Making Rear Sprocket: Few Questions


I drew up a design for a sprocket and have a few questions. If I machine it out of 6061 aluminum, should I expect it to get eaten up extremely fast? If so, what should I be looking for, 7075? Also, does anybody have any information on what type of fixture I should look to make to set the sprocket up for machining? I was thinking a square block with the center bored out and the bolt holes drilled/threaded, and just bolting the sprocket stock to it? Any pictures of these fixtures that aren't set up for production jobs would be awesome. All my cutouts will have a chamfer on the edges and I want to be able to flip the stock over and machine both sides without screwing up the work's position.

Any help/ideas are appreciated.



Here is my drawing in mastercam. I was aiming at a design sort of like tags' sprockets.


I build things myself from aluminum and steel all the time. Often it's to save money, or because it can't be bought elsewhere, but many times it's just for the thrill of making it myself. If you've got a MetalSupermarkets close by talk to them. I buy my stuff there and they have other allows besides just 6061 and 7075. Just so you know, you can buy an RMA aluminum sprocket for $16.

It looks like you have a class project going.

Are you going to CNC mill the sprocket ?

It looks like you have a class project going.

:bonk: Disregard my previous comments :bonk:

At school, but making this for fun on my own time. I can get plenty of 6061 from the school, but I might have to dig a little deeper to find something a bit more strong.

And yes, the sprocket will be cut out on a cnc mill. Mastercam practically writes the program for you, you just tell it the details like what tools you're using and depths and whatnot.

I'm thinking of squaring up a peice of stock, then boring the center of the squared peice to size. Then drilling/chamfering my bolt holes. Thn I will take this square peice with holes and bolt it to some sort of fixture where I will machine my pockets and teeth. Thats the way I am thinking of it in my head, but am looking to see if there are other methods that are more simple/quicker.

And yes, the sprocket will be cut out on a cnc mill. Mastercam practically writes the program for you, you just tell it the details like what tools you're using and depths and whatnot.

I know what you mean. I use MasterCam V.10 at work and love it.

If you can get your hands on a second, relatively thick plate (.500"+) of aluminum, you can hold this in the vise, or clamp it to the table. Ideally, the plate should be larger than the o.d. of the sprocket. You can then clamp the sprocket blank to this, then drill the bolt pattern in the sprocket blank. Remove the sprocket blank, then drill the same bolt pattern in the fixture plate, but for the tap-drill size.

Tap your bolt threads in the fixture plate. Then you can bolt the sprocket down and you'll have a repeatable/concentric X/Y axis. Your Z axis can be zeroed on the fixture plate. Now you can cut the O.D.,the teeth, mill the cutouts, and interpolate the inside diameter all in one operation.

I hope this helps.

The 7075 is gonna make a lot structurally stronger sprocket. Personally, I wouldn't recommend 6061, if you're gonna use it on a big bike. You could always use the 6061 for proof material, though.

I assume you are planning on anodizing it ? If so, the surface hardness of the teeth after anodize will be comparable, with either material.

I don't think you'll be standing the sprocket on end to do any milling. The vibration will be your first issue. What you need is a corner rounding end mill or possibly a special tool made, depending on what kind of profile you are wanting. Might even check with Iscar Tooling to see what they make for that. I don't think the 6061 will last long, but if you have the program made it's worth a try.

You could always use the 6061 for proof material, though.
I don't think the 6061 will last long, but if you have the program made it's worth a try.

Do you guys run the CNC programs on plastics, etc for prototypes?

Do you guys run the CNC programs on plastics, etc for prototypes?

Not normally, unless it's a real sophisticated program and/or high $ material. The programs can be proven out with both the MasterCam software and the graphics on the cnc machine tool before a cut is ever taken.

We do have a 3D printer that can produce a prototype out of ABS plastic using the file from a CAD program.

Thanks for the replies. I'm definitely going to prove it out with 6061 to make sure it bolts up and everything works out since it's readily available. 76xtdvr that is a good idea, along the lines of what I was thinking. Making the holding plate larger will eliminate a lot of vibration

zwr250f, I have many endmills available, corner rounding, ball, etc. I was going to use a straight endmill for everything but the chamfering, what issues would there be with this?

