Exhaust pipe manufacture?

[Chris Stevens]

Anyone with any knowledge of making very tight radius bends in thin wall tubing? Its probably going to involve a mandrel bender of some sort with ball mandrel, and just wondered if anyone on here is familiar with this area at all?

 

[hotrodder]

Familiar yes, proper experience of owning (or using on a regular basis) 'high end' rotary draw tube bending kit with mandrel tooling and wiper dies; no.
I presume you're talking about a production run rather than one off/bespoke stuff?

What's needed in the way of tooling depends on various things for example wall thickness doesn't mean much without know the tube OD and, generalising, it goes along the lines of

Tube OD divided by wall thickness = wall factor
CLR (centre line radius) divided by OD = degree of bend i.e. a 50mm OD tube bent on 125mm radius is a 2.5D bend
Wall factor divided by degree of bend = difficulty factor

As the wall factor number gets bigger and/or the degree of bend number gets smaller the difficulty factor goes up

Various different manufacturers offer free bending guides that often include tooling selection charts that plot wall factor against degree of bend (D of bend) & suggest the limits for a basic plug mandrel through different segmented/ball mandrels to close pitch segmented mandrels with lots of balls to provide more support. For example http://toolsforbending.com/wp-content/uploads/2012/03/Cap_broch.pdf and http://www.bendtooling.com/BTI_RotaryDrawTubeBendingGuide.pdf

 

[Wallace]

What sort of radius do you need Chris?

 

[Chris Stevens]

Thanks for replies. Heres the type of thing I am trying to make. This is the tightest radius on the pipe, and I get the feeling that welding sections may well be the only way to do it?

 

[Chris Stevens]

Just spoke to someone who makes pipes for historic F1 cars, and he advises 45mm CLR bends in 1 5/8 od tube quite possible but would need specific formers, which cost about £1k.

 

[Shox Dr]

I think you'd need one of those fancy machines that extrude it, as the bends are too close together. Comes out the end like spaghetti

Such as this bit of kit

 

[Wallace]

That is one awesome CNC bender.

 

[Chris Stevens]

I think you'd need one of those fancy machines that extrude it, as the bends are too close together. Comes out the end like spaghetti

Such as this bit of kit

Perfect for small diameter tube, but get the feeling anything made with one of those would cost a great deal of money!
Going to try some 50mm CLR bends and see if the basic design can be altered a little so they will work.

 

[Wallace]

Jetex do a tight radius bend with a 50mm clr but they are two pressed halves welded together.

 

[whm_fab]

what diameter is the tube?

 

[Chris Stevens]

1 5/8.................guy not far from me can do some 50mm CLR in MS, and hopefully it will be possible to use those? Thanks Wallace, a lot of OE pipes are made from 2 pressings welded together, which I guess is probably cheaper than tight bends on tube?

 

[Wallace]

Is that 1 5/8" o/d or i/d Chris? Yes, cheaper to make in two halves as the clr gets tighter. Jetex list stainless but only down to 1 3/4". When I was trying to find some tight 1 3/4" bends locally I found Profusion Customs in Colnbrook via the internet who listed T304 1 3/4" bends, might be worth a call to see if they do the size you want. Is the photo you posted for a bike application?

 

[hotrodder]

My memory of Jetex 2 piece tight radius bends is that they're properly nasty things(?), both the bends in the pic appear to be made the same way.
1 5/8" (42mm) rules out hygienic bends unfortunatly but they exist in 1D CLR for example http://www.berkeleystainless.co.uk/products/hygienic-fittings/1xd-2xd-3xd-90-bends/ Steve (Langy) sells stainless bends that are better quality than a lot of the exhaust suppliers. Better prices too and a wider range of sizes than hygienic stuff. You'd have to ask him but IIRC 1 5/8 shouldn't be a problem, 1D CLR might be?

