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I want to build my own front sprocket! but how? - Page 2

post #16 of 23

Re: I want to build my own front sprocket! but how?

FoSi wrote:
> Earl Bollinger wrote:
>
>
>>"FoSi" <fosibox@gmail.com> wrote in message
>>news:1167430292.102350.78650@48g2000cwx.googlegroups.com...
>>
>>>Hi all..
>>>recently i converted my bike to SS fixed gear! using 17rear sprocket
>>>33front sprocket! i have horizontal "drop-out" so i made a 10mm rear
>>>Cr.Mo bolt axle to fit my Deore Hub! then i also did machined two chain
>>>tensioners.. to micro-adjust the tension, and to have the wheel always
>>>in place! untill here everything its fine!
>>>
>>>so.. i purchased a BMX 1/2x1/8" chain, puted it in place.. and noticed
>>>that the i need a thicker 33t sprocket at front!! like those BMX
>>>sprockets to fit the 1/8 chain... so im thinking in designing and
>>>building my own 33t front sprocket in 8mm 7075 aluminium !
>>>but i dont know were i can find technical info on how the sprocket is
>>>designed! is there a document with the standards for this?
>>>my setup>> http://img127.imageshack.us/my.php?i...procketbq6.jpg
>>>
>>>i have a 4bolt truvativ hussefelt crank, with the standard truvativ 33t
>>>Cr.Mo sprocket.. i need to design a BMX thick 33t sprocket
>>>like these: http://wethepeople.de/V3/bilder/product/war119_004.jpg
>>>(equal to this one, but to fit the 4bolt crank arm)
>>>
>>>can someone please helpme to find technical info about the bmx sprocket
>>>design + plus the truvativ 4bolt crank arm radius? this would be really
>>>helpful!!
>>>thank you very much for reading
>>>

>>
>>Well, you could make your own. But you need a new chainring to use as a
>>pattern, so you can get the teeth done OK without using a worn chainring
>>with worn down teeth.
>>Then you use a rotary table mounted on a milling machine. Drill the center
>>hole in a plate of aluminum or steel your choice of suitable thickness.
>>Then carefully mill out the circular shape in the plate of metal.
>>Then carefully mill out all the teeth. Then after you have your internal
>>pattern shape doen, mill out the internal web design.
>>Finally angle the rotary table and carefully mill out the angles as best you
>>can on all the teeth. You could even use a hand file or two to do this part
>>too.
>>
>>Now you could use a CNC machine, but the devil is in the details, as you
>>have to program in your chainring design. For some people this can be a
>>major project in itself. But once you have the CNC program done and working
>>well, you can save it and reproduce your chainring anytime you want to.

>
>
> Hi Earl!
> thats why i asked for the bmx sprocket standard technical paper/draw!
> so i dont need a pattern.


The 'recipe' is always secret. Once you have the 'recipe' anybody can
cook. Try TA, Shimano, or Campagnolo for their drawings or 3D models.
Good luck.

Lou
--
Posted by news://news.nb.nu
post #17 of 23
Thread Starter 

Re: I want to build my own front sprocket! but how?

Ok people... i just found this tool: http://www.camnetics.com/ and
this: http://www.wadeproco.com/
just needed this...
i have already the standard for the truvativ 4bolt arm perfurations!
i will later post the design of the custom chainring!
thanks again

Tim McNamara wrote:

> In article <p56dnfUGhY1O4wvYnZ2dnUVZ_h-vnZ2d@comcast.com>,
> "Earl Bollinger" <earlwbollinger@comcast.net> wrote:
>
> > "FoSi" <fosibox@gmail.com> wrote in message
> > news:1167430292.102350.78650@48g2000cwx.googlegroups.com...
> > > Hi all.. recently i converted my bike to SS fixed gear! using
> > > 17rear sprocket 33front sprocket! i have horizontal "drop-out" so i
> > > made a 10mm rear Cr.Mo bolt axle to fit my Deore Hub! then i also
> > > did machined two chain tensioners.. to micro-adjust the tension,
> > > and to have the wheel always in place! untill here everything its
> > > fine!
> > >
> > > so.. i purchased a BMX 1/2x1/8" chain, puted it in place.. and
> > > noticed that the i need a thicker 33t sprocket at front!! like
> > > those BMX sprockets to fit the 1/8 chain... so im thinking in
> > > designing and building my own 33t front sprocket in 8mm 7075
> > > aluminium ! but i dont know were i can find technical info on how
> > > the sprocket is designed! is there a document with the standards
> > > for this? my setup>>
> > > http://img127.imageshack.us/my.php?i...procketbq6.jpg
> > >
> > > i have a 4bolt truvativ hussefelt crank, with the standard truvativ
> > > 33t Cr.Mo sprocket.. i need to design a BMX thick 33t sprocket like
> > > these: http://wethepeople.de/V3/bilder/product/war119_004.jpg
> > > (equal to this one, but to fit the 4bolt crank arm)
> > >
> > > can someone please helpme to find technical info about the bmx
> > > sprocket design + plus the truvativ 4bolt crank arm radius? this
> > > would be really helpful!! thank you very much for reading
> > >

