All MetalShaping

Go Back   All MetalShaping > General Metal Shaping Discussion > General Discussion
  Today's Posts Posts for Last 7 Days Posts for Last 14 Days  

Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 05-06-2009, 07:40 AM
Kerry Pinkerton's Avatar
Kerry Pinkerton Kerry Pinkerton is offline
Administrator
 
Join Date: May 2009
Location: Near Huntsville, Alabama. Just south of the Tennessee line off I65
Posts: 8,321
Default Is a shrinking disc really necessary? - John Kelly

John Kelly Post subject: Is a shrinking disc really necessary?
Posted: Tue Apr 07, 2009 9:42 am

Joined: Wed Apr 01, 2009 9:21 am
Posts: 15
Location: Moclips, on the Washington coast The more I learn from using a shrinking disc, the more I learn about how to work without one. They are a great tool, but the main thing is you can shrink with much lower heat than is recommended on most of the hundreds of heat shrinking threads I have seen on autobody sites etc.

If you heat with a torch just until the metal swells a little bit, and far short of any color change, then quench (you should see steam), you are shrinking in a very controlled manner that does not distort the surface as much as heating to red hot. The metal stays easier to work using low temperatures as well. You can shrink multiple times in the same spot if you need to.

A guide coat is something I do not use anymore when shrinking with a disc. The disc burnishes the surface making a guide coat unnecessary. If you are shrinking with a torch, a guide coat is probably a good idea on a panel with lots of surface irregularities. Either way, using lower temperatures, you can use a hammer and dolly as much as you want to, then shrink and tune up the surface, repeat hammer and dolly work, shrink again etc. There is no over-working a panel... at least not as quickly as many seem to think.

The lesson I learn for this is to be reckless, not careful. I don't worry about sneaking up on a shape or a surface condition, I attack it knowing I can fix anything that I screw up. This works for me.

I have had success using a shrinking disc to make a reverse. My next experiment will be making a reverse with a torch. We'll see how it goes.

John http://www.ghiaspecialties.com

_________________
Free Metal Shaping Videos: http://www.youtube.com/my_videos?pi=0&p ... 0&sq=&dm=2


tdoty Post subject: Re: Is a shrinking disc really necessary?
Posted: Tue Apr 07, 2009 1:37 pm
Help Desk
Joined: Sat Mar 14, 2009 7:23 am
Posts: 158
Location: Rantoul, Illinois John, I totally agree! Almost everything I've ever read on torch shrinking says to heat the metal red hot and hit it with a hammer. You can shrink sheetmetal really effectively with a propane torch - though you sacrifice some control since the propane torch distributes the heat further as it heats much slower than O/A.

I'm terrible about not taking pics while I work. When I shaved the door handles on my Monte Carlo a while back, there were a few high spots left when the patches were welded in. I had my low crown shrinking disc, but hadn't bought a big grinder yet. So....out came the propane torch to knock down the high spots.

I'm not much of a fan of the guide coat even for torch shrinking though, because the torch will just burn it off, or at least scorch it. I have a sanding stick made out of a piece of 3/8"x1" alminum (about 10" long). It uses paper from a "shop roll" clamped in place. I just give it a quick, very light, run across the panel and it kisses the highs enough to let you see them. I generally go over the surface with a red Scotchbrite first to give it an even scratch pattern. It's kind of like using a file, but all it does is scratch the surface without removing enough metal to hurt anything. I use it with the disc, the torch, or hammer and dolly work. Going over the surface with a big marker before sanding really helps the scratches stand out, and it doesn't make a mess if the heat starts to lighten the marks. I also keep a wide variety of Shapie colors handy, and use a different color as work progresses.....that way I know which level of work the marks are from.

The disc is the best shrinking tool I have used......but it is kinda noisy

Tim D.



mindover Post subject: Re: Is a shrinking disc really necessary?
Posted: Mon Apr 20, 2009 10:08 am

Joined: Sun Mar 15, 2009 6:08 pm
Posts: 26 John, the way you describe shrinking a panel is exactly the way I do it however I do often heat the panel to anything from blue to cherry red depending on the amount of metal that needs to be shrunk and how much shape there is in the panel I also use a flipper (thats the proper name for a slapper -slapper means something completely different here in England)to help the metal 'gather up'.
I agree with what you say about attacking the panel knowing that whatever you do you will be able to sort it out, This is what defines a craftsman, someone who can do the job without constantly having to check with measuring intruments and guides, knowing the shape in your head and being able to produce it. This only comes with confidence gained from years of experience.
I have never used a stainless shrinking disc, but I use a sanding disc turned face side in, works in the same way (probably a lot less noisy) I think this is an old trick I cant remember where I learned it.



John Kelly Post subject: Re: Is a shrinking disc really necessary?
Posted: Mon Apr 20, 2009 2:36 pm

Joined: Wed Apr 01, 2009 9:21 am
Posts: 15
Location: Moclips, on the Washington coast Hi David,

The reversed sanding disc method has been around for many decades... the prelude to the brilliant step of going to a stainless disc (although a cold rolled disc will work). I believe Scott Knight came up with the shrinking disc idea. A disc is much faster, and yes, noisier than a sanding disc reversed... lasts a bit longer too : ) You should try one. I think you would be pleasantly surprised at how much more controllable shrinking becomes. I know I was. Not great for making friends with your neighbors though.

John http://www.ghiaspecialties.com

_________________
Free Metal Shaping Videos: http://www.youtube.com/my_videos?pi=0&p ... 0&sq=&dm=2
__________________
Kerry Pinkerton
Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

All times are GMT -5. The time now is 03:39 PM.

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.