Mandrel Bends - I may be the world expert

[variant22]

Well maybe not the world expert, but I have an unfortunate tale of someone sourcing mandrel bends. I am building up a custom set of headers for a car I am restoring. I decided I would check out the usual suspects:

Aussie Ebay Seller #1 - I purchase a set (4x of varying degrees) of stainless bends from Ebay, and eagerly awaited their arrival. After receiving these bends, I noticed a few things that were disturbing for what are meant to be mandrel bends. The pipe (they were surprisingly not tube) had serious necking around the bend radius. There were also dents in some of the bends. Clearly not of a high quality. I contacted the seller who was very honest and told me in no uncertain terms that they were "cheap Chinese bends".

Not happy with these bends, I decided to find some "real" mandrel bends.

Aussie Ebay Seller #2 - Having been burnt on the dodgy test bends from Seller #1, I decided to purchase some mild steel bends from another seller. These bends turned up and to my horror they had many clamp marks (threaded clamp) on each pipe (not tube) and serious necking around the bends. So much so that when the bend was cut into sections there was at least 1mm of overhang on the complete 360 degrees when married up against a set of straight pipe from the same seller of the same OD. I was quite shocked to say the least.

I clearly could not use these in a production system, but decided to "cut and shut" them for dry-run to get the bend radius's tacked and worked out. It is a real pain to do this as when I use a Strong Arm tube clamp it does not clamp both pipes due to the difference in radius of the bend and straight sections. :oo:

Aussie Ebay Seller #3 - Having been burnt again, I decided to quiz the next Ebay seller on the bends before purchase. He told me that the bends had been bent without oil and had some rust spots on the inside which he cleaned up. Said they were good on the whole though. I decided to take a punt and order a couple for a look. These bends were by far the worst of all. The actual pipe was not only seriously necked in the bend, but also had surface porosity in the metal as though it was pipe left out in the rain for months rusting and then given a quick rub with a wire brush! The investment was low on this one so no real damage, just another example of terrible quality Chinese bends.

So all in all no dice on the Aussie Ebay mandrel bend suppliers.

UK Ebay seller: I emailed this seller about the "A Grade" stainless mandrel bends. I had 5 questions that would help me to confirm the quality. The seller told me there were no clamp marks, and no necking on the pipe. These bends turned up today. Unfortunately these are no better than the local bends. These bends had serious necking which is easily felt by hand and will be hard to fabricate to a straight section for instance without internal and external grinding around the join. All in all a great disappointment, but not a financial loss as I only purchased a 45 and 90 test bend.

All in all to this point I do not have any bends that I would feel comfortable using on a performance engine. A pretty sad state of affairs given I have made purchases from 4 distinct sellers.

So with all this in mind I decided to get serious and order some Stainless and Mild Steel test bends from SummitRacing in the US. I purchased 45 and 90 degree bends made by Hooker Headers and one set by the house Summit brand. I am hopeful that these bends will be high quality. Hooker is owned by Holley so I expect the bends to be of good quality (from what I have read). I guess we have to wait and see.

I am happy to supply photos if of interest to anyone reading this thread.

If you have a great Mandrel Bend suppler in Australia please post their details in this thread and I will check them out.

[MuellerNick]

I have built two mandrel benders by myself. And they work! :D
That job is a bit tricky. It takes some time to learn to read the faults. Folds on the inside, diameter in the horizontal plane too small, breaks on the outside, ...

What really works best is a work hardening steel/material. So stainless/brass is perfect, as long as you start with the annealed state.
The smaller the ratio bending radius :: outer diameter gets, the more complicated it is.


But I bet my mandrel benders are too small for your job. Maximum OD is 10 mm.


Nick

[MuellerNick]

Oh, here is a sample of my failures:
221858
IIRC, 6mm brass tube.


