I'm currently installing the duct work for a cyclone dust collector and needed some exotic fittings when branching off to multiple tools at the end of a run. Custom built fittings are easier than I expected and offer a much cleaner installation. The following is the procedure I used and can be easily adapted to other duct sizes and arrangements.
Step 1: Tools and Materials
- Angle grinder with cut-off blade
- Sheet metal shears
- Blind rivet tool
- 1/8" x 1/8" steel rivets
- Drill with 1/8" drill bit
- Work gloves and eye protection!
- Round duct (I'm using 6" spiral duct for this example)
- Galvanized sheet metal 24-26 gauge (I'm using 22 gauge because that's what I found in the shop)
Step 2: Make the Templates
Step 3: Transfer Templates to Metal
Using a permanent marker, transfer the templates to the round duct and sheet metal. The length of the wye will be determined by the amount of material left under the curve seen in the second photo. Leave a 1/2" strip to form tabs around the sheet metal template.
Step 4: Cut Along the Lines
Use the angle grinder to make the opening in the round duct and cut out the sheet metal. Cut the strip along the curve into 1/2" tabs (see photo). Leave the straight tabs intact but remove the corners where the two meet.
The sheet metal shears can be used to adjust the cuts, or for the entirety of the cutting when using thinner metal.
Step 5: Form the Wye
Form the wye arm around a steel pipe of smaller diameter. A rubber hammer can be used to assist with the bending. The straight taps should overlap without support after forming. Clamp the taps together, then drill and rivet.
Step 6: Bend the Tabs
Check if you can insert the wye arm into the hole on the round duct from the inside. If this is possible, bend the tabs along the curve of the wye until they match the outside profile of the round duct and then insert into the round duct from the inside. If not possible, insert the wye from the outside and bend the tabs over from the inside of the round duct.
Some trimming of the hole in the round duct might be necessary to achieve a good fit.
Step 7: Rivet and Seal
Support the wye while drilling through the outside of the duct into the tabs. Make sure the tabs are sitting flush against the inside of the duct when drilling. Install the first few rivets one at a time. Drill a single hole being careful to avoid the notches between tabs and install the rivet before going onto the next. This approach will prevent misalignment between holes that could occur if multiples are drilled at once. Add enough rivets to achieve your desired strength.
Multiple wyes can now be added in close proximity along a single duct using this method. Seal the seams using an appropriate calking material after you are satisfied with the results.