The haynes chassis design

[kev87]

Hi there, just joined the forum, been reading up a lot on locosts after buying the haynes manual and definitely wanting to give building one a go.

Am currently having a go at modelling the haynes chassis in CATIA, I'm doing the bottom rails section and using the haynes dimensions my rail number BR10 seems to be too long by about 7.5mm. I've checked all the angles and dimensions over and over, has anyone else noticed thi problem or is just likely me doing something wrong?

Cheers for any help.

[dogwood]

Can't say I noticed the problem.

It could be you are taking it from BR1 & BR2 not BR4 & BR5

David

[TQ_uk]

Hi there, just joined the forum, been reading up a lot on locosts after buying the haynes manual and definitely wanting to give building one a go.

Am currently having a go at modelling the haynes chassis in CATIA, I'm doing the bottom rails section and using the haynes dimensions my rail number BR10 seems to be too long by about 7.5mm. I've checked all the angles and dimensions over and over, has anyone else noticed thi problem or is just likely me doing something wrong?

Cheers for any help.

I've just come across this exact same issue (modelling in 3ds Max) in that the book figure of 882mm for BR10 makes it too long to fit between BR3 and BR4 in the position shown on Pg 34 (ie at the joins of BR3 to BR1, and BR4 to BR2).

Obviously it will fit if moved back towards BR11 (approx 25mm) - is that what people have done, or is the book dimension wrong?

Trying stuff 'virtually' first to try & eliminate such problems:)

[deezee]

Its not a problem. Having built a chassis out of actual steel, the rails do fit.

[eSteve]

kev87,

I believe the book is correct.

The length of the back edge of BR10 (i.e. the length given in the cutting list on page 161) can be calculated from Fig 4.2 (on page 34) as follows, assuming 25 mm RHS is being used rather that 1" (25.4) not that it makes much difference:

Width of rail BR3 measured with respect to the centre line of the car and allowing for its angle (10 deg), is:

25 / cos 10 = 25.4 mm (it's wider than the 'stock' size since it is at an angle)

Take the twice width of the rail (25.4 calculated aboved) to account for BR4 and BR3 from the width of the chassis at BR10 given in fig 4.2:

924 - (2 * 25.4) = 873.4 mm This is the width ot the front of BR10.

So to calculate the width of the rear of BR10, since its ends are chamfered at 10 degs.:

873.4 + ( 2 * ( 25 * tan 10 ) ) = 882.2 mm

Cutting diagram on page 161 says 882 mm so QED.

Hope that helps (just remember S = O/H, C = A/H, T = O/A from your school trogonometry :D )

eSteve.

[Talonmotorsport]

The thing with CAD is that it measures to 0.001mm where as steel box section comes with sides that are not perfectly flat,sqare or even uniformal and most people can only measure and cut to within 0.5mm. CAD does have it uses for 3D modeling but making it 3D in steel is another matter.
Fabricators will use real world methods for making things fit such as jigs ,squares diagonal measurements and common sense. Any body that has made their own chassis will have found at least 3-5 problems, mistakes,irregulaties with the design it just depends on how carefuly you measure and how critical you want to be with your build. People that have had to put packers in their front suspension brackets have found one problem but don't know why it happens, as others have found that the bars in the engine bay don't fit and theres the problem the the rear suspension to name but a few.

[eSteve]

kev87, TQ UK,

have our answers helped, or left more confusion?

Have you resolved your queries relating to your Catia/3ds Max models?

[TQ_uk]

Thanks for your responses - I've been off work last few days (where I've left my book) so can't refer to rail numbers etc, but the last thing I found when 'making' the engine bay rails, was that when positioning them the lengths all worked out but only if the position of BR10 was moved back about 25mm.

So seems the cutting lengths are ok but the position of BR10 so it will fit properly is further to rear of chassis than described in layout diagram

I'll put up some pics when next back in work as it should explain better - Talon, I realise the tolerances are different but my issue is inches (fnaar) rather than hundreths of a mm...:)

[eSteve]

TQ UK,

two things cross my mind as to why you are seeing a problem:

(I'm sorry to say your problem, but as stated before in this thread many people have built from the book and no such large anomaly has been found).

I have two suggestions, the first is a 'school boy' error which I wouldn't think has been made but I'll still mention it:

1. The length of BR10 is 882 mm at its widest point. That is the side of BR10 facing the rear of the car. If BR10 was 882mm on its front edge it would indeed need to be moved back 25 mm.

I think this one is more likely:

2: I what order are you constructing the drawing? The sensible order of constructing the chassis (in model world and real world) would be from the rear forward, so as the 'square' part of the chassis is established first. I have used this method in my drawing of the chassis and when working out the length of BR10 with some trig. [see above]). That is; create the BR6, BR5, BR12 and BR11 section first, then position BR10 and fit BR3 and BR4, and so on moving forward. When doing this you will also see some partial gaps at a few of the joints where angles tubes meet.

As deezee and dogWood state in real life this is not a problem since the tubes are fettled to fit and a small gap can be bridged by the weld. I would imagine that if you construct your model from the front to the rear then this might cause the misalignment when you get to BR10.

In your model don’t expect BR1 to butt with BR8 along the whole of the length of the chamfer on the end of BR8 similarly with FF1 and the chamfer on BR1 and BR2 and at other angled joints.

The angles and lengths in the cutting list (for the bottom rails) should NOT be treated as absolutely precise, else Chris Gibbs would have had to quote angles and lengths to many decimal places (which would be nonsense) to form gap free angled joints.

Or stated another way:

We basically have two sets of information enabling us to build the lower chassis, that given in fig 4.2 and that given in the cutting list by way of the dimensions of the bottom rails. Either could be used to construct the bottom rails, but the correct one is fig 4.2 as stated by Chris Gibbs (see below) and for the reason I give above i.e the limit on the tolerances of the cutting list, to the nearest degree and millimetre.

Remember to keep a foot in the real world whilst modelling. Think about construction. The dimensions given in fig 4.2 are the important ones and what a welder would use to build the chassis rails, in fact all the lower chassis could be built from the dimension given in fig 4.2. Without using the cutting list for the lower rails! This is why Chris Gibbs states that fig 4.2 is used to layout the chassis and tubes are cut to the correct length to fit, (note: not necessarily cut to the cutting list lengths and angles).

So don't get hung up on the cutting list dimensions for the lower rails, draw it and build it to fig 4.2.

Sorry this is so long, but I hope it helps.

[twinturbo]

I have jsut redrawn br10 with it centered and measured from the back rail BR12..

BR 3&4 or now 3.8mm too long..

TT

[twinturbo]

Definatly not got 25mm of problems though..

TT

[twinturbo]

front of my br10 now measures 873.2 ( .2mm short of what steve calculated from )

TT

[TOLiSGR]

Having built the chassis in CAD in 3 different ways, I found out that the easiest and fastest way (for me at least) was to use the dimensions from the 'jig' template. That was my 2nd try...

The first try was making each tube by itself and then making the assembly, then I had to trim or extend a few pieces in order to fit.. at that point, I thought that the dimensions of the real part should be slightly shorter than 100% fit in order to be properly welded and I stopped..

The 3rd try was calculating midpoints and making a weldment assembly.. was the most difficult way to do it.. but after that, you can change material profiles very easily, and make stress analysis even easier.. !!

[architect]

front of my br10 now measures 873.2 ( .2mm short of what steve calculated from )

TT

Isn't that the right figure?

924 - (2*25.4) = 873.2?