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IRS chassis - cad, 3d ..and moving on to discuss chassis stiffness


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On 6/6/2019 at 8:25 PM, Waldi said:

Think we should gather for a beer in the pub, makes this sort of conversations so much easier:)

maybe one day.

Cheers,

if you're at Stratford this coming weekend Waldi, I'd be glad to take you up on the invite.

Pete.

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Hi Pete,

thank you for the invitation.

The only excuse I have is that my car is not finished, I hope to be there next year, with the TR.

Best regards,

Waldi

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What sort of excuse is that ! ?  :P   I haven't even got a TR yet..  The one I'm still trying to buy is in Arkansas, so I'm going in a Daimler-Chrysler Grand Voyager  - excellent for car-camping.

Hopefully next year then,

Pete

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Hi Pete,

if you haven’t got a TR yet, that’s another reason to go! I look forward to meet the forum fellows, see other cars and drive on the wrong side of the road:)

Hope you enjoy Stratfort.

Waldi

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.

Ostensibly because I'm so tall, I would like (actually.. need) as much sideways legroom as possible - I'd like to not use / fit the gearbox bridge / H-frame within the American TR4A (I'm still trying to buy). 

So, after repeatedly hearing how the IRS  is "not as good"  / "not as stiff"  as the TR4 chassis,  and then sitting down and considering the chassis and body structures - I took my first practical step this weekend to stiffening the car's body-tub up  ..and that was to buy a steel gearbox cover original to the TR3.  Thank you Brian Chiswick in Hertfordshire.

P1260085.thumb.JPG.cf3d03ab08b03ed59e9945e4bc914392.JPG

P1260086.thumb.JPG.039651d3f92ea447e962062c7094c6e8.JPG

I accept this one has a hole where an ashtray had been fitted by the gear-change, and also the cutout for the speedo drive  ..and otherwise may need modification to actually fit a TR4A..  but even with it sitting end up on the floor, the conical shape of this steel cover is very nicely torsionally rigid.  I anticipate when bedded and securely bolted all around the gearbox aperture in the floor and bulkhead it will make a notable difference.   Of course it weighs a sight more than a fibre or plastic one,  but as that weight is low down and central to the car I'm guessing this will not detrimental ..in the big picture of weight n' balance.  And in any case  I can save that weight elsewhere.

Pete.

 

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Pete,

you can still make a removable (bolted) strip or plate between the steel tunnel and the dash for added stiffness. As wide as your legs allow.

Regards,

Waldi

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21 hours ago, RogerH said:

Hi Pete,

I think the central 'H' section gives the body sideways support.  It keeps the dash a fixed distance from the floor.

Not sure what good the steel cover will do.

Roger

Hi Roger.  Someone from a London group of TR's  said to me at Stratford on Friday night  "Over there, that's Roger off the forum in the black bobble hat".  I hasten to add that it was said in a most kind and appreciative way ..in gratitude to the time and trouble you put into helping others on this forum.  And then the conversation went off on a tangent and I met colleagues from my local TSSC group - so I never got to meet you.  That's a shame as I would have liked to have have done so, not least to put a face and voice to the forum name.  Another time I hope.

But anyway..   Yes I'd concur - the H section would give the scuttle body shell  both sideways and vertical support. 

"Not sure what good the steel cover will do".   

If the existing bulkhead cutout had a much stiffer and wider flange - would that bulkhead not be stiffer as a panel ?  And if that 'much stiffer and wider flange'  had steel braces taken from many places around it - to the chassis mounts where the H-frame bolts through - would that not also stiffen / brace it even further ? 

Of course, once the bulkhead is braced to be much stiffer - it would be quite easy to better support the dashboard from that (..like shelf supports screwed to a wall).

But what if..  the floor, from the bulkhead to the driveshaft tunnel was securely fitted / filled in with a steel cone - would that cover and driveshaft tunnel not be just like a deep corrugation for the whole length of the floor  ?  And surely that would carry significant bending loads ..just as any monocoque car's backbone-tunnel does ?

And as the bulkhead is mounted to the forward diagonal stays - then this tunnel  (in essence : a top-hat section beam which is mostly twice or three times as high / deep as chassis &/or door sills) would help brace the front suspension turrets all the way through to the IRS spring hanger.!