> > Well, you could make your own. But you need a new chainring to use as
> > a pattern, so you can get the teeth done OK without using a worn
> > chainring with worn down teeth. Then you use a rotary table mounted
> > on a milling machine. Drill the center hole in a plate of aluminum or
> > steel your choice of suitable thickness. Then carefully mill out the
> > circular shape in the plate of metal. Then carefully mill out all the
> > teeth. Then after you have your internal pattern shape doen, mill out
> > the internal web design. Finally angle the rotary table and carefully
> > mill out the angles as best you can on all the teeth. You could even
> > use a hand file or two to do this part too.
> >
> > Now you could use a CNC machine, but the devil is in the details, as
> > you have to program in your chainring design. For some people this
> > can be a major project in itself. But once you have the CNC program
> > done and working well, you can save it and reproduce your chainring
> > anytime you want to.

>
> You're making this far too difficult Earl. You can scribe a circle on a
> 1/8" sheet of aluminum, mark the points where the chain pins would ride,
> drill it out with a hand drill and cut it out with a jeweler's saw. A
> lathe is handy for profiling the flat edge and rounding the ring, but
> even that can be kludged with the power drill. It's been done this way
> for years. The math is pretty simple given that bike chains use a 1/2"
> pitch.
>
> ISTR that instructions for doing this are available on the IHPVA Web
> site, maybe even with patterns. http://www.ihpva.org and check under
> "builder's resources" or something like that.
post #18 of 23

Re: I want to build my own front sprocket! but how?

FoSi wrote:
>
> but i dont know were i can find technical info on how the sprocket is
> designed! is there a document with the standards for this?


I have CNC machined a bunch of sprockets from 18t to 144t. This is the
method I've developed through trial and error:

1) Generate a polygon of [n] number of sides with a facet length of
exactly .500". The vertices of this polygon correspond to the centers
of arcs in the gullets between the teeth.

2) Upon one vertex, place a circle of the same diameter as the chain
rollers. I haven't got my drawings or measurements handy, but it's
close to .308". It is_not_ exactly 5/16" or 8mm. The exact radius is
probably not of critical importance; I simply want the sprocket to bear
the load from the chain rollers as conformally as possible. Draw a
radial line from the center of the sprocket to the vertex/circle
center.

3) Add a line segment representing a tooth face, tangential to one of
the circles but tilted 20 degrees from the radial. Trim away all of
the circle except for the segment that connects the tangent point to
the radial line. The remaining arc should span between 50 and 65
degrees in angle depending on tooth count. The relief angle allows the
chain to mesh smoothly into place without binding on the faces of the
sprocket teeth.

4) Duplicate and mirror the tooth face and the half gullet. Rotate the
duplicated half a small fraction of a degree about the sprocket center
such that the arc ends are separated by a distance of approximately
..010" (so that the gullet is in effect .010" wider than the roller
meshing into it). Connect the arc ends with a line segment. Widening
the gullet this way allows the chain's rollers to settle all the way
down to the bottom of the gullets without binding or sticking. Making
this clearance wider than necessary subtracts material from the
sprocket teeth; .010" of clearance has always worked for me

5) Join the tooth faces with a .080" radius fillet to forrm a rounded
point on the tooth.

6) Select one tooth and gullet worth of geometry and radially duplicate
it [n] times around the sprocket center. Confirm that all the lines
and arcs connect to each other and that all the gullets coincide with
vertices of the original polygon. Delete the original polygon and any
extraneous geometry.

That kind of sprocket profile is what I used to generate toolpaths
using Mastercam. At other times, I wrote code by hand and specified
only the contour of a single tooth, adding a recursive loop and
coordinate system rotation (G68) to cut all the other teeth. It was
pretty cool to cut a 144 tooth sprocket with something like twenty
lines of code.

After machining a sprocket, I beveled the tooth tips by hand using a
file. This feature could be machined, but was never worth the effort
and setup for just a single sprocket.

Just so you know, you probably can buy a 7075 chainring for about the
same amount of money that a plate of 7075 would cost you. I never
machined a sprocket when I could buy one instead-- there are plenty of
opportunities to make things that you _can't_ buy off the shelf. And
as others have pointed out, you don't need a 1/8" ring to carry a 1/8"
chain.

Chalo
post #19 of 23
Thread Starter 

Re: I want to build my own front sprocket! but how?

thanks Chalo for the help!
i just want to make a custom chainring! i know i can buy.. but i want
to make one myself..
fo you all who want to do the same thing: here is a good link on how
chains and sprockets work and the procedures to layout a sprocket:
http://www.gizmology.net/sprockets.htm

thanks..

Chalo wrote:

> FoSi wrote:
> >
> > but i dont know were i can find technical info on how the sprocket is
> > designed! is there a document with the standards for this?

