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    Default Sprocket Fixture

    I have to make some sprockets for son's Drag bike. I'm looking at making fixture like the one in the picture, What I'm trying to workout is what would be the best way the index the sprockets to the fixture so I can flip them?

    sprocket-fixture.jpg

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    Make the fixture two pieces and keep the chainring bolted to the center piece that keys into the center of the flat part of the fixture. Unbolt the center with the chainring attached and flip it. That or give up two of the bolt holes for pins but the first idea is definitely going to be more repeatable. Are you going to chamfer the windows or are you just doing profile work on the teeth?

    I assume that is waterjet cut? Is it oversized on the teeth or are you hoping it is accurate enough to locate off the current part before starting?

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    Rick,

    What about a precise hole directly underneath one of the teeth?
    You could use a gage pin to locate the radius of a single gear tooth (assuming you can buy/make a pin close to size) once you flip the gear.

    Or pick up one of the pockets previously milled through the gear. (think a male mandrel, a few 0.001"s smaller than the pocket)

    Or just machine in any type of locator you can, into the gear. Since it for you son's use, you can pretty much do anything you want...

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    Quote Originally Posted by doug925 View Post
    Rick,

    What about a precise hole directly underneath one of the teeth?
    You could use a gage pin to locate the radius of a single gear tooth (assuming you can buy/make a pin close to size) once you flip the gear.

    Or pick up one of the pockets previously milled through the gear. (think a male mandrel, a few 0.001"s smaller than the pocket)

    Or just machine in any type of locator you can, into the gear. Since it for you son's use, you can pretty much do anything you want...
    I was assuming he was going to chamfer the windows so was trying to avoid adding something inside them for locating purposes.

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    Just add a couple dowel holes in the outer ring that you can drop onto pins installed in the fixture. They can be small like .125" if you're worried about strength.

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    what am I missing? Why can't you just pin off one of the bolt holes?

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    What bike is your son dragracing ? Sprocket Fixture

    Sendt fra min EML-L29 med Tapatalk

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    I am about to machine some 530 blanks for my own dragbike. These are sprocket blanks and I don't really care about the rotation/indexing of sprocket. I just clamp it down and machine the center and holes and pockets.

    Sendt fra min EML-L29 med Tapatalk

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    Quote Originally Posted by EnginCycles View Post
    Make the fixture two pieces and keep the chainring bolted to the center piece that keys into the center of the flat part of the fixture. Unbolt the center with the chainring attached and flip it. That or give up two of the bolt holes for pins but the first idea is definitely going to be more repeatable. Are you going to chamfer the windows or are you just doing profile work on the teeth?

    Yes, I'm looking to chamfer the windows and profiling the teeth.

    I assume that is waterjet cut? Is it oversized on the teeth or are you hoping it is accurate enough to locate off the current part before starting?
    No, I was looking at doing it in a two part job first cut the centre hole, teeth and the bolt holes then send it out to be hard anodised put it back in the fixture finish the pattern and chamfer the lot.

    Quote Originally Posted by doug925 View Post
    Rick,

    What about a precise hole directly underneath one of the teeth?
    You could use a gage pin to locate the radius of a single gear tooth (assuming you can buy/make a pin close to size) once you flip the gear.

    Or pick up one of the pockets previously milled through the gear. (think a male mandrel, a few 0.001"s smaller than the pocket)

    Or just machine in any type of locator you can, into the gear. Since it for you son's use, you can pretty much do anything you want...
    Couldn't pick up on the pocket's he want a few different patterns.

    Quote Originally Posted by EnginCycles View Post
    I was assuming he was going to chamfer the windows so was trying to avoid adding something inside them for locating purposes.
    Correct.

    Quote Originally Posted by Larry Dickman View Post
    what am I missing? Why can't you just pin off one of the bolt holes?
    Not sure that will work.

    Quote Originally Posted by Nikolaiownz View Post
    What bike is your son dragracing ? Sprocket Fixture

    Sendt fra min EML-L29 med Tapatalk
    It's a turbo funny bike.

    Quote Originally Posted by Nikolaiownz View Post
    I am about to machine some 530 blanks for my own dragbike. These are sprocket blanks and I don't really care about the rotation/indexing of sprocket. I just clamp it down and machine the center and holes and pockets.

    Sendt fra min EML-L29 med Tapatalk
    The chain is 630p, blanks would be good but they are impossible to get here and when you get them the cost is ridicules.What is your drag bike?

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    regarding pinning off bolt holes, ive made hundreds of sprockets that way. we made the bolt holes a snug fit to the fixture bolts, then bench reamed the sprocket holes for more clearance. 2 bolts locate the sprocket. like a poor mans dowel setup.

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    Quote Originally Posted by metlcutr55 View Post
    regarding pinning off bolt holes, ive made hundreds of sprockets that way. we made the bolt holes a snug fit to the fixture bolts, then bench reamed the sprocket holes for more clearance. 2 bolts locate the sprocket. like a poor mans dowel setup.
    OK, I didn't think it would work. This may be my lack of experience working with fixtures but with 6 bolt holes in the sprocket how do I know for sure after removing the sprocket for anodising that it go's back on the fixture in the same place so I can finish the job? or am I just over thinking this?

