Flat pack GT40 chassis kit
Discussion
The other day I came across the Gt Forte 'flat pack' chassis kit. It's basically all of the tubes needed to build a space frame GT40 chassis pre cut and ready to be welded together.
Does any other company sell the same sort of thing? i.e. a chassis pack (or drawings of a chassis!) that, once it's put together, will fit a bodyshell they sell?
Does any other company sell the same sort of thing? i.e. a chassis pack (or drawings of a chassis!) that, once it's put together, will fit a bodyshell they sell?
Notwithstanding the GT Forte's dismal reputation, tubes that are laser cut to CAD dimensions are so accurate that they will virtually slot together and stand up without welding. You only need the most basic jigs - to ensure accuracy of dimensionally critical points like suspension pickups and the like.
To answer the OP's question, the only current chassis kits I know of that would meet his requirements are those for Locost or Haynes Roadster-type 'Seven' style cars, where you can buy flat-pack kits of pre-cut chassis tubes to build up according to 'book' plans.
There was the Reynard/Andre Brown Inverter, which was open source on all the design material (including chassis drawings), but I think that project is now defunct.
To answer the OP's question, the only current chassis kits I know of that would meet his requirements are those for Locost or Haynes Roadster-type 'Seven' style cars, where you can buy flat-pack kits of pre-cut chassis tubes to build up according to 'book' plans.
There was the Reynard/Andre Brown Inverter, which was open source on all the design material (including chassis drawings), but I think that project is now defunct.
chuntington101 said:
Never heard of a kit car company doing it though. How would you gone on with getting one through the IVA?
Plenty of manufacturers use laser cut tubes, these days, though of course they tend to weld them together themselves, rather than supplying them as a flatpack to their customers to do it. Increasingly, the tubes are even pre-drilled for rivets too (with matching pre-cut and drilled ali panels ready to rivet to them). Take a look at the capabilities of companies like Caged Laser Engineering.There are companies who will supply you with a pack of pre-cut tubes for the Haynes Roadster or it's predecessor, the Ron Champion Locost.
Why would it make any difference to the IVA, compared to a Locost/Haynes roadster that had had its tubes cut and shaped by a man in a shed with a hacksaw and a b
d file?Back in the distant past I worked for a kit car manufacturer ,all tube were precut and it was procedure if you were on chassis fab to cut 10 tubes if you took the last one out of the rack, nearly all square tube but some round nothing bigger than 1" except roll over bar the system worked very well . We used a jig built for us by Arch motors Happy days!!
As others have said, I don't think a full jig's necessary to weld up a decent chassis provided you're careful. It's a project I'm looking to do with my dad in his imminent retirement - he's been a welder for about 40 years and he was happy with the idea!
It was specifically a GT40 chassis I was after. Quite a lot of people seem to have 7 style plans/'chassis packs' available. We were more or less about to order a pack from GT Forte then I did some 'due diligence' googling of them...
It was specifically a GT40 chassis I was after. Quite a lot of people seem to have 7 style plans/'chassis packs' available. We were more or less about to order a pack from GT Forte then I did some 'due diligence' googling of them...
You don't think a jig's necessary?
Just as background, I served my time on aircraft, Harriers & Hawks as a production fitter.
All the parts were manufactured to incredibly fine tolerances and as you'd expect all fitted together reasonably well.
Here's the thing, there is no way on gods earth you could of assembled a sub assembly together out of a jig and get anywhere close to a finished article that resembled a quality product that conformed to drawing, it just wouldn't happen.
I'm not saying a kit car chassis need's to be built to the same tolerance as an aircraft but the principles the same, without a jig the thing will move whilst assembling especially if your welding and the end result won't be as accurate as it could / should be.
So in my view and for all the right reasons, building within a jig is the way forward.
Just as background, I served my time on aircraft, Harriers & Hawks as a production fitter.
All the parts were manufactured to incredibly fine tolerances and as you'd expect all fitted together reasonably well.
Here's the thing, there is no way on gods earth you could of assembled a sub assembly together out of a jig and get anywhere close to a finished article that resembled a quality product that conformed to drawing, it just wouldn't happen.