Then, as a cone is especially good at resisting torsion - the steel gearbox cover (..a segment of a cone) securely tied-in to the bulkhead, the driveshaft tunnel (closed off with a breast plate on the underside) and bolted along its length to the floor and through that to the chassis - will also be torsionally stiffer. 

That's the direction my thinking is exploring.

Peter

 

Edited by Bfg
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6 hours ago, Waldi said:

Pete,

you can still make a removable (bolted) strip or plate between the steel tunnel and the dash for added stiffness. As wide as your legs allow.

Regards,  Waldi

Thanks Waldi,

Yes that's certainly a possibility ..using the gearbox cover instead of the lower half of the H  - Good idea,  and certainly a darn sight easier to fit than trying to get the original H-frame over new under-felt and thick-pile carpet.  B) 

Taking this a step or two further I could use a triangulating V  ..from the top of the gearbox cover to the underside of the dashboard .. and could if required even fit that slightly across over to the passenger side.

. . .

We might start a new trend, of existing gearbox fibre or plastic covers being reinforced with a band of 30x6mm flat steel ..which the carpet neatly fits over and conceals. And then a neat power socket / cigar lighter / communication ports,  plus GPS  &/or audio equipment housings  (..which are part of the structural support) bolted directly from the top of the gearbox cover's reinforcement band. 

As an Industrial Designer I have just copyrighted the idea, with a date and time stamp 19th August 2019 - 23:10 - so be quick Waldi you must now sell this our new sensation to Moss.  Perhaps you'll be so kind as to manage it ..and just send me a cheque each month with my share of the royalty payments.  

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Hi Pete,

make sure to add to your patent that the bracket is installed above the chassis-fixings, so at the same location as the H-frame:)

Waldi

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4 hours ago, stuart said:

FWIW That cover wont fit a 4a at all.

Stuart.

[....beat me to it.......]

 

unless you you beat the heck out of it on the well known kerbstone with the trusty club hammer

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  • 2 months later...

If I had a hammer I'd hammer in the morning
I'd hammer in the evening all over this land
I'd hammer out the lumps, and I'd hammer out its hollows
I'd hammer out love between all of my brothers
All over this land..

 

And as an aside.,  I really liked this < here >  design aid.

Pete.

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Pete--

I'm not sure how helpful this will be, but I was able to gain at least a couple of inches of knee room by fabbing a new dash support.  It fit over a more form-fitting fiberglass tunnel.  with more fiddling, I think I could have gotten another inch or two.  Most of the knee room benefit is on the left side, though.

Ed

IMG_3882a.JPG

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.

I like that Ed  -  Thanks.   I'm still trying to buy this TR4A project in America (the seller has not had a good year and so packing the bits in has taken much longer than he or I had hoped)  but I'm still thinking to keep it LHD drive ..so any additional space to that side is particularly useful. 

Pete

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  • 7 months later...

Hi there. I am planning to make an onshape model of the TR6 chassis - it's the same, right?

I want to try some studies on electric motor installation. I'm not planning to convert my TR6 to electric but I want to build a classic EV at some point in the future. Don't have the space or time (or money) yet so I am starting by making some studies on my existing collection - Scimitar, TR6 and Esprit.

Scimitar is partly there so far. I am hoping I can fit a Nissan Leaf motor and transmission in the back.

Here is the Scimitar so far. It is an SE5. For the Nissan motor to fit, I might need to base it on the slightly wider SE5.

Onshape models can be shared publicly. Anyone with a free Onshape account should be able to view this, copy and make modifications.:  https://cad.onshape.com/documents/a3a31bd9f163da8c374fce83/w/755e15eaa45a84633ff6acb3/e/e9d5e9096a76a3938751b6cf

In another project, I want to make a Surrey type top for the TR6, for that I either need to make a model of my existing hardtop via photogrammetry or find CAD of an existing one.

