OK,

I'm still pretty new to this forum and machining, and have learned a tremendous amount from reading this forum. I'm now in my third semester and working on a few projects of my own/with a buddy now. I decided to make my own sprockets. the steps I have taken so far:

1.Sketch the design I want
2.Draw in mastercam
3.Produce the code for it
4.Draw/Design/Make the fixturing
5.Cut out of particle board to see how it turns out!



I ended up with three fixtures to complete the sprocket. The first fixture is for doing the bolt holes and the center pocket(for the hub). The second fixture(one in the picture below) I bolt the drilled square onto it and cut out the rest of the sprocket. The third fixture is a lathe peice that holds the sprocket so I can turn down the 1/4" stock to the proper thickness, and put a relief on the teeth.

Here is a picture of me cutting out the particle board sprocket..Not sure how long this would last on the bike haha.

In the picture above you can see me roughing out all the pockets. I come in with an 1/8" endmill to clean up all the pockets.

Here is the finished particle board sprocket.




And here is a crappy picture of the engraving I put in it. I have 6 "174's" engraved around it, since that is my racing number.


Now,

Most companies out there make their sprockets out of 7075. I'm having a hard time finding sheets of 7075 at a reasonable price...Wait, I don't really know what a reasonable price is..So, what is a decent price for this material?

Would I be better off machining them out of 6061 and hard annodizing them? They take a good amount of abuse and all the sand/dirt that finds its' way between the chain and sprocket act as an excellent abrasive.

An aftermarket rear sprocket from a company is generally between 50-60 bucks. Can they sell them for this price because of the quantity and price cuts(from buying in such large numbers)?


Any help is truly appreciated,

Tim

My compliments on a nice looking project. As to material you might check with Metal Source in Woburn MA.

http://www.metalsource.com/default.htm

Talk to Ed and I am sure that he will be able to help you out. They will cut to order and UPS the material to you. I am fortuate to be (sort of) close enough to them to visit in person on occassion but of course that doesn't help you!

Errol Groff

Errol,

Thanks for the info. I have called around locally, and no one seems to have what I'm looking for/take my inquiry too seriously.

Thanks,

Tim

Tim,

I 'am in your area...call Metal stock in Phila...I have another Al source buts it is on the tip of my tougue.

Jay
www.CandLMachine

looks really nice Tim. if you can't find 7075 material and want to give it a shot with 6061, try electroless nickel plating instead of hard annodizing. its more ductile. it may still wear out pretty quickly.

also, is that a standard tooth profile? maybe its the view, but it looks a little pointy, almost like a worn sprocket.

Mike

I never understood why sprockets would ever be made out of aluminum.
So they wear out and sprocket companies sell more of them??
I know it is 1/3 the weight of steel, but softer in general.
I know 7075 can be heat treated to be harder than mild steel, but steel is cheaper.
I can't see any weight advantage other than if it were going into flight.
Might be the same reason some people call anything aluminum, billet.
Make it out of steel.

--Doozer

I take it you don't do much cycling up hills? Weight IS very important. If you want cheap, use steel. If you want the ultimate use titanium, Al falls between the two. Because of the relatively large diameter of the chainring and the number of teeth, they do actually last quite a long time; I just got almost 20,000 km out of a 53 on one of my road bikes.

Tim here is a site of a local company that manufactures chainrings, it may provide some info. I'm about to order 2 from them soon. http://www.cycleunderground.com.au/chainringdesigns.htm

I agree with Mike, they do look a bit "pointy"

Sproclets are pretty easy to make with a rotary table on the mill. I have made several sprockets out of aluminum and CRS. Sprockets are dirt cheap I would never make a sprocket that I can buy. I only make sprockets that are not available to buy. Shifting ramps are easy to add.

Here is a 72T sprocket I made for a bicycle.

http://i67.photobucket.com/albums/h2...aver/72t-2.jpg

http://i67.photobucket.com/albums/h2...aver/72t-1.jpg

That's very true for a bog standard fixie or similar, but a high quality chain ring, such as a Shimano Dura-Ace, designed for shifting, is actually a highly complex piece of machining. Looks deceptively simple but in fact there are numerous shifting ramps around the perimeter to improve shifting speed. Indeed I believe every single tooth on a Dura-ace chainring has a unique profile. Try doing that with a rotary table and mill

Who would have thought 'eh

Tim I didn't get to see all your fixtures, but it's important to ensure they're perfectly concentric when machining. No biggie if they're a bit out on a multiple gear bike, but on a fixed gear bike it will cause the chain to vary in tension. Sounds plainly obvious, but I mention it because it seems remarkable (to me anyway) how many commercial rings aren't concentric.

that sprocket looks to me like its for a moto, probably a 520 since he's starting with 1/4" material, not as thick as most sportbike (street) sprockets.

weight still matters a whole bunch on motorcycles especially dirtbikes, as the sprocket is unsprung weight. they generally use steel for the small (~13-16t sprocket transmission output) sprocket, and aluminum on the rear and they last a reasonable amount of time.