>
> I have CNC machined a bunch of sprockets from 18t to 144t. This is the
> method I've developed through trial and error:
>
> 1) Generate a polygon of [n] number of sides with a facet length of
> exactly .500". The vertices of this polygon correspond to the centers
> of arcs in the gullets between the teeth.
>
> 2) Upon one vertex, place a circle of the same diameter as the chain
> rollers. I haven't got my drawings or measurements handy, but it's
> close to .308". It is_not_ exactly 5/16" or 8mm. The exact radius is
> probably not of critical importance; I simply want the sprocket to bear
> the load from the chain rollers as conformally as possible. Draw a
> radial line from the center of the sprocket to the vertex/circle
> center.
>
> 3) Add a line segment representing a tooth face, tangential to one of
> the circles but tilted 20 degrees from the radial. Trim away all of
> the circle except for the segment that connects the tangent point to
> the radial line. The remaining arc should span between 50 and 65
> degrees in angle depending on tooth count. The relief angle allows the
> chain to mesh smoothly into place without binding on the faces of the
> sprocket teeth.
>
> 4) Duplicate and mirror the tooth face and the half gullet. Rotate the
> duplicated half a small fraction of a degree about the sprocket center
> such that the arc ends are separated by a distance of approximately
> .010" (so that the gullet is in effect .010" wider than the roller
> meshing into it). Connect the arc ends with a line segment. Widening
> the gullet this way allows the chain's rollers to settle all the way
> down to the bottom of the gullets without binding or sticking. Making
> this clearance wider than necessary subtracts material from the
> sprocket teeth; .010" of clearance has always worked for me
>
> 5) Join the tooth faces with a .080" radius fillet to forrm a rounded
> point on the tooth.
>
> 6) Select one tooth and gullet worth of geometry and radially duplicate
> it [n] times around the sprocket center. Confirm that all the lines
> and arcs connect to each other and that all the gullets coincide with
> vertices of the original polygon. Delete the original polygon and any
> extraneous geometry.
>
> That kind of sprocket profile is what I used to generate toolpaths
> using Mastercam. At other times, I wrote code by hand and specified
> only the contour of a single tooth, adding a recursive loop and
> coordinate system rotation (G68) to cut all the other teeth. It was
> pretty cool to cut a 144 tooth sprocket with something like twenty
> lines of code.
>
> After machining a sprocket, I beveled the tooth tips by hand using a
> file. This feature could be machined, but was never worth the effort
> and setup for just a single sprocket.
>
> Just so you know, you probably can buy a 7075 chainring for about the
> same amount of money that a plate of 7075 would cost you. I never
> machined a sprocket when I could buy one instead-- there are plenty of
> opportunities to make things that you _can't_ buy off the shelf. And
> as others have pointed out, you don't need a 1/8" ring to carry a 1/8"
> chain.
>
> Chalo
post #20 of 23

Re: I want to build my own front sprocket! but how?

FoSi wrote:
>
> fo you all who want to do the same thing: here is a good link on how
> chains and sprockets work and the procedures to layout a sprocket:
> http://www.gizmology.net/sprockets.htm


For what it's worth, the tooth profile they describe is very similar to
what I first tried when I started from first principles. The trouble
is, if you make sprockets that way, the chain won't mesh right. It
will stick where it should leave the sprocket, the rollers will
hesitate before settling all the way down onto the sprocket, and it
will play hell with any loosely tensioned chain like that of a
derailleur bike. (And I made my sprockets to a level of precision even
Campy can only dream of.) Such a sprocket didn't work satisfactorily
even on the tensioned chain of a one-speed trials bike when I tried
that.

If you look at commercial sprockets for industrial machinery, you'll
find that the teeth are shorter and their faces more sloping than the
tooth profile in the diagram at the link you provided. Bike chainring
teeth tend to be even stumpier than industrial sprocket teeth, probably
to aid derailment but also having the effect of tolerating worn chain
pitch.

Chalo
post #21 of 23

Re: I want to build my own front sprocket! but how?

FoSi wrote:

> i just want to make a custom chainring! i know i can buy.. but i want
> to make one myself..


And that is a very cool thing to do. You might find this link
interesting:

http://weightweenies.starbike.com/articles.php?ID=26

Mark
post #22 of 23

HI,

 

I know you want to try to make them yourself BUT believe me it is not necessarily practical to do on a small scale....

 

We can make custom chain rings for you ( I manage Kings Sales and Service Group....We manufacture Super Sprockets and Top Hat Sprocket Adapters)....all we need to know are the number of teeth you like and the mounting pattern....We made some custom made Campy chain rings for a customer in CA (they rode vintage road bikes but since most of the members were getting older, we made them some replica chain rings in a smaller size than was available from the factory....we kept the same factory look to keep the bikes looking stock)....

 

I have a web page where you can see some of our work (I'll try to find the chain ring pics and post them up BUT we are in the process of making a new web page so that may get delayed.

 

Our web page is : kingssalesandservice.com

 

Hope this helps you.

 

Andrew

post #23 of 23

Fella, this is a four-year-old thread you have bumped.

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