I'm not saying a kit car chassis need's to be built to the same tolerance as an aircraft but the principles the same, without a jig the thing will move whilst assembling especially if your welding and the end result won't be as accurate as it could / should be.
So in my view and for all the right reasons, building within a jig is the way forward.
Darranu said:
You don't think a jig's necessary?
There are jigs and jigs, though.You need to jig up the front and rear suspension pickups, but if you're building a one-off, that can be done using something as simple as MDF jigs with the relevant holes accurately drilled in them. And you need a decent, flat build table to which you can clamp the tubes.
But in the real world, what happens between the front and rear suspension pickups really isn't all that critical to within +/-5mm. or so (+/-10mm, if you're not so fussy), for a kit car with fibreglass bodywork. You can achieve that easily, if you tack weld everything together first, then weld in distributed sequence to even up the stresses.
Proper, heavy-duty steel jigs are only necessary if you're planning series production of chassis. Otherwise, you're better off spending your time and effort elsewhere, I reckon (but likewise, just my opinion).
There are a few GT Forte builds on gt40s, you can see how the tabs slot together if you look
what the kit does is speed up time, as you don't need to design the chassis and you don't need to cut all the tubes.
there will still be plenty of fabrication required, little brackets and other bits and pieces as per a kit car.
I guess it fits into a price bracket, allows things to be shipped, meaning someone can get started and on there way without a big up front cost. That's only required once you get to the body stage.
That's if for me, i'm off home from work now so that I can work on my GT40......
Regards Ryan
what the kit does is speed up time, as you don't need to design the chassis and you don't need to cut all the tubes.
there will still be plenty of fabrication required, little brackets and other bits and pieces as per a kit car.
I guess it fits into a price bracket, allows things to be shipped, meaning someone can get started and on there way without a big up front cost. That's only required once you get to the body stage.
That's if for me, i'm off home from work now so that I can work on my GT40......
Regards Ryan
Equus said:
There are jigs and jigs, though.
You need to jig up the front and rear suspension pickups, but if you're building a one-off, that can be done using something as simple as MDF jigs with the relevant holes accurately drilled in them. And you need a decent, flat build table to which you can clamp the tubes.
But in the real world, what happens between the front and rear suspension pickups really isn't all that critical to within +/-5mm. or so (+/-10mm, if you're not so fussy), for a kit car with fibreglass bodywork. You can achieve that easily, if you tack weld everything together first, then weld in distributed sequence to even up the stresses.
Proper, heavy-duty steel jigs are only necessary if you're planning series production of chassis. Otherwise, you're better off spending your time and effort elsewhere, I reckon (but likewise, just my opinion).
My current project is based upon this idea entirely, and I'm perfectly happy with the notion. Frankly, I expect to get better results than some supposedly professional builds I've had and seen. Marcos used to build the chassis to chalk marks on the floor. Then again, they didn't seem to have the first idea about suspension geometry if the level of bump steer from both ends of the car was anything to go by.You need to jig up the front and rear suspension pickups, but if you're building a one-off, that can be done using something as simple as MDF jigs with the relevant holes accurately drilled in them. And you need a decent, flat build table to which you can clamp the tubes.
But in the real world, what happens between the front and rear suspension pickups really isn't all that critical to within +/-5mm. or so (+/-10mm, if you're not so fussy), for a kit car with fibreglass bodywork. You can achieve that easily, if you tack weld everything together first, then weld in distributed sequence to even up the stresses.
Proper, heavy-duty steel jigs are only necessary if you're planning series production of chassis. Otherwise, you're better off spending your time and effort elsewhere, I reckon (but likewise, just my opinion).
A production item where you need to be able to interchange parts and provide spares that fit without fettling is an entirely different animal of course.
one eyed mick said:
To the above if the floor is flat and your measurement accurate you might stand half a chance but other wise you are weeeing in the gale
It's a tried and tested method, flat, true build table, datum lines, build the chassis to the best of ones ability & accuracy then jig the suspension pickup points to the datum marks. As long as the pickup points end up true then as already noted, what joins them together isn't all that critical give or take a few mm. It might offend the eye and the purist, but it won't affect the geometry. More important to be accurate if you are fitting bodywork perhaps, but most fibreglass offerings are far from dimensionally perfect even when they leave the mould, let alone after they have sat for a while so I'm not sure I even buy that argument TBH.We aren't building production cars here, these are hand-made one-offs.