Nick

[variant22]

I have built two mandrel benders by myself. And they work! :D
That job is a bit tricky. It takes some time to learn to read the faults. Folds on the inside, diameter in the horizontal plane too small, breaks on the outside, ...

What really works best is a work hardening steel/material. So stainless/brass is perfect, as long as you start with the annealed state.
The smaller the ratio bending radius :: outer diameter gets, the more complicated it is.

But I bet my mandrel benders are too small for your job. Maximum OD is 10 mm.

Nick

Interesting work Nick. It would be great to see your machine. Any links for me to check out? The OD I am using is 42mm. The real killer with the bends is the time wasting. I end up waiting for a week plus for sub-standard bends to show up. Then it just puts me another week behind in my project.

I am at the point where I think I could get better results than what I currently have by sand (baked) bending with some heat on a normal pipe bender. :no:

[Jekyll and Hyde]

Unfortunately this is pretty common on mandrel exhaust bends. The best I've come to expect from a mandrel bend in exhaust is about a 1mm reduction in pipe diameter at the centre of the bend (on 1.75 inch diameter bends).

I've had some from about 3 or 4 different exhaust suppliers in Melbourne, and one lot had about a 3mm reduction in diameter at the centre of the bend... Needless to say, that lot was very speedily returned. The last lot I got, although 'only' having a reduction of a bit over 1mm at the centre of the bend, had gouges in the ends from the clamps, and appeared to have had slightly the wrong size clamps used, as the pipe was pressed a bit square. They also seemed to be sort of overbent, in that a 180 degree bend, instead being a U shape, was starting to take on a R shape. More like 185 degrees, then a 5 degree bend back the other way to keep the ends paralell. Very strange.

The best I've found so far are the 'Aero' branded ones, no clamp marks, correctly shaped, and 'only' just under 1mm reduction in pipe diameter. If I remember correctly they were supplied through Pro-ex, but whether they retail direct I don't know (I'm in the automotive trade).

I will be interested to see if your imported ones are any better than the Aero branded ones, as this has been annoying me too. I've sort of written it off as unavoidable at this stage however, as the only way to improve on what I've got is to get the full pipes bent up as one unit. Solves the problem of getting steps at the join, and that 1mm reduction in diameter on its own isn't going to make a great deal of difference to the flow characteristics. Don't know if anyone still does this in Australia though, I believe Di Fillipo exhausts used to do it, but no longer do. I suspect cost would be prohibitive, particularly in my case (very low volume), and chances are you'll still have to tweak the pipes by a couple of degrees to get them exactly where they need to be.

Now, I'm off to research this Strong Arm clamp you speak of, I'm sick of burning my thumb with the tig trying to tack pipes together, and I'm too cheap to buy a mig and rent another bottle!

[MuellerNick]

I'd have to make pictures of them. The first bender took 3 prototypes to get it working and to understand the tricks.
A 42 mm tube can't be bent by hand. Mine are hand operated.

Bending with sand doesn't make a perfect bend. It's physically impossible, because the volume in the bent area increases. Bending with sand only works to say a radius : diameter ratio of 5 : 1 or bigger.

And (not completely subject-related), a T-joint and the tool. 6 mm OD:

221859

221860

Is that called notching?

I'll make pictures of my bender if I have more time.

Edit:
With my 6 mm tubes, the OD-reduction was 0.1 mm in the horizontal plane. Can't get much below due to variations in OD and ID of the tube.


Nick

[Jekyll and Hyde]

I see Nick and you posted while I was composing... That is another thought I've had, to make my own mandrel bender... The principle is very simple, the execution would be very much trial and error, not to mention quite expensive in terms of material to make the dies out of, given you're working in 1 and 5/8 inch pipe, and I'm working in 1 3/4 to 2 inch...

Doesn't stop me contemplating it every now and then though, I do have the facilities to machine the dies and mandrel/s....

