Aluminium Grades

[norlander]

I am looking to make a front mudguard support for my motorcycle. Initial research seems to suggest I should use 2024.
Choice would be flat at 5mmx25mm. 2 pieces 90mm long will need to be bent round to 90°.

The support will be 2 separate supports handed L&R.
The job will be subject to vibration of various frequencies and some stress through shocks from road surface. Torsion stresses probably not too severe as the forks are USD, but it is difficult to guestimate.

The current brackets were made up in M/S and have failed three times, my guess the cause being their weight.

Initial thoughts were to weld the ally brackets up, but I am now considering bonding to avoid the HAZ etc caused by TIG.

Another plan is that once the supports have been fabbed up, fitted and road tested, I will be asking Hotrodder to weld up a pair in Ti.

The design is like this; any advice:suggestions appreciated.

 

[Pete.]

Try profiling those brackets from 3mm sheet and bend the tabs round with a nice radius.

 

[norlander]

Try profiling those brackets from 3mm sheet and bend the tabs round with a nice radius.

nice one-I overlooked the obvious there-and they could be cut out 4 off in 3mm and bonded together to make 2 off if I wanted them thicker. You also made me think of an ali/carbon fibre sandwich for the job as well.

 

[awemawson]

Why are they breaking - surely the load on them is minimal unless you are always bashing into things, so are they vibrating and fatiguing? If so you need to stop them vibrating somehow, aluminium will be no better if this is the cause.

 

[zx9]

I don't know the answere but I do like the copper sheet wrapped round that heavy channel, I will have to copy that idea.

 

[norlander]

Why are they breaking - surely the load on them is minimal unless you are always bashing into things, so are they vibrating and fatiguing? If so you need to stop them vibrating somehow, aluminium will be no better if this is the cause.

I think it is down to the weight of the M/S used, the forks design requires a lightweight mudguard assembly the mudguard mounts are here
https://www.wwag.com/cgi-bin/WebObjects/WebSite.woa/wa/DirectAction?page=!WW28638

the guard is here https://www.wwag.com/cgi-bin/WebObjects/WebSite.woa/wa/DirectAction?page=!115172 the problem is max wheel dia is 18" and my wheel is 19" . I am looking to source a guard for a 19"" wheel to see if its possible to raise it 1" in which case I can use the proper guard and mounts but until I am sure I aint commiting meself to around 1k euros to find it dont work.
I'll know more this weekend, as I am picking up a 19" guard and I'll be with my bike.

To complete the picture the forks are here; https://www.wwag.com/cgi-bin/WebObjects/WebSite.woa/wa/DirectAction?page=!WW27657

 

[norlander]

I don't know the answere but I do like the copper sheet wrapped round that heavy channel, I will have to copy that idea.

its my heatsink/jig thingywotsit for tigging allydidlium trays I make up for keeping thingymajigs in. I don't have a foot pedal and I got a clonking greet 26 torch so I came up with that as a heatsink, and I do beads of bout 60mm, then switch to another part if the puddle starts running away, but the heatsink has worked quite well.

I am thinking of copper claddng some smaller channels so I can make a jig adjustable for width

 

[hotrodder]

Where are the current brackets failing? Same place each time? Folding them from profiled sheet was my first thought too but 2024-T3 is gonna need a minimum bend radius of 5 - 6t for thicknesses in the 3 - 6mm range. 2024-O should be happy with a radius of 1t but then you need to get it heat treated... in industry they'd solution anneal, form and then artifically age or even uses posh techniques like HFQ (hot forming cold die quenching) where the part is formed hot and quenched while still in the dies for increased productivity and a more accurate part as springback is reduced

I know you're thinking of avoiding welding a bracket out of ally anyway but with 2024 you'd have to bond, rivet or whatever as conventional welding would totally trash the properties if it didn't crack severely during solidification

6063 or 6082-T6 would let you get away with a slightly smaller bend radius but that'd be negated if you upped the thickness to compensate for it's lower strength. If you want/need a sharper bend radius due to available space etc then 7020 is available as flat bar. No help on the bend radius front but it's the same animal as 7005 used a lot in bicycle frames as it 'recovers' well from welding and so can get away without fully heat treating/making the thing heavier to compensate for the HAZ. Basically cheaper/heavier frames are just left for a few days to age harden naturally while higher end ones are just artifically aged which you could do (albeit a bit crudely) in your oven at home- Eastern specs for their 7005 frame tube sets are 6 hours at 200°F followed by 4 at 320°F. More scientific, and headache inducing, take on natural vs artificial aging of 7020 here http://cdn.intechopen.com/pdfs-wm/13396.pdf but as said aluminium is gonna be worse than steel from a fatigue POV regardless. Some (many?) motorbikes use 7005/7020 or proprietary variations on it

