Jacko
So, I was chatting to Dennis from Siltech Racing, and we were talking about our respective obsessions about reducing weight. On their Westfield they
have replaced steel bolts for ally bolts in non-structural circumstances. Smart move of course.
I then got to thinking and in the past, I've used adjustable nylon locking p-clips which are great if a little less aesthetically pleasing than
the ally/rubber ones.
Where a clip needs to be attached to a panel I would use something like an m4 socket headed cap screw - relatively light and in no need to be strong.
So, to take this to its cheap logical conclusion, what about nylon bolts? They're going to be even better when going through my CF panels (steel
and carbon tend to have a galvanic reaction. I'm also going to make some CF chassis clips (basically, using a piece of 1" square tube as a
former) and to then mould over that. The end result if you then make a part from this mould in something like 2 or three layers of 200gsm is you get a
part that is slightly sprung, and will then clip over the steel chassis tube I have. Extend this out a bit and you have a bracket a bit like below:
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The spring effect means they nicely clip over the chassis, and with a bit of adhesive, they're going nowhere and they weigh grammes. Then if I
was to nylon bolt what ever I needed to over the extending part I think I am onto a lightweight winner. I don't want to drill the chassis - I
have spent ages welding shut all the drill holes, and don't want them back.
I will buy some bolts and test them, both in stretch and what torque they take before they knack. For anti-vibration I was thinking of still using
nyloc nuts or loctite. I know it will have trouble sticking to nylon, but the other job it does in anti-vibration is fills the gaps between threads
which is a major cause of vibration loosening.
Any thoughts/ideas? have you been down this route?
Thanks
Mark
Well i hope the bolts you use are better then number plate bolts
Jacko
Is nylon that much lighter than alloy? Particularly for the required level of strength.
If you have a clip mechanism, rather than bonding it to the chassis couldn't you bond it to the panel?
Personally I would just keep it simple, see what panels actually need to be removable and bond in all the rest.
Hi Slimey
I'm thinking in terms of mounting removable things, such as pipes, harnesses. Everything else will be bonded
Saving a few grams?? Not worth it is it? How about looking at what you wear or going on a diet to save a couple KGS??
quote:
Originally posted by coozer
Saving a few grams?? Not worth it is it? How about looking at what you wear or going on a diet to save a couple KGS??
I work on commercial aircraft where weight saving = huge savings. However on a recently introduced aircraft there were many plastic parts introduced
including various clips and securing points and even plastic connectors and back shells. We have been replacing lots and the manufacturers have gone
back to guess what? Alloy. The savings just aren't worth it in their eyes vs the reliability. And that's when the savings are weighed in
kilos and not grams.
For a car application I just don't see the benefit of a minute weight saving where the reliability is questionable.
All just in my opinion of course
On many tin tops things like wheel arch liners and trims are often held on with plastic rivets. Things like looms are held on with Fir tree
fixings.
New 10pcs Auto 6mm Hole Dia Plastic Rivets Fastener Fender Bumper Push Pin Clips
(8-9 MM) PEUGEOT BLACK PLASTIC FIR TREE SID SKIRT PANEL DOOR BUMP SUPPORT CLIPS
there are many types and varieties of "plastic" of which Nylon is a generic description applied to a huge number of different materials. For
example Nylon 6 is a good tough material, and nylon 12 is used for fuel storage and distribution in cars.
When using Nylon in a tensile application as a bolt for example, then the addition of glass fibre will improve the situation considerably, however as
glass is more dense then some of the weight saving is lost.
Density of Nylon is typically 1.14, less than half that of aluminium and one seventh that of steel. Nylon fasteners are used to great effect in modern
cars, although not as bolts, often as the annoying little rivet thing that the middle pops out of.
For Nylon, un-reinforced the tensile strength at 5% strain is about 100MPa, after this the material moves in to "plastic deformation" and
will no longer return to the previous shape.
It is note worthy that most nylons will degrade in sunlight too, that is they will embrittle.
Having said that on the average tintop there are tens of kg of plastic including pressure vessels, fuel tanks, inlet manifolds, as well as many loaded
components,. the clutch clevis on a volvo 360 for example.
If it is appropriate, well engineered and inspected frequently then nylon is a good engineering material.
good luck, it is an interesting proposition
I'm going to test this. I will take a few bolts and see what I can torque them to before I snap the head off. I don't have a bolt stretch
gauge though otherwise I could see what torque gives 5% deformation.
Then I'll hang a container from a bolt and start filling it with water will the bolt gives. It should be an interesting test.
Mark,
sounds good, however,....
cross sectional area of m6 bolt is say 4xpi = 12mm2
therefore at 100MPa the bolt will support 12x100N = 120kg
that is at 5%, for break the extension can be >20%
hope that helps
Hi Howard. That makes a nice simple calculation. This seems to actually make a little sense. Something like a wiring harness can't weigh more than 500g at the support if supported every 300 MM. Even with a 10G impact the bolt isn't going to see more than 50kg. Normal track vibration isn't going to do that.
