CBD's Second Nelson Chimney Cap Page

This project was inspired by this photo of an 8 sided bell shaped copper dome built by some other craftsman. David Nelson in Tampa, Florida sent me the image on the left to show me what he had in mind for the chimney cap cover as part 2 of 2. The other chimney cap he had me build resembles a Bishop chess piece: http://copper-by-design.com/cc/cp/Nelson.htm

He first contacted me 4/29/09 and we gradually worked out this project through exchanging over 70 e-mails along with several diagrams and photos like this photo on the right to show this bell stretched to match his limited specification to fit under this tiled roof over his chimney pipe along with a 24" tall finial.

I just before fabrication began I volunteered to build this with twice as many sides, so this has 16 faceted sides, instead of just 8. This helps make this look a lot more rounded, as you can see here. This enhances the bell shape without generating a much greater cost to form this in a completely circular manner by stamping or hammering the copper to bend in 2 directions.

This is the structure I needed to make this fit inside. I had a limited height inside of just 57". It is rather trick to do this all remotely; relying on just the clients measurements. It is also important to design this with a near invisible attachment as well.

Building the Base Pan:

This show the varnished 3/4" oak plywood I use for the base under the pan that will help anchor this down in a strong wind storm. I bevel cut the sides at a 45 degree angle on my table saw for added style. I made this inset rim to attach the plywood from underneath and also to raise up the pan, so it can shield over the top edge of the roof tiles surrounding it.

Then it gets covered with this copper skin to keep it shielded from the elements.

Covering the Base Pan w/copper:

I needed to make this rain shield in the middle to surround the flue pipe. The 6" tall spark arrest screen vent area around this is made with a 16 gauge stainless steel expanded metal screen in an 8 sided unit that the whole bell will be supported over to look as if it is suspended above the pan 4", so this exhaust area was very limited.

I needed to make sure there was enough exhaust vent area displacement, so I had to make the area horizontal as well to add more ventilation surface to this design. The client approved this design and has been very pleased with the results after seeing it in these photos I had sent as I built it.

Building the Bell Support Base/Flue Vent:

The hood exhaust head to set over this has to transition from an octagon to a 16 sided shape to look more cylindrical. These screens are what I get my hands lacerated on more than any other aspect of my work, so it's important to wrap all the edges of this SS screen in copper sheet metal, so there will be no sharp edges exposed once completed.

As all these pieces get fastened down it gradually adds more and more strength to this structure, but it still needs some cross bracing. The client had me add this 14.5" flue liner. I made this circular with a rim on the top and bottom edges for added strength. It is connected with 32 rivets through the rain shield

Building the Support Braces:

It took me a few days just to build these 32oz copper roof support frames and attach them securely. I designed these where the exhaust can still flow up under these braces.

Then the one piece 34" wide outer bell rim gets made and attaches outside these support frames and the edges get folded under the SS screens frame work.

As usual this was a bit more tricky to build than I had imagined and not something I can charge more for, but I feel it was worth the extra effort towards the Client's long-term satisfaction. It is much easier to build it well now, than to have to rebuild it later on.

Building the Bell:

Here is the decorative copper bell mid-section being formed in one single sheet of copper and attached right over the cross bracing. I thought the whole weight of the bell would be resting on the outer edges of the bell's rim, but this construction made the thicker copper cross bracing less important. I am often guilt of over-kill in many aspects of my work and this is a good example.

I was going to just make a simple slope from the outer edges up to the mid-section, but at the last minute while forming the aluminum templates I came up with this added bend to give this a bit more ornate styling.

Here is some shots of the outer bell hood being formed. The many rivets are very noticeable at close inspection, but after this has tarnished to a dark brown they should be a lot less noticeable. Solder may be a way to attach these without rivets, but it would not be able to withstand 1/4 the heat that copper can handle. Everything is only as good as it's weakest part.

Building the Finial Support:

Here is some shots of the finial support pipe being formed and securely attached within the dome of the bell. The bottom of the pipe is soldered together with a double cap system and attached inside this plate that is attached over the bell's mid-section. The right photo shows this plate upside down over the bell.

Then there's this cross brace attached over the bottom caps and riveted together.

Then this is attached over the bell's mid-section.

Then I made and attached this cone over that plate to help support the top of the pipe.

Building the Finial Support:

This support also gave me a narrow surface to attach the 16 dome pieces to in the middle. I decided to also add this middle support ring for the dome.

As you can imagine this is a rather tedious process. It was not necessary to seal these sections with solder of caulk, since this will be sitting under a roof cover. Even if hard driving rains were to splatter over this dome the plate below will channel the water out to the edges of the bell anyway.

Here is the last pie section needing to go in to complete the dome cover, and a photo of the final assembled bell with the finial in place. I had to do some work to adapt the finial here to work the way I wanted it.

Here is the detailed weights and cost break-down I had kept track of during this fabrication:

115# total weight w/brass rod & finial
185# weight of the crate
300# total weight of crate w/contents

111.6# weight w/o brass rod & finial
- 9.7# 2x3 wood weight - 12.67 ln'
- 24# oak plywood weight - 11.12 sq'
- 5.2# SS screen weight - 8 sq'
- 18.9# copper pan cover weight - 15.12 sq'
= 53.8# copper weight
x 0.8
= 43.04 sq' 20oz copper
x $40 sq'
= $1,721.60 for copper bell portion
+ $145.98 for 24.33 ln' of 2x3 boards x $6
+ $166.80 for 11.12 sq' of 3/4" oak plywood x $15
+ $472.50 for 15.12 sq' copper pan cover portion x $ 25
+ $200 for 8 sq' of 16 gauge SS screen x $25
+ $300 for the custom wood shipping crate
+ $400 truck freight home delivery w/lift-gate service
= $3,701.88 grand total for this part of their project
- $2,500 paid 9/17/09, which left a balance of $1,201.88