And slowspokes, if I anodize the 6061 its hardness will be comparible to 7075? I didn't know anodizing is a hardening coat type of deal.

Thanks for the help,


I was going to use a straight endmill for everything but the chamfering, what issues would there be with this?

For any chamfering, you can preset your Z axis high in your program, and then keep adjusting the Z setting in the mill to "sneak up" on the desired chamfer depths. Also, make sure the countersink angle for your sprocket bolt seats match your sprocket bolts. Probably an 82 degree c'sink cutter.

Do you guys run the CNC programs on plastics, etc for prototypes?

No, between surfcam verify and Solidworks there is no reason to. Also, assuming your setup guy is half-assed competent they should be able to see any obvious errors on your part.

Many of the jobs we run are prototypes, we might run 30 jobs a week of quanities of no more than 2pcs/ea.


zwr250f, I have many endmills available, corner rounding, ball, etc. I was going to use a straight endmill for everything but the chamfering, what issues would there be with this?


No issues that I know of, as long as you can fit the tool in there you should be fine. The sprocket itself is not thick, as far as worrying about taking deep cuts. However if you have relief around the teeth as many sprockets do you won't be able to machine them easily with a square endmill. It's possible but not desired.

good some pics when you get it done.


Yeah I took note of the relief cutouts on most sprockets. I'm going to cut one out straight and see how it is after I run it for a bit. Next week I should have atleast one sprocket cut out. Monday I'm going to start working on my fixture.

I'll be sure to put pictures up of both.



Colored Anodize (Soft Anodize) will not help hardness. The reason for 7075 is through hardness. It will be much harder for sand to destroy the sprocket.


Regular Anodize will not help the hardness much, but you can have it hard anodized. That will penetrate deeper into the surface, however, you will be limited to the color of light grey to black. I believe a few companies are offering hard anodize in maybe a green or brown now. We don't currently do that color, though.


Haven't updated this thread in a bit. I have finihed my fixturing for the sprockets, and cut one out of particle type board today just to see how it ran. 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 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 number.


I'm still calling around to find a decent price on some stock, then I'll start cutting out some metal ones.

Let me know what you think,


6061 is usually hardened after milling, T-6 is the hardening protocol. I believe 7075 also has to be hardened too, can't recall the method or protocol though.

I may be wrong, this is from memory from long ago, but 6061-T6 will bend long before it breaks, 7075 will up and break on you without warning. Don't know if that help as respect to wear, but it seems to me that the 7075 will last longer since it has more tensile strength and hardness.


After looking on several companies websites, it seems most make there sprockets out of 7075, and things like triple clamps are machined out of 6061. So I'm thinking 7075 is the material of choice for the abuse that sprockets take. I may even cut one out of steel and run it for a little while to see how it holds up.



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      If you look directly under the carb, the round hole is aligned with the pilot jet. Take the float bowl, and put it back on.
      Untie the rear clamp and the front clamp as well. Slip the carb back the way it used to. Make sure that it is straight up and down with the rest of the bike. The notch on the front boot should be aligned with the notch on the carburetor, and the notch on the carburetor should be in that slot. Tie the clamps down securely.
      Let’s put the needle in. These are how the needle numbers go:

      The top clip position is #1, the lowest one, closest to the bottom, is #5. (The picture says six but it is five in this case) For reference #1 is the leanest position, while 5 is the richest. I put the clip in the 4th position. Read at the bottom of the page and you can know what conditions I ride in, and you can adjust them to your preference.
      Put the clip in the new needle, slip it in. Take the vise grips off your grips and start guiding the plunger holder down to the bottom. Remember not to let that assembly come apart because it is a pain in the ass to get it back together! Once you get it to the bottom, put the two screws on, and then put the cover on.
      Now that you have done the carburetor mods, there is still one thing you want to do to complete the process. Don’t worry, this takes less than a minute! On the top of the air box there is a snorkel:

