Wishbone Material

[SteveMX5]

Hi This is my first post so please be gentle!

I am coming to the end of building the chassis for my MX5 based roadster using the Saturn (or NTS?) plans (with a few tweeks). Looking forward to the next stage which looks to be the suspension wishbones.

Maybe I need to go to specsavers but I cannot find any specs for the material used for the wishbones apart from the obvious dimensions. Do I need ERW or seamless and what wall thickness?

All help greatfully recieved
Steve

[andysredmini]

The Haynes book says to use 19mm and 25mm Seamless (CDS). I don't think a wall size is given. I am planning to use approx 2mm wall thickness but I have read on this forum about people using as thin as 1.6mm. I recall someone saying that westfield use 1.6mm on theirs.

Regards

Andy

[stew]

Hi This is my first post so please be gentle!

I am coming to the end of building the chassis for my MX5 based roadster using the Saturn (or NTS?) plans (with a few tweeks). Looking forward to the next stage which looks to be the suspension wishbones.

Maybe I need to go to specsavers but I cannot find any specs for the material used for the wishbones apart from the obvious dimensions. Do I need ERW or seamless and what wall thickness?

All help greatfully recieved
Steve


Ive just started making my bones.... I went for 19mm and 25mm CDS, and its really expensive!!! Think its 3mm wall! The tube bushes are made from 33.7mm x 2.6mm ERW, but i think you can only get 2.5mm or 3mm in general. Its pretty cheap per length, but you dont need a full length obviously. I could only get 3mm wall, so i will be machining mine down just a touch to fit the bushes.

As far as i know, the book spec for the saturn/NTS wishbone adjusters is 25mm diameter mild steel bar stock, threaded to M18x2.5mm. This is a bugger of a job to do in my opinion! I drilled the holes in the lathe, then hand tapped the thread, took me 2 hours to do all 8!!!! If i was doing it again i would use M16x2.5, or M20x2.5, as M18 is a hard size of bolt to get!!! I have got some M18x2.5mm threaded rod, but the problem is its only 4.6 grade, but ive calculated that this should take more load than it will ever recieve. Only problem would be hitting a kerb or such like i guess!? M18 bolts seem to be hard to come by from local suppliers, and are expensive where i did find some!!

The front upper wishbone takes a 30mm diamater mild steel bar stock, threaded to M14x1.5 to suit the BMW drag link. Im sure at some point andy (saturn) said that 25mm round was used for this, but im sticking to book spec, to keep the angle the same.

One thing that isnt in the saturn guide, is the angle of the front upper wishbone jig, but im assuming its the book 78 deg! Maybe andy / nathan could verify this for you?

Hope this is of some help, best get back out to the garage and get my next wishbone made...

[SteveMX5]

Cheers gents.

Have just got a quote for CDS tube, eek :eek:

That decides it I'm gonna be lazy and buy some ready made :rolleyes:

[andysredmini]

What was the damage?
I have been quoted £40 for a 6m length of 20mm
And £42 for a 6m length of 25mm.
Only tried one stock holder so not sure if this is good or not.

Out of interest, any idea What total length is needed?

[stew]

What was the damage?
I have been quoted £40 for a 6m length of 20mm
And £42 for a 6m length of 25mm.
Only tried one stock holder so not sure if this is good or not.

Out of interest, any idea What total length is needed?

Think thats not a bad price at all! What wall is that for?

I was £170 (and that was mates rates), for

1 x 6.1m length 19mm CDS (think the wall is 3mm)
1 x 6.1m length 25mm CDS (think the wall is 3mm)
1x 6.1m length 33.7mm ERW tube x 3mm
1 x 6.1m length 40x3mm flat bar
1 x 6.1m length 25x3mm flat bar

I did two of my wishbones yesterday, and to be honest they aren't that bad. Just get the jig spot on, and you're laughing.

[SteveMX5]

It was £50 + very annoying tax for 25mm x 6m, 2mm wall CDS.

I gave up asking after that as I reckon by the time i've made all the jigs, mucked about with loads of silly angles, brought and machined the threaded bits and bunged the pro welder in the unit next door a few quid for tigging them up they'll probably only be 100 quid cheaper than buying them in. Not to mention the many hours involved.

[robo]

Hi This is my first post so please be gentle!

I am coming to the end of building the chassis for my MX5 based roadster using the Saturn (or NTS?) plans (with a few tweeks). Looking forward to the next stage which looks to be the suspension wishbones.

