Ducati Monster Forum

Got into an interesting discussion at work today about how exhaust pipes are made.

Bent vs assembled.

My gut tells me bent is better but trickier.  Esp with "soft" metals like Ti. 

Thoughts?

There are limits to how sharply you can bend tube in a mandrel bender, which is why you see some of the cut/welded sections or "pie cuts" out there.


Some of that is simply to show off welding skills.

There is MUCH more potential for problems with the welded method, and it takes a lot of time fitting, and skill welding to make sure the inside of the tube is smooth as well.


There is also a cost factor as well.....I could mock up a complete exhaust system, and have it mandrel bent in one shot.  Unfortunately the cost to program, setup, and make one system would be prohibitive, so I buy mandrel bends and cut/fit/section them to work.

I would also think that bent is better as you would get a less turbulent flow.

By running a high pressure liquid through the pipe you are bending you can get more extreme bends.  (I know that is how they bend the harley v-rod frame)

yeah, i've read about that method, but i am looking at picking up a mandrel bender... those hight pressure liquid benders are $$$$$$$$$$$$$$$$$$$$$$

Wow, that sounds similar to "hydroforming" that some car-makers use on their frames (Corvette jumps to mind)

Didn't know that an individual could get a machine to do that, doesn't surprise me that its bank.

yes an individual can get one, but i didn't see anything less than 7 figures for them. 

so that individual would have to be pretty connected.

the regular mandrel benders with cnc I am seeing start around 40k and the NC type start at about 7k

http://www.vansantent.com/tube_bending_machines/Baileigh150-S.htm (http://www.vansantent.com/tube_bending_machines/Baileigh150-S.htm)

not a mandrel bender.

Sharpe Products NISSIN 3D Tube Bender Video (http://www.youtube.com/watch?v=ot0Cxmk2aa4#normal)

A decent mandrel bender starts around 25K, and goes up quickly from there.

yeah, i gathered.  i didn't see any that cheap though, they were all in the 45k range.

these 6k tube benders -- how do they compare to a proper mandrel bender?  from what i've seen, the tube output is pretty good.

Not familiar with the ones you are talking about, but I'd venture a guess it's going to kink thin-wall stainless or mild either way.

The less than $1K die type tubing benders do a reasonably good job on heavier wall DOM tubing.  The external dies keep a pretty good form around the tubing OD as it's being bent but I understand that they will do a crappy job on thin wall exhaust tubing.

I've seen some pictures of some nice bends done free hand by packing the tubing very tightly with sand using a threaded ram packing device on the end.  Then heat the tubing with a torch and bend it free hand.  I think this involves a lot of artistry to get right.

I'm guessing that the lower end (under $1k)  non mandrel benders from the likes of JD2, Baleigh and Pro-Tools might work OK with  exhaust tubing if it was first packed tightly with sand to hold it's shape while being bent.  But this is pure conjecture and I tried Google and didn't find anyone trying it.

I wonder if truckinduc, the kid with the great thread over on the Accessories and Mods board has any thoughts on making exhausts.  Haven't seen him post for awhile though.

Bob

The lower end are called Rotary die benders, but the one I am looking at is a compression bender (EB-300) that is made specifically for exhaust tube -- it's not even close to $1K !

I watched the video link below and there was a drastic change in the tubing cross section in the bend area.  Suitable for repairs to a beater pickup truck, but not something I'd want for making a motorcycle exhaust.

http://www.bii1.com/videos/exhaust-bender-video.php (http://www.bii1.com/videos/exhaust-bender-video.php)

Bob

Happened across this website:

http://www.bendtooling.com/index.htm (http://www.bendtooling.com/index.htm)

This company evidently makes mandrels for benders.  I wonder if there mandrels could be adapted to work with  a lower priced rotary die type of bender.  Never used a mandrel bender but it seems like getting the mandrel back out after the tubing is bend might take some hydraulic power.

Bob

Tiz, how many exhausts are you planning on building?  If its not hundreds I wouldn't think a bender would be worth the price.

Im assuming you have some way to cut and weld tubing. Should that be the case check out http://www.schoenfeldheaders.com/U&JBends.htm (http://www.schoenfeldheaders.com/U&JBends.htm)

Lots cheaper than a bender and you get mandrel bends.