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This article is in the Features category, and was posted on 14/11/2002.

Step by step: the making of a chainring (Author: Anders)

The Machinist

The Machinist

Step by step: the making of a chainring



This was meant to be a project, that could be done over the summer, but here in Denmark we have had one of the best summers in a long time, so it has taken a bit longer than expected.

The rings are made on a FADAL 2016 '99 model with the old 88 control. This is a CNC milling machine with a maximum speed of 7500 rpm.

For anybody interested, the CAD/CAM used here is SolidWorks/CAMWorks.

The CAD/CAM work could be done in about 2-3 hours if one could stay indoors for that long!! The process pictured is the making of a 42T 5-arms design. It’s a long process to implement it at first, but when it’s all in place, it goes pretty fast. When it is all optimized it will takes about 15-20 minutes to make one of these chainring.

The Aluminium used is 7075 T6 heat treated 4 mm alloy plates, these are very precise with almost no warp.

The chainrings are not made for sale!

The first thing to be done, was making a fixture for the Aluminium plate.
This is made of 20 mm thick Aluminium:

Making a fixture

Here the topside of the tool is finished:

Finished topside

The plate will be fixated to the Aluminium tool with normal chainring bolts:

Fixating the Aluminium plate on the tool with normal chainring bolts

Next we start out with a square aluminium plate:

Square Aluminium plate

The holes are being made for the bolts, and then it is fixed in the tool made in the start:

After making the holes

The plate is bolted to the tool:

The plate is bolted to the tool

Here is the picture off the chainring drawed in SolidWorks:

SolidWorks

Now we start making the teeth:

Machining the teeth

Machining the teeth

Machining the teeth

Now the topside of the chainring is finished:

Topside finished

Now the other side of the chainring can be made.
This will be implemented in the CNC milling machine, so there will be no need to use this machine:

CNC-milling the other side

The teeth has to be cut in angle, so the chain can't "ride" on the teeth, but instead fall into place.
On this picture you can also see, that the inside edges of the chainring has been cut in an angle of 45° to reduce weight.

Closeup of the teeth

Here it is compared with a T.A. Specialites chain ring.

You can see, that your design is much smaller in profile, and therefore lighter. The shifting ramps are also different.

Compared with TA Specialites

Our new design is very light, only 58 grams with 4 hardsteel shifting ramps:

On scale: 58 grams

Chainring mounted on my bike

The ring seen on the picture, has been tested in very muddy conditions, on our 26 km home trail. It performed flawlessly, no shifting problems and no chainsuck.

The future modifications will include a design, so that the shifting ramps may not be needed. It's a special 45° cutting on the back, that acts like a shiftingramp going all the way around the chainring. Finally they will be anodized black.

We will also round the edges some more and optimize the design of the holes. This may result in a weight under 50 grams.

UPDATE:

We have shaved of some more material and removed the shifting ramps, so now the weight is down to 56 grams for the 42T. We have also made a 32T middle ring, and that weighs 34 grams. We are going to make a bit more milling to the edges of the chainring, which should save about 2 grams more.

We have made a custom tool, for the process of cutting the teeths in angle, so there's no more need to use the green machine, shown in the pictures above. The CNC milling machine can now make the whole chainring in one process. It takes about 13 min to make a 42T and about 8 min for a 32T.

The new design with bigger holes and rounded edges:

The new design with bigger holes and rounded edges


UPDATE:

We have made a new 30T chainring type for our 2x9 setup.

30T chainrings stacked

It weighs only 25 grams, which is 5 grams lighter than a 30T TA Specialites ring.

30T chainring on scale

The chainring set is now down to 80 grams. That is 16% lighter than TA Specialites.

42T and 30T chainring

Here are pictures of the used machining tools:

Tools

Tools in detail

Hope you found it interesting.

Coming up, very light hydraulic shifting device that works!!!! No mud in your cables anymore.



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