Also forget to mention, if you try Pro-ex to see what the Aero bends are like, make sure you specify that you want the Aero bends, even if they have to order them in. They have previously sent me some others, which happened to be the 3mm reduced diameter ones. The Aero bends are easily identified, as they actually have 'AERO' and a part number stamped into one of the straight ends.

[variant22]

Unfortunately this is pretty common on mandrel exhaust bends. The best I've come to expect from a mandrel bend in exhaust is about a 1mm reduction in pipe diameter at the centre of the bend (on 1.75 inch diameter bends).

It is a bit of a sad state of affairs if 1mm is the best there is. 1mm is a significant pain in fabricating the "tube". On the inside of the tube there will be a lip in one direction which will create turbulence. Maybe this is a slight over reaction but when one spends 20+ hours on a port job reaching ones best attempt at perfection it is a tough pill to swallow to have a sub-par exhaust. The engine I am building has every single nut and bolt replaced for new. It is literally down to that level of detail. Bolting a substandard exhaust to it would be entirely the wrong thing to do. In case anyone is wondering why I don't just get a set of headers "off the shelf", it's because there are no off the shelf exhausts made to suit this build.




I've had some from about 3 or 4 different exhaust suppliers in Melbourne, and one lot had about a 3mm reduction in diameter at the centre of the bend... Needless to say, that lot was very speedily returned. The last lot I got, although 'only' having a reduction of a bit over 1mm at the centre of the bend, had gouges in the ends from the clamps, and appeared to have had slightly the wrong size clamps used, as the pipe was pressed a bit square. They also seemed to be sort of overbent, in that a 180 degree bend, instead being a U shape, was starting to take on a R shape. More like 185 degrees, then a 5 degree bend back the other way to keep the ends paralell. Very strange.

Unfortunately I have the same experience. When I mentioned 1mm above I was being kind. It is in many instances much worse than 1mm. Totally unacceptable in my book. I also have in my possession some of the infamous R bends. They are definitely over bent in some instances. I assumed these pipes were bent in Australia and was shocked to hear from the seller that they were Chinese.



The best I've found so far are the 'Aero' branded ones, no clamp marks, correctly shaped, and 'only' just under 1mm reduction in pipe diameter. If I remember correctly they were supplied through Pro-ex, but whether they retail direct I don't know (I'm in the automotive trade).

I will have a look to see if I can find any of these Aero bends. I am interested to see how they shape up compared to what I already have.



I will be interested to see if your imported ones are any better than the Aero branded ones, as this has been annoying me too.


I will be posting back to this thread. Hopefully they are here in a week or so. I will be pulling out the micrometers and checking them in sections to see what they are like. I am actually quite optimistic on this.



I've sort of written it off as unavoidable at this stage however, as the only way to improve on what I've got is to get the full pipes bent up as one unit. Solves the problem of getting steps at the join, and that 1mm reduction in diameter on its own isn't going to make a great deal of difference to the flow characteristics. Don't know if anyone still does this in Australia though, I believe Di Fillipo exhausts used to do it, but no longer do. I suspect cost would be prohibitive, particularly in my case (very low volume), and chances are you'll still have to tweak the pipes by a couple of degrees to get them exactly where they need to be.

This is done in Australia. The guys at Uneek used to have the equipment. I was informed that they sold it off to the people at Bends.com.au (http://www.bends.com.au). Apparently these guys can do single pipe bending but it comes at a cost. I do not have a direct quote but I was told that it would be circa $600 to setup the machine and $25 to $30 per bend. I really wanted to hand build my headers. That said if I cannot get a result from these bends, I may place an order with the folks at bends.com.au.



Now, I'm off to research this Strong Arm clamp you speak of, I'm sick of burning my thumb with the tig trying to tack pipes together, and I'm too cheap to buy a mig and rent another bottle!

