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Black_Moons
08-03-2011, 03:14 PM
Hi, I recently got a request to make a shaft (Well, Multiple really) outta aluminum to replace a steel shaft. Never seen aluminum shaft in use so I thought I would ask here.

Shaft is about 5" long, 5/8" OD (Shaft is solid), Sprockets held in place with cerclips and keyways on either end, Supported by two bearings about 1" away from the sprocket on the inside of the shaft (No outer support)

HP specs are about 6HP outta a 2 stroke engine, Running into a 17 tooth sprocket on the left and a 10 tooth sprocket on the right, Estimating shaft RPM at 1200RPM.

Some issues im wondering. Iv never seen aluminum shaft. Am I right in thinking under such stress it will fatigue and eventualy snap? Or the keyways will mushroom out? Im also suspecting it has to be DEAD on accurate OD or it will quickly deform/wear as it 'rolls' around inside the bearings and sprockets.
Not sure if aluminum stock is accurate enough outta the box, Not really willing to do a run of turning larger stock to exact size due to precision required. Existing steel shaft is allready keyed and (ground?) exact size compaired to the sprocket bores, Like -0.0002 or something undersize, No notiable play. Any shaft marks stop the sprocket from sliding.

And is $10 per part too much or too little to be charging in small batchs to put 2 keyways in and 2 cerclip grooves? (Allready have the cerclip groove tool ground), Assuming I don't need to turn the stock to size. Shop is equiped with manual Mill and Lathe.

J. R. Williams
08-03-2011, 03:29 PM
Sometimes you have to learn to say NO.

JRW

jep24601
08-03-2011, 03:39 PM
If you were just being asked to key and groove the shaft to fit the specific parts, then the design would be your customer's responsibilty as to whether it worked, but since you have been given the power transmission requirements by the customer there is the appearance that there might be some expection on his part for you to have some liability for the design and future capabilty of the assembly performing up to his expectations.

If you do this get him to pay first and make sure that everything you own is in your wife's name.

KiddZimaHater
08-03-2011, 03:40 PM
$10 per part sounds good. Aluminum is easy to work with, and those parts sound simple enough. key each end = 5 minutes, groove each end = another 5 minutes. No problem.
The only hassle might be getting a good fit into the bearings. Aluminum stock usually comes +/- .005, and isn't exactly round.:mad: .
You might have to get 3/4 stock and turn each end.
Just asking, but why is the customer requesting Aluminum for a shaft? 1018 is just as cheap, but stronger for a shaft. My 2 cents...:confused:

mochinist
08-03-2011, 03:46 PM
Yeah I make parts for a guy that makes drive thru car washes, the shaft I do is 2"dia though and they must work fine since I have only had to make new ones for new car washes. If they didn't work fine it really wouldn't matter to me, the engineer/designer gave me a print of what he wanted.


I know you're in Canada and Mcmastercarr doesnt ship there, so Im not sure what you can use for metal suppliers, but for example for 5/8 DIA X 12" piece of 7075 aluminum that is ground to plus zero minus .0005" it is $15.14 mcmaster #9063k171

same thing in 6061 aluminum would be about half that, but 7075 would be a better choice(I think, but I'm not an engineer)

Weston Bye
08-03-2011, 04:08 PM
Pretty far fetched: Maybe your customer wants a one-time torque limiter - sort of a mechanical "fuse".

Black_Moons
08-03-2011, 04:35 PM
Customer wants to replace steel shaft with aluminum shaft to go with this new aluminum (hard chrome coated?) sprocket he got. I believe its for lack of rusting (part is exposed to elements on a motorbicycle), for looks (Shiny aluminum, Matchs new chromed sprocket) And to a lesser extent weight.

I wasent given transmission specs, this is based off my knowage of the parts usage. I would just rather inform my customer that I don't think the part is going to work well before taking his money to make a lot of them, If he still wants the part, thats up to him.

How well do aluminum hard chromed sprockets hold up compaired to unhardened steel ones (That are currently wearing a little, Hardened steel sprockets in similar applications show absolutely no visable wear signs)?

My biggest fear is fatigue, If the shaft is continiously torqued, Won't it weaken over time due to aluminums very low fatigue?
My other fear is the keyways being distorted over time, With just using cerclips, the keyway/shaft accuracy is the only thing that stops impact stresses

charlz
08-03-2011, 05:16 PM
I ride/race dirtbikes and aluminum is used alot for sprockets, frame etc. but the axles are still steel. However the wheel hubs are aluminum and the sprocket actually attaches to the wheel hub. Had me curious and I found this:

http://www.axle-exchange.com/

They are using 6061 for drive shafts on Mustangs, gotta be some torque there.

charlz
08-03-2011, 05:26 PM
I just re-read your description, are you talking about a jack shaft? An intermediate shaft with sprockets on each end?

topct
08-03-2011, 05:36 PM
Hard chromed aluminum sprockets?

That's funny. :D

Black_Moons
08-03-2011, 05:37 PM
I just re-read your description, are you talking about a jack shaft? An intermediate shaft with sprockets on each end?

Yes, I am.

Id wonder about that website.. They seem to be making parts for dragsters, Where the life of a part would not be such an issue compaired to weight. Also those are some DAMN huge tubes.. And no keyways to worry about.

Intresting information however, But yea, as a jack shaft it has some seriously unsupported pulling forces, as well as the torque forces.

charlz
08-03-2011, 05:49 PM
I don't think a jack shaft failure would be that catastrophic given the use you have described. Depends on what the chains do when it fails. I would explain your wear concerns, maybe having this part made out of aluminum is 'cool enough' for it to be considered a wear part. Dirtbikes run aluminum rear sprockets, everyone knows they wear faster than steel but accept that as the price for the weight savings.

