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
  #21  
Old 02-14-2022, 11:32 AM
blue62 blue62 is offline
Member
 
Join Date: Aug 2016
Location: Woodland Wa.
Posts: 315
Default

Quote:
Originally Posted by BTromblay View Post
Hi,

I have struggled with reverses as they are very common on airplanes, here is several things to consider.

When developing a reverse, the edge must become thinner that the middle of the panel. We can do this by shrinking the middle and stretching the edge. Shrinking of the middle is the most challenging of metal shaping processes, for some reverse's, you can get a way with only stretching the edge. What is critical, is not stretching at all in the middle or what we call the "No Blow" zone. Only extremally light planishing can occur in the middle or you will take the shape back out of the panel, if you can avoid planishing this area, the better off you are. The "No Blow" zone can be found with a paper pattern, where the cut in the paper ends, is the start of the no blow area, in basic terms. For the work that I do on aircraft, material thickness can be critical, so I can't always stretch the edge into oblivion to develop the reverse. I use a Anticlastic stake and shrink the middle first, then go onto the edge stretching. By doing this, I can create a tight reverse and only loose several thousand of an inch in material thickness. I can post pictures, but if you look up "anticlastic forming" on Youtube you will get the idea.

All of this can be done with basic tools and it appears to me that you would not need to shrink the center as your reverse is not that tight.

I'm in Mukwonago Wi, if you need help.

B

Bill

I agree that the Indy car panel does not need any shrinking in the center.
If he is worried about the edge getting to thin he could cut the blank a few inches long on that end. Use that extra metal to help create the reverse by stretching then cut that thin excess metal off.
__________________
Dave Bradbury
Reply With Quote
  #22  
Old 02-14-2022, 01:37 PM
crystallographic crystallographic is offline
MetalShaper of the Month October '14 , April '16, July 2020, Jan 2023
 
Join Date: Dec 2010
Location: Western Sierra Nevadas, Badger Hill, CA
Posts: 4,388
Default "Shrinking" on a "reverse, saddle, or flip."

From the bit of metalworking I have done, "shrinking" does not help to make a "reverse, saddle, or flip" .... (As Mr. Bradbury is so gently pointing out.)
.... BUT - shrinking helps correct the mistaken shaping strokes that have taken the reverse too far or in the wrong direction.

Mostly, anyway....

Once, on a very rare occasion .... I used shrinking to shape a reverse :

I had a big aeroplane re-skin job come into the shop which needed a large shaped reverse. 5feet long and 3feet across and only .032" thick, 2024 .... T3 ... and on a "one-off" experimental modification for a jet .....

I was greatly reluctant to stretch a big reverse into such an odd and thin panel. But stretching is the way to do this in production - 99.9% of the time....

But the shape can be shrunk into a panel ... for sophisticated application, and on large panels ... (not just for small shop demos of also can do thusly ...)

P1120519 copy.jpg
Good thing I had a pneu. shrinker with an 18in throat on hand ....
Hulk, proto, copy 2.jpg
.... so I carefully shrank the center over the long distance needed ...

P1120522 copy.jpg
and then just planished the whole panel to fit nice and tight.

It worked! (Very critical inspections were done on this job - micro-photo inspections, x-ray flaw-checks, laser contour measuring, hardness specs .... sheesh! ...
no rejects, tho ... )
__________________
Kent

http://www.tinmantech.com

"All it takes is a little practical experience to blow the he!! out of a perfectly good theory." --- Lloyd Rosenquist, charter member AWS, 1919.

Last edited by crystallographic; 02-14-2022 at 03:08 PM.
Reply With Quote
  #23  
Old 02-14-2022, 02:18 PM
Jaroslav Jaroslav is online now
MetalShaper of the Month April 2020, September 2021, November 2022
 
Join Date: Dec 2012
Location: Czech Republic
Posts: 2,601
Default

Kent. Yes, know how and when to use the right way.
I think shrinkage is the right way for this part.

The tapes that hold the shape for inspection are also quite important.

Large panels with a small bend are "panels from hell". They look simple, but if they are to be accurate, they will not forgive the wrong move.
I admire parts for planes. I would be afraid of cracks ....
__________________
Jaroslav
Reply With Quote
  #24  
Old 02-14-2022, 02:30 PM
blue62 blue62 is offline
Member
 
Join Date: Aug 2016
Location: Woodland Wa.
Posts: 315
Default

Kent,
You do some amazing work.
When I asked my question in post #18 as to if there was any shrinking in the panel I mentioned, I already knew there was not. I was trying to point out to Denny G. that stretching would be the easiest way to do his panel.
I figured conformation from someone of your experience and ability would help get my point across.
__________________
Dave Bradbury
Reply With Quote
  #25  
Old 02-14-2022, 02:53 PM
Jaroslav Jaroslav is online now
MetalShaper of the Month April 2020, September 2021, November 2022
 
Join Date: Dec 2012
Location: Czech Republic
Posts: 2,601
Default

Dave, there's a problem with thinning material on the plane.
You can stretch material for design things. However, the central fiber must remain at its original length or shrink as Kent demonstrated. But that's a different level .....

Or you can do smaller things my way ... again, not touch the center thread.

https://www.allmetalshaping.com/showthread.php?t=20460

https://www.allmetalshaping.com/showthread.php?t=18968
According to the zero reaction, no one in EW tried it ... That's a mistake on your part. Hammer and sack is the highest science.
__________________
Jaroslav
Reply With Quote
  #26  
Old 02-14-2022, 02:57 PM
crystallographic crystallographic is offline
MetalShaper of the Month October '14 , April '16, July 2020, Jan 2023
 
Join Date: Dec 2010
Location: Western Sierra Nevadas, Badger Hill, CA
Posts: 4,388
Default

Quote:
Originally Posted by blue62 View Post
Kent,
You do some amazing work.
When I asked my question in post #18 as to if there was any shrinking in the panel I mentioned, I already knew there was not. I was trying to point out to Denny G. that stretching would be the easiest way to do his panel.
I figured conformation from someone of your experience and ability would help get my point across.