The Strong Arm clamp is pretty good. They are a bit expensive but they do tend to work well. That being said, I was watching a Ron Covell DVD a few nights back and he had two techniques he uses when making headers. He either uses straight Masking Tape, and just peels it back. He mentioned that it works surprisingly well, and his other option was a hose clamp with a window cut out of it. He clamps, tacks and then moves the window around (by rotating the clamp) to the next spot and tacks it. I tried to make one myself. I was however foiled by the difference in pipe diameter! The hose clamp would hold one pipe perfectly and the other would be loose and drop out. Cheap mandrel bends are nothing but pain and frustration I am afraid. :)

[Stustoys]

The pipe (they were surprisingly not tube)
The difference in this case being?

Not that I know a great deal about mandrel bending but I would have thought "some less that 1mm" in 42mm would be pretty good?

If google images is anything to go by, just what "mandrel bending" means is open to interpretation. Some seem to think what I would call the dias are mandrels and have no mandrel.........?

I know ARB used to have a mandrel bender, I dont know if they still have it or if they will talk to you though.(I've no idea what sizes they have other than "bull bar" size)

Stuart

[variant22]

The difference in this case being?

As someone once so eloquently put it, "pipe is for poop". Pipe has an internal seam which will create flow turbulence, restriction and upset pressure waves in some instances. Lets not assume that one is joining each section where the seam runs. In some cases this is just not possible. Good exhaust headers are built with tube, not welded pipe which has a high ~1mm internal rough seam.



Not that I know a great deal about mandrel bending but I would have thought "some less that 1mm" in 42mm would be pretty good?


<1mm may well be "pretty good". We will have to wait and see where the definition will sit. At the moment I only have cheap Chinese bends so nothing really to benchmark. That all being said, I have a press bent header that has less necking than the mandrel bends that I have.



I know ARB used to have a mandrel bender, I dont know if they still have it or if they will talk to you though.(I've no idea what sizes they have other than "bull bar" size)


I would be surprised if a company (public) the size of ARB were interested in doing a one-off mandrel bend of a few tubes. I could be wrong, but seems like a big ask.

[Greg Q]

Is there any way that you can smooth the trailing edge of the offending piece prior to assembly? A four degree departure angle should still yield laminar flow at the transition zone and beyond. If you end up with a larger diameter downstream then you can well afford some surface texture due to the different Reynolds number/ flow velocity. Laminar flow isn't always the optimum case, either.

Greg

Who once spent four days with a die grinder and diamond paper to get 5% more horsepower out of smoothing a boxer crankcase internal gas paths. Then gained four kilos and ruined the whole enterprise.:doh:

[Hunch]

You must be a yank, headers? :D

Sounds like the same experience with uneek too...can't remember now whether they were the qld or vic companys I contacted that could bend thin tube.

I think you'll find the tube will be distorted no matter where you buy, usually not helped by worn out tooling - locally at least.

I use something resembling a steel egg, of appropriate diameter, on a stick to get the joins evened up, a tip picked up off an older Williams F1 doco showing the fabricator making SS ones....so must have been a while back.....with their throw away inconel ones now. Anyhow goes to show even there, no perfect mandrel bend.

Don't know where you are, mild steel/ss 16g bends and donuts are available, from at least a couple of exhaust shops in Sydney - and I imagine most states would be the same, but you can expect a bit of what you describe. If it's thin/exotic material needed, usually the US is the place, I've bought from a mob in Huntington Beach in the past....name escapes me at present.

[Stustoys]

As someone once so eloquently put it, "pipe is for poop". Pipe has an internal seam which will create flow turbulence,
No no Tube has(can have) the internal seam*, you wouldnt want an internal seam on a poop pipe.
Still what ever its called you don't want a raised seam. How is the mandrel going to fit properly?

As far as ARB goes, you're right, I was thinking you might have been able to buy some on the bends they use for something else... but they would be in MS... its was late is my only excuse.

Stuart

*As I understand it. Its pipe if you are worried about the internal size for transporting a fluid. Its tube if you are worried about the outside size building something. I dont think seamed or seamless comes into it.

