Technical Tech Week -- Cutting and Routing Exhaust Mandrel U-Bends

I’ve had a few projects in the past where I’ve built my own exhaust from mandrel u-bends. The first one I did simply because I wanted to save a few bucks, the second time was because I was a long ways off before I had a road worthy vehicle.

For cutting the mandrel bends I have a jig I made up that works well for me. A picture of the jig is below. I get into the details later but in summary the jig helps you to cut your mandrel u-bend at the correct angle and in a manner such that the end view of the cut is round.

You can see how I made the jig and how it works in the pics below.



I used MDF to make the jig. The jig body is built up from several pieces of MDF. The thickness of the jig will need to be less than the diameter of the pipe. Here, I used three pieces of MDF. The width of the jig will be the inside width of the u-bend. U-bends will have a long radius bend of 1.5xD (diameter). To get the inside width of the u-bend you can calculate it as 1.5xDx2-D, or measure it. You will find out most of the time it’s a little greater than “theoretical”.









Once you have the jig body assembled, find the center and put a half circle on it with a compass as show below. I then nibble away the excess with a chop saw then finish it off on a sander.







You will also need to drill a through hole on your center mark. I also recess the hole a little on the back for a carriage bolt. You will attach a radius cutting guide with the center bolt. The radius cutting guide is simply a strip of metal with a hole drilled in the middle of it and a slit cut down the center of it. I stack a couple of washers under it to get it to the height of the pipe.





The finished jig is show below. The finished jig allows you to cut the correct angle to match the routing of your exhaust. The jig also ensures you cut along a line that intersects the radius center point of the bend to ensure the plane end of the cut is round.





I use an adjustable square to find the angle of the cut. Put one end of the square on your pipe and adjust the square to the direction you want to route it, see below:



Once you know the angle of the cut from your adjustable square, use it to set up the appropriate angle on the jig. No measuring or math here. The two pictures below show two different methods for finding the correct angle on the jig from your adjustable square.





Once the jig is adjusted, cut the pipe.



The picture below shows the final cut piece and the angle of the cut.



Below shows how to jig up a pipe angle without the straight leg of the u-bend. I often make use of the straight leg but if you have some left over and un-utilized bends you can cut angle sections out of it. The first picture shows setting the piece in the jig. The second and third pictures show the two different methods for finding the correct angle on the jig from your adjustable square.







I use an inexpensive Harbor Freight band saw. I like to use the bi-metal blades by SuperCut. They don’t always have them at Harbor Freight. I think the bi-metal blades are worth ordering because they last much longer.

You can tilt the chop arm up and turn it into a table top band saw as show in the previouse pictures.



For my exhaust supply I prefer aluminized piping and u-bends. U-bends can be hard to find other than mail order. There’s a muffler shop in Tokepa, KS that has a mandrel bending machine, which is really rare given how expensive the machines are. I live about an hour from there so I made a trip to pick up some pieces from him. He may be willing to ship; the shops name is Hogan Muffler & Brake, www.hoganmuffler.com.

For the straight sections I would check with a local exhaust shop before a parts store. In my experience an exhaust shop will give you a better price on exhaust piping.

Hanger and exhaust clamps I get at the parts store. Carquest seems to have good selection of various types of hangers.

You will need a separate jig for each size of exhaust piping you are working with since they all have a different bend radius. For far I have one made up for 2, 2-1/2, and 3 in. pipe.

Building exhaust like this is fairly easy to do though it can be a bit time consuming.

Below are some pics of the exhaust I build for a 52 Chevy I used to own after splitting the stock manifold.











The y-pipe below is for another project I’m working on.









If you’re curious about tone…

Here’s a 216, split manifold, dual exhaust, with 30 in. Smithies:


Here’s a 350 TBI, headers, two into one, with a Flowmaster Series 40:

 

That's a really cool idea. I might have to steal that one

 

Great tech and great job explaining the steps. Thanks!

 

Very cool, thanks for taking the time to share.

 

Very timely tech tip. I am about ready to start this part of my build, and exhaust building is more voodoo than science to me. This really simplifies the process of getting the bends cut in a way I can wrap my head around it, and I have all of these tools already.

Thanks!

 

Very nice. thanks for the tech.

 

That jig is a great idea. would have liked to have one for my last project. I'll be making one this weekend. Bob

 

Nice! Hope to make use of it in the next 6 months .

 

That's clever, nice presentation.

 

Very cool ideas, thanks

 

Nice !!!

 

super neat and handy idea! I build a lot of stainless exhausts from bends, and I think because I've done so many I can eyeball the cuts nearly perfect. Kinda wish I'd thought of this years ago! I use a 12" disc sander to true up the cuts, then you can TIG the joints perfect with no filler rod. makes for a super neat finish.

 

great write up and idea............gonna have to use this one for sure.

 

Thanks. Very good!!


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Nice little tool there!

 

Ingenious!! Installed in my memory bank..{ printed out!]

 

SUPER NEAT IDEA

 

nice! Looks like another reason I need to buy a band saw....

I've built a few systems using straight tube and U bends, but I kind of faked it on the cuts.

I like making the butt welds with my O/A torch...just because...do you mig them?

 

I think you got my vote...

 

I love cheap tech ideas! Great one. BTW, that "square" is actually called a Sliding T Bevel

 

Excellent post! I can now get my cuts correct using a jig! Thanks.

 

Well done Hussey !!!

 

Slick!

 

I like it. Great clear explanation. And your exhaust work looks really nice

 

Simple and effective very good post many thanks

 

That was a great tech, thank you.

 

Good job, I'll be using this one when the time comes. Great pics and write up !

 

awesome!

 

really cool and nice sounding and beautiful looking exhaust.

 

Thanks all! Hope to see some exhaust pics.