Metal Round Bottom Sail Boat

A break press can be used to create a faceted surface which approximates a curved surface. More, narrower facets with shallower angles between adjoining facets improves how close the faceted surface approximates the curved surface. With sufficient facets the resulting surface can be very close a rolled surface.

Several decades ago the group I worked in was building a wind tunnel and turning vanes with quarter-circle profiles were needed. The in-house shop said they couldn't make them because they didn't have large enough rolls so the job was sent out. The outside shop used a break with the angles between facets of a half-degree or less. When the in-house shop saw the vanes they protested and said they could have made them with a break if they had thought of it.

 

It seems you are the biggest fool here Your comment and bad mouth about welding just sums up your knowledge of steel manufacturing and total lack thereof when it comes to welding steel hulls, period.
Seems like you are also short minded, in your very first opening post you mentioned what you do and I quote; "I work well with metal, grew up in my Pops shop, and have the know-how, but lack the experience with this sort of build. " Why do we need to ask what you do? Surely, your comments and lack of metal behavior clearly suggest otherwise...

This is not my style and ethical to do this but under the circumstances and tone of your post quoted, I believe Mr Dennis Schaffer would understand and forgive me by mentioning this.
I actually received 2 emails from Mr Schaffer re the issue at hand and the content would rock your flat world but is confidential. At least he wrote in a civilized manner as a professional do and I responded also in a civilized manner to his questions and observations with quite a few pictures to clarify some issues raised. And I invited him to contact me again should he need further information or discussion of issues.

Your tone of voice and serious insults are not welcome here and I suggest you take it elsewhere. In post #1 you asked for input and you received some. Most people here are professionals in their fields, many whom had built boats and know what they talk about. Others structural engineers and yacht designers, but as a new greenhorn here you would not know that.
If you needed confirmation of something you had already set your mind to, sorry to disappoint you. That said, if it was really a new and easy way of building procedure in steel as claimed, these guys on the board would have debated it in a big way pointing out pro's and cons. But, basically everyone contributing had the same thoughts about what was claimed and said their piece.
Finally, to be honest is a virtue and although you can fool others, you cannot fool yourself, hence the straight answers given here by all involved, even if it is in contrary what you want to hear or believe.

 

David, you are correct. The more bending lines you have the smoother the result when forming a curved section with press brake. I had formed many cones on a press brake during my tenure as boilermaker before retiring, and most of them you would be hard pressed to notice it was formed on press brake looking at the outside (bending lines on inside)

However, the only times a press brake was used is when the smaller end diameter of the conical section is smaller than the plate roll roller diameter. The plate roll is the preferred method shaping plates.

 

I found a pic of a plate roll (new term to me although I've seen 'em before) and it certainly makes more sense than using a break for approximating a curve. Does it only do cylinders or is it capable of cones? I can see how it could be automated to produce a bezier, but is that actually done?

 

Yes you can vary the radius from one side to the other just by adjusting the rolls . If you were rolling a full cone shape first you would have to figure out the pattern for the cone then when you run it through the roller you have to stop and adjust the metal every so often to keep the rollers square with the radius's on the ends. It is more operator skill with trial and error.
I use to get a kick out of watching a friend of mine doing sheet metal work
He did everything old school, he would make a rollation pattern for the cone, some where offset cones and some were square on one end, but he made it look so easy

 

Terry, the correct term is pyramid plate rolls. You get different types and the most common ones are those that have the two bottom rollers fixed and the top roller adjustable. The adjustment are "flexible" so to speak and the roller can be lowered or lifted more on the one side or the other or be lifted parallel.
These adjustments can be done manually or hydraulically - depending on machine.
Another limitation of these plate rolls is the fact that you have to add at least the diameter size to the edges (joint) of the plates rolling tubes or conical sections because it cannot roll to the ends. You usually roll until the ends overlap and the off cut marks align - then trim off these ends and fine tune rolling until ends meet - align and tack weld together. The cone or tube is removed from the plate roll by opening the end holding the upper roller in place. To prevent roller from dropping, you have to lock it in place with lever for that before opening the roll.

Then you have plate rolls that have all three rollers adjustable and this calls for some real operators skill, but usually these plate rolls are CNC driven, but I did time as an apprentice on a manually adjusted one.
The benefit of this plate roll is the fact that you do not need to add the off cut piece as described above to your plate - it rolls the edges directly till the ends (joint) meets.

Rolling a concentric or eccentric (the so called Bezier section) cone is very simple and is done on the end of the rolls. An adapter roller or guide is fitted against the opening end support on which the smaller end / diameter of the cone plate will run against. The flat developed cone plate (usually banana shaped) get inserted in the rolls and end of plate aligned square - iow parallel with top roller and the small side against the inserted guide or roller. Then it is just a matter of running the roll forward and backwards - no further alignment - adding pressure gradually and being careful not to over do it and let the cone fall out of roll..

When you want to roll a section that has more curvature on one side than the other or some cambered plates, Tazzman's description is correct and you can put more pressure on the one side than the other by manipulating the top roller adjustments. BUT, a cone cannot really be rolled that way (will form a spiral if rolled in centre of roll) and have to be rolled against the end on a roller to take the arc / swing the plate will need and it needs to slow the smaller end so the large side of the plate can swing through at the same time as the smaller end against the guide roller. Much like a car differential when taking a turn whereby the outer wheel will turn faster than the inner wheel

No roller can form a cone when the smallest diameter of cone is smaller than the diameter of the roller, period. This is when the press brake is called upon if the small side of the cone is smaller than the roller diameter. The drawback of press brake cones are the fact that the have to be made in half shells due to the limitations of a press brake in forming round forms and leave you with two joints instead of a single joint when cone is formed on plate rolls.

Hope this ramble helps you understand the basic workings of pyramid plate rolls.
However, as Tazzman said, it is really operator skill that counts but more importantly, the plate has to be developed accurately to have a proper and decent cone. Luckily concentric cones are easily developed with only a pair of dividers or similar or triangulation (more advanced method) if no large dividers or "treble points" are available.
Eccentric conical sections can only be developed by triangulation method making it unsuitable for amateurs.

 

Very interesting Wynand --and well written, I followed every word of that.

 

Thanks Wynand
Lot better description than I can give , I have a small manual one IE hand crank. I will have to see about attaching a guide roller to it
Anyone interested take a look at YouTube, Lot of plate and cone rolling videos
http://www.youtube.com/watch?NR=1&feature=endscreen&v=ekicY_oNE7I

 

Here is also a nice video showing a cone being rolled. If you look closely you can see the cone guide or dolly fitted at the end just short of the yellow gate under the top roller.
Pity it does not show how the end gate opens to remove the cone.
http://www.youtube.com/watch?v=8YAOPpAH1E0&feature=related

 

I went out to the shop yesterday using the roller to make basket strainers, simple straight rolls of expanded metal and flat strip. took a look to see about mounting a side roller, not an easy task on this one, top roller is stationary with both bottom ones adjustable . might be able to make something that mounts to stand on one side and keep it as close as possible to the pinch and upper roller, they are vertically inline with each other