[twopintsplease]

can you tell us were in australia you are, of the top of my head in adelaide, there will be more about

Pacemaker Headers Pty Ltd
6 Reese Avenue
Richmond SA 5033
Ph: 08 8352 6488 Fax: 08 8443 5131

B.R.F ENGINEERING Tube Bending - Wingfield, SA

48 Wingfield Rd, Wingfield SA 5013, Australia
(08) 8268 8460

no afiliation with either , used pacemaker years ago for some bends, depending on what you are doing you may be able to get the bends close enough that you dont need to join bits save on welding and is a better job doing the primary pipes in one piece

i dont understand why ebay would be your first place to look for engineering service, the bends would have to be cheep as you are shiping a lot of air

in the early 80's i worked i tube bending workshop (in stepney, long gone) its no big deal to make a mandrel bender and tooling, its virtually blacksmith technology, but there is an art to fine tuning the bender and tooling to get good bends

[MuellerNick]

I just realized, that I do have already pictures of my mandrel benders...
221945
This is my small one with an assortment of clamps, dies and mandrels.
It's a bit odd looking, because you can bend to the left and the right. That's necessary sometimes with consecutive bends. The shortest clamping length that works in brass is 0.5 * D, but that needs some taking care of.

221949
This is a bend with my "big" bender. 10 * 0.5 mm SS tube. That's a typical pattern when the mandrel hasn't enough stick-out.

221947
Properly adjusted. I just needed two tubes of these. :(

221948
Parts of the "big" bender. Mandrel & clamp missing.

221951
From the top ...
221950
... the side.

221946
And a closeup with die and mandrel. Clamp is missing. Also the sliding horn, where the unbent part of the tube rests on.

There are 3 types of mandrels. Mine is the most complicated to make, but gives the best results. As it was made in my pre-CNC-age, I completely had to file it by hand. The disadvantage of these is, that you need a mandrel for every bending radius. They do work a bit above or below, but you get the best results when it exactly is of the right size.
The shape is the shape a cylinder (with the ID of the tube) and a torus (with the ID of tube and bending radius) do have in common.

The simplest shape of a mandrel is a cylinder with a ball at its end.
A more complicated (impossible with small tubes) is a cylinder with a ball at its end plus a few balls/olive-shaped-thingies following and connected with a cable/chain. Actually, they shouldn't be of any advantage. The reason is, that the following balls support the tube in an area, where there isn't any bending taking place. The tube had already been bent there and work-hardened.

Clamps:
They are just reamed bores, split in half and the edges slightly rounded. The shortest clamping length in brass is 0.5 * OD (with problems). With l = OD, you get slight marks that are gone with fine scotchbrite. In stainless, the miniumum is l = OD, l = 2 * OD works better.
What took me some time to find out is, that the clamps have to be floating. That means: slip tube on mandrel, slip clamp over tube and tighten. Push the tube into the die. Now clamp the clamp to the swing arm.
If the clamp is in a fixed position, you always get marks on the tube.

The smallest and perfect bends I made in brass was 4 * 0.5 tube. Bending radius 4 mm, bent 90°. Bending radius is measured at the center line of the tube.

It helps, if you have a straight part at both ends of the tube that you cut off later.

That's it.

Nick

[Iggsy]

I recently brought a heap of 1.5", 2" and 2.5" 316SS bends to fabricate an exhaust for my offroad buggy. Got them from "Midway Metals". With company discount, they we about $8 each.

Any SS metal supplier (i.e. Atlas, Midway, Sandvik) should be able to get them for you.

http://i164.photobucket.com/albums/u38/SimonsPhotos1982/SL371608.jpg

[danielhobby]

i have some 50 mmod ss tube bends(1.6mm wall) that are pretty damned good that i got from "swadesir" in thomastown.they are 180 degree and aprox120 mm od radius.maybe look him up.i cant help you with prices,they were a sample of his bends.