Hi Dave,
Thank you.
Yes, I understand ... and was supporting your line of reasoning with the follow-on posting.
I'll add a thread pertinent to this topic ... thanks for the kind nudge.

__________________
Kent

http://www.tinmantech.com

"All it takes is a little practical experience to blow the he!! out of a perfectly good theory." --- Lloyd Rosenquist, charter member AWS, 1919.
Reply With Quote
  #27  
Old 02-14-2022, 03:15 PM
crystallographic crystallographic is offline
MetalShaper of the Month October '14 , April '16, July 2020, Jan 2023
 
Join Date: Dec 2010
Location: Western Sierra Nevadas, Badger Hill, CA
Posts: 4,388
Default

Quote:
Originally Posted by Denny Graham View Post
Kent, I've been beating my self to death, or should I more correctly say, beating a $200 sheet of .063" 3003 to death for the last two months in a futile attempt to form an extreme reverse curve in the upper cowl of a 3/4 scale Miller 91 Indy car that I'm building the body for. I have an air hammer, I have an e-wheel, I have many hand tools, that is, slappers, hammers, mallets, stumps, bags. I do 'not' have a Pullmax or any sort of expensive power hammer, etc. with linier stretching or shrinking dies.
The discussion in this thread seemed to be about as close to the shape that I'm looking for as it is very similar to a Hyperbolic paraboloid, which was mentioned in one of the earlier replies.
This saddle or potato chip or reverse curve shape obviously is one of the hardest to master as there is NO, NOTA, ZIP video taking you thru the process. Lots of metal shapers get you started on the basics for a 'shallow' reverse curve, but I have yet to see anyone complete the shape for an extreme reverse curve. Having been an EAA member for many decades, I've seen this shape applied to many wing farings where the wing meets the fuselage. Many of the 20's GP cars used flared cockpit cowl's around the steering as did most of the 30's thru the 60's midget, sprint and Indy dirt cars. Any advice would be greatly appreciated.
dg

Hi Mr. Graham,
What sort of "air hammer" do you have?
I might be able to help you modify that air whacker - so that it makes your "teaching errors" happen a whole lot faster - so you can arrive at yer accurate completion much quicker ... .....
(learn from others' mistakes b'cuz ain't 'nuff time ter make 'em all y'sef.)
__________________
Kent

http://www.tinmantech.com

"All it takes is a little practical experience to blow the he!! out of a perfectly good theory." --- Lloyd Rosenquist, charter member AWS, 1919.
Reply With Quote
  #28  
Old 02-14-2022, 03:55 PM
blue62 blue62 is offline
Member
 
Join Date: Aug 2016
Location: Woodland Wa.
Posts: 315
Default

Quote:
Originally Posted by crystallographic View Post
Hi Dave,
Thank you.
Yes, I understand ... and was supporting your line of reasoning with the follow-on posting.
I'll add a thread pertinent to this topic ... thanks for the kind nudge.


Kent,
I think once Denny G. starts to get the idea that his panel is created by controlled stretching and some practice on some scrap that he will begin to get some where.
__________________
Dave Bradbury
Reply With Quote
  #29  
Old 02-14-2022, 04:01 PM
blue62 blue62 is offline
Member
 
Join Date: Aug 2016
Location: Woodland Wa.
Posts: 315
Default

Quote:
Originally Posted by Jaroslav View Post
Dave, there's a problem with thinning material on the plane.
You can stretch material for design things. However, the central fiber must remain at its original length or shrink as Kent demonstrated. But that's a different level .....

Or you can do smaller things my way ... again, not touch the center thread.

https://www.allmetalshaping.com/showthread.php?t=20460

https://www.allmetalshaping.com/showthread.php?t=18968
According to the zero reaction, no one in EW tried it ... That's a mistake on your part. Hammer and sack is the highest science.

Jaro,
Yes I see airplane parts need special treatment.
I always block out any shape I am having problems with.
The hammer and stump or hammer and sandbag help me understand what the panel needs to get the shape I am going for
It does make the arm tired though
__________________
Dave Bradbury
Reply With Quote
  #30  
Old 02-14-2022, 04:43 PM
Jaroslav Jaroslav is online now
MetalShaper of the Month April 2020, September 2021, November 2022
 
Join Date: Dec 2012
Location: Czech Republic
Posts: 2,601
Default

Dave, while studying shaping, I started shaping with a machine - a very old Eckold with a very bad tool. Later, I made one of my own bombing tools that worked very well. Later, I equipped myself with other machines and tools. Later I welded EW from some old transport truck. Later I made EW from a band saw. At the saw, I already knew exactly what I wanted and what I expected it to do. Only then did I buy the first mallet. I use the mallet as an additional tool. That's the huge difference in thinking and shaping.
Using paper, I understood what fibers I should adjust and where.
It doesn't matter which method is used. I try to combine all the ways.
I remember a sentence from Peter Tomashini. The plate must always be soft. If you hurt him with a hammer, you've reached the end of shaping. It's hard and you're done.
Sometimes it's good to bend the sheet metal on the table or over the knee and you see places where you need to pull or stretch the fibers, but that's about experience. Everything needs its time and peace for thoughts, to break a lot of metal, to try, to try and to try. Don't be afraid of stupid experiments and the fact that someone is better. He also started.
__________________
Jaroslav
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 09:44 AM.

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