Extreme shrinking?

[raferguson]

I have been playing around with my new helve hammer, and decided to make my first project making a bowl with a 5 inch radius out of a 8 inch diameter circle of 18 ga steel. It went pretty well, the hammer seemed to dome the center of the bowl fine, but then I had to shrink the edges. I was using a tuck fork and hammering down the tucks, but the shrinking seemed to be going very slowly, so I came up with a scheme based very loosely on something I had seen elsewhere on the metalmeet site. The picture below shows it as a three-step process, essentially clamping the tuck to a steel plate to restrain the sides of the tuck while it is heated and hammered.

http://fergusonsculpture.home.att.net/tucking.gif


Did I invent something here? (I doubt it). I don't think that I have seen this technique shown in my sheet metal books, but then I don't have a large library on the subject.

Are there problems with this technique that I should know about? I was amazed at the relatively quick and painless results, in terms of getting a lot of shrink in a short time. I have not rolled it yet, building an e-wheel is my next project.

Richard

[John Kelly]

Hi Richard,

I think one of Kent White's videos has something similar in it if I remember right. I would try heating it to somewhat less than red heat so that it does not deform. I have not tuck shrunk 18 gage, but I've had great results with 20 gage without using heat. The only time I've used heat when shrinking sheet metal tucks is when I had a very stubborn ripple against a hammer form, and then sparingly. Are you doing multiple tucks in the same area? Sometimes it is a question of just doing them over and over until you get the shrink you want. Have you tried hitting the very edge of the tuck one hard hit to form an "M" shape so as to help lock the tuck in place before doing the rest? This seems to help. You can shrink tucks with your helve if you get it set up right as well. It sounds like the way you have come up with works great too!

John www.ghiaspecialties.com

[Gene_Olson]

Hi Richard,

is this what you saw?
http://www.metalmeet.com/photopost/data/500/320forming1.jpg?295
It was in my post about making the repousse cows for the fireplace.

http://www.metalmeet.com/forum/viewtopic.php?t=860&highlight=

Gene

[raferguson]

Yes, Gene, that was what gave me the idea. I did not remember exactly where I had seen it or who posted it. Thanks.

Did you heat it to beat down that big ripple/tuck?

Richard

[Gene_Olson]

Yes, Gene, that was what gave me the idea. I did not remember exactly where I had seen it or who posted it. Thanks.

Did you heat it to beat down that big ripple/tuck?

Richard
Nope, no heat, but this was left over stuff from a project long ago. It starts out real soft on a roll for deep draw machines. It is about as low a carbon as you can go without spending money on the pure iron stuff.
On the other hand after playing with the same piece of sheet for over half an hour this AM, forming, planishing, forming, planishing, forming, . . . no attempt to anneal.
I am going to have to join Wray's camp. Annealing shouldn't be necessary for mild steel if you can planish the whole thing out. If you have a high carbon steel, you might need to anneal it.

Gene

[John Kelly]

I remember Wray posting on the other group a long time ago about clamping the metal to hold the tucks in place. I have found that to be a good way to go... sometimes just one clamp can be used while you hold the other side pressed against it to hammer. I've had luck with wrapping my arm around an almost spherical piece while hammering as well. Most of the time I just do it without clamping.

John www.ghiaspecialties.com

[Gene_Olson]

I remember Wray posting on the other group a long time ago about clamping the metal to hold the tucks in place. I have found that to be a good way to go... sometimes just one clamp can be used while you hold the other side pressed against it to hammer. I've had luck with wrapping my arm around an almost spherical piece while hammering as well. Most of the time I just do it without clamping.

John www.ghiaspecialties.com

I gotta admit, It is Wray's fault, mainly.

A few years ago, he started talking about wheels over on the artmetal forum.

I said, "Say what? How can that work, it's too simple . . ."

Coincidentally, Don Hammer (http://www.metalsmith.org/edu/equipment/ewheel/index.html) invited Chrissy and I over to talk about having an english wheel class.
He demonstrated tucking and trapping the tucks and shrinking the edges, and I was kind of hooked.
He had a post dolly anvil kind of like a tailors ham, symentrical with a constantly varying radius so you could find a good spot to match.

http://www.metalsmith.org/edu/equipment/ewheel/pic07.jpg

Gene

[raferguson]

I will sure try this trick again, since it seemed to work pretty well, but next time I will try it without heat, easier and faster. Thanks.

Richard

[danz]

Richard, I'm going to go out on a limb here, and see how strong it is<G>.

I have heard the process we call 'shrinking' termed 'upsetting'. I think it's a Blacksmithing term and uses heated metal to make the work easier. This a connection I've made in my head, and may not be correct, strictly speaking.

However, if you wanted to put a ball on the end of an iron rod, you might start by getting it red hot (or more?) and then hitting the rod square on the end. You'd be pushing the soft metal into a lump larger in diameter than the iron rod. And you'd do it by hitting in a direct line with the direction you wanted the metal to move.

I think the important concept here is to hit the curve of the tuck in the sheet metal on a tangent. If the force of your hammer blow is directly in line with a perpendicular to a line tangent to that curve, given sufficient force, metal will move and it will tend to be in equal amounts on either side of that perpendicular line (or around that 'point'). So the key is not how cold or hot the metal workpiece is, but the vector of the hammer blow. Skillfully aiming the trajectory of the hammer head will move the metal where you want it to go (back on itself).

Heat makes it easier, faster makes it more effective and a BFH makes a mess<G>. So use a manual hammer, or a power planishing hammer.

Point your hammer in the right direction, and you too, can shrink, I think...

Where *are* my nomex pajamas? HTH...

danz

[raferguson]

I think that upsetting is the blacksmith term for making the bar larger in cross-section, such as by hitting the bar on the end, or just using the weight of the bar against the anvil. All done hot, of course. So I agree with Danz on this, but I am a novice blacksmith.

I am not sure about the angle of the hit making much difference. I was using a fairly flat hammer, and did not want to hit at an angle to avoid making a large mark in the sheet metal. I was pretty much swinging straight down with a one pound ball peen hammer, flat end. With the clamps in place , I was not able to hit at much of an angle even if I wanted to, nor did I have the option to hit first on one side, then the other, I just had to hit straight down in the center, with a little variation, until I had shrunk the tuck.

Richard

[danz]

Hi, Richard. Your reply makes me realize that I left unspoken, that Iwas talking about those instances where the tuck can't be captured by clamps or other means, but that the efficacy of each hit can be maximized by changing the angle according to that 'tangent to the tuck' concept.

I think Wray's illustration shows blows from the hammer at all different points on the tuck, and I think his description of using straight pien or cross pien style hammer heads depending on the contour you are working next to, helps me think in terms of driving the metal into itself starting at that infinitely small point where the hammer face first contacts the work surface and expanding from there like ripples in a pond. The closer the hammer face comes to being tangent to the formed curve of the tuck, at the point you wish to hit, the more effective the strike will be.

Of course, this could be nothing more than a metalshaping philosopher's argument about how many angels can dance on the head of pin. I expect Wray will let me know if he thinks that's so<G>.

danz