mabe

I have read of guys doing that. I would practice on a piece of scrap to see how much heat and how big a bead to make. and you might have to have a buddy back up the spot with a dolly to flatten it

 

i would use a shrinking disk as they are easy to make even if there is not a vendor around..in a pinch one can use a mapp or propane plumbing torch as well..

Sam

 

My apologies for opening up such an old thread, but how exactly do you make a shrinking disk? I want to try to use one but really don't want the spend the $100 plus on one.

 

Sometimes you will have to go back and cut the panel to let the metal move..When I weld up panels, I take a damp rag and make my welds, then pass the damp rag on the sides of the weld..This will keep the panels nice and striate..

 

shrinking

Using a shriking hammer with a dolly on the back side would be your best bet. Using a dolly and just a regular body hammer will further strech the metal. It sounds to me like you have a pretty good idea on how to shrink metal using a torch couldn't you use just M.A.P.P gas to do that? Like a small propane torch?

 

If you ever picked up a shrinking disc you would do one of two things, grind the "shrinking dolly" flat to make it a regular dolly or you would toss it in the garbage.

SHRINKING DISC is where you go with this, IF it really needs to be shrank at all.

Shrinking with the mig is possible, but making a weld to do it seems backwards. If you are welding on metal you know is stretched, then cooling the weld, that will shrink it. This is why cooling the weld to NOT warp is going against science. You can keep the metal cooler I guess as mentioned in an earlier post. But literally cooling the weld after welding IS shrinking, pure and simple.

You need to get John Kelly's video at Ghiaspecialties.com and see how you can use a shinking disc to do some amazing things.

Brian

 

If your panel has distorted due to the heat of welding it is because your metal has shrunk in the heat affected zone(Weld joint and blue area around weld). Shrinking the panel further will only make the distortion worse.

This can be reversed by stretching your weld, first grind the weld on both sides of the panel so the bead is just slightly proud of the surface and then hold a dolly on one side of the panel and hammer using an on dolly technique, if you hear a nice ringing sound and see what looks like a polished smudge on the surface it means your stretching. Work slow and check you progress to be sure you don't over stretch but if you do you can re shink using a shrinking disk will provide a perfect metal finished panel once you get used to using it.

 

Thats for the feedback guys!

well ive had a fair bit of success with the mig. the metal was definatly stretched, it had the old oil can effect. I zapped a few spots on the high areas and quenched each one, and it all pulled in nice, The mig was really good, i was able to concentrate the heat in very small areas. Once i was done with the mig i had a second chance to shrink the areas that little bit more, by grinding the welds and quenching again. it worked very well.

I would definatly like to try a shrinking disc in future...

 

If your panel has distorted due to the heat of welding it is because your metal has shrunk in the heat affected zone(Weld joint and blue area around weld). Shrinking the panel further will only make the distortion worse.

This can be reversed by stretching your weld, first grind the weld on both sides of the panel so the bead is just slightly proud of the surface and then hold a dolly on one side of the panel and hammer using an on dolly technique, if you hear a nice ringing sound and see what looks like a polished smudge on the surface it means your stretching. Work slow and check you progress to be sure you don't over stretch but if you do you can re shink using a shrinking disk will provide a perfect metal finished panel once you get used to using it.

I thought heating metal and letting it cool slowly expands it? Thats definatly what happened in my case.

 

If you ever picked up a shrinking disc you would do one of two things, grind the "shrinking dolly" flat to make it a regular dolly or you would toss it in the garbage.

SHRINKING DISC is where you go with this, IF it really needs to be shrank at all.

Shrinking with the mig is possible, but making a weld to do it seems backwards. If you are welding on metal you know is stretched, then cooling the weld, that will shrink it. This is why cooling the weld to NOT warp is going against science. You can keep the metal cooler I guess as mentioned in an earlier post. But literally cooling the weld after welding IS shrinking, pure and simple.

You need to get John Kelly's video at Ghiaspecialties.com and see how you can use a shinking disc to do some amazing things.

Brian

ive been watching a few videos on youtube of using shrinking discs, they look very simple, i might have a go at making one

 

Putting a quick weld and then a cold wet towel right after will often bring enough heat and then re cool after grinding the weld off. the little added material also stiffens up oil canning.

A sharp wrap with the hammer just before to cold water will wake it up and help get it moving inside too...

http://www.youtube.com/watch?v=P9x7BRTOTMc

 

Stepside and Brian have it right. Welding shrinks (thickens and reduces surface area). If you shrink more, you are reducing the surface area even further.

The metal will swell up and expand as it is heated, but it contracts as it cools (more than it expanded) and ends up with an overall shrink.

You must either fill the shrunken area, or stretch the weld to get your surface area back. People often mistake the relatively high area next to the weld as a stretch. It is not.

John

 

shrinking disc

my experience with a shrinking disc was that it was the final step after working with a hammer and dolly. I couldn't do the roughing as fast as I could with a hammer and dolly. But that might just be the way I was doing it.

 

my experience with a shrinking disc was that it was the final step after working with a hammer and dolly. I couldn't do the roughing as fast as I could with a hammer and dolly. But that might just be the way I was doing it.

When shaping metal the initial work is done on the stump and then with the slapper on a finishing head. the shrinking disk is used for the finish. lots of the little divots on car body can be taken care of with the disk as we are only moving the metal a small distance to alleviate an oil can or something..

