I know this subject has been covered before multiple times before, but I can't find anything that helps with my current problem.

I am trying to source the steel required for my bones, and the only choices I can find locally are as follows

19mm x 2mm CDS (£6 pm), this is for the arms, no problems here (?)

For the bush tubes though I have a choice of either 25.4mm x 3mm CDS (£8 pm) or 31.75mm x 1.6mm CDS (£8.50 pm)

I was looking for the 31.75 stuff with a 2.5 wall but no one locally seems to have it.
Would I be correct in saying that the 25mm stuff is too small (with a 3mm wall) for bushes? And is the 31mm stuff too thin?

So if anyone can point me to the right choice from the available sizes I would appreciate it?

Cheers

Alex
PS
Left things too late as usual, off tommorow and friday and this may be my only chance to get my bones done, for the next month or two anyway.

I personally dont see why you would need to use CDS for the bush tubes. Fair enough for the wishbones themselves. You will find it much easier to get the sized tube you want for the bush tubes in normal ERW tube.

My wishbones are made completely from ERW tube (some pics on my site somewhere) but it is all oval. Similarly the trailing arms are all ERW as well. With careful positioning of the welds running down the tubes, they will cause no problems. However I wouldnt make my wishbones from 19mm ERW, but would from 19mm CDS...

David

After much debate about the same problem and many unanswered e mails to various companoes I bit the bullet and bought my bushes and eye tubes from lolocost (i know i know).
I reckoned they'd fit the book brackets but they didn't so i still had to borrow a lathe and face them off. The tubing was erw.

I should probably have mentioned this first, but I am making wider than book size bones so wanted to make sure they would be strong enough, hence the search for CDS rather than ERW.

But supposing I stick with the 19mm CDS for the wishbone tubes, what size erw should I aim at for the Bush tubes, 25 x 1.6 or 2.0mm or something bigger (32x2 maybe?)

Cheers

Alex
PS
Good point about the weld line though, I will keep that in mind.

Omega: what was the wall thickness on the ERW?
I am slightly concerned that with the extra width I am building in I should be using stronger material, although I have possibly been reading the bent bones thread too much


Cheers

Alex

I'm using Luego bushes and the ERW tube to suit is 34mm OD x 29mm ID

Mick

im building a plus 442
i searched all over for info on wide bones
came up blank , wanted to make my own
so i went to see a nice chap called mark
@ mnr he rigged me up with all my bits
and off i went home and fabbed my own
a very helpfull guy
tube is oval erw, bush tubes are cds

After long posts before and speaking to various folk, 25mm or 1" is much better diameter for the bone arms with a 2mm or 3mm wall - you can't go wrong then.

Pat...

Pat: Is that ERW or CDS tube?

Nige: I have emailed Marc 4 times and spoken to him (or his old man) 2 or 3 times, each time he has promised to get back to me and hasn't (maybe its my accent ) but thats why I am now sourcing locally

Lots of questions, the answers to which only create the need to ask even more questions

Thanks everyone

Alex

Top bone or bottom bone? Top bone 19mmx1.6 is plenty. Bottom bone I'd go substantially bigger. 3 reasons for the difference
1) tubes are longer on bottom bone so need to be bigger to withstand the same forces
2) due to leverage the bottom bone sees quite close to double the cornering and braking force
3) bottom bone also subject to bending forces because of the spring/damper fitment.
I'd have said ERW would be fine for the top bone. re: use of oval tube - bending and aerodynamics dictate different orientations on bottom bone - hmmmmm what to do.....
ciaou
Bob C

The o/d of the erw eye tubes is inch and a quarter with an id of an inch wall thickness is eight of an inch. One of the problems you might have, when you use larger size o/d tubes than the book, is that when you cut the fish mouths for mating to the eye tubes the resulting eliptical shape can be as long as the eye bushes themselves (if you know what i mean). And can therefore mean you would need wider brackets on the chassis.

If you try using a bigger distance between the wishbone bush eyes you will end with trouble getting enough caster --- really best to leave this dimension as per book unless you plan to redesign the front of the chassis.

Just make the wishbone in a similar to the style GTS and other manufacturers are now building and strength just won't be an issue.

Bob C: I never even thought of using different size tubes top and bottom (Dooooh!), that helps a lot as I was struggling to make anything bigger than 19mm work on the top tubes due to the lenthening effect (as per Omega's comments and my CAD work) on both the bush tube and the TRE tube.
As my bones are gonna be longer/wider the effect is exaggerated even more at the TRE

BritishTrident: do you mean style as in the bottom plate or in the tube shape itself?
I was going for 6mm plate, is that overkill, is 3mm enough

Wishbone design (okay, hardly groundbreaking I know ) as below
Rescued attachment bottomwishbone-plate.jpg

If 19 mm o/d is small, and 25 mm causes probs with fish mouth width,
then how about instead of o/d tube, use nominal bore.

1/2" nb (sch 10) is about 22 o/d, 2 mm wall.

Paul G

Damn, just when I think i'm getting the hang of this someone throws a new word at me
What is nominal bore Paul? Is that what I ask for or does it have another name?
22mm od sounds about perfect for my plans (top bone) though, I'll start phoning around tomorrow and see if anyone keeps it.

I've spent more time thinking about wishbones than anything else so far, not complaining mind most fun I've had with my clothes on (sad or what!)

Cheers

Alex

Nominal bore pipe is a range of pipes where the o/d stays the same and the i/d varies in relation to the wall thickness.
It's the stuff that will take a BSP or NPT thread, hence the o/d must be constant.
The wall, or pressure the pipe will take is known as "schedule",(5,10, 40, 80, or 160) hence sch 5 is thin tube and sch 160 is solid bar with a little hole down the middle.
Sch 10 is what I used, be it stainless, for my w/b's, 1/2" for top & bottom fronts, & top rear. Bottom rears are 3/4" nb.

It comes in various qualities from seamless to erw.


hth

Paul G

Make the lower wishbone as V shaped as possible. The two tubes should be arranged so that their centrelines point at the centre of the lower ball joint.

The main load on the tubes is in bending. The bending is caused by two things-
1) the distance from the lower ball joint to the spring mount.
2)how close the tubes are to a V shape

Note that the book design has the tube centrelines meeting a fair way outside the lower ball contact and that the distance from the lower ball to the spring pick up is 4.3 inches. Thats bad and a lot, which is bad again, respectively!

The Caterham uses a true V shape and has the spring pick up about 2 inches from the lower ball joint.

That's about as good as you'll get it. I'd suggest 1 inch diameter tubing in either 16 or 14 gauge but this depends on lots of other factors like the weight of your car and where you decide to put the lower spring mount.