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  #31  
Old 10-01-2016, 10:50 PM
Charlie Myres Charlie Myres is offline
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Quote:
Originally Posted by Futterama View Post

Charlie Myres, thanks, good advise on the acid, but I'll try to avoid putting hot metal into acid as leoitch mentioned, it could be a bit dangerous.


Attachment 38951
It is not as scary as it sounds.

A plastic apron and gloves and some eye protection is wise, but I have been doing it for over 30 years without any issues.

The beauty of the method is that it saves a lot of mechanical cleaning.

I like the progress you have made so far!

Cheers Charlie
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  #32  
Old 10-02-2016, 02:18 AM
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Cut the blank into a circle and try it again.
You have to much metal around.

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  #33  
Old 10-02-2016, 02:38 AM
Futterama Futterama is offline
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Cut the blank into a circle and try it again.
You have to much metal around.
Thanks, I actually wondered if it makes a difference whether the blank is square or round. I'll cut the next one round and use stronger plates that doesn't break.
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  #34  
Old 10-02-2016, 07:43 AM
Futterama Futterama is offline
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Some progress. Got some really hard wood floor planks from my father and tried those. They worked better but still gave in.
The blank is OD 120mm.
The wood punch survived the abuse.

Wood plates prepared:
DSCF4213.jpg

Rounded edge on the lower plate:
DSCF4214.jpg

Spacers, total of 0.8mm:
DSCF4215.jpg

The blank on the lower plate:
DSCF4216.jpg

Refurbished wood punch (reused the one with the marks):
DSCF4217.jpg

Top plate mounted, blank in place between plates:
DSCF4218.jpg

Bottom side of the plates with countersunk bolts:
DSCF4219.jpg

All set up in the press:
DSCF4222.jpg

The lower plate broke at 2t (4000 pounds) pressure:
DSCF4223.jpg

Bottom view:
DSCF4224.jpg

Punch and top plate removed:
DSCF4225.jpg

The result. Now quite there yet:
DSCF4226.jpg

Next attempt with 10mm steel plates:
DSCF4227.jpg
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  #35  
Old 10-02-2016, 07:52 AM
tom walker tom walker is offline
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Martin, thanx for documenting your project. I'm sure i'm not the only one that learned something thru your efforts. Tom
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  #36  
Old 10-02-2016, 08:18 AM
John Francis John Francis is offline
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Thanks for posting you project. We are following your progress.(over 1,000 views!). Some clamping force/resistance may help some, watch video https://www.youtube.com/watch?v=RhG8gISbWMA
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  #37  
Old 10-02-2016, 08:19 AM
Larry4406 Larry4406 is offline
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Interesting and learning as well.

The attempt with the wood plates looks like you are almost there. I'm betting that the metal plates will work for you.
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  #38  
Old 10-02-2016, 09:41 AM
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Cut a smaller size circle

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  #39  
Old 10-02-2016, 10:18 AM
Futterama Futterama is offline
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Quote:
Originally Posted by Ben View Post
Cut a smaller size circle
Quote:
Originally Posted by mark g View Post
I'm just suggesting to start with an oversized piece of metal, so that the metal has more resistance to being pulled into the die. The metal will tend to "draw" better and with less puckering. Then trim to finished size after.
So if I started with a too small blank, and now use a too big blank, what size blank should I use when half sphere diameter is 42mm?
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  #40  
Old 10-02-2016, 11:21 AM
Marc Bourget Marc Bourget is offline
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I'd add more radius. The sharp corner forces the shrinkage to occur all in a short distance. The slip ring method (relieve the bottom side of the clamp plate so the blank will more-or-less stay flat while being (stretched and shrunk) pulled into the hole.

The radius dimension controls the relative degree of stretching and shrinking. If the radius is small, the force is also higher, making it tougher on the female forming block.

FWIW
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