All MetalShaping

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

Reply
 
Thread Tools Search this Thread Display Modes
  #21  
Old 03-18-2011, 11:30 AM
german8rcoupe's Avatar
german8rcoupe german8rcoupe is offline
Member
 
Join Date: Jul 2009
Location: Glasgow,Scotland
Posts: 110
Default

I always thought that an oil can was stretched metal contained by a tighter perimeter.
__________________
Ross

If at first you don't succeed....skydiving is not for you.
Reply With Quote
  #22  
Old 03-18-2011, 12:33 PM
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

Quote:
Originally Posted by german8rcoupe View Post
I always thought that an oil can was stretched metal contained by a tighter perimeter.
Or non-stretched metal surrounded by (at least at some point) by shrunk metal. It's the tighter perimeter relative to the effected area that causes the problem. That's why they are so confusing. Sometimes you shrink the oil can to 'fix' the problem and in doing so, accidentally shrink an adjoining area. Problem still exists so you shrink some more and now you're going to chase...and chase....and chase. Sometimes the problem is caused by a shrink, not a stretch.
__________________
Kerry Pinkerton
Reply With Quote
  #23  
Old 03-18-2011, 05:49 PM
robert robert is offline
Member
 
Join Date: Dec 2010
Location: the netherlands
Posts: 341
Default

Quote:
Originally Posted by Dyce View Post
I'm going against the shrinking by heat. I beleive there is heat there, but there is also pressure from the sand hitting the panel. Steel will streatch easier with heat involved. I've done repairs from careless sandblasters that throw there rocks at panels and inside body supports and I always have to shrink.
i agree with this i think this is the reason why its a strange problem
but i want to ad ,shrink by heat does happen
using spot sandblasters on a roof panel will result in sort of the same dents you get welding holes used for mounting chrome parts

i think it starts with heat shrinking and if and when angle ,pressure, etc.
are wrong it changes to stretching.

in my oppinion we all agree on how the oilcan gets in our panel
now we need to know how to read our panel if we have to shrink ore stretch and where.

at this point i stay with my experiance to overshrink
and stretch the panel back in shape, because the wheeling machine gives a better finisch then shrinking with a torch
__________________
robert veldman
Reply With Quote
  #24  
Old 03-18-2011, 08:56 PM
Dyce Dyce is offline
MetalShaper of the Month Jan. 2011, Nov. 2016
 
Join Date: May 2009
Location: Souix Falls, SD
Posts: 901
Default

Quote:
Originally Posted by robert View Post
i agree with this i think this is the reason why its a strange problem
but i want to ad ,shrink by heat does happen
using spot sandblasters on a roof panel will result in sort of the same dents you get welding holes used for mounting chrome parts

i think it starts with heat shrinking and if and when angle ,pressure, etc.
are wrong it changes to stretching.

in my oppinion we all agree on how the oilcan gets in our panel
now we need to know how to read our panel if we have to shrink ore stretch and where.

at this point i stay with my experiance to overshrink
and stretch the panel back in shape, because the wheeling machine gives a better finisch then shrinking with a torch
I think the metal could shrink or stretch depending on the panel and which side you are blasting. If you are blasting down on the top of a crown it would be like taking a slapper and working the panell down. You can cold shrink this way. Flip the panel over and blast the under side of the crown it would stretch.

Just like Richard said "What makes it very hard to fix is the fact that the stretching is very uneven across the panel. Depending on how close, how long and what angle the blast nozzle was from the sheet at any given point on the panel." It really helps if you know how the damage was done.