      As you can see, you can slip your fingers in and pull it out. Do that. This lets more air in to the air box. Don’t worry about water getting in. There is a lip that is about 1/8” high that doesn’t let water in. When you wash, don’t spray a lot under the seat, but don’t worry about it too much.
      The next thing you must do is remove the exhaust baffle. The screw is a torx type, or you can carefully use an allen wrench and take care not to strip it:

      The screw is at the 5 o’clock position and all you do is unscrew it, reach in, and yank it out. This setup still passes the dB test. The bike runs 92 dB per AMA standards, which is acceptable. Just carry this baffle in your gear bag if the ranger is a jerk off. I’ve never had a problem, but don’t take chances.
      That’s it! Start putting your tank on, seat, and covers. After you put the seat on, pull up on the front, and the middle of the seat to make sure the hooks set in place.
      Turn on the bike, and take a can of WD-40. Spray the WD-40 around the boot where it meets the carburetor. If the RPM rises, you know you have a leak, and the leak must be stopped. You must do this to make sure there are no leaks!
      Here is my configuration:
      04’ 230F
      Uni Air filter
      132 Main Jet
      45 Pilot Jet
      Power up needle, 4th clip position
      Fuel screw 1.75 turns out
      Riding elevation: 2000ft - Sea level
      Temperature – Around 60-90 degrees
      Spark Plug Tips
      When you jet your carb, a spark plug is a best friend. Make sure your spark plug is gapped correctly, (.035) but that’s not all that matters. You want to make sure the electrode is over the center, and you want the electrode to be parallel, not like a wave of a sea. Put in the plug, and run the bike for 15 mins, ride it around too then turn it off. Then take off the spark plug after letting the bike cool. The ceramic insulator should be tan, like a paper bag. If it is black, it is running rich, if it is white, it is running lean. The fuel screw should be turned out if it is running lean, and turned in if it is running rich. Go ¼ turns at a time until your plug is a nice tan color.
      Making sure your bike is jetted correctly
      While you are running the bike for those 15 mins to check the plug color, you want to make sure it’s jetted correctly now. Here is what the jets/needle/screw control:
      0- 3/8 throttle – Pilot jet
      ¼ to ¾ throttle – Needle
      5/8 – full throttle – Main jet
      0-Full – Fuel screw
      Pin the gas, does it bog much? Just put around, is it responsive? When you’re coming down a hill, the rpm’s are high and you have no hand on the throttle, does it pop? If it pops, it is lean and the pilot jet should be bigger. If it’s responsive your needle is set perfectly. You shouldn’t have to go any leaner than the 3rd position, but I put mine in the 4th position to get the most response. Your bike shouldn’t bog much when you have it pinned. If it does it is too rich of a main jet.
      Determining the plug color, you will have to mess with the fuel screw.
      That’s it, have fun jetting, and any questions, post on the forum, but remember to do a search first.
      Also, if your bike requires different jets due to alititude, humidity, or temperature, please post the following so we can better assist you:
      Average temperature
      Altitude (If you do not know this, there is a link in the Jetting forum that you can look up your alititude)
      Average Humidity
      What jets you are currently running
      What the problem is (If there is one)
      Just do that and we'll help you out the best we can.
      EDIT: The girl using this login name is my girlfriend. You can reach me on my new login name at 250Thumpher
      Then again, you're more than welcome to say hi to her!
      -Phill Vieira
    • By kashlak
      JUst curious of how many bikes,quads,trikes people owned over the years and what they were?
      78 honda atc 70
      85 honda atc 110
      ?? handa trail 70
      78 yamaha mx 80
      85 yamaha yz 60
      82 yamaha it 125
      85 kawasaki kxt 250 tecate
      79 yamaha yz 400
      86 yamaha yz 125
      85 yamaha yz 80 (playbike)
      92 kawasaki kx 250
      93 yamaha xt 350
      and last but not least a 99 kawasaki kx 250
    • By Bosch232
      Were the XL's the predecessor to the XR's?
      I have a friend who's looking at an old XL350, and I don't know anything about these bikes.