I wont presume to understand all the physics involved with this but in my opinion a few grams saved with the chance of failure is not worth taking the plunge. Static loading is entirely different to a dynamic loading on a method of fixture. Remember that a relatively light weight component that becomes detached at, say 60 mph, becomes a missile that can do serious damage. Also if that damage occurs to someone or something and an insurance claim results then some difficult questions could be asked. Just my opinion though.
quote:
Originally posted by FuryRebuild
Hi Slimey
I'm thinking in terms of mounting removable things, such as pipes, harnesses. Everything else will be bonded
A long time ago I used epoxy to bond wing panels and nose cones on fighter planes (real ones), in order to verify the bond a peel test was conducted,
invariably the aluminium would tear before the bond broke.
I used the same technology when refitting a few bits on my landy, they are still there more than 20years later.
The main issue with adhesives and bonded joint is ensuring that the loads are applied in a sensible way, peel is very bad, shear is better.
The other issue that you have touched on is surface prep, and to a certain extent the cure process, the hight strength epoxy resins are heat cured, I
used to use a hair dryer and a thermocouple to ensure that I didn't over cook it.
above all have fun and stay safe
I'm using permabond ET15 s mi flexible epoxy adhesive. It's been designed to give full cure at room temp. TDS says 0.5 to 2mm bond thickness so I'm going to tack 0.75 thickness washers along the bond seam to ensure things seat well. I will also rivet through at the end of every seam to help protect against peel.
Good plan, although I seem to recall a paper on peel reduction that I read, something to do with gap and flare, might be worth some research to reduce
the number of rivets that you have.
To be fair every time I look at the floor on mine I think I would prefer a glass aramid bath tub, especially if it went up both sides...
Hi Howard
You can see the extent of the tub mould here and on some other related posts.
It's the full deal. The only thing that's not part of the tub is the footwells.
The layup will have in all areas 2x300gsm aramid facing down and out (and including the transmission tunnel), mirrored with 2x300gsm carbon on the
face for cosmetic reasons. Depending on there in the tub it is, there will be either a 10mm, 5mm, or for the tunnel, flexible foam core. Depending on
where in the tub we are, there will be between 2 and four layers of 600gsm carbon (it's like woven rope - great stuff) and a couple of layers of
e-glass for a little but of splinter absorption.
I've also got some posts in the blog where you can see the tests I did on various pre-made parts of this stack, and the thickest point of the
stack will take 300 kg/square inch/mm deflection (tested in a load-cell).
Hi Mark,
Perhaps there is scope for a full slot in - retrofit- tub, one for each side.
Subject to cost etc, I would be interested in such a thing, maybe as part of the winter 16 rebuild when I do the back axle, diff and hubs
The weekend was full of elation as the new engine loom and additional harness bits that I made worked. So chuffed! Almost like a "first
start" all over again.
maybe when the weather is better I can make a trip up in mine and we can compare notes. As a composites engineer I am always please to see such
dedication to "plastic"
quote:
Originally posted by FuryRebuild
I'm using permabond ET15 s mi flexible epoxy adhesive. It's been designed to give full cure at room temp. TDS says 0.5 to 2mm bond thickness so I'm going to tack 0.75 thickness washers along the bond seam to ensure things seat well. I will also rivet through at the end of every seam to help protect against peel.
Interested to read about bonding. In the past at work we've used 3M double sided tape to bond stainless steel and mild steel sheet together - it doesn't come apart easily.
Hi Howard
I have to admit, the further into this journey I've gone, the better it is, and it took me a while to get my truly into thinking in 3D
My mould is a single piece, and I cut the transmission tunnel out as part of it. The tunnel gives the tub huge strength in bend when its there, so it
is a single-piece. I don't intend to destroy the mould though, so it could be reused. There's 20kg of steel and ally to come out.
quote:
Originally posted by HowardB
Hi Mark,
Perhaps there is scope for a full slot in - retrofit- tub, one for each side.
Subject to cost etc, I would be interested in such a thing, maybe as part of the winter 16 rebuild when I do the back axle, diff and hubs
The weekend was full of elation as the new engine loom and additional harness bits that I made worked. So chuffed! Almost like a "first start" all over again.
maybe when the weather is better I can make a trip up in mine and we can compare notes. As a composites engineer I am always please to see such dedication to "plastic"
there was a build blog where the builder had attached all the panels with 3m tape, again having used VHB it is phenomenal.
It's also not too bad if it gets wet either.
Much more expensive than rivets though
I've used monster building tape to hold pieces together when making moulds but I wouldn't trust it structurally. The epoxy I'm looking
at is permanent. when the tub's in, it's in. If I need to get access to anything it will have to be from underneath. I've even bought
an electric handbrake which is mounted near the diff so that I don't need that mince in the tunnel.
quote:
Originally posted by nick205
Interested to read about bonding. In the past at work we've used 3M double sided tape to bond stainless steel and mild steel sheet together - it doesn't come apart easily.
quote:
Originally posted by FuryRebuild
I've used monster building tape to hold pieces together when making moulds but I wouldn't trust it structurally.... I've even bought an electric handbrake which is mounted near the diff so that I don't need that mince in the tunnel.
I went for one of these and I had to import it, so not
exactly locost.
However, the advantages were many:
If you are after nylon, plastic in general bits and pieces then you might give Essentra a try.
I'm not advocating plastic bolts as such, but everything has its uses.
Permabond have a lot more than the product mentioned above and a chat to their technical guy can be very helpful. I've been using their stuff
since 1990. Unfortunately, a good many of the really good adhesives they formulated got dropped when the company split.
Gurit have a couple of good epoxy adhesives as well, used in raceboat building.
Cheers,
Nev.