ground to do an oil change, swap master cylinders, and cv joints without jack stands. Head and tail winds effect speed over ground, your steering wheel at speed is more for yaw, in the end she goes where she wants, or doesn't.

Buy her quality parts, or she'll spit them back at you. Your bus is half truck and half home; sometimes a magic carpet to distant places… other times a squatter. Wandering down the road with a smile on her face, the grins and thumbs up from those on the same path make her day. If you wish to show off your wrenching skills, she'll humble you. Trust her, lover her... and she'll be one happy camper.

You've got to love her deep down or she'll leave you stranded, half the battle is the will to keep her on the road. If you don't think she will, she'll know it... scratch her rattles, lube her squeaks. Never forget she’s an aging mistress; her joints aren't what they once were... if its cold it takes a little bit longer to get motivated. One day you will too.

You've had your fair warning. Spend your time cuddling and she'll fire up when you need her, but if you've got other projects you've got to give an offering. When she humbles you, give a prayer to the gods of speed and give the bus in question a shot of oil. Mostly problems come from not driving her, buses get sad… some more than others, and if you don’t drive them they question your love. Miles are the VW anti-depressant.

Give her a pat on the dash and thank her for the trip at the end of the day.