Sam

 

Thats for the feedback guys!

well ive had a fair bit of success with the mig. the metal was definatly stretched, it had the old oil can effect. I zapped a few spots on the high areas and quenched each one, and it all pulled in nice, The mig was really good, i was able to concentrate the heat in very small areas. Once i was done with the mig i had a second chance to shrink the areas that little bit more, by grinding the welds and quenching again. it worked very well.

I would definatly like to try a shrinking disc in future...

Shrinking the metal from welding can also cause an oil can especially if you are welding near a sharply curved section of the panel or a body line. When the metal shrinks it wants to pull on the sheet metal around the weld and will put a stress in the panel and depending on the exact constraints of the panel could show up as an oil can. Normally a oil can due to shrinking will feel almost like the sheet metal is loose and flimsy where an oil can due to stretching will pop back and forth with that standard oil can popping sound.

 

Hi Stepside,

Did you mean the reverse of what you said in your last sentence?

John

 

Metalshapers Assoc. Community Sites

 

small disc

I made a small one to use on a 4 1/2 grinder from a plumbing clean out cover
6 in. Stainless Steel Wall Cleanout Cover Plate-6-CPLSS - The Home Depot

drill out the center hole and reshape to fit your grinder.

 

I have an interesting project for ya'll, concerning strech/shrink of metal.

Start with a piece of sheet steel about 12" long by 1" wide. lay it flat on the bench and clamp a block to the bench, tight to each end of the metal strip. Then slip a razorblade between the metal strip and one of the blocks. Then observe the result. Is the metal deflected? if so, How much? The answer might surprize you.

 

shrinking with a carbon rod.

I just had to install a 44 lb roll of .045 wire on my lincoln SP 200. wire feed, I am building metal porch railings for the duplex. Inside the door on the monster are instructions on using a carbon rod for shrinking sheet metal . it says to turn off the breaker for the wire feeder then use a carbon rod to contact the high spot and heat it up. I have a lot of carbon rods down south where we usually spend the winters,
Has anyone tried shrinking with the carbon ?
I still have the old 2 carbon rod torch from the 50's we used on the ranch with a Forney plug type welder, and an Air Arc torch that used a carbon rod, It is supposed to work like a plasma cutter.

 

I would have hammer and dolly'd the area with harder blows on obvious shrinks and use the shrinking disk last to smooth it out. Fixing things in primer is parallel to trying to fix things with the shrinking disk. Sure it does a lot for you but you have to do a lot for it to really get a good use out of it.

 

Will the shrinking disk be effective on the high spots on a weld seam that has been planished but not ground on the back side?

John

 

You can't really "plannish" it at all if the back side has a proud weld. That is one of the problems with MIG butt welding panels. But if you weld hotter faster welds you can cut down that extra weld build up.

Brian

 

I've never tried it but I have to assume the thicker metal isn't going to shrink as much because it can't get hot as fast or as much, But if all the metal around it is shrinking, it's going to be just about as good as no welds?

Brian

 

I would think it could still be effective with the welds on the back but obviously not for planishing directly over the weld . The high spots where his disk would be is away from the weld seam. I equate the situation to pushing down on one of those flimsy hoods with little to no support on the bottom. You push one area down and another raises. Ideally you'd want to raise that low to fix it, which in itself will lower the adjacent high spot . In this situation, you consider backside access before welding and keep it cool where you can't address it, but with two people there's a lot of areas you can address as long as the guy inside the car has a nice pillow and ear muffs. Stretching those seams would be the first thing I'd do, not shrink, then I'd block the metal and planish from there. Then again, we're talking behind a quarter with access issues on the back side.

the process of using a shrinking disk right around the seam is only tightening things up around the sunken in weld area. In other words, you're just smoothing out the contour but loosing radius. If it's possible to stretch the weld seam it will release some tension pushing the metal up , and that alone would help some of the perceived stretch and you'd be able to get the proper contour/less bondo. Without access to the seam or a helper you can use a stud gun and wrestle with pulling the shrunk up. It won't properly stretch the metal but if you're hitting your highs down while pulling you are somewhat planishing the metal. I would do that after blocking as well to show me where to hit while I pull up the shrink.

 

minimum bead

Here[s a link from metal meet about tig welding body panels with no filler rod.
Tig welding body panels - No hammering method - Metal Meet Forums

I posted a youtube that Cris Boggess. The instructor at the UVU street rod program did showing an exercise he had his students do to fit up practice panels with NO gap. and the use of Cleco's. the tight fit-up allows minimum filler rod
https://www.youtube.com/watch?v=oUH4aRPX4F4

https://www.youtube.com/watch?v=VIm3ptWE-kY

in the past
I have also posted up links to cris Davenport all aluminum 40 willys he built as a student
Metalshapers Assoc. Community Sites

 

the no filler rod technique works great. In the future I'd maybe try to use rod on the back side and then do with no rod in front. I think that would work better, for me anyways.

 

I have tried that with O/A but making two passes creates more shrinkage even though that does leave very little weld bead to deal with.

I have no experience with TIG but it obviously would generate less heat.

John

 

I hear Covell mention doing it that way and it made sense to me . Obviously this means you have room to planish and grind both sides.