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i have only just come across this thread on chassis torsional stiffness  and i have found the comments most interesting.  I can't really offer too much on the IRS  chassis but when I was building my all alloy special TR4  I did consider having an aluminium chassis made.  However, as it has been pointed out above the chassis is not that heavy and would have a much shorter fatigue life.  As my bodyshell is all aluminium ( apart from the windscreen frame)   i had already made significant weight savings.  I have also used many alloy mechanical parts too in order to get the weight down.  However,  i have added some weight by fitting not only a roll bar behind the driver but another one under the front bulkhead. These 2 hoops are the connected by longitudinal bars running from the front suspension turrets  , through the door gaps and from the rear hoop down to by the rear spring hangars.  This has  effectively made my chassis about 10 inches deep and triangulated approx 10 feet of it.  The alloy body  effectively just sits on and around the new chassis.   Yes, the suspension rates have been changed to compensate for the stiffer chassis  but the car was designed for the track.  You may ask why I did all this. Well i can blame Jaguar for that. Many , many, many  years ago Birmingham science museum had on display one of the  factory lightweight E types  ( needless to say its not there anymore!)  I thought why not make  an alloy TR ?  I contacted Triumph  and asked if they could produce such a body shell. They laughed at the idea  but not to be put off I used my contacts in the trade and over the years I had all the various panels made  using ST originals as patterns. 

Hoges. 

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On 6/3/2020 at 10:50 AM, Paul Hogan said:

i have only just come across this thread on chassis torsional stiffness  and i have found the comments most interesting.  I can't really offer too much on the IRS  chassis but when I was building my all alloy special TR4  I did consider having an aluminium chassis made.  However, as it has been pointed out above the chassis is not that heavy and would have a much shorter fatigue life.  As my bodyshell is all aluminium ( apart from the windscreen frame)   i had already made significant weight savings.  I have also used many alloy mechanical parts too in order to get the weight down.  However,  i have added some weight by fitting not only a roll bar behind the driver but another one under the front bulkhead. These 2 hoops are the connected by longitudinal bars running from the front suspension turrets  , through the door gaps and from the rear hoop down to by the rear spring hangars.  This has  effectively made my chassis about 10 inches deep and triangulated approx 10 feet of it.  The alloy body  effectively just sits on and around the new chassis.   Yes, the suspension rates have been changed to compensate for the stiffer chassis  but the car was designed for the track.  You may ask why I did all this. Well i can blame Jaguar for that. Many , many, many  years ago Birmingham science museum had on display one of the  factory lightweight E types  ( needless to say its not there anymore!)  I thought why not make  an alloy TR ?  I contacted Triumph  and asked if they could produce such a body shell. They laughed at the idea  but not to be put off I used my contacts in the trade and over the years I had all the various panels made  using ST originals as patterns. 

Hoges. 

^ Excellent Hoges.  

As a fan of lightweight cars in general (I worked alongside Frank Costin's son in a summer vacation job and we got talking)  and equally of the Lightweight E-type  (I very nearly bought a kit-car company which made a version of one in GRP a few years back) -  I very much appreciate where you are coming from.  Never having been in the position to afford an aluminium special, and also wanting the car for daily road use,  I was glad to be buying a TR4A with grp panels. That purchase fell through but your and my thoughts are quite in parallel.  Is there a thread or perhaps your own website which will show us more of what you did with your 4 ?  

Many Thanks, Pete

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  • 1 month later...

Hi All,  TR-Register Newbie here ,   i was wondering if anyone had an accurate CAD drawing or 3D model of the standard TR6 chassis ?   I am wanting to make some brackets for a Celette Jig that i can use to measure and do basic repairs.

Any help is greatly appreciated.

 

Paul W.

Edited by Paul Wike
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Hi all,

One option I don't think has been mentioned so far is to manufacture the entire chassis from square RHS. That's much more torsionally rigid than the original externally welded section. Still not as rigid as a chassis with additional torsional bracing would be (I *think*), but a useful improvement with no change in dimension or weight (assuming the correct RHS could be sourced). That's what I have, btw...

JC

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When Rubery Owen stopped manufacturing chassis one of the guys who used to work there made his own from box section, they were very good unfortunately he only made about a dozen. Picture below is one of them.

Stuart.

200866123_jeffstr5155.thumb.jpg.7261a7742edb4a36bd5ca210b1d2cec6.jpg

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Hi Stuart,

That looks like mine. Including the mountings for tubular shocks concentric with the springs. Just being picky, but I believe "box section" refers to the original method of (cold) folding a flat plate and then welding an external flange (i.e., the original TR6 chassis section). RHS is a continuously seam-welded hot rolled section. That's what my chassis is made from. I can't see any flanges, so I suspect that's what the one in your photo uses.

Cheers,
John

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