The only other laser cut tube pack is for a Cobra, from the same company!
I've built the GT-Forte chassis from the laser cut tube pack. As a system is actually works very well, you build in flat sections, direct on the build table. I used a couple of layers of 3/4" marine ply on a steel frame.
Due to the tight tolerances it's very easy to see if something's off even a tiny amount. basically if there's a tiny gap in the fit of the laser cut joint something's not right.
If you tack everything first, then assemble the layers to make the full spaceframe, then fully weld afterwards then to a certain extent the tack welds stop the whole lot from twisting and buckling.
Obviously you need to be a competent welder, or if not tack it all, and spend a few hundred to get a certified pro in to make the final welds.
I'm at the panelling stage with mine, and am very happy with how straight and true everything is, but then I did take my time, establish datums, tack everything first etc. I haven't found a panel where I can't simply transfer the template to the other side of the car and it not fit. As far as I can tell / measure everything is straight/true to less than a mm across the major sections.
That said the kit is quite hard to put together, needs a lot of figuring out of where bits go from photos etc. Took me about 4mths... Help is there if needed though.
My build thread is here if you are interested: http://www.gt40s.com/forum/gt40-build-logs/44873-d...
though a bit out of date.
I've built the GT-Forte chassis from the laser cut tube pack. As a system is actually works very well, you build in flat sections, direct on the build table. I used a couple of layers of 3/4" marine ply on a steel frame.
Due to the tight tolerances it's very easy to see if something's off even a tiny amount. basically if there's a tiny gap in the fit of the laser cut joint something's not right.
If you tack everything first, then assemble the layers to make the full spaceframe, then fully weld afterwards then to a certain extent the tack welds stop the whole lot from twisting and buckling.
Obviously you need to be a competent welder, or if not tack it all, and spend a few hundred to get a certified pro in to make the final welds.
I'm at the panelling stage with mine, and am very happy with how straight and true everything is, but then I did take my time, establish datums, tack everything first etc. I haven't found a panel where I can't simply transfer the template to the other side of the car and it not fit. As far as I can tell / measure everything is straight/true to less than a mm across the major sections.
That said the kit is quite hard to put together, needs a lot of figuring out of where bits go from photos etc. Took me about 4mths... Help is there if needed though.
My build thread is here if you are interested: http://www.gt40s.com/forum/gt40-build-logs/44873-d...
though a bit out of date.
Darranu said:
You don't think a jig's necessary?
Just as background, I served my time on aircraft, Harriers & Hawks as a production fitter.
All the parts were manufactured to incredibly fine tolerances and as you'd expect all fitted together reasonably well.
I serviced Harriers for a living. Just as background, I served my time on aircraft, Harriers & Hawks as a production fitter.
All the parts were manufactured to incredibly fine tolerances and as you'd expect all fitted together reasonably well.
You're taking the piss when you say you used jigs, right?
some of this jig stuff appears to be overstated. As an example, take a bicycle frame....... Some old-school builders used to pin the tubes at the lug joints to keep the lengths correct, and then braze them. Others swear by a massive steel jig to hold the tubes in place whilst brazing (and subsequent cooling) takes place. But it can be argued (and I agree with this) that the jig method can be criticised for holding it all in place and setting up stresses which (in the pinned structure), will settle in the position where the metal 'ends up'. This may mean cold-setting to get the alignment good. Having watched one of the old school frame builders in my youth, it was impressive to see how he could carefully use the heat to best effect and end up with great alignment using simple measurements and straight edges.
Jigs are not necessarily the best. They are for bolted assemblies, but not for welded. As sometimes it will ping as soon as you remove it from the jig and you will find its been under stress as its cooled/heated from the welding process.
Have you seen the process that is still used to make Orange Bikes? Its tacked on a jig, then welded off. Then put on an alignment jig and they tap it here and there until its knob on. Worth a youtube search.
Have you seen the process that is still used to make Orange Bikes? Its tacked on a jig, then welded off. Then put on an alignment jig and they tap it here and there until its knob on. Worth a youtube search.
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