ikb Posted April 24, 2011 Report Share Posted April 24, 2011 Looking to make a new back wheel spindle for my Cota 200 to replace the old rusty thing!! And was wondering if anyone new which grade of aluminium is best?, I plan to copy my Gas Gas pro spindle bit a bit longer. Thanks Ian Quote Link to comment Share on other sites More sharing options...
totalshell Posted April 24, 2011 Report Share Posted April 24, 2011 (edited) save yourself a whole lot of hassle take the old spindle down your LBS and pick a new one out.. get the length about right ( longer rather than shorter) and keep an open mind about spindle diameter ( as long as you can get a bearing to fit) and you'll have the pukka stuff.. running a Sherco spindle in my 1950's francis barnett hub that cost me shy of 20 quid..) Edited April 24, 2011 by totalshell Quote Link to comment Share on other sites More sharing options...
gii Posted April 24, 2011 Report Share Posted April 24, 2011 Armac design use 2014A for their Triumph Tiger Cub alloy spindles. Even stronger and tougher is 7075 T6 - you can pick up a couple of suitable lengths of that for Quote Link to comment Share on other sites More sharing options...
fish06 Posted April 25, 2011 Report Share Posted April 25, 2011 I'd second the 7075/T6. Cheers. Quote Link to comment Share on other sites More sharing options...
ikb Posted April 26, 2011 Author Report Share Posted April 26, 2011 Thanks, Will try and find some, cant see any on ebay though. Ian Quote Link to comment Share on other sites More sharing options...
gii Posted April 29, 2011 Report Share Posted April 29, 2011 Maybe you need to improve your search techniques Try searching ebay for "twinshock alloy spindle", you might find what you want. Quote Link to comment Share on other sites More sharing options...
michaelmoore Posted May 18, 2011 Report Share Posted May 18, 2011 Aluminum is 1/3 as stiff as steel and every time it is cycled it is one step closer to failing from fatigue. Also, the smaller the diameter of the axle the more the stiffness is reduced. You'll probably be better off with a tubular steel axle for both lighter weight/performance as well as longevity. Remember the problems that BSA had when they duplicated the steel scrambles frame in titanium (which is less stiff) and had the thing flexing so badly. You can make aluminum axles, but do as John Britten did and go up a LOT on the diameter and plan on replacing them on a schedule. Let's say you've got a 15mm solid steel axle now. You'd want to go to a 20mm aluminum axle to have roughly the same stiffness. Harry Hindall used to offer tubular 4130 axles that had a mild heat treat to strengthen them some more. You could also use 4140 or 4140HT that comes with a moderate heat treatment, but that only improves strength, not stiffness. As the hardness goes up ductility goes down and you want to take even more care with avoiding sharp inside corners that will act as stress raisers. I've had a front axle break (Suzuki TS185, sheared at the shoulder where the diameter stepped up) and I've been behind a Duc single that had a rear axle break in a road race, and I'd suggest you won't find a broken axle to be a lot of fun. The recommendation of going to a breaker and rummaging through their big box o' axles to find something to shorten/rethread (as needed) sounds like a good plan to me if you are wanting to reduce the amount of aggro. cheers, Michael Quote Link to comment Share on other sites More sharing options...
ikb Posted May 18, 2011 Author Report Share Posted May 18, 2011 Maybe you need to improve your search techniques Try searching ebay for "twinshock alloy spindle", you might find what you want. Thanks Gordon, I was focussed on ally round bar!!!!! Great technical reasoning Michael, I was after making something neater than the original rather than saving weight and my theory was its the same size as my GasGas spindle so it must be OK!! Quote Link to comment Share on other sites More sharing options...
michaelmoore Posted May 19, 2011 Report Share Posted May 19, 2011 Some of the high-strength aluminum alloys are as strong as some steels but they are not as stiff. Here's some numbers off of Matweb: 7075-T6 83ksi Ultimate Tensile Strength, 73ksi yield strength, 10400 ksi Modulus of Elasticity, 9% elongation at break 2024-T6 60ksi UTS, 46ksi yield, 10500 ksi MoE, 5% elongation 4130 97ksi UTS, 63ksi yield, 29700 ksi MoE, 25% elongation note that the MoE for the steel is almost 3X that of the aluminums even though 7075-T6 is almost as strong in UTS and has a higher yield point. But ductility and stiffness on those strong aluminum alloys is much lower than the 4130 steel. Aluminum is great stuff when used properly. But you wouldn't normally swap aluminum for steel without changing the part sizes (presuming that the steel part was not massively overdesigned). cheers, Michael Quote Link to comment Share on other sites More sharing options...
pat Posted May 19, 2011 Report Share Posted May 19, 2011 (edited) 7075 is gods gift to us :-) up to 70% weight red.. Some examples, confirmation of available design and copy paste: Yamaha TY250R 1984, *stem 7075 adonized 25mm drilled ~18mm hole, perfect condition after 26 hard years *rear spindle 15mm steel, drilled 8mm, I have replaced it with 7075 solid *all nice spindle/stem replacement parts from Craig *cam shaft wheel for eg C15 -yes, big OD and drilled is superior smaller solid of course, eg. all modern front spindle MX, RR, trials... stem at my RR bike, perfect condition Edited May 19, 2011 by Pat Quote Link to comment Share on other sites More sharing options...
michaelmoore Posted May 20, 2011 Report Share Posted May 20, 2011 (edited) *stem 7075 anodized 25mm drilled ~18mm hole, perfect condition after 26 hard years *rear spindle 15mm steel, drilled 8mm, I have replaced it with 7075 solid I've used 2024-T6 25mm tube for a roadracer steering stem and I'd have no issues with that as the diameter is big enough to work OK. But a solid 15mm aluminum round and a 15x8 steel tube both have nearly the same (the solid is slightly better) second moment of area, so the aluminum axle will be about 1/3 as stiff as the steel tubular axle. Most vintage teleforks are pretty bad in twisting and the less stiff 15mm aluminum axle isn't going to improve that and it wouldn't be something I'd care to do, but YMMV. You have to run the numbers and see how they stack up. Some people think "oh, I'll make a sneaky high performance lightweight frame by keeping the standard OD but significantly reducing the wall thickness" and ignore that while they've saved a bit of weight they've also reduced the stiffness of the frame, irrespective of if they are using 531/4130 instead of mild steel or not. cheers, Michael Edited May 20, 2011 by MichaelMoore Quote Link to comment Share on other sites More sharing options...
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