Maybe I need to go to specsavers but I cannot find any specs for the material used for the wishbones apart from the obvious dimensions. Do I need ERW or seamless and what wall thickness?

All help greatfully recieved
Steve

http://www.rorty-design.com/content/tube_work.htm

A bit about the differences between the tube types and why the are used. This end of things is more important as your health and well being are at stake, when it comes to any of the suspension stuff I wont short change anything just to save a few quid. Have seen enough failures in this department and its never pretty.

Bob

[SteveMX5]

Good find Robo

Trouble is I fancy building one of those buggies now :eek:

[MarkB]

ERW is fine for wishbones, wishbones should be seen as expendable items in the event you clout a curb or worse they want to absorb the impact and bend, that way the chassis suffers less damage.:) Use 14swg (2mm wall)

[Not Anumber]

I'll second Mark B's comment. The lower wishbones on my MK Indy bent and broke when the previous owner had the knock which turned it into a Cat C loss. The great thing is there was no structural damage to the chassis as they worked just like crumple zones hence it's not an expensive process to get it back on the road.

[Oscar]

This is very interesting to me; I'm at the stage where I'm looking at wishbone materials.

I was under the impression (probably wrongly) that the wishbones had to be seamless? Is there any risk that the ERW would fail during normal driving/ harsh cornering?

Also, as I wouldn't mind doing track days in the distant future (when I eventually get it finished). Would the use of ERW cause problems here?

[MarkB]

For track use I would use 18swg but for road use I would go up to 16swg or even 14swg...all ERW.

[Talonmotorsport]

I would think that CDS / Cold Drawn Seemless tube was specified to stop people using any old length of tube and not knowing what it was for the wishbones. ERW will be fine for the wishbones although I would not go any thinner than 2mm wall top and bottom,don't forget that they are only bolted to 3mm suspension brackets and half of those have 50% material coverage welded to a 1.6mm walled chassis.

[robo]

I'll second Mark B's comment. The lower wishbones on my MK Indy bent and broke when the previous owner had the knock which turned it into a Cat C loss. The great thing is there was no structural damage to the chassis as they worked just like crumple zones hence it's not an expensive process to get it back on the road.


I would be horrified if my wishbones broke before it ripped the chassis brackets off that piece of 1.6mm wall thickness box section. I would rather believe that the wishbones were not properly made or welded:eek:

Bob

[trick-kit]

I would be horrified if my wishbones broke before it ripped the chassis brackets off that piece of 1.6mm wall thickness box section. I would rather believe that the wishbones were not properly made or welded:eek:

Bob

The wishbones are made to be the sacraficial part of the build, if you ever had an accident (god forbid) they are designed to give before the chassis.

Which would you rather after an accident?

1. Replace one maybe two wishbones at £80 ish

2. Strip down the entire car, replace the £700 chassis (or make repairs to the damaged part) and then rebuild the car.

TK

[MarkB]

I would be horrified if my wishbones broke before it ripped the chassis brackets off that piece of 1.6mm wall thickness box section. I would rather believe that the wishbones were not properly made or welded:eek:

Bob

Shows how much you understand cars then!!!
For exmaple: Alloys are used over steel wheels as they break so they don't damage the suspension. And wishbones as TK points out are sacrificial. Better to damage a wheel and a wishbone than wreck a whole chassis.

[MarkB]

If a car like a 7 is shunted the chassis is scrap and should be replaced as you can't repair it properly as it will have bent it, I have seen it first hand and been asked to repair an early Westfield but even though it only had a slight slap at the front the whole thing was out of shape. I turned the job down and the lad bought a new chassis.

[robo]

Alloy wheels are used because they are lighter and for that reason only ,there is nothing wrong with steel wheels and they are still fitted to many cars. They are not part of some sort of engineered crumple zone. As for the wishbones you may have forgotten they are triangles therefore strong. A bit of 3mm bracket welded to a 1.6mm thick box should give out long before a wishbone period! I would sooner all four wheels were still on my car in a knock over a bent chassis any day as you might be travelling at speed still. Sod the chassis.

I cant think of a single car made that allows its suspension to be ripped of in a knock , most of them just mangle up the subframe and bend things.

