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Large flared cone shape: how?
I haven't posted in a while as I have been sidetracked on a historic house reno. Finally getting back to things I enjoy making.
I had someone contact me about making a table base that was basically a cone, cut in half with a vertical slice and then the two pieces walled off and separated by a few inches. Fairly simple but I decided that their request was not very stable. The proposed solution is to flare the bottom out to make a larger base (think trumpet shape with 12" diameter top, 28" dia. bottom, 30" long) see sketch below Material will be CRS with an internal structure to actually support the tabletop. The sheet metal CRS will be a shroud to conceal the frame and not weight bearing. Probably apply some sound deadening material on the inside of the shroud to make it seem heavier than it truly is. The problem is I'm not exactly sure how to make it. It seems like it's too much stretching/shrinking to make each half out of a single piece. On the other hand, making each half out of several vertical pie slices presents it's own problem of matching butt seams. Thoughts? bob_card_base_conical_1_smooth.jpg
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Steve Better to be a learn-it-all than a know-it-all Facebook Page: fab.weld.wood WWW: http://www.fabweldwood.com |
#2
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The larger the base the less leg room.
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Norm Henderson |
#3
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This is a classic example of a shape that is perfectly executed by being spun.
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Karl Heinz |
#4
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I had the same thought about spinning but don't have the equipment to spin it. Not worth the time and money to make equipment for a single piece. On top of that, it's a skill that is not easily learned especially when dealing with large pieces.
In regards to the leg room, I agree. A large flat base plate was initially proposed but quickly shot down.
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Steve Better to be a learn-it-all than a know-it-all Facebook Page: fab.weld.wood WWW: http://www.fabweldwood.com |
#5
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Plasma
Go to your local Sheet metal shop have them plasma out a 24" to 12" (or whatever you want for the top and bottom diameter minus a couple of inches for the flare) reducer over 36" length this may seem tall but you will be able to cut to the correct H after forming. This top end may change from 12" to 13" or so when cutting down but that shouldn't be a show stopper. Shear the blank in half or thirds, have them roll it to a cone. Now just e wheel a reverse into the base.
Later Mig
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Matt Mig |
#6
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Quote:
The conic layouts are online. Just plug in your numbers and run the calc. I use a large round T stake for rolling the cone, hammering the point area to help it close. Butt weld and planish. I have found through much practical experience that a good solid air hammer makes reverses accurately and in a practical amount of time. I just used a flimsy blue deep throat "planisher" that bounced like mad and pounded my metal DOWN rather than simply smoothing the weld. It did make a lot of noise tho.
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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. |
#7
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Hi Steve,
I've made smaller versions of these shapes by starting with a cone made to the average shape of the trumpet, then "raising" the cone into the trumpet shape with stakes and hammers (wooden is fine, if that's easy for you). A section of the finished shape can also be made of wood as a form to finish the work over. Working with both halves of the cone temporarily tacked or riveted together will help keep the cone in a favorable arrangement as you work it. Move around the work in a gradual regular pattern. Make one of your plywood/threaded rod bucks to check your progress?? There's some guesswork and variability involved in the process as described but I'm supposing you're ok with that. I found this to be a interesting, and valuable exercise; one where the work goes more easily than expected. Converting a flat (or conical) to a reverse shape while holding the part in arrangement is a good example of a drawing process. Alternatively, would your customer be open to the look of overlapping riveted pieces or a multi-faceted trumpet approximation? |
#8
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wow! thanks for all of the great input!
Being new to sheet metal work (frankly all metalwork), I don't have a sense of how much stretching and shrinking is possible. Starting with a conical section makes sense. Making the cone halves in a single piece would awesome as there won't be any welds to smooth out. Riveting sections has been discussed and is being presented as an option. Being a recovering engineer, the math isn't an issue and have done it before on other projects. Of course, having a web page to help with calculations is a plus. Making a wood form sections, bucks, stakes, and e-wheel are all immediately in my wheelhouse. I don't have an air hammer at this point as it's out of my budget (money, air CFM, shop space, etc.). Depending on the customer's decision, I plan to make a scaled down version to figure the technique out. Even if the customer goes another direction I may still make a scaled model just to learn from. Many thanks.
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Steve Better to be a learn-it-all than a know-it-all Facebook Page: fab.weld.wood WWW: http://www.fabweldwood.com |
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