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    Can you leave a small feature on the part somewhere that will be removed when you do your finish passes

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    Quote Originally Posted by rick-b View Post
    or am I just over thinking this?
    I believe so

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    Quote Originally Posted by rick-b View Post
    No, I was looking at doing it in a two part job first cut the centre hole, teeth and the bolt holes then send it out to be hard anodised put it back in the fixture finish the pattern and chamfer the lot.



    Couldn't pick up on the pocket's he want a few different patterns.



    Correct.



    Not sure that will work.



    It's a turbo funny bike.



    The chain is 630p, blanks would be good but they are impossible to get here and when you get them the cost is ridicules.What is your drag bike?
    Just a simple Harley Sportster dragbike.

    I love turbo funnybikes. Good they are making a comeback.


    I would think some fitter bolt holes would be enough to hit it fairly accurate. If it just to contrast cut it after anodising it's more than ok.


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    I guess I am failing to see the question. There is literally a hundred ways to fixture this component, and flip it accurately. It seems you are machining this from flat bar or plate. You could index off of the cutouts, the external teeth or drop in one or two dowel pins in non-critical areas. The last one is the way I generally do these types of parts.

    If I was making this part from bar stock, I would do as much as I could on OP1 and put in a couple .126" thru holes. Then I would flip it on the dowel pins and machine the back side. I suggest thru holes, because then you can get back into both sides of the part after anodize.

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    Quote Originally Posted by metlcutr55 View Post
    regarding pinning off bolt holes, ive made hundreds of sprockets that way. we made the bolt holes a snug fit to the fixture bolts, then bench reamed the sprocket holes for more clearance. 2 bolts locate the sprocket. like a poor mans dowel setup.
    Quote Originally Posted by rick-b View Post
    OK, I didn't think it would work. This may be my lack of experience working with fixtures but with 6 bolt holes in the sprocket how do I know for sure after removing the sprocket for anodising that it go's back on the fixture in the same place so I can finish the job? or am I just over thinking this?
    As an alternate, but similar, idea to what metalmunchr suggested, you could buy some shoulder bolts to fixture in the holes.

    Not sure what hole size you have there, but you could order up shoulder bolts that fit snug in the holes.

    If not familiar, shoulder bolts are bolts with a "dowel pin" built right in. An 8mm shoulder bolt, for example, would have an undersize 8mm shank followed by a 6mm thread on the end.

    If shoulder bolts don't exist to closely match your hole diameters, just turn or grind them down so they do.

    You could do similar with 2 simple dowel pins with the rest of the holes regular bolts.

    If you are worried about locating back with the same holes, in the same orientation, after anodizing, make a mark on them so you know how to clock em after they come back.

    Or if you really wanna get slick, get a machine with a probe, use G68 to rotate your program so even if you happen to be off 1/2 a degree, you'd still be good.

    I agree you're overthinking it.

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    I thought I may have been over thinking it I seem to do that a lot when it comes to fixtures. I think it comes from the fact I have had a bit of trouble in the past flipping parts. I suppose this an inherent problem of being self-taught.

    Thanks, everyone I now have a few ideas that I'm going to try.

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    Quote Originally Posted by Nikolaiownz View Post
    Just a simple Harley Sportster dragbike.

    I love turbo funnybikes. Good they are making a comeback.


    I would think some fitter bolt holes would be enough to hit it fairly accurate. If it just to contrast cut it after anodising it's more than ok.


    Sendt fra min EML-L29 med Tapatalk
    The son wanted a Prostock bike I wanted a nitro bike so we met in the middle and I'm building him a turbo funny bike which we can run in Topbike here in Australia.

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    Quote Originally Posted by rick-b View Post
    The son wanted a Prostock bike I wanted a nitro bike so we met in the middle and I'm building him a turbo funny bike which we can run in Topbike here in Australia.
    That's awesome. I love everything about dragbikes.

    Nitro can get very expensive is my guess. The turbo busa's on bar prostock frames are closing 5s very fast. And I think the turbo bikes are way better to run. Nitro is just to damn crazy Sprocket Fixture

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    Quote Originally Posted by rick-b View Post
    I thought I may have been over thinking it I seem to do that a lot when it comes to fixtures. I think it comes from the fact I have had a bit of trouble in the past flipping parts. I suppose this an inherent problem of being self-taught.

    Thanks, everyone I now have a few ideas that I'm going to try.
    Since you are self taught, I’ll also point out that flipping a part is not a big deal if you plan your cut strategies. Where people run into problems is when they try to flip a part and have two cuts come together. Take for example a 2”x2”x4” block. If you hold that in a vise or fixture and cut half way down around the OD, then flip it and cut the rest of the OD from the opposite side, you will fight blend lines forever. On the sprocket, it looks like you can do all of the OD and pockets in op 1, and then only need to flip it for edge breaks. Lots of times, I’ll do those edgebreaks on op1 with a dovetail cutter just to avoid having to flip the part and have a potential mismatch.


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