Scenario. I am diving down a dual carriageway and drive over a brick, I am now driving down the road with three wheels on my wagon at 70mph thinking great my chassis is still good. Bxllxcks

Totally unconvinced Bob

[MarkB]

Alloy wheels are used because they are lighter and for that reason only ,there is nothing wrong with steel wheels and they are still fitted to many cars. They are not part of some sort of engineered crumple zone. As for the wishbones you may have forgotten they are triangles therefore strong. A bit of 3mm bracket welded to a 1.6mm thick box should give out long before a wishbone period! I would sooner all four wheels were still on my car in a knock over a bent chassis any day as you might be travelling at speed still. Sod the chassis.

I cant think of a single car made that allows its suspension to be ripped of in a knock , most of them just mangle up the subframe and bend things.

Scenario. I am diving down a dual carriageway and drive over a brick, I am now driving down the road with three wheels on my wagon at 70mph thinking great my chassis is still good. Bxllxcks

Totally unconvinced Bob

That my old fruit gump is why some design and build cars/bikes and others don't.

[Oscar]

Going back to the original question (in the hopes of preventing a war...)

After chatting to a mate, the only problem we could come up with regarding ERW is the chance of fatigue.

Due to the high levels of vibration the bones will experience, the greatest chance of causing problems during normal driving (excluding bricks, kerbs, other cars, etc...) will be from fatigue.

The weld in the ERW will act as a harder, more brittle area and as such will be slightly more susceptible to fatigue. Presumably this is more than made up for by the slightly larger tube thickness.

Thoughts? (The seeds of a new war have been sown, the facilitator sits back to watch the chaos...;) )

And yes, this discussion was held down the pub!

[trick-kit]

Before or after beer? :D

TK

[robo]

It was suggested to me to use 4130 by a motorsport fabby but the trouble with that is you are then commited to 4130 welding rods + 4130 for any plate used +heat treatment after. It gets a bit overkill for a road smoker. I trust the book bones have proved durable so I will go with talon on this.

Bob

Must get the delivery driver to avoid and speed bumps just in case they break.

[baz-r]

It was suggested to me to use 4130 by a motorsport fabby but the trouble with that is you are then commited to 4130 welding rods + 4130 for any plate used +heat treatment after. It gets a bit overkill for a road smoker. I trust the book bones have proved durable so I will go with talon on this.

Bob

Must get the delivery driver to avoid and speed bumps just in case they break.

4130 is just cro-mo (stuff thay make bike frames from) so i dont see why you are tied to using 4130 rods (there is prob not a exact match in wire or rod anyway) you do have to take care not to over heat and harden it more like meny other metals.
you should have a look at some of the classic racers thay used hardend tubing and brazed everything together :rolleyes: so the tube wasnt over heated and hardend more.

i cant see why a roadster needs anything other than a mild steel tube realy and a seemless one is a better option if you can get it.
i got some for my roll bar back stays from a hyd hose co. and was fairly priced

[robo]

4130 is just cro-mo (stuff thay make bike frames from) so i dont see why you are tied to using 4130 rods (there is prob not a exact match in wire or rod anyway) you do have to take care not to over heat and harden it more like meny other metals.
you should have a look at some of the classic racers thay used hardend tubing and brazed everything together :rolleyes: so the tube wasnt over heated and hardend more.

i cant see why a roadster needs anything other than a mild steel tube realy and a seemless one is a better option if you can get it.
i got some for my roll bar back stays from a hyd hose co. and was fairly priced

Now someone has got to tell him hes been a twat for the last 30 years and in all that time he could have welded all those wishbones with an old coat hanger:o lol No he merely mentioned that is what they use and thats the way they do it and if I wanted some made he would do it but i think cds is more than good enough for my job. You will be seeing some of his work soon and there wont be anyone out there knocking his stuff. He knocked me up some collectors and its a shame to put them on the car. They would be more at home in a glass cupboard.

Bob

[Bonzo]

Bob

The advice you were given Re: 4130 tube was quite correct ;)

Here's a link to the science of it all :)

Heat treatment & 4130 tube (http://www.netwelding.com/Heat_Treated_4130.htm)

In my humble view, any CDS tube would be suited to the Roadster & would not explore other options unless I was into extreme motor sport :)

[baz-r]

the point i was tring to make is that the filler has no effect on what you are welding its the heat you need to put it in that causes the problem hence the braze on old racers.
heat treating is a remidy to the effect of the heat on an already hard metal.
but there is more than one way to skin a cat
there are meny diffrent fillers (rods,wire whatever) in the welding world trust me i know i had to sell them over std mild stuff :rolleyes:
we dont need anything other than a good old mild steel tube for a wishbone and making it without a welded seem makes it better