I had a '36 Cabrolet I spent a good 12 hours on with the shrinking disc and slappers. Most of the damage was done when the blaster did the inside supports. You could see the panel was raised in straight lines that match up to the body supports and braces perfectly.
__________________
Jeff Dyce
Hell, there are no rules here - we're trying to accomplish something.
Thomas A. Edison
Reply With Quote
  #25  
Old 03-20-2011, 12:26 PM
BobPer's Avatar
BobPer BobPer is offline
Member
 
Join Date: Jul 2010
Location: New England
Posts: 50
Default

Quote:
Originally Posted by TheRodDoc View Post
With blasting, Stay in one spot a little to long and you get a spot stretched more then the rest.
O.K. Just going to throw this out there, so here goes. Can we use this to our advantage? Suppose I WANT to make a low crown panel (a roof insert, or door skin), and I cut my rectangular blank. I then lay out a pattern of concentric oblongs getting closer and closer until I reach the middle of my blank. I support the perimeter with a 2X4 form (maybe or maybe not partially filled with sand), I then use a sand blaster straight on at a constant distance to follow my pattern tighter and tighter until I reach the center. Will I have just formed a controlled low crown panel, or added to my scrap pile? Can we shape intentionally with the force of a sand blaster? Bob
__________________
Bob Persson
Reply With Quote
  #26  
Old 03-20-2011, 01:15 PM
mark g mark g is offline
Metal Shaper of the Month, April 2011, December 2012, May 2016
 
Join Date: Nov 2010
Location: Southern VT
Posts: 362
Default

Bob,

I like the way you think. You should get an A just for the suggestion. I would make some room on the scrap pile and give it a try. It would be a great experiment.

-Mark
Reply With Quote
  #27  
Old 03-20-2011, 02:07 PM
Richard K's Avatar
Richard K Richard K is offline
Member
 
Join Date: Nov 2010
Location: Minneapolis, MN or On the Road
Posts: 1,131
Default

Possible idea, blast to shape. Consider using a medium that is non abrasive so as to not wear away metal. Blasting to shape consists of millions of impacts on the material's surface. This will cause work hardening. thinking of many tiny impacts it may only work harden to a limited depth. Not sure of the effect. The work hardening would yield a stronger panel. Exactly what a low crown panel needs.

Interesting to about. As Mark stated " I would make some room on the scrap pile and give it a try. It would be a great experiment."
__________________
Richard K
Reply With Quote
  #28  
Old 03-20-2011, 03:18 PM
steve.murphy steve.murphy is offline
Member
 
Join Date: May 2009
Location: Brisbane, Australia
Posts: 650
Default shotpeen?

Perhaps find a commercial shotpeenshop top try this out on? If I recall they have differnet size steel shot depending on the application. Air pressure can be adjusted to get the desired velocity.
__________________
Steve

ærugo nunquam dormit
Reply With Quote
  #29  
Old 03-20-2011, 03:50 PM
BobPer's Avatar
BobPer BobPer is offline
Member
 
Join Date: Jul 2010
Location: New England
Posts: 50
Default

I guess I'm always trying to make lemonade (I do like lemonade)! We all pretty much have had to fix sand blasted distortion, so yes it is work hardened, but still workable. Millions of tiny hits vs. thousands of hits with a Yoder. Which would make scrap faster? I like the shotpeening, with non-abrasive media with variable air pressure to control the results. Also can experiment with patterns and density of patterns. Now to hook it up to an X-Y table (like a plasma cutter or torch) to write CNC programs to not only experiment with the patterns, but to be repeatable when you finally get good results. Save programs for Ford doors, Dodge roof inserts, trunk lids, etc. Hmmmm, even bigger scrap pile! Bob
__________________
Bob Persson

Last edited by BobPer; 03-20-2011 at 03:53 PM.
Reply With Quote
  #30  
Old 03-20-2011, 06:50 PM
steve.murphy steve.murphy is offline
Member
 
Join Date: May 2009
Location: Brisbane, Australia
Posts: 650
Default

That's an interesting idea ob.. I was thinking a female mold made from concrete or something similar.Steve
__________________
Steve

ærugo nunquam dormit
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 On

Forum Jump

All times are GMT -5. The time now is 05:20 AM.

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