Aluminium Specs

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Pushrod Twin

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I am making a sprocket carrier for our twin racer I am making it out of 6082T6 this seems suitable and available in the large size i need commensurate with cost
I am thinking perhaps I should harden it after machining, as I have had some wear in bolt holes on previous items (OK they may have come loose :eek:)
comments welcome
To late to harden it, if it comes as T6 the job is done. T6 is by definition solution heat treated & artificially age hardened which means it was heated in an oven or salt bath to its upper critical temperature, from memory about 525Deg C, then quenched in room temperature water. The hardening is followed by reheating in an oven to 120-170C then air cooling.
If you are concerned about wear in bolt holes then I would suggest fitting interference fit shouldered steel sleeves to spread the load. Use the 10 bolt hole hub, no question. I know it's a racer & you want to add lightness, try the 5 bolt hub, no steel sleeves first, when it cracks or comes loose on the bolts, you have next season's solution. :)
 

vibrac

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Tim are you and Ben running a 4 or 5 speed box.......I found with the 5 speed I never needed to change sprockets, the bike had enough torque and flexibility to cope with small and larger tracks. I know on the smaller capacity singles and the like that you have to change them more to suit the tracks.
No 5 speed I am afraid the pockets are empty I would like another set as they seem to be a operational improvement apart from the gear range advantage but we will have to see later
 

oexing

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Aluminium 6061 is not common in my country but you get lots of 7075 any day. But in places like the sprocket bolts at the rear I´d most likely put a good amount of low strength Loctite on the threads and shanks of the bolts. This produces some sort of plastic bushes in there and should transmit all forces evenly in all joints consisting of threads and parallel fits. It is not easy to fabricate perfect fits on serial production parts like drilled sprockets and hubs. So Loctite is a good way to spread loads in all components like here. Low strength is good enough, higher viscosity could be good depending on how big the gaps may come in drilled and tapped parts. Still in the design phase I am trying to dream up a design with axial splines like the Hirth spline , perfect for torque and positioning duties. When seeing cracks in sprocket adapters this is a telltale of too high loads due to uneven load spreading or overly stressed crosssection at these places. Aluminium does not forget high stresses and this reduces useful life in components - unlike steel components. Anybody who got alu conrods in his engines will know to change them in intervals when used in racing engines - or high mileage engines like Norton or Triumph twins or so.

Vic

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bmetcalf

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Is the depth of those splines tapered? If so, as a non-machinist, that seems quite a challenge to make the mating component fit with full contact. I suppose CNC machines would go a long ways for that. How the Hirth crankshafts are made to have the throws in phase has always mystified me.
 

oexing

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Hi Bruce,
yes, the splines are a bit of a challenge, there are variations: You aim for parallel tops on the splines. As the grooves are radial this requires grooves at an angle. Plus same goes for the corresponding spline so at that part you have different angles to match. There are ways to calculate all sizes but then I am no good in maths. So instead I do as I believe and later I try to get a measurement of the result and figure out what angle I need for the matching spline. But anyway this type is a fascinating bit of engineering. The spline in the photo is a propeller adapter machined on my round table - and the second try : The first would not fit as I had just one single groove too short , made a mistake in counting numbers of grooves. You would not believe just one groove wrong in total numbers and the lot is useless - and CNC would not help . . . . .

Vic
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vibrac

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Oexing was in line to what I was thinking with my 5 bolts so its just a case of using the correct loctite.
I think bearing in mind the thin wall between the 5/16 bolt hole and the central hole this would be the best solution
Obviously this loctute application would have to be done at the final tightning stage or the bolt could move after setting under tightening torque especially.
 

oexing

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In case you are worried about motion in the bolt assembly after applying Loctite, this is not critical. The glue will still be in there and any required locking effect in the threads is not compromised by some twisting at the bolt. Just try some Loctite on a bolt with its nut, you will need all the force for several turns to undo the nut finally. This is quite different to any other locking devices like split washers or so. But of course you don´t pick high strength Loctite types, low or normal is OK, else you will need a torch to undo later.

Vic
 

Cyborg

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There are ways to calculate all sizes but then I am no good in maths. So instead I do as I believe and later I try to get a measurement of the result and figure out what angle I need for the matching spline. But anyway this type is a fascinating bit of engineering. The spline in the photo is a propeller adapter machined on my round table - and the second try : The first would not fit as I had just one single groove too short , made a mistake in counting numbers of grooves. You would not believe just one groove wrong in total numbers and the lot is useless - and CNC would not help . . . . .
Vic

Nice work! I suspect that if I tried to cut something like that I would end up under my bed curled up in the fetal position sucking my thumb and crapping my pants. I made my first gear about a year ago. Reading the Machinerys Handbook just about caused my head to explode. Thank goodness for YouTube.
What a thrill when the last tooth turned out the same as the others. I was told that thrill never really goes away no matter how many gears you cut.

On a side note, I find it interesting how strong even the low strength blue Loctite is when the fasteners are absolutely clean. I also find it interesting that my bride complains bitterly about the acetone stink, but she has no problem using nail polish remover??
 
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