Alright fellas, I'm sure you guys have figured out that every step of the way for me involves new questions for all of you...

Anyway, when i cut the wheel well rot out, seems the panel warped a bit. It's kinda banged out. I need to work it back in, shrink it. I know, I know, next time ill use nibblers...

My question is this, should i hammer it or try and use a shrinking disk? I've never used a hammer and dollie on sheet metal before, but like anything else with this project i guess i'm gonna learn... Any tips or watch out for's?

Duke

 

My suggestion on hammer and dollie work is to practice on a piece of scrap first, bang it up a bit, then grab your shrinking hammers and such and practice practice practice. The shrinking disc is pretty much the last step in the process, it will take out minor high spots and such leaving you with a nice finished piece of metal, but you still have to work it first.

 

I agree with Indy. You can read about it, but you will NEVER learn how to bang sheet metal without lots of practice. On that scrap metal, start by learning to hit the dolly by feel and sound. Once your sixth sense is telling you where the dolly is, you can then start to try to move the metal where you want it.

When you're dealing with stretch, the best way to shrink it is with concentrated heat, the second best is with shrinking hammers and dollies.

Good luck,

 

If its real bad, just make a cut or 2 with a wheel or saw. Start tacking at the eye, as it the weld cools it will draw it in. Then again your welding skills need to be up to snuff. The use the hammer and dolly to smooth the weld out, grinding will cause warpage.

 

I agree with you all. I understand that to bring a low spot out to use a hammer and dollie and to shrink a high spot down with the disk. My problem is that i don't know how, or better yet understand how, to shrink with a hammer and dollie. I have a slight warp out, in the panel, if i try to hammer it back in the only thing i'm doing is really stretching, i need to shrink... I'm not sure how to tackle this one. What do you suggest?

By the way i tried the welder again, i had a small spot i cut out, rear bed corner. Fabricated a new panel and tack'd it up. Looked really good, the first time around. I had a bunch of goo tacks on it, decided to grind dowm the welds to get some more room. Went back for round 2 and blew some holes in the patch...ticked me off...i'm going to have to get something behind the welds to take the heat...i bought some copper pipe caps and magnets...we'll see how it goes today. Thanks for the help.

 

The idea behind shrinking hammers and dollys is to wrinkle the metal. You do this by hitting off dolly whether you are using a shrinking hammer or shrinking dolly (never use both at the same time.) When you wrinkle the metal it makes is smaller. As an example wrinkle up a sheet of copy paper (8 1/2" X 11") and then try to flatten it out. After flattening it out, it will measure something less than it's original measurements.

Again, practice on some scrap metal before committing to your baby.

The problem today is finding good shrinking hammers and dollies. The only new ones that I know of being available are the Martins. I bought a pair sight unseen and found them to be MUCH different than the shrinkers I've seen in the past. Instead of machined grooves about 3/8" apart, they have a series of small peaks probably an 1/8" apart and do not seem to effect the correct wrinkle. I would like to find an old pair at a swap meet or somewhere.

BTW, when MIGing sheet metal together with a series of tacks, be careful not to grind all the weld away. Remember, you are not trying to straighten the welds and welded metal to be straight enough for paint. You will need a thin layer of filler. Over the welds themselves, make it fiberglass reinforced filler so as to protect the welds from corrosion problems later on.

Good luck,

 

Definitely practice first.
For me on versus off dolly is a feature of sound. I can hear the difference.
You hammer on dolly for stretching and off dolly for shrinking. If it clinks the metal is stretching.
In my experience you always need heat to shrink, but I'm not a professional.


This is a little off topic, but I am working on a couple of instructional articles on shrinking metal (totaly not qualified for it, but I did it anyway). Would the articles be helpful? I'd appreciate comments on them.

You can see them here.
I'm sure there are flaws
http://pen.eiu.edu/~gddavis/

 

Harbor Freight carries a decent starter kit for not much money and it has a shrinking hammer in it. Occasionally one of the tool trucks, Snap on and such will carry shrinking dollies on board. The most important thing to remember when starting is that when trying to shrink down a dent, DO NOT start in the middle.

You want to start easy on the outside edge, then work your way in. One of the nifty things about metals is that when your working with it, you're going to build heat just from the hammering process, granted it isn't very noticable but it is changing the metallurgy of the piece you're working with, and like anything else, it's all practice and more practice.

 

hold the dollie on the low spot and hit the high spot or vice versa... if it needs to be shrank you can do it with a rosebud torch head, heat a spot about the size od a quarter, then put a wet rag on it to cool it quickly, then hit it with a body hammer, this will shrink it and make it stronger

 

i have a book on sheet metal work and it says to hit it before it cools off

 

Careful. Cooling metal quickly will make it harder and more brittle. Not stronger.
I avoid shrinking metal by rapidly cooling it. It can be done without the rapid water cooling, and you will avoid making the metal harder to work next time. (there's always a next time).

You're just trying to move the metal around. Shrinking is as simple as that. The rapid cooling makes it shrink up a little like a slug when you add salt (eeww!).
You can accomplish the same thing by pushing the metal around with a hammer and dolly while its still red hot. It works just like clay. In fact someone suggested I practice my blacksmithing skills on modeling clay before I wasted a lot of metal. It actually works exactly the same, but with less burns.

A thin long peice of clay can be made shorter if you just push some of the length into thickness instead. Metal works exactly the same way.