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Duct Construction and Uses
Discussion in fabricating and use of products that move air including spiral pipe, duct board and typical sheet metal work.
       


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  #1  
Old 10-21-2013, 04:59 PM
JamesL JamesL is offline
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Default Joining segments of a 4 piece 45deg. elbow

I am a 79 yr. old newbie making one four section 6 in.round- 15 inch mid line radius elbow for my son's hobby wood millworks chip collection system.
I have no trouble making the patterns nor the segments.
But, I am at a loss as how to join the segments. I tried the overlap
method but did not think much of that.
I can braze 24 ga. but not the 30 gage I used because I had it.
In summary,the joints are flush butt joints. I can make new pieces if need be. Should I scrap the 30 ga and make new from 18 ga. and braze or arc weld? I have facilities to fab 18 ga.segments. Or, is there another solution?
Thanks, Jim
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Old 10-21-2013, 08:39 PM
ncscribe ncscribe is offline
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Hi Jim, and welcome. There is a machine made specifically for what you are doing. It is a rotary machine and it is on page 78 of the Pexto catalog in the library here. Some of the rotary machines take some getting used to though. At least for me they have. I have seen them pop up on ebay from time to time. It makes a V shape groove around the lip. It will work the 30 ga well. Doubt if it would do any good on 18ga though. Let us know how it works for you.
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Old 10-31-2013, 07:12 PM
cactassdupree cactassdupree is offline
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Default blowpipe

I've only done a few jobs like this. I remember my Journeyman tell me that "blowpipe needs to be smooth on the inside. Make sure you lap it so the flow is in the right direction. Even though you said it was a hobby thing I question the 30 ga. Might think about something a bit heavier depending on how much use it will get. 30 ga. might wear out. peace Dupree
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Old 11-01-2013, 08:40 AM
JamesL JamesL is offline
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Thanks!- I scrapped the 30 gage and made new sections of 18 gage.
Iam ready to MIG weld the butt joints.
I never thought about the thickness in terms of wear. Makes sense.
I think 18 gage normally uses flanged rings for connections from one piece of existing ductwork to another.
Perhaps I might have to build a power crimper to go along with my home made Vincent Gingery slip roll. Not interested in making flanged rings. Again thanks, Jim.
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Old 11-01-2013, 04:21 PM
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Quote:
Originally Posted by cactassdupree View Post
I question the 30 ga. Might think about something a bit heavier depending on how much use it will get. 30 ga. might wear out. peace Dupree
I agree. 30 gauge is absolute garbage.
It will wear out, and soon.
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Old 11-03-2013, 04:38 PM
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Default Assembling a round elbow

I have 40 years of building sheet metal items. I have made lots of round elbows.
For blow pipe work like someone else already wrote it must be smooth and all laps have to be lapped in a direction that the saw dust will not catch on the raw edges. These elbows I made were spot welded together. All small diameter under 12" round fittings are made out of 24 gauge galvanized sheet metal. If you do not have a spot welder I have riveted the seams, here again do this in a way that no tails from the pop rivet stick in the inside, only the head. I have also hand set & riveted the seam together. You need to allow about 3/8 of an inch for a lap on one side of your pattern. After rolling the gore up and fastening together use a burring machine (thin edge) to put a crease on the lap 3/8 in from the edge. Once that is done, on all gores gently with a tinners hammer using the chisel end over the edge of a piece of steel used as a stake stretch the throat lap out to accept the throat of the next gore edge with out the lap addition. Start in a way so you can rivet the gores together because you can paint yourself into a corner and screw up and can not get into the inside to rivet or spot weld. So look these gores over and figure out the best way to assemble them so you can rivet the laps. I even smash down the rivet part sticking on the inside to make it as smooth as possible.
I wish I could have you in front of me to show you all this.
Good Luck
Mike
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Old 11-03-2013, 09:31 PM
JamesL JamesL is offline
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Default Joining segments of an elbow.

Mike- That was terrific. Would make a good you tube video for us wannabes. For context, I am a M.E. and E.E. Just like to do my own work, and learn something new. I think I understand. I do not have access to a seamer, nor do I know what the seam looks like. I will do some studying.
All the Tinners I knew in the maint. shop are long gone. No one to ask.
Very few shops nearby who make anything except square duct for home
HVAC systems.

Here is what I did on the first one I made. laughing is OK.
I used 18 ga. crs, cut out stock with hand held electric Jig Saw and
finished with one inch vertical belt sander. Rolled with home made slip roller.
Used butt joints,and welded all joints about every half inch with MIG spot
of weld.
After welding one section( gore?) to the next I ground away any interior roughness at the joint with a conical grinding wheel.
I have some short gaps in some the joints about 1/16 wide.
Trying to determing what compound to use to furthur smooth out the inside.

Thanks - Wish I could watch you in action.
Jim
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Old 11-03-2013, 10:11 PM
seems39 seems39 is offline
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Default Assembling elbow

Hi Jim
Good to hear you figured out a way to build that elbow. The way you did that was similar to the way we fit a stainless 16 ga elbow for welding with a TIG welder using a disc sander to get the edges to fit up tight.
To smooth the gaps on the inside where the gores meet, I would use some 2 part epoxy metal like "Devcon steel" or something similar. You can make it aerodynamic with smooth transmission from one gore to the next. The area to pay close attention is the "heel" the outer radius. This where the air wants to scrub along the inside of the elbow surface. The throat (the inner radius) is a area of least scrubbing. The wear always occurs on the heel and we would make elbows with a flat heel that could be un bolted and a new flat curved piece of metal installed.
I retired from the City of Portland as a Building Maintenance Engineer for 20 years.
After working 15 years as a Sheet metal Journeyman & being out of work 6 months out of a year I decided to find another way to make a living. But Sheet Metal Work is my first love (started when I was 13 years old taught by a real old timer in his home shop a old school tinsmith) next to working in a machine shop & Aero space welding.
All the time I was in the Sheet metal Workers Union I had a full commercial shop at home. When laid off I was making house payments out of my shop building stuff that the other shops did not know how to do. Race car, antique car, custom one of a kind sheet metal copper work, stainless, anything to make a buck. Me and the union did not get along. Their teaching apprentices was very bad. They would turn out not knowing much of anything. I spoke up and told them what I thought of their set up and soon found myself black balled and not being dispatched out on jobs.
I even taught in the apprenticeship school and after quitting taught NON union sheet metal workers how to do layout and fabrication shop work.
Enough of my ranting. If I can be of any further help let me know.
Mike
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