Slightly mickey mouse but 'cheating' the radius is sometimes neater/better than nasty pressed bends if the radius can't be increased, this sort of thing but not as extreme as the drawing

ETA, probably almost impossible to find in the UK and i suspect the quality probably varies a chunk but FWIW https://www.google.co.uk/search?biw....0....0...1c.1.64.img..28.16.1162.kHdOWzqhzN4 let you cut whatever bend angle you need

 

[Chris Stevens]

My memory of Jetex 2 piece tight radius bends is that they're properly nasty things(?), both the bends in the pic appear to be made the same way.
1 5/8" (42mm) rules out hygienic bends unfortunatly but they exist in 1D CLR for example http://www.berkeleystainless.co.uk/products/hygienic-fittings/1xd-2xd-3xd-90-bends/ Steve (Langy) sells stainless bends that are better quality than a lot of the exhaust suppliers. Better prices too and a wider range of sizes than hygienic stuff. You'd have to ask him but IIRC 1 5/8 shouldn't be a problem, 1D CLR might be?

Slightly mickey mouse but 'cheating' the radius is sometimes neater/better than nasty pressed bends if the radius can't be increased, this sort of thing but not as extreme as the drawing

ETA, probably almost impossible to find in the UK and i suspect the quality probably varies a chunk but FWIW https://www.google.co.uk/search?biw=1271&bih=670&tbm=isch&sa=1&q=1+5/8+stainless+donut&oq=1+5/8+stainless+donut&gs_l=img.3...294384.303541.0.303808.44.23.0.6.6.0.224.2368.8j12j1.21.0....0...1c.1.64.img..28.16.1162.kHdOWzqhzN4 let you cut whatever bend angle you need

Thanks for that very useful info! Some trials bike exhausts are made using 2 pressings welded together, although in my view are pretty nasty........but I guess were cheap to make and light.

Talked to Dave Durrington who runs Maniflow yesterday, and he can help with 1D bends in 1 5/8 tube, which I think may well work fine with slight alterations to the basic design I have in mind.

Pipes I have made to try some ideas are cut and shut ones from other bikes, which work ok, but take ages to make and are really only any use to experiment with.

Have got some pressed aluminium silencer parts though, which are certainly feasible for small scale production, and should work well when done.

 

[hotrodder]

Cheers. Yeah, i reckon it's 'cheap to make' that's responsible as two pressings (or hydroformed sections) welded together can be very high quality although they rarely are. Another reason why they may do things that way is due to the amount of stretching that occurs at the outside of 1D bends reducing the wall thickness?

Dunno if you have a big enough press and/or are already of rubber press forming but

 

[Chris Stevens]

I think Akropovic exhausts are often hyrdoformed formed now, and have seen home built expansion chambers made in that way. Have made silencers using aluminium male/female tooling on small shop press, but a fair amount of hassle getting the tools cast though. Saw a replica RTL Honda back box the other day, which looked as though it had been made with epoxy tooling, which guy was selling for £450 a hit. Guess that once you had the pressings it would only take an hour to make a silencer, thats pretty good profit.

Guess that Maniflow are probably one of the very best exhaust manufacturers in the country, and I will go up and see them next week and get their views on the exhaust front pipes.

 

[hotrodder]

Maniflow may be up there, especially with regards to value for money for some of their products for classics, but in absolute terms there's quite a few others about like OJZ, Alunox, Chris Tullett, Primary Designs, GoodFabs etc
I wouldn't be suprised if Akrapovic are using DMLS, at least for prototyping, alongside hydroforming and various pressed and cast parts

Laser sintered collector and some other components getting assembled into a GoodFabs exhaust...

and a 4-1 made from two pressed halves http://www.goodfabs.com/bends-and-pressings/pressing.aspx

 

[Chris Stevens]

Thanks I will have a look at the people you mention. Always found its a good idea to have a supplier who is close enough to visit personally though, and Maniflow seems to fit that bill perfectly.

 

[hotrodder]

Yeah localish is always nice and i suspect of the names mentioned OJZ are possibly the only one that'd be interested in smallish numbers and sensible prices? For 'simple' 90° bends (as they're gonna need cutting and clocking like the origional due it being a compound bend) if Langy can get 1 5/8 in 1D CLR i suspect he'll be one of the best value and nicest to deal with sources there is

 

[Chris Stevens]

Talked to Dave at Maniflow about front pipes 4 or 5 years ago, and while he wasnt interested in making them can supply bends no problem, and going to pick up some in MS next week, to prototype a complete front pipe. Dave used to work at Downton Engineering, which seemed to have played a big part in the success enjoyed by the BMC Mini in serious competition.