Mike

Also for the the pro manufacturers I believe the sprockets are Laser cut, as that's more of an economics thing. Very easy to change designs then.


Nowadays they are building sprockets with steel teeth and an aluminum hub. In motorcycle racing, that unsprung weight makes a BIG difference in handling and they are always trying to lower it. since they aren't quite as worried about longevity they make the sprockets out of aluminum.

Thanks for the replies.

This sprocket is for an mx bike, not a bicycle. I'm really doing it for fun/learning things along the way. I realize it would be easier to go out and buy a 60 dollar sprocket, but there just isn't as much fun in doing that.

I also agree on the teeth being somewhat pointy. I used the sprocket program in mastercam, and simply selected the number of teeth, and the chain size I was using and mastercam came up with that tooth profile.

-Tim

Ahhh, ok, sorry. I did wonder why you were calling it a "sprocket"

Gary what did you use a 72T for, that's HUGE? A recumbent?

A 51 tooth Renthal is about 10.5" OD. There is a piece of .25 x 10.625 x 11.19 7075 on the Yarde metals drop zone for 22 bucks. Looks like a perfect candidate.

http://www.yarde.com/cgi-bin/dropsho...size1=++0.2500

Nice touch putting your number on them!

What do you have for a scooter?

Have fun

T174M... Is that really 'particle board' that you made your practice piece with? Looks more like Masonite, or at least MDF. Just curious...

Mike

ARB,

I've found a piece of 1/4" plate that I could get 4 sprockets out of on ebay for 67 bucks..Thinking I might jump on that.

And, I ride an rm125 turned rm144.

mm58,

Masonite seems more reasonable than particle board. I'm not really sure what it is...It's what they cover the countertops in the shop with here at school and I found a peice of it laying around and it seemed like an adaquate canditate to test run it.

-Tim

Basically, I agree with you on steel. I'd never use aluminum on a road bike. I suspect that you already know that aluminum is mainly used on dirt and road race bikes to reduce unsprung weight. It improves handling due to less rebound on rough ground.

It's true that they don't last very long but the typical road racer will be changing sprockets and wheels on a routine basis so wear on a sprocket is of small concern.

Personally, I never liked aluminum sprockets when I was riding in the dirt and I never used them. Steel was much more durable. On the other hand, I was never a professional with an unlimited budget.

One thing i did see written about on your fixture plate is a way to align X or Y in relationship to your 6 mounting bolts. this has been a mistake of mine when making a fixture and removing it from the table and having no easy way of re-indexing the part's mounting holes. great job so far! matt

You guys are pretty much on the spot with steel v.s. aluminum.

I have been a dirt demon for most of my 39 years. I have found that the aluminum is pretty much for the bling effect. For most of us mere mortals we could not tell the difference in unsprung weight.

I still buy aluminum sprockets because i like the way they look and they will last the life a good O-Ring chain. Back when I raced hard core a chain and sprocket set would last me 2 seasons. I figured that was decent service.

If I was to make one I would go the aluminum route too. It's just easier and they look snappy when done.

I can't wait to see the finished product from T174M.

I too was ready to make aluminum sprockets and was going to use the better 7075 T-6 aluminum as the quality of the chainwheel would be longer lasting.
Renthal and others produce their sprockets from this grade and others will use 6061.
I agree an aluminum sprocket will last the usable life of a high grade 0-ring chain.
Here is a link to a program I found to cut different tooth profiles:
http://www.idleamusements.com/Software/sprocketeer2.htm
I have not yet used it .
I ran into the same delima about material pricing.
I am a dealer for many companies and I can not buy the material at a cost that will allow me to produce the sprocket and still make a profit.
I have made a couple sprockets for a customer that we could not determine what the rear wheel he was working with came from.
I used a rotary table back then and cut 1 tooth profile then indexed the table to repeat the same program again until the sprocket was complete.
that was before I had the machines I have now.
I may still look into material pricing and see if I can find a source for 7075 and 6061.
I race myself and would still like to make my own with my company logo on them .
TOP PERFORMANCE RACING