20 replies to this topic

[mini-reub]

Hi All!

 

After butt welding my boot floor repair panel, I'm left with the usual slight warping from the heat. This is only very slight as I use the usual pulse then wait method.

 

I've ground off the majority of the weld bead and would like some tips on how to flatten out the junction. I've got various hammers/dollys!

 

Cheers

[samsfern]

A shrinking hammer might do it, its a hammer with a few swirl things on the face.

[mini-reub]

That sounds like it could work..

Do you know if there are any YouTube vids showing the technique?

[minidaves]

the srinking hammer with the rubber twisty bit is good, 

[Ethel]

You can't actually "shrink" sheet metal with a hammer, every time you hit it it will get thinner. The trick is to stretch it more evenly to get rid of the dents. This is planishing, where you hammer  around a bump to make a bigger but less pronounced bump. Shrinking hammers actually create little bumps that hide the "width" of the stretched metal, a bit like corrugated sheet. The "corrugations" are then hidden by filling - or sanded/filed smooth, which leaves the sheet even thinner.

 

There are some decent vids on youtube, try restolad's channel.

[tiger99]

The method of shrinking using heat supposedly works, without thinning, because you hammer the hot spot flat, when the metal is soft, and it pulls very tight as it cools. I don't have, and don't intend to get oxy-acetylene equipment (don't like the safety aspects!), so I have never been able to try it. A high level of skill and experience is probably needed.

[skoughi]

Its rather easy with a little practice. I use one of the gas torches with the disposable canisters, this will give all the heat you need. Planish out the streached metal into one raised area then get ready with torch, planishing hammer, flat faced dolly and a bucket of water and rag. Heat the center of the streached and raised metal to cherry red about 50p size, then place the dolly behind the heated spot and start hitting around the hot spot working in decreasing circle until you get to the center, then quickly quench with the wet rag. The hammering pushes metal into the center then the rapid cooling draws the metal in. This will put tension back into the panel removing the sprining that happens when its dented and streached. On small dents you can shrink the metal without the hammering and just heating then quenching. It can take a wee while to suss the technique and sometimes you'll make things worse but it is handy. Plenty of clips on you tube showing you how.

[skoughi]

Forgot to add, please use gloves, safety specs. Also because you'll be using a naked flame make sure there's nothing flammable behing the panel such a waxoyl or paint thinners etc close at hand. A handy fire extinguisher would be a good idea. Please if you're gonna give it a go be safe.

[mini-reub]

OK I'll give the heat n cool method a go. I get the feeling it's a better idea to spend extra time on the prep n weld cooling, rather than trying to fix the warpage afterwards!

Thanks for the advise as ever!

[tiger99]

Skoughi, thanks for that explanation, which is similar to, but much clearer than what I had heard previously. Makes it seem a lot easier! As it can be done with a simple gas torch, that makes it more likely that I will give it a try, one of these days.

[skoughi]

The butane torches a very handy, they can give enough heat to loosen rusted bolts, nuts etc as well. Heat shrinking isn't as difficult as you may think, definitely one of those things you should try and as long as you're prepared to make mistakes and learn from them then you'll suss it out! I had to shrink and put tension into both my clubmans rear quarter panels as the rear wheels had been hitting the top of the arches from previous owners having her too low. The quarters were all bowed out also warped from welding patches at the bottom so most of the panel had to be shrunk. I heated about 20 hot spots in total to get it back in and tensioned up to stop springing . A lot of planishing followed to get it good enough for filler. How good you want it to be depends on how much time you want to spend on each panel. As I said go on you tube as there's lots of clips showing how to do it. I also have a shrinking disc for the angle grinder which works ok, do an ebay search to see what I mean.

[skoughi]

OK I'll give the heat n cool method a go. I get the feeling it's a better idea to spend extra time on the prep n weld cooling, rather than trying to fix the warpage afterwards!
Thanks for the advise as ever!

Thats the best idea! Mostly I get carried away and weld like a loon then spend a wee while trying to shrink everything back to what it should be!

[minidaves]

this is the hammer i use for strinking http://www.google.co...0Q9QEwAQ&dur=44

[skoughi]

Strinking?! Whats that? Is it when you make something smaller then do a big fart?

[ryan22_lgm]

Another method is to clean a springy area up to bare metal and mig weld a spot. Do not use high power low will do fine this will then tighten the panel up again. Grind weld off jobs a gooden !!!