Black_Moons
08-03-2011, 06:00 PM
I don't think a jack shaft failure would be that catastrophic given the use you have described. Depends on what the chains do when it fails. I would explain your wear concerns, maybe having this part made out of aluminum is 'cool enough' for it to be considered a wear part. Dirtbikes run aluminum rear sprockets, everyone knows they wear faster than steel but accept that as the price for the weight savings.

Do aluminum rear sprockets wear faster then unhardened steel? And do they wear faster in street bike applications too? (Less debrie, its a street application for this shaft)

Chain can't do... too much when it fails as theres a freewheel in the back wheel, But it could theorticaly jam in beween the back tire and the frame.. but somewhat unlikey.

Hmm intresting, Mcmaster has keywayed 'Aluminum Shafts—Made of Alloy 2024-T4 aluminum, these shafts are lightweight and have more corrosion resistance than steel shafts. Hardness is Brinell 120.'
Wiki says 2024 has high strength and fatigue resistance.

I wonder how this alloy stacks up to the mild steel shaft I made for myself? (Or the unknown alloy shaft thats included with the kit that I bent one day accidently)

charlz
08-03-2011, 10:16 PM
Do aluminum rear sprockets wear faster then unhardened steel? And do they wear faster in street bike applications too? (Less debrie, its a street application for this shaft)

They do wear faster, how many times faster I don't know, you rarely find steel sprockets although they do make 'hybrid' sprockets these days where the outer ring/teeth is steel riveted to the rest which is aluminum.

I don't know about between street and dirt but my thought is dirt would wear much faster as you are on and off the throttle a lot all the time versus street. Maintenance of the correct chain tension also effects wear.

Carld
08-03-2011, 11:10 PM
Black_Moons, in the 1970's when I raced sprint gokarts with 12 hp 2cycle engines we used aluminum sprockets on the axle. They were blue anodized and lasted about half a season of hard use on asphalt tracks. I don't remember the sprockets wearing a lot but they did deform some from the torque. I replaced them and the chain as needed.

As to the aluminum jack shaft, I suspect the keyways would get beat out but since it's on a motorbicycle I doubt the torque will be high.

sasquatch
08-03-2011, 11:24 PM
Many vehichles now have aluminum driveshafts, my old 92 chev pickup does.

Black_Moons
08-04-2011, 12:58 AM
Hmmm, Now the trick is figuring out where to buy 5/8 2024-T4 keyed shaft.. besides MCmaster.. Guess my first look should be the phone book for the local metal supplyers. And maybe lordco..

Boostinjdm
08-04-2011, 01:59 AM
Many vehichles now have aluminum driveshafts, my old 92 chev pickup does.

A solid jackshaft and a tubular driveshaft are two totally different situations.

I'm going to just come out and say it. I think an aluminum jackshaft is a stupid idea. If you're looking for corrosion resistance, go with stainless or get a steel shaft coated. An aluminum shaft for something like this is going to fail, it's just a matter of when.

Willy
08-04-2011, 02:08 AM
BM, I take it your mention of Lordco auto parts is some sort of twisted humour.:D

But yes nothing wrong with using aluminum, it's been used for years in high stress apps where weight reduction is a primary goal.
Aluminum driveshafts have been in use for decades so it does have a good history.
I realize the driveshaft application is more one of tubing versus a shaft, but still the yoke ends of the shaft that hold the u-joint cups don't wear from repeated shock loads imposed on them and look at the strength to weight vs. steel.

Why not use 7075 T-6, it should be readily available. Also have you considered cutting your own keyway rather than trying to find keyed shafting.

There is also the option of having them hard anodized, sprockets so done last a lot longer than you may may think. Coatings of up to 70RC are available.

Here's a link you may find helpful:

http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=MA7075T6


Material Notes:
General 7075 characteristics and uses (from Alcoa): Very high strength material used for highly stressed structural parts. The T7351 temper offers improved stress-corrosion cracking resistance.
Applications: Aircraft fittings, gears and shafts, fuse parts, meter shafts and gears, missile parts, regulating valve parts, worm gears, keys, aircraft, aerospace and defense applications; bike frames, all terrain vehicle (ATV) sprockets.

Black_Moons
08-04-2011, 02:15 AM
BM, I take it your mention of Lordco auto parts is some sort of twisted humour.:D

But yes nothing wrong with using aluminum, it's been used for years in high stress apps where weight reduction is a primary goal.
Aluminum driveshafts have been in use for decades so it does have a good history.
I realize the driveshaft application is more one of tubing versus a shaft, but still the yoke ends of the shaft that hold the u-joint cups don't wear from repeated shock loads imposed on them and look at the strength to weight vs. steel.

Why not use 7075 T-6, it should be readily available. Also have you considered cutting your own keyway rather than trying to find keyed shafting.

There is also the option of having them hard anodized, sprockets so done last a lot longer than you may may think. Coatings of up to 70RC are available.

Here's a link you may find helpful:

http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=MA7075T6



My reason of picking 2024-T4 was because it actualy existed on mcmaster as the only aluminum keyed shafting.

Id assume MCmaster would only stock a part if it had SOME demand.

Iv considered cuting my own keyway, but to be honest I think it will be cheaper for the customer to just buy pre keywayed shaft, and likey more accurate. Standard rod won't be accurate enough, so id have to very accurately turn it to size. Too much work really.


Where I live, theres very few places that will order things in. Iv had a very strange luck asking lordco to order things in for me, of all types. They even have delivery vans running around like crazy. I think they are the only real parts supplier around here... They have a suprising amount of drive line stuff stocked (Generic bolt on sprockets, pullys, chains, belts, etc), And seem very good on ordering plumbing fitings and other odds and ends. They just call who needs to be called and order it from them.