I've got some 3mm grade 2 Ti sheet in stock if you're feeling rich No way i'm cutting that shape out of Ti by hand though, i'd give it to Matt at Fabcuts along with a dxf

One last thought, regardless of flavour/strength aluminium is gonna be around 1/3 the elastic stiffness of steel. Titanium about 1/2

 

[norlander]

Cheers, HR, I'm back with the bike and brackets next week, they failed at the holes drilled in the bottom of the bracket or in between the holes- the bit resting on my welding bench is the bottom bit,one failed once at the gusset you can see on the lower bit.
The mounting point on the forks is three 5mm bolts and thats it-see here https://www.wwag.com/cgi-bin/WebObjects/WebSite.woa/wa/DirectAction?navi=1&page=!WW32237, thus the mudguard and weight of the supports is resting on 5mm bolts, the assembly is subject to roadshocks as some of the french back roads have bumps that can launch your bum out of the saddle if you do not spot em first-and you can't spot em all.
Re the grade 2 Ti and price of, if I bought the Ohlins mountings and mudguard, the price is around 700 quid, and then the guard will need to modified because its for an 18" wheel and mine is 19".
So, I would be looking at around 750 quid or so. That would be the comparison cost against the Ti fab cost.
I have guards for 19" wheels in a couple of flavours, so getting brackets fabbed up was my first plan of attack.
My gut feeling is that the brackets are failing due to their weight-hence my thought of fabbing em in a lighter material if the cost is lower than the purchase of the Ohlins kit and modifying it.
Other option is to purchase the Ohlins mountings, which will negate the need for bending, as the mounting struts would bolt on to them.

 

[hotrodder]

Only just clocked the prices in those links! Ohlins tax is higher than i thought it'd be What are the mudguards made out of, similar plastics to fairings?

If i was in your position i'd be thinking of getting something similar to the Ohlins brackets machined or fabricated and modifying one of the mudguards that are in stock to fit them before pulling a mold off it and having it laid up in kevlar or carbonfibre. Might be very wrong as i don't know the going rate for getting stuff made from the posher flavours of FRPs but i would've thought you should have a healthy chunk of change left over compared to buying the Ohlins stuff and the result would be neater/better/lighter than large adaptor brackets (even Ti ones) to get a different mudguard to fit?

 

[norlander]

The Ohlins guard is in fibreglass and weighs in at over 2kg, my original steel mudguard for the original forks comes at 880 grams so yes-I have now found a source of carbon fibre and that is now my thought, to make supports up in CF for one of the 19" mudguards in my collection which fits in the ohlins forks-which are wider than average forks-which compunds the problem of fitting a non ohlins product.
The CF route will be cheaper materials wise, so that is now the plan.
For info http://www.easycomposites.co.uk/

 

[graffian]

Only just clocked the prices in those links! Ohlins tax is higher than i thought it'd be What are the mudguards made out of, similar plastics to fairings?

Not had Ohlins but I used to make carbon guards for several forks, I always ditched the brackets and made them completely
from carbon, I know of a guard on a gsxr that is now 24 years old and the only damage is from the bloke riding it on it's side.

2kg for a glass guard sure that's right?
I have one for a set of forks from a J1 kwaker front end, I will weigh it, it's not as deep as an ohlins one would be.

 

[hotrodder]

Fibreglass reinforced plastic is what, approx 1/4 the density of steel? It's not uncommon for 'kit car' type stuff to be mostly chopped strand instead of cloth and over 1/8" thick...

 

[norlander]

I am going to get my bike shop to call the suppliers and check that the weight of the guard is correct.
For info btw, the reason I am being picky is I knew a chap who was killed when his front guard came adrift at speed and cut his brake lines.

 

[norlander]

Thought I would update and top off this thread. I gleaned enough info off this forum to make me think that I could have in fact attempted the job myself welding up mounting brackets in ali and heat treating them afterwards.
However, as I am not a professional welder, and, as I consider the mudguard brackets to be a critical item, I followed my self imposed rule of not welding anything critical unless I have done it before and its stood up to my non technical test regime.
My gut feeling was to leave this one alone, so I went on to purchase the breathtakingly expensive bits to mount the front guard. As often happens with this kind of kit, when it arrives and you fit it, you usually find the price less painful due to the quality of the kit.
So here is the front guard at long last:





one minor fitting tweak to do to if I can be bothered as its only a gnats out, if at all, the guard of course did not weigh 2.5 kilos as stated, its exceptionally well made, and the mounting brackets weigh virtually nowt.
I may cut the back of the guard down later, but at the moment I am leaving it long as its been ok on the road tests so far,but I have not been on the bumpy back roads yet.
What I might do next is make up mini spoilers to deflect crud and insects off the exposed lower stanchions.